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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hello all, this is my first post here at Third Gen. I looked for an intro thread, but didn't see one. Please let me know if one exists and I'll update.
First off, my project is an old 1968 corvette, but there are a few reasons I'm here for advice/discussions. 1) very few 60's corvettes run EFI, 2) all the EFI corvettes either have hood clearance issues or are LS based, and 3) I plan to play a little with nitrous which appears to be more common in your neck of the woods. Hoping for some can be some mutual benefits
This project was my 'everything' at one time, but then life got in the way and I haven't touched in since about 2014. My goals have always been performance street car, occasional driver, interested in autocross, but likely no time, and any dragstrip time will be just for fun. I wanted creature comforts like a/c, ps, pb and not too obnoxious. I had what I think was a good plan, but I'm wanting to change some things and now concerned about how everything will work together. Of note, I've never fired the motor and now changing up the induction and ignition. Here are the details:
'68 convertible on SRIII tube frame w/C4 susp, steering and brakes; now plan on C5 brake upgrade Rearend - C4 D44 w/3.45:1 TKO 600 w/2.87, 1.89, 1.28, 1.0, and .64; clutch is hydraulic RAM dual Vehicle weight dry is a tad under 3000 lbs. Engine: - Dart SHP w/forged Eagle/SRP (4.155x3.75), 5.7" H-Rods; decked .003; dished SRP pistons ring gaps at .020, .018 and .015; internally balanced - AFR 195 Eliminator Street Heads; 65cc, yield about 10.6:1 static comp; still have stock springs that haven't moved in 6 years; will change springs
- Comp XFI 280; 280/288 advertised, 230/236 at @ .50, .570/.576 w/ 113 lsa and 109 ICL; its installed straight up which I understand as 4 degrees advanced - Edelbrock Victor E EFI; this is a change from RPM Air Gap; plan to port match; intake is topped by 1/2" thick ZEX perimeter plate for future small shots - Holley HP MPFI; this is change from Powerjection III TBI; the Holley 4BBL throttle body is supposed to flow 1000 CFM - Hooker Super Comp Side Exhaust w/ 1 7/8" primary OD and 46" primary length
- Valve train consists of stock spider, GMPP roller lifters, 5/16" .080 wall Comp pushrods and 1.6 Harland Sharp RRs - Windage tray pan, aluminum water pump and radiator, electric fans - Ignition will be Holley unit to work with EFI, planning batch fire - Accessory drive is factory serpentine from '88 F-body and using factory F-body PS pump, pancake A/C comp, and aftermarket smog pump delete pulley
So my combo concerns are mostly regarding Victor E EFI intake, the XFI 280 and the exhaust. I haven't seen many of these used and most, I think were carbed race applications on smaller motors. I basically painted in to a corner on the exhaust because the tube chassis was spec'd to run side exhaust. There are options, but none I really want to do. I never considered nitrous in the original plan and regrettably didn't gap for it. On the plus side, I've read the cam should work well with it. I only plan on small shots.
I can post some pics if anyone's interested.
Hope there's some interest discussing this setup.
Welcome to thirdgen.
While not an EFI guy I do have some experience with small block Chevy's.
A question and an observation to offer (and this might get the ball rolling).
Have you verified your compression ratio? That is, other than part number specs. For me, first thing is to determine what that number is using head volume, piston dish volume, how far down the piston is at TDC, head gasket etc (as you are probably aware).
That's the question. And it ties into the observation which is the cam you've listed. One thing that stands out is the very wide LSA. Especially for a 400+ CID engine. Normally aspirated (EFI notwithstanding for a moment), a 400 with heads like the AFRs (amongst others) could use a separation angle as tight as 104 degrees. This is for best peak HP and torque. There are exceptions to that but that's how my understanding of that cam spec works. LSA first. Overlap next and the duration falls into place.
Maybe that'll get the conversation going.
Nice car by the way. I had the enjoyment of driving and servicing a 68 Vette way back in my college days. Lots a fun with the 4 speed that's for sure.
I think your combo is fine. It will drive very nice and be very torquey. Cam on the wider lsa isnt a huge concern as 400 inches will make lots of grunt. And bit wider lsa will like nitrous but could go tighter. Cam is good match to the heads. Afr has 8019 springs which are perfect for that cam
i’ve run the afr 195’s and a set of speier racing 245’s on a low comp 400” motor built for turbo. Same victor E efi intake. First cam was a 233/233 on a 112. Very mild and torquey. 0-5500 rpm it was very strong. Smooth idle. With the 245 heads i ran a 246/252 cam on a 113.5 lsa. Radical idle but still very well mannered with efi and still drove nice. Broad smooth powerband.
you made a good choice with the mpfi
i’d probably run afr 210’s on it at the minimum and a 236/242 based cam on a 110-112 if more of a street deal. 220 heads and a 242 ish cam on a 109-110 or so lsa for more hot street and drag.
I think your combo is fine. It will drive very nice and be very torquey. Cam on the wider lsa isnt a huge concern as 400 inches will make lots of grunt. And bit wider lsa will like nitrous but could go tighter. Cam is good match to the heads. Afr has 8019 springs which are perfect for that cam
i’ve run the afr 195’s and a set of speier racing 245’s on a low comp 400” motor built for turbo. Same victor E efi intake. First cam was a 233/233 on a 112. Very mild and torquey. 0-5500 rpm it was very strong. Smooth idle. With the 245 heads i ran a 246/252 cam on a 113.5 lsa. Radical idle but still very well mannered with efi and still drove nice. Broad smooth powerband.
you made a good choice with the mpfi
i’d probably run afr 210’s on it at the minimum and a 236/242 based cam on a 110-112 if more of a street deal. 220 heads and a 242 ish cam on a 109-110 or so lsa for more hot street and drag.
I'm sure it'll be "fine" too but...
Do you have advertised specs for those cams Orr? I'll do a little reverse engineering. Maybe run a DynoSim.
It's pretty much a given that the greater the CID for a given cylinder head (in particular the intake valve size for the greater range of seat profiles for SBCs and not LS or big block Chevs), the tighter the LSA needs to be for best output. 350 = 108. 383 is 106. 400 gets to 104. Few do it. But those that do make power. I'm not talking driveability or subjective observations. Just best torque and horsepower. No turbo built design or nitrous either. Just NA power.
EDIT: What I can't comment on is the difficulty of tuning such a combination with EFI. The overlap, which is what will determine where peak torque is made, could represent a problem but I'm sure a pro could work through that.
Lsa is simply a byproduct of the valve events. I dont really worry about it much. Better heads and broader power curves tend to favor wider lsa. Sbc stuff is known to work well with 106-112 but combos vary and desired power curves vary. More street and autox type stuff i think likes wider lsa. Especially on the tuning side of things, using self learn capabilities but honestly havent had much issue with higher overlap and or tighter lsa stuff in the past. The only stuff i see using tighter than 106-108 are circle track stuff or superstockers but they have different things to deal with that you dont have in a street car
Difference between a 106-108 and a 112-14 may be 20 lb ft down low, sometimes more. Sometimes maybe nothing. But its hard to say exactly. I know the Vizard way of doing things is ultra tight lsa stuff. It seems to work but thats just one method.
I’ve seen very stout builds using abit wider lsas.
Good heads and big exhaust header may not do well with high overlap. Too much exhaust scavenging, maybe reversion.
If you arent building max effort drag stuff i would lean toward wider lsa for manners and tuneability imo. But most 350-406 sbc stuff with cams between 220-230 deg for 350’s and 224-240 degs for 383+ builds will run well and tune well on 108-110 lsa’s. These will be custom grinds since shelf cams are usually wide. Or be a thumper bootleggers cam for the sound but not be optimal for overall average power.
That's just it. LSA isn't a by-product of the valve events. They are a product of LSA. Regardless of the application, I'm talking about the biggest bang for the buck. That's the most torque out of a given CID. This is strictly SBC and similar in-line valve headed engines with an intake valve CD of .7 in the .100 to .200 lift range. Tens of thousands of dyno tests demonstrate empirically what the best LSA is for the combination. The combination includes the CD as mentioned as well as the compression ratio and CID. LSA first. Then overlap which determines peak RPM torque production. With those two in place, duration is a result rather than the target.
But to each his own I suppose.
Some argue that the IVC is the most important of all the cam specs but those same dyno results show that that is not the case. Once you have the overlap you're seeking in combination with the proper LSA, you can tune that IVC with came degreeing. But again, with the right cam, that shouldn't be required.
And I'm not talking about maximum effort drag stuff. I'm talking about the most torque possible. That can be translated into whatever application you want. And the differences are greater than you think.
SkinnyZ,
I went this direction about 10 years ago, and at the time, the affordable EFI/TBI stuff was pretty new, as was/is my knowledge of EFI tuning so that played a lot into cam selection. I agree that it is likely a conservative grind for the CID. One thing I wasn't betting on, is the apparent difficulty controlling valves due to the lobe design, or so I've read. I'm hoping the upgraded springs will be enough since it'll be a relatively low RPM motor, but since then I've read of stouter lifters/pushrods, maybe chromoly rockers instead of aluminum.
You asked about CR. It's been a while but with gasket thickness to get a .040 quench I came up with 10.6:1. I did not cc the heads though.
Orr89,
Your car must be nuts! How did the 401 hold up? I see you've moved onto bigger and better...
So you think this intake will work out? It appears to have pretty straight paths and the runner exit areas are a bit less than the RPM Air Gap...my logic is that with since its air only, it should have decent velocity. Did you ever run it non-boosted? Or been around others who used it?
How do you guys think the headers will affect things? I've read a little on the topic, but I've also seen some varied information. The primary tube ID is 1.775 which by most calculators is too big for the motor and RPM range.
How do you guys think the headers will affect things? I've read a little on the topic, but I've also seen some varied information. The primary tube ID is 1.775 which by most calculators is too big for the motor and RPM range.
The books say 1.75" ID based on the exhaust port flow at maximum lift (AFR 195, 218 CFM @ .550" (no spec for .570")) and best overall performance on the street. If you don't mind giving up a little low engine speed torque (and by most accounts here you'll have some to spare), then the pipe size can be bumped a little. It's not until you get into road racing or similar where the lowest engine speed isn't less than about 75% of the maximum that a 1 7/8" ID primary is suggested.
That's just it. LSA isn't a by-product of the valve events. <em>They</em> are a product of LSA.<br />Regardless of the application, I'm talking about the biggest bang for the buck.
whats the lsa on a dual overhead cam 4v ford motor? Only reason we have lsa is because the exhaust cam and intake cam are stuck on the same shaft
The vizard method seems to work well dont get me wrong. I see you are a fan but its not the end all be all because you have to look at other factors like tuning, idle, part throttle, vehicle use, etc. in the end torque doesnt matter down low to me when you have more than enough to roast tires. I dont do any manual trans driving so there may be something to be said for lower end torque but i do know high overlap can cause some issues at cruise in high gear. Surging/bucking. Some of it can be tuned out tho. If auto trans, gear and converter overcome torque.
A 280 cam on a 106-108 may work really well too. Call comp cams and ask for it ground on a 108. I just dont feel the gains are anything super special with a 195 head and street performance driving in mind. If you already have it then i would not go replacing it and spending money for lsa.
Your car must be nuts! How did the 401 hold up? I see you've moved onto bigger and better...
So you think this intake will work out? It appears to have pretty straight paths and the runner exit areas are a bit less than the RPM Air Gap...my logic is that with since its air only, it should have decent velocity. Did you ever run it non-boosted? Or been around others who used it?
it did well for several years but the last yr it got hurt from a blown turbo after it ate some foreign objects. I kept running it hard and found alot if parts bent inside so i had to change up
i never ran it on motor alone but normal driving off boost it felt pretty decent given the fact it was low compression. Theres alot of room to port the intake if needed which i ended up doing to fit the new heads. My buddy ran that intake on his 406 with ported afr 195’s that flowed 308 cfm. Was a miniram and the victor e picked up 2 tenths and 2 mph right out the box. That car made 521 whp all motor and 775 on a 250 shot
[QUOTE=Orr89RocZ;6343986]whats the lsa on a dual overhead cam 4v ford motor? Only reason we have lsa is because the exhaust cam and intake cam are stuck on the same shaft
... other factors like tuning, idle, part throttle, vehicle use, etc. in the end torque doesnt matter down low to me when you have more than enough to roast tires.[QUOTE]
4V engines are a different animal altogether though the VVT aspect of dual cam arrangement is directly targeted at changing the LSA on demand isn't it?
Anyway, with respect to the tuning, idle, etc and the torque "down low", that's not what I'm getting at. It's more of an absolute and what makes the most power. And it's not just LSA I'm driving here. Just saying that it's to be considered first when trying to define the engine's spec. What has been proven to work best? I can think that sometimes the successful engine building enthusiast's results, (not the guys that are pros at the top of the game) have a decently spec'd cam by backing into it. And I will agree on your point of is it that much gain. For me and my past performance, there may not be a lot there. I'm one of the guys who backed into it as mentioned. But there is something and I could have done better. If you've got a clean slate, then I say it deserves attention. And certainly more than the average guy gives it.
As for Postal, the engine spec is already defined and like you said, it'll be fine. At this point it seems a matter of details.
4V engines are a different animal altogether though the VVT aspect of dual cam arrangement is directly targeted at changing the LSA on demand isn't it?
if considering the coyote engines, they can move the installed centerlines of each cam many degrees. Which means lsa changes constantly since lsa is defined as the average of the intake centerline and exhaust centerline. So there may be an optimal lsa for each operating condition, but since sbc cams are on one lsa, its a compromise for a given operating range. Where you build the torque is strictly a choice. We only have one set valve motion, one set intake length and one set exhaust effect.
I suppose sub 6500 rpm stuff may work best with much tighter stuff. But that comes at a cost. Everything is a compromise. The top na producing engines are pro stock and they have used lsa’s over 120. On the other end with superstock with stockish heads and intakes depending on class rules, they run alot of ultra tight lsa stuff. All depends
Read that before. Interesting points made although it never comes to any conclusions and kind of wanders off the subject matter which in this case is a 400 CI with a 2.05" intake valve. (Not sure about what the OP was trying to build over there at Speed Talk). As for Pro Stock engines, that's hardly a SBC with conventional heads or a reasonable compression ratio. At 15:1 CR and a tiny combustion chamber the overlap and consequent scavenging isn't needed. But that's apples to oranges and doesn't have any relevance to this OP.
As for Vizard, he's certainly not alone with the tighter than "traditional" LSA, (which I would like to emphasize is not the only factor to consider seeing as how this is how my comments appear to be construed). I've latched onto it as there appears to better than "traditional" results when defining best power output. But, as you point out Orr, it's just as importantly application specific. I can leave it at that (and hope the OP returns an offers further input).
FWIW, I'm stuck on a cam spec for my small headed 383 project. While a tight LSA of 106 is recommended, with the 70-75 degrees of overlap targeted (seat to seat), the resulting duration doesn't amount to much. Got to dig a little further. Ultimately I'll probably make a request of Mike Jones and Terry Walters (although the latter charges 175 bucks for a spec) and end up with something uniquely designed.
Cam (valve) events are measured from the intake centerline, i.e., peak opening. From there, LSA is the # of ° between peak exh valve opening, and peak int valve opening. Since int valve peak opening is "zero" for purposes of that discussion, wider LSA means the exh valve opens earlier (more degrees before the int valve). Earlier exh valve opening means that the cyl starts to "blow down" sooner; the last little bit of cyl pressure time that could be pushing the piston down is lost, but lower cyl pressure when the int valve opens is the benefit you get in return, which means less reversion (reversion is what causes "lope"), better cyl fill, and less contamination of the new cyl charge by spent exh gases. "Dynamic compression" - a proxy for the pressure developed in the cyl during actual operation, as opposed to merely the mechanical property of piston motion vs cyl volume - is also significantly affected.
In general, if you take 2 cams that are otherwise identical but have different LSA, the one with the lower LSA will have the torque and HP peaks closer to the same RPM, and both higher. It will have higher torque at lower RPMs, may tend to ping a bit more. It will idle rougher. It will use more fuel. The torque (and therefore HP) will fall off faster once past the peak RPM. The one with the wider LSA will have lower peak HP and torque both, but will be farther apart in RPMs, generally with the curve "smeared" upwards. It will idle better. The one with the narrower LSA will win the race if its RPM can be kept in the range of the peaks; the one with the wider LSA will often be more "fun" to drive on the street because it will stay in its optimum, or nearly so, RPM range for more of the time. In short, there's no "right" LSA to use; you pick a cam's intake duration and lobe center to match the intended RPM the engine will be used at, the int lift to open the valve up to or just past the point at which the int port in the head quits increasing its flow, the exh duration and lift to allow the exh port to fully evacuate the cyl before the next int event, and the LSA to create the torque/HP vs RPM curve you need to match your converter, gearing, vehicle weight, and usage requirements. Advancing a cam tends to lower all of the RPMs at which things occur: 4° is usually good for a 250 - 300 RPM drop or so, starting at idle. Idle vacuum therefore tends to be better. The actual peak values won't change much, only the RPMs at which they occur. Torque will come in sooner and peter out earlier.
Keep in mind always, in all of these things, that there isn't necessarily one setup that's "better" than any other, universally. All of these parameters are best thought of in terms of SUITABILITY FOR PURPOSE. Like, you might think that a Vette is "the best" car; but if you have 10 tons of gravel to haul, a dump truck suddenly becomes "better". Cams aren't too much different: you should select them based on their match to what YOU want YOUR motor to do for YOU. A "custom" cam might be worthwhile IF there's no off-the-shelf one that gives the characteristics YOU want, especially if what YOU'RE doing is uncommon or off the beaten path (not many are); and IF you can characterize what you want accurately and clearly enough for someone with the right knowledge to translate that into cam numbers. "Advertised" "RPM range" is a PERFECT example of HOW NOT TO buy a cam, for instance.
IMO the intake and cam you list are appropriate selections for what you say you want to do, although the heads are a bit on the small side for a 400. I'd suggest upgrading the valve springs FOR SURE. Your biggest issue will be hood clearance; if that intake uses a downdraft TB, which I think is what you're doing, then you won't have enough room for much of an air cleaner at all. A "drop base" is DEATH to a large motor, because dropping the base ALSO drops the lid, and it hardly matters what's underneath it, if all the air has to sqweeeeeeeeezzzzzze through a tiny little crack between the lid and the top of the TB, and then make a hard 90° to head down into the motor. An elbow and a side-draft TB would be a MUCH better choice than that. Exhaust will need to be 1¾" primaries minimum, long tubes are better of course but that's not as easy as it sounds in many cars, 3" collectors probably 10 - 12" long or so. While "possible" in theory, it's REAL HARD to put "too much" exhaust on a 400 in the real world.
Last edited by sofakingdom; 12-18-2019 at 06:41 PM.
For an elbow and throttle body, talk to chad speier about what he did for his street car build. It was a 535 hp short stroke 380” deal. He had a single plane and custom porting to his elbow to minimize flow loss as 90 deg elbows have been known to kill some flow over the short turn. His didnt lose much at all
Right: while a downdraft TB might be better IF IT FITS, that's not necessarily the case if it DOESN'T. Which an air cleaner lid jammed down on top of the top of the TB is pretty close to the very definition of NOT fitting.
"Best" in the real world can sometimes be very different from "best" on paper, or on a dyno, or in somebody else's car.
Rob, I think you’re going to enjoy the combination with the new Victor E and 1000cfm 4150 style throttle body. I wouldn’t worry about changing anything. I would gasket match the intake to the heads though. Single planes are more suited for nitrous plate systems as they typically have more even distribution or less variance between cylinders than dual planes. So that's an added plus.
Ring gap should be fine for up to a 150 shot as long as the nitrous tune is good. Would definitely recommend a fuel pressure safety cut-off, window switch, and timing retard to be on the safe side of things.
I’ve run across a few engines that have sat with the springs compressed and have had them checked on a couple – those compressed showed no loss in pressure. From all accounts, the springs wear or degrade from repeated opening and closing. So, before I bought new ones, I’d mark those that were heavily compressed and have them checked.
You should be good on the push rods and rocker arms also. Years ago I ran 5/16” pushrods and Harland Sharps on a daily driven 406 with a fairly aggressive solid roller with .640 net lift for many years without a problem.
The header's primary diameter won’t hurt much if any on your engine – it’s probably better to go bigger than smaller considering the length and number of bends. Seems like there are inserts for the side pipes that act as a muffler, or is there a decent straight flow through muffler like the DynoMax bullets? If they’re an insert and fairly restrictive to flow, you’re MUCH better off with a wider lobe spread on the cam. The tight lobe spread cams require a “zero-loss” or near zero-loss exhaust or you’re get nasty peaks and nulls.
Guys, thanks again for the assistance on this. I made a pretty long post, but it hasn't shown up. I gave bad information in my initial post. My pistons are actually -21cc dish, but the bad info part is that my static compression calculates to just over 9.7:1 using the 65cc head. If the other post appears it will explain more on that, but short answer is I don't know or remember how/why I thought the other was correct. So it's approx a 1 lower than I initially stated. I don't mean to derail the conversation, but this does seem to degrade things a bit. I'll sit tight and see if the other post appears so I don't cause too much confusion.
I was thinking the same thing on the heads when I first realized this. With all the discussions on cam characteristics I really do think I'll be happiest with a nice steady curve as opposed to something radical. Thanks for the read and those posts, by the way.
I didn't mention this, but one of the reasons this project sat so long was that I moved. I'm now in CA and 91 octane is the best within reasonable distance. This brings me to my next question.
In the disappearing post, I mentioned that, once i discovered this I tried to calculate the dynamic compression ratio. The calculator required IVC @ .050 and has a separate calculator to devise this spec from comp cams since they list events at .006. For my cam I came up with 44 degrees at .050. Using this and the other specs is provides a DCR of 8.04:1. I expected lower so I'm doubting the inputs? I used the calc at gofastmath.com. For the others I'm not sure how to add in cam info.
With CA pump gas as a requirement, and everything else considered, what are your thoughts. I will have the heads milled if it makes sense to do so; was going to pull them anyway.
Everything should fit under the modified hood with about 1/2" to spare; intake -> Plate-> Holley TB -> 3" flat-base air cleaner. This is a '67 BB scoop grafted to '68 SB hood.
Here's the most complete pic I've got, but shows the hood closed. RPM Air Gap, PJIII TB and same 3" flat base air cleaner; almost too low. The Holley TB is like an inch shorter than what's shown in this pic.
Or pick a cam that's better suited to 9.6:1 and 400 CID.
But that's not going to be easy.
9.6 is still plenty of compression to make some power. But it be easier to mill the heads some to get a half point back. But its all just grasping for the last dozen ponies or so
i tuned a 9.8:1 360” with the 280 xfi and a stealth ram. Definitely made power up top and peaktorque was up in the mid high 4000’s rpm. Definitely preferred more rear gear but ran ok even with a cheap s10 converter for a few months before the 3600 went in. A 400 with its cubes should help tame things and get torque down lower
If you are restrained to warm weather and 91 gas, i’d leave it alone. You will enjoy it
Gorgeous car. I wouldn't change anything. Just tune it for best idle and run it. Perfection is a hard thing to achieve anyway, and I'd say you're not too far off. You've built a beautiful car that will be a blast to drive, and a real head turner too. The only real issue you may have if dynamic compression is low is a lopey idle. By 3,000rpm, you won't feel any difference. And if the calculator is correct, 8.04:1 isn't bad at all. At 9.6:1 you will be much safer running 91 octane, especially in hot weather.
Looks like it's about ready to drive. What a beauty.
9.6 is still plenty of compression to make some power. But it be easier to mill the heads some to get a half point back. But its all just grasping for the last dozen ponies or so
i tuned a 9.8:1 360” with the 280 xfi and a stealth ram. Definitely made power up top and peaktorque was up in the mid high 4000’s rpm. Definitely preferred more rear gear but ran ok even with a cheap s10 converter for a few months before the 3600 went in. A 400 with its cubes should help tame things and get torque down lower
If you are restrained to warm weather and 91 gas, i’d leave it alone. You will enjoy it
There is something to be said for that last 1/2 to 1 point in compression. And something I've learned that's often not worth chasing as stated above. Unless of course you're building a race car and not a daily driver. I suppose there's a middle ground there somewhere.
What irks me though is not taking advantage of those cubic inches but rather saying the extra cubes will help crutch up an otherwise under performing engine. At this point, given the CR and cylinder heads, it comes down to the cam. And most certainly there's a better choice than 280 with a 113 LSA. Especially with a 6 speed.
But, now having said that (again), I'll leave it at that.
It WILL be enjoyable to watch this Vette hit the road and I'll be following. Good luck.
Given the specs and compression so far and assuming a nice 6000 rpm peak with those heads
i get
280/284
228/231 at .050
.376/.365 lobe lift
.593/.575” with 1.6 rockers
107 intake centerline 110 exhaust
108.5 lsa
given the street nature and manual trans potentially operating at cruise speeds in overdrive, 113 lsa would not be super terrible imo, the 280 xfi is really close to being a great cam for that deal. On a 110-111 it may be abit more spunky down low. 108.5 be abit lopey and rowdy, but doable. Just need to spend extra time tuning in the cruise areas
Orr and SkinnyZ, thanks again. I've been crunching numbers a little more. I don't want to be overly conservative, but I also want to enjoy this thing without worrying too much. This DCR calculation seems to be black magic; both in how to accurately calculate it and how high you go based on fuel and head design. I've been on multiple calculators, and its funny how the same inputs output different results. I ran numbers on the calculator provided by SkinnyZ. The first group is current and so you can check my work with cam timing. The other sets show SCR and DCR if I mill the heads to 60 or 58cc. My number crunching is the attached pdf.
ASE Doc, thank you. This was a divorce gift, and at the time, I had all kinds of time to put into it. I got caught again so its a little tougher these days. Its definitely the most extensive car project I've ever attempted; hence why its still not done. Close though...!
Numbers look ok. Should be fine between 7.5-8.0. Its just a number, with rough correlation to pump gas performance capability. Not the end all be all design parameter. The tune can also influence it, your timing curve and fuel richness can make certain things work. Along with engine coolant temp. I think afr heads have good fast burn chambers. Somewhat conservative timing is good. I’ve been over 8:1 dcr and ran on 89/93 mix just fine.
I ran a bret bauer hydraulic roller in my old 383 setup with 10.5:1, miniram intake, hooker 2210 1/3/4 headers, arf 215 heads and it ran great. 230-230 .600-.600 107lsa. It sounds radical on paper but was the easiest cam to tune i have had since i have been doing this. When i told people it was a 107 lsa cam they didn't believe it. Great bottom end and midrange and it pulled up to 6350 on my 383. I think the best mph at the track was 118.5 at 3600 lbs.
Best advice i can give is this: Get a custom cam from someone who knows what they are doing and not an off the shelf cam.
Interesting. I ran a bauer cam that was 230/245 on a 109. Also fairly easy to tune and drove great with an automatic. Idle took some work and it didnt seem to like closed loop warm restarts but i think i could have tuned that out now looking back on it
i have however heard the 6 spd lt1 guys complain about the old LE heads cam packages when Bauer was doing them. The bigger cams on the 107-108 lsa had some bucking surging issues in high gear but fine elsewhere.
Numbers look ok. Should be fine between 7.5-8.0. Its just a number, with rough correlation to pump gas performance capability. Not the end all be all design parameter. The tune can also influence it, your timing curve and fuel richness can make certain things work. Along with engine coolant temp. I think afr heads have good fast burn chambers. Somewhat conservative timing is good. I’ve been over 8:1 dcr and ran on 89/93 mix just fine.
I'd say 8:1 at a minimum and this is here you and I have disagreed in the past Orr. Should one select a cam with specs that kill low engine cylinder pressure, you'll lose that torque that would be available otherwise. Sure, cylinder head port design and combustion chamber efficiency will prop some of that up but why give it away?
Be all and end all? No. Certainly not. But every bit as important with respect to the engines personality as LSA and overlap. Get them right and you've built a rock star. Get them wrong and you've got a lounge singer.
Originally Posted by 89gta383
I ran a bret bauer hydraulic roller in my old 383 setup with 10.5:1, miniram intake, hooker 2210 1/3/4 headers, arf 215 heads and it ran great. 230-230 .600-.600 107lsa. It sounds radical on paper but was the easiest cam to tune i have had since i have been doing this. When i told people it was a 107 lsa cam they didn't believe it. Great bottom end and midrange and it pulled up to 6350 on my 383. I think the best mph at the track was 118.5 at 3600 lbs.
Best advice i can give is this: Get a custom cam from someone who knows what they are doing and not an off the shelf cam.
A 383 on a 107 LSA is a text book spec. Typically, those cubes with a typical 2.02 valved head would perform best (and by best I mean most torque and horsepower and nothing else) with a 106. The AFR heads and their better than average low lift flow (.100-,200") let the LSA spread out a little. Hence 107. Similarly, the BBC has those qualities. LS engines on the other hand have superior head flow and the lobe spread can get even wider.
Of course, the other cam specs need to be considered as well. Particularly the overlap. Then there are the cubes that need to be fed so sufficient lift comes into play.
As for your cam 89 GTA, do you have the cam card specs? I've real interest in those numbers in that I'm still searching for something for my own 383.
Perhaps of interest, this from Bauer Racing Engines:
Camshaft lesson time... had a shop ask me for a upgrade at cam for a 427 Cube LS motor for a Chevy SS. Street car stuff here, nicely ported LS3 heads, LS3 plastic intake, headers... standard stuff. The requirement was now the motor doesn't need to pass a sniffer test for Smog.
This was dual PAC Racing Springs RPM series valve springs, 1.8:1 Yella Terra Roller Rocker Arms, and both cams were ground at Comp Cams.
I don't really post up cam specs because someone paid me to design this for them, not everyone who wants free cam specs! BUT we can discuss the difference in what is going on here since this is a good example of what I see adding overlap and tightening LSA does, if done correctly....
The two cams have virtually the same Intake Valve Closing (IVC) point (different by 0.5° @.050") and Exhaust Valve Opening (EVO) point (different by 2° @ .050") but there is a big difference in overlap... it increased from 0° @ .050" to 11.5° @ .050". This is basically a 4° tightening of the LSA.
The lobe profiles on the new lobes allowed us a little more lift (.020") so that helps as well but it's minor in comparison to the overlap changes.
We got a net change of 27hp and 42 lbs ft.... and it was basically shifting the whole curves upwards from when you get on the throttle to when you shift. So that should be a noticeable gain in the butt-O-meter.
Some people realize the value in better designed parts, and pay for that difference, this is what you get. Little things do matter.
Based on some of Brets cams i have seen and my own personal grinds from him, he does like the magnum high lift comp lobes. Those LE grinds were old before alot of comps newer lobe profiles came out.
But the magnum high lift are decently aggressive yet stable at rpm. 286/230 and .376” lobe. The bigger duration stuff can go to .400” lobes. Comp has several other new high lift hyd roller lobes out but most builds do not need that much lift anyway
Notice how he said If done Correctly lol. Not everyone does it correctly. Look at how the ivc and evo stayed similar. That means intake centerline remained the same or very very close. The exhaust centerline would have to change to make the lsa change then but that would mean an evo event that would open later. His came stayed close to same. So he had to add duration to make that work and can see it in the graph . The exhaust lobe area is greater.
They may have similar advertised but way different at .050, .100, .200”
this is why you have to read into valve events. They determine where the overlap period occurs with the centerline angles. Lsa is what it is but dont let bret fool you in that post. Thats a different lobe profile and that changed alot more of the engine parameters than lsa.
do a lsa only change and see what happens. Sometimes it works sometimes it doesnt. Most comp cams come with 4 deg advance built in. So a 113 lsa cam should install on a 109 intake centerline, if installed “straight up” on the timing chain. A 108 lsa would be 104 intake. Way different valve events and overlap periods. A 108 lsa in on a 109 centerline would be an interesting test as the intake valve opens and closes the same position
Who said anything about an LSA change only? The IVC event is by some arguments the most important but that's only some arguments. It has to be considered also as it affects the DCR as previously discussed.
It comes down to this. The XFI 280 on a 113 is not the right cam. Sure. It'll work "just fine". But there most certainly is a better spec that will not only build more power but also fit into the OPs goals.
Just saying.
Who said anything about an LSA change only? The IVC event is by some arguments the most important but that's only some arguments. It has to be considered also as it affects the DCR as previously discussed.
It comes down to this. The XFI 280 on a 113 is not the right cam. Sure. It'll work "just fine". But there most certainly is a better spec that will not only build more power but also fit into the OPs goals.
Just saying.
it basically says that in the post you attached. I just wanted to point out and clarify that it wasnt just an lsa change.
I never stated it was the best cam either. There isnt one. My view of best for that combo is different from yours and different from the OP. Cam performance is user defined mostly. But given the choices of an off the shelf easy to find cam do you have a better option? Please list it. Shelf cams suck for the most part, not a lot of options imo. But many have used the 280xfi shelf and its a solid performer
it basically says that in the post you attached. I just wanted to point out and clarify that it wasnt just an lsa change.
Help me out here. Which post specifically? I've stated that there's tons of data to say that the LSA with respect to a given cylinder heead and the CID requires the LSA to be altered accordingly but perhaps I assumed that readers would know that other significant valve events, namely the IVC, would also have to be addressed. My bad if that wasn't clear.
Originally Posted by Orr89RocZ
I never stated it was the best cam either. There isnt one. My view of best for that combo is different from yours and different from the OP. Cam performance is user defined mostly. But given the choices of an off the shelf easy to find cam do you have a better option? Please list it. Shelf cams suck for the most part, not a lot of options imo. But many have used the 280xfi shelf and its a solid performer
That's just the thing Orr. Listing it is easier said than done but you know and I know there is one. There's real relevance with the "user defined" statement and I'd like to know exactly what that is.
Rob has a 68 Vette body on a tube frame chassis and big freaking spoiler on the back.
6 speed.
Etc. Etc.
Street car?
He's expressed his intentions but...
Sounds like a track car to me. Or at least it should be and the engine should be spec'd accordingly. 195's on a 406? Smallish by what's been posted here and elsewhere. Give it more cam and let it eat I think was the expression used.
If Rob's is truly a street car with that sophisticated chassis and rear spoiler, then so be it and I am out of here.
Otherwise, tighten up the LSA, select the overlap that suits the RPM range intended (which currently sits at a measly 53°), use that 6 speed and make sure it has enough lift given the duration to feed all those cubes.
That said, picking that cam is not a cut and dried thing and as has been suggested, might be better put to an expert. I can add values into a calculator or the like but, I will say and as you said, it's still very much user based.
That's all I have for now but I'll try and crank out of few suggestions and I look very much look forward to feedback, criticism or whatever.
Quick look at what's been proven to be successful. Strictly book-speak.
282/231. (single pattern). 106 LSA 102 ICL
With a SCR of 9.6:1, DCR value is 7.85.
If a weak exhaust is to be accounted for, then add something to the exhaust duration.
Better still.
282/231 (single pattern), 105 LSA. 101 ICL. DCR goes closer to 8:1.
Not splitting hairs here. Just tossing out a few examples that'll work with 9.6:1 and average pump gas.
The above is recommended to have a higher ratio rocker. Getting the valve opened to .600" helps feed those cubes with the somewhat depressed duration.
what is going on here since this is a good example of what I see adding overlap and tightening LSA does, if done correctly....
it increased from 0° @ .050" to 11.5° @ .050". This is basically a 4° tightening of the LSA.
this is from Bauers text you posted. I read that to imply the lsa was mainly the thing that changed but i see the entire story, the lsa is just one of the chapters there.
i also will note that i am not a clutch guy buy do have close friends in the tuning and performance car building business that do have alot of clutch experience. You can get away with big cams on certain clutches compared to others but the tune is a big factor. And driver preference comes in to play. Some guys dont mind a tough clutch and a radical cam. Some guys do. Thats harder to define without having experience with many clutch types.
If I was building a street 406, i’d have atleast afr 220 heads or something from speier in the 227 range. 10.5:1 to 11:1 with a 240 deg hyd roller on a 110-ish lsa. Peak lower mid 6000 rpm with that victor E and make near 600-620 hp. But i like alittle more aggression in my cars and dont autocrossor road race, mainly straight line
then again, everything i touch now will have a turbo or two on it
In building a street car, I would tend to overlook a lot of nitpicking over "numbers". Arguing about cam minutiae belongs in that category. While either, or both, Skinny and Orr might be "right", it's not relevant to the task or the situation at hand.
Building for max HP isn't going to get you what you want. Max torque won't either. What WILL get you what you want, is an understanding of what makes the "fun factor".
Which is, when you push the gas, the car plants your butt in the seat. It starts easy, idles good, isn't too dreadfully thirsty, doesn't require lots of maintenance, doesn't tear up other parts of the car, air blows cold, battery stays charged, nothing leaks, no funky burning smells, runs on the stuff that you can get out of the pump down at the corner, your SO won't mind getting into it, you can close the hood and JUST DRIVE IT without worrying about something failing, … not at all the same things you might want in a strip car.
IMO your combo is just fine for the application at hand. Could you change something and get "more power"? Of course. Always. Are you "leaving something on the table"? Also of course. Will someone else have a faster car? Goes without saying. Can't be helped. Is there some little detail you could attend to, some part you could change, that would gain you acoupla horsepuckers or feet-pounds somewhere? Well yeah.
But at some point, ya got what ya got, and ya might as well put it together and see what it does. Then, a BOM only tells you part of the story; the rest of it is in the attention to detail during assembly, and above all, TUNING. Getting all wrapped up in the BOM is kinda losing sight of the forest because all these trees are blocking your view.
Personally I think that for just a personal cruising vehicle to have some fun in, it'll be just fine, no matter what the "numbers". Even if there's a minor mismatch here or there, it's not so bad that it'll turn the whole thing into a failure. (think, RV cam in a 305 with a single-plane intake and a Dominator, or 8.2:1 L48 with a 302 Magnum cam) I think arguing over what some particular cam properties will do compared to some others is a useless exercise in self-pleasure, when the timing cover is already bolted on.
[QUOTE=sofakingdom;6344709]Building for max HP isn't going to get you what you want. Max torque won't either./QUOTE]
The relevance here Sofakingdom, is that is exactly what I'm talking about. and something that appears to be lost here.
I see a tube chassis body conversion with a 406 CID 6 speed and I'm thinking...what? Well why don't we just dumb it down a little so we can all go home happy. That was not my point at the outset and it still isn't.
Nice engine. Poor cam selection. A potential miscalculation of 8 degrees regarding LSA is hardly minutiae.
And as it turns out, for a decent assembly of parts, hell, even a great assembly of parts (who wouldn't want an SHP block and AFR heads?) not to mention the excellent tuneability of EFI, there's a lot of potential wasted.
But again, here we go.
I'll tell you what. If that wonderful 68 Vette on that chassis and that wing pulls up behind me on the on ramp, it better be freaking fast or it'll get spanked by a better thought out, smaller displacement sleeper. You know it. I know it.
But, and I will concede this much, it's been put together, right up to the timing cover and there's nothing really to be lost with giving it a go. Other than I suppose, pulling the heads and or cam and giving it a redo.
But, and I will concede this much, it's been put together, right up to the timing cover and there's nothing really to be lost with giving it a go.
and thats the point. If its already together, i dont see the point in changing stuff out now. Get it up and running with a cam that you know is proven and going to give you good vacuum and stable idle and work decent with the holley self tuning etc. then decide what to do if you dont like it. I think its gonna fly. I havent seen that cam and head combo NOT work yet
Guys, I do appreciate your time and knowledge on this. From the outside looking in you’re all basically saying the same thing regarding what I ‘could’ do to optimize my basic foundation; that’s a good thing and very much appreciated. That’s exactly why I jumped on here and asked the question. A lot of good and knowledgeable folks on the CorvetteForum also, but only the minority there are truly performance oriented builds, and of those, most are either carbed, or big block, or efi with hood height limits. Now to what I ‘should’ do...
My original goal was to build something with the look, sound and feel of a classic corvette, but I wanted performance, handling and reliability on par with the newer performance cars...mind you that was 10 years ago. Part of it was the challenge to create something cool and unique and the other part was to enjoy it. I’m not a car show or car club kind of guy and I don’t have the extra time to really get into and good at any form of racing. So what’s my plan...not too sure? I live about 5 min from PCH on central CA coast and nearest strips or road courses are 2-3 hours away. What we do have are a ton of great day cruise options with great destinations and great weather.
I mentioned auto cross because I’ve done a few performance driving schools and loved every minute of it. I’d rather abuse it than not use it.
SkinnyZ, just to clarify, there’s no wing, just the early C3 rear lip. I looked and think you’re seeing the deck cover on a stand. In the trailered pic you can see the deck lids still not installed. Also just a 5 speed, not a 6 speed; wish is was though.
Here’s where you might have to try to relate. I’ve done a decent amount of car, motorcycle and aircraft work and engine work; most it on stock/stockish motors. I’ve hopped up a few motorcycles, but the only performance car I’ve ever had I bought already built and was a ‘67 355 /4 speed/4:11 Camaro. That was almost 30 years ago (47 now), I guesstimated 350-375 chp and had no idea of internal specs. So fast forward to my compromise; when you all talk about no low end, cubes making up for larger cams, giving up low end for traction limits or for top end 1/4 mile surge, etc I don’t have much to compare it to. The general non-optimal decisions made were due to a lot of magazine reading (agendas), my ignorance of what actually worked well in the real world and being unable to relate when advised on things like good/acceptable/bad street manners...
I’ve got some thinking to do and will be pulling the intake and heads at a minimum. Several non motor projects as well before I’ll really be able to provide a decent update. I can’t promise when but I promise I will. My going in thoughts are to 1) ensure matched springs, 2) mill for approx 1/2 point scr, match intake and get it to a pro tuner. I might run the cam as is, but I’ll at least talk to a few custom grinders before I close it up. My thoughts at the moment anyway.
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SkinnyZ, just to clarify, there’s no wing, just the early C3 rear lip.
Thanks for that Rob. To tell you the truth I was somewhat mortified when I saw what I thought I saw. As I mentioned I've some personal experience with this era of Corvette and have always had a soft spot for them. Glad to hear you didn't decide to ruin it (objectively speaking).
Good luck and I'm looking forward to your progress. Maybe you'll get yours done before I get mine done.
Kevin
This is a Corvette Forum member with a Gen 1 SBC 383 in a '89 C4; posted in 2017. He doesn't state header info, but from pics they look like 1 3/4 and are definitely long tubes; he doesn't state in car exhaust. He ran the Victor E intake; unspecified carb for engine dyno and Holley HP EFI (using an adapter and LT style plenum on top of the Victor E) for chassis dyno. Probably a 3300# car. He doesn't state how 11.2 SCR is achieved to include quench. The "2618" listed for pistons is a forging ID, not a part #. Omitted is fuel used, injector sizing and if any tuning compromises were made.
Found another mis-speak in my original post; my bore is 4.125, not 4.155 so 401 CID. My motor is 350 journal size as well. A 60cc chamber at .041 quench gets me to 10.1 and 58cc to 10.3.
This has me thinking I'll try to raise SCR and run the XFI cam, especially since it's supposedly efficient with small N2O shots. Was only planning a 125 shot and just for fun.
Aside from SCR (which I plan to improve), slight cam differences and the affects of 18 cubes and larger bore I'd hope for something similar with a very slight edge. I was glad to find a 5.7 rod example.
Just thinking out loud, but I think I'd be content with something in this ballpark, at least for now.
IIRC, flat top pistons, a 64cc chamber and in or around a .040" quench will land you in the11.X range with a 383.
Headers are probably typical dyno headers which tend to be better optimized and most certainly will have zero back pressure which otherwise hurts output (such as most chassis headers plus exhaust). Peak power at 6300 too. RPM matters!
Maybe it would be worth getting the advertised specs on that cam and check out the overlap and DCR.
Nearly identical to my old motor but i had stealth ram and 230/245 cam on a 109 lsa 108 icl
392 whp heat soaked after 10 pulls in summer heat. Colder fluid temps and it be 400+ whp. 6250-6300 peak as well. Held to 6600.
Its very typical of a 383 with afr 195’s and a 230 deg lobe with mid high 500’s lift to make closer to 390-400 whp. Theres nothing sluggish about that power band. A 400” will do similar power, probably bit more about 300 rpm lower and more peak torque because of the rpm shift
12-13-2019, 12:54 PM
