When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
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!
So I have wanted to do heads and a CAM on my 91 Z for years, and I think I may be ready to start taking bites into it. It would be much easier on my bank account if I could do it in steps, maybe over a year or two...
Question is, is ridiculous, problematic, or is there any other reason I should not first upgrade heads on my engine, then change out my cam later on?
As far as I know to upgrade heads you pull the distributor, intake then valve train, and heads, then reassemble in the reverse order. This requires other supporting parts like head, exhaust, and intake gaskets, new valve covers (perimiter bolt), all new hardware, and possibly different length pushrods...
To change out the cam, (hopefully without having to discharge my AC system that I just had completely redone last year) You pull the distributor and intake, then valve train, then pull a ton of stuff off the front of the engine, remove the radiator, and shift the condenser out of the way somehow? Then swap the cam and reassemble. This will require all new front end and intake gaskets and would be a good time to upgrade the timing set on my 150k engine.
Based on my understanding above, doing the heads first shouldn't be an issue mechanically. and it will sort of split the work up nicely into two separate projects.
Secon part of my question, is will I see any benefits performance wise by changing out the heads first if still running off my stock '91 cam with 1.6 rockers? You can see in my sig, I have full exhaust, Holey stealth ram, 1.6 rockers, dual 58mm TB. So as far as pumping air, I should be able to pump as much as the engine wants to!
I don't see any reason you'd want to take it apart again. Others may have a different opinion on it, and that's fine, but if the heads are being changed there's not a ton more that has to be taken apart to change a cam. Honestly, just pluck the engine out and do it all on a stand.
More importantly, what intake are you using and how are you going to tune it?
I think you should pull the motor and do both at the same time so you only have to tune it once. You can freshen up and clean everything a lot better with the motor out, not to mention ease of access to components and full range of motion for accurate torquing.
If you wanna do the work you can. Heads will make more power even wth stock cam. Esp with an intake
But yeah you will need two sets of intake gaskets, coolant, and possibly new pushrods depending how much the new lifters and cam base circle changes things. May get away with stock pushrods on the new heads but likely valve lengths are different, but might want to upgrade anyway if the new springs are setup for a more aggressive hyd roller, 140-150 seat 350-400 open for example.
Pull the engine and do it all at the same time. While you're at it, completely remove the oil pan and replace the rear main seal and the front cover crankshaft seal. And as already mentioned, you're going to need some way to tune the new combination; the existing factory tune will now be somewhere out in left field
It would be much easier on my bank account if I could do it in steps, maybe over a year or two...
....and the enjoyment of doing the "work" is NBD. I did a cam ONLY in my first F-bod. For ~$100 bux ($89 Summit cam/lifter kit in the early '90's + gaskets) I dropped a full second off my 1/4 mile time. I'd do it again.
15 years ago I put a GM LT4 hotcam and 1.6 rockers in a 1990 Corvette with the aluminum head L98 with a 700r4 and tuned it. Took it from a 13.50 @ ~100 to a 12.70 @ 107-108 mph. GM Hotcam kit was fairly inexpensive back then and I used a few of them. I also ran a couple of inexpensive ZZ4 cams in 113 head engines. Had both 081s and 113s on an 18cc dished piston L05 with a ZZ4 cam in my G20 van that was TBI at the time. I really like the 113 heads, especially with some port work and some of the tamer GM Performance cams. Some people want to hate on them, but they drive very stock like, are easy on the valvetrain, are easy to tune and run pretty darn well especially with the old OBD1 speed density ECMs. I put a few sets of AFR 195s and larger cams in a few ZZ3s and ZZ4s years ago and bought the take off cams and heads fairly inexpensively a few times. The ZZ4 heads were a bit better than the OE Vette 113s, they had valve spring improvements and factory bowl work done on them. The old ZZZ through IIRC ZZ2 crate engines had a long obselete cam that I actually like even better than the ZZ3/ZZ4 cam but they are very hard to find and not all that ECM friendly without a good bit of tuning. Luckily the Elgin E1135P is a near copy of the ZZZ cam.
Keep in mind that doing the cam also involves dropping the oil pan enough to release the timing cover. Getting the pan re-installed leak free is a tall ask. I did this a few years back but I had previously installed a 1-piece oil pan gasket in an earlier rebuild. This made the prospect of a good seal somewhat better.
There's a lot involved and it's a little awkward done in the car but as said, it's doable.
The heads can be done without the rad and condenser coming out. Of course everything else topside has to go as has been pointed out.
The cam on it's own doesn't involve removing the heads a 2nd time (if you elected to them first). Conceivably the exhaust can remain intact although access to those oil pan bolts might be limited. As it is, the crossmember does a good job of hiding a few bolts. But along with a repeat of the top end parts, you have to make room for the cam to slide in. In addition to the rad etc., I had to remove some of the hood latch bracing as it's right on centre with the cam tunnel.
Never do just heads. You are leaving power on the table, ALOT of it. The stock cam will never take advantage of the new heads because it doesn't let the engine rev high enough to utilize the extra flow.
Also, I'd talk to Lloyd Elliot, or Advanced Induction (I know, they are known for LT1 and LS1 builds) but they can also recommend a good cam grind to fit your purpose that will make more power than older cam profile tech while staying within the same RPM range.
Do yourself a huge (and free) favour and forget those cams for now. Go to Jones Cams and fill out one of his cam recommendation forms. By all accounts (and there are too many to actually count) he hasn't missed on a spec. Especially if you lay out all of the details and include ultimate end use in the paperwork. Jones is a designer and not some cam company tech guy going through a catalogue of off the shelf cams.
Once you've done that, post back here and the crowd can compare the Hot Cam and the Comp cam to an actual spec. It may prove enlightening. At the very least his lobe profiles are the latest in design and not something engineered twenty years ago (or more).
I've been looking for new heads for my old Camaro too. I noted you mentioned Brodix heads as an option. I was comparing the Brodix and AFR heads too and saw that Brodix heads have no warranty, zero. The AFR heads have a lifetime warranty. This could have changed - and I didn't see it - but that's a game changer for me. Basically the same price on the budget line of the heads. For sure the nod goes to AFR.
The story is I've been wanting to do heads and a cam for years, but each time I start planning it out, I start realizing how many parts and seals, and cost ends up going into it. This is why I was exploring the option of doing the heads first, then the cam maybe a year later to spread out the costs... I guess I could just save up for a whole year, then do everything next year... But it also feels like a big undertaking. I liked the idea of braking the project up into smaller more manageable pieces. I also just dropped my trans to change my torque converter ( and rear main seal, front trans seal) and to pull the engine I would have to drop the trans all over again.
If it turns out I need to just save up, then suck it up pull the engine and do it all at once, I should be able to make it happen at some point in the future...
To address other comments:
-I did put in chromo pushrods when I put in my 1.6 roller rockers. Im hoping ill be able to reuse them.
-my current intake is a ported Holley Stealth Ram with the dual 58mm throttle body
- I have equipment for burning new ecu chips, I'll have to work with someone online to fine tune the tune.
I can feel your pain.
My lists of engine development has always overlapped work done previously. Even something as simple as having to get new header gaskets after having spent 40 bucks on a new set just the year before makes you want to rethink the approach altogether.
I'm into yet again. The engine and trans were yarded out because the shortblock needed a redo. That's after the heads and cam went in years previous (but less than 5000 miles) and a roller lifter self destructed. Just before that, the torque converter broke which eventually cascaded into an avalanche of expense and repair. Not to mention rework.
Even to this day, with the engine completely redone, the newly rebuilt but gently used transmission, which itself was part of that 5000 mile lifespan, decided to become a one-speed. How may litres of transmission fluid does it take when it's all said and done? 30 and counting by my last estimation.
Hot rodding, to me anyway, has always been incremental. I've learned though that certain upgrades have a genuine payoff when brought together as a single project. Heads, can and intake are popular groupings. Having it on a stand makes all the easier but if you're willing to go through the contortions of working in the engine bay, or under it, then it can be done.
Ha! I'm in exactly in the same spot as you, more or less. I did the 1.6 rockers, I put on an Accel/Lingenfelter intake and now I have a set of ProMaxx heads (with hyd.roller springs capable of .600 lift) on the bench but......should I do the cam as well? It's another ~1000 bucks or whatever it might sum up to?). And the cam I'd chose wouldn't be very far off the stock cam specs anyway since I have no interest in revving past 5000 rpm.So, should I change the ProMaxx overkill springs to comp 981? I just want a strong csb with excellent tq from idle to midrange, where I spend most of my time. And I think removing some weight from the front with alu heads also will be much appreciated
Atleast I already have the head and intake gaskets but stripping the front completely sounds like a headache with the engine still in the car, not to mention doing this in my extremely small place that some ppl calls a "garage"
I bet adding another ~80 hp will just move the weak spot to the 4L60 and then I'm in deep waters! (you can tell I really don't want to do the cam thing, don't you?)
I'm not even sure I have the mental strength to do the heads? Hmm......decisions decisions.... I you do the cam I will at least do the heads
Project x 185 cc with roller springs
Heads and cam are stock L98 from 91. Can't remember the casting# right now.
Btw, let's not hijack the OP's thread completely
While I can't vouch for the heads and their machining integrity (as in quality of the valve job, spring setup, etc.) they look to have some decent flow numbers and the port isn't too large. That said, I think you'd be remiss if you didn't compliment them with a cam upgrade.
Your comment about 5000 RPM is a curious one though. Why bother with heads and intake if you're happy with the TPI as it was? My guess is you'll leave 5K far behind once you realize a bump in performance.
As for transmission, well, that's hit and miss. I'd certainly add something like a TransGo kit. Either the shift kit or reprogramming version (I've the latter). A Corvette servo and an upgrade in the boost valve wouldn't hurt either. All done without removing the transmission. That'll give it a fighting chance. At least it did for me.
See how hot rodding goes!
Let's hope the OP finds the information relevant to their thread.
While I can't vouch for the heads and their machining integrity (as in quality of the valve job, spring setup, etc.) they look to have some decent flow numbers and the port isn't too large. That said, I think you'd be remiss if you didn't compliment them with a cam upgrade.
Your comment about 5000 RPM is a curious one though. Why bother with heads and intake if you're happy with the TPI as it was? My guess is you'll leave 5K far behind once you realize a bump in performance.
As for transmission, well, that's hit and miss. I'd certainly add something like a TransGo kit. Either the shift kit or reprogramming version (I've the latter). A Corvette servo and an upgrade in the boost valve wouldn't hurt either. All done without removing the transmission. That'll give it a fighting chance. At least it did for me.
See how hot rodding goes!
Let's hope the OP finds the information relevant to their thread.
What's your take running the promaxx springs on a stock cam? With 1.6 rockers I'm in .470 territory with the stock cam. .130 until coil bind. I worry about too high spring pressure with them.
About 5000 rpm. Of course I will floor it from time to time but the absolute majority of time will be spent at 2500. Highway speeds.
I upgraded the intake because of information I read about the super ram increasing torque and being overall a superior design (except installation.....)
Also have dyno don headers. My goal is getting the engine to perform its best with a stock shortblock (not taking intake gas train speeds and VE into the calculation).
Last edited by Andreas_91GTA; 01-08-2024 at 01:20 PM.
My cam guy always suggests to use enough spring and nothing more. Of course to err on the heavy side is better than the other way around.
Each cam and application is obviously unique.
You may be right in your thinking about those Promaxx specced springs being too much. But without knowing what they are and at what height they've been installed at, you're guessing ( and so would I be). Certainly more than the stockers though. Will that bleed down your lifters?
Makes another case for cam and lifters doesn't it?
At .470" lift, you're barely getting into the meaty part of the flow curve.
Remember too that despite keeping RPMs in check and just generally cruising around, if you don't take the necessary steps, it only takes one tour through 6000 RPM territory to undo a lot of hard work. If you know what I'm saying.
Case in point: Vortec heads. OEM wheezy stock springs. Flat tappet cam at .454". One missed shift and I was 6k(+) before I knew it. That bent two exhaust valves.
I'm not one to spec a cam for anything other than what I have personal experience with.
That said, whether that Summit cam would suit whatever the intended purpose of the vehicle is would depend on a long list of variables.
Try this: http://jonescams.com/cam-recommendation/
It's free and the turnaround is quick. Then you'll have a very well informed idea. But it's not likely to be $300 USD. I made the choice to buy a high quality product and have no regrets.
But, what that spec in hand, you can probably find a very near shelf grind from some vendor. There are several companies that offer that service.
I filled out the form at Jones (monday) but no reply yet.
He's been pretty good with the couple I've inquired about. I did a follow up on each of those too. He gave a spec based on my street performance option. Then I asked again for a drag racing version.
Might take a day or two. There are holidays to consider as well.
Here's what I recommend to use with the OEM lifters.
Cam#: LT1, HR66316-69316-110
211/220@.050"
.316"/.316" Lobe Lift
.505"/./505" Valve Lift
110 LSA
Seems like a reasonable choice with good street manners.
But right now my mind is set on NOT changing the cam. I simply have no space working Infront of the car/engine.
Here's what I recommend to use with the OEM lifters.
Cam#: LT1, HR66316-69316-110
211/220@.050"
.316"/.316" Lobe Lift
.505"/./505" Valve Lift
110 LSA
Seems like a reasonable choice with good street manners.
But right now my mind is set on NOT changing the cam. I simply have no space working In front of the car/engine.
Fair enough. If you're going to indulge in the hobby, it's always better when things are properly set up. I'm in exactly that position now. Having moved to a house renovation project, I'm for the first time in nearly 35 years, without a garage. It's severely curtailed my car crafting but I did manage a few jobs last year.
As for space, are you talking about in front of the engine, as in the engine bay or in front of car? The engine bay work requires a lot of parts removal to get the cam out. Not mention dropping the oil pan so as to free the timing cover. I can understand your unwillingness if your not comfortably set up in a garage or shop.
As for the cam, I'd like to compare it to some of the earlier suggestions. We'll see how a Jones lobe profile stacks up against the rest.
Fair enough. If you're going to indulge in the hobby, it's always better when things are properly set up. I'm in exactly that position now. Having moved to a house renovation project, I'm for the first time in nearly 35 years, without a garage. It's severely curtailed my car crafting but I did manage a few jobs last year.
As for space, are you talking about in front of the engine, as in the engine bay or in front of car? The engine bay work requires a lot of parts removal to get the cam out. Not mention dropping the oil pan so as to free the timing cover. I can understand your unwillingness if your not comfortably set up in a garage or shop.
As for the cam, I'd like to compare it to some of the earlier suggestions. We'll see how a Jones lobe profile stacks up against the rest.
My "garage" is a family shared space with my GTA, wifes winter storage of flowers, toys, garden tools and everything else. There's hardly any room for anything but I somehow managed to keep my car away from winter in there, which I count as a big win
I'll stick with changing heads. Actually got a set of 128's (Corvette 87, aluminium) that I'll go with this year and save the Promaxx:es for later - when I have a cam and working space to match.
Looking a second time at my cast iron heads and comparing the intake runners to an ordinary intake gasket there's up to 5 mm of material that could be ground out. The 128's look almost perfect in comparison.
Do yourself a huge (and free) favour and forget those cams for now. Go to Jones Cams and fill out one of his cam recommendation forms.
Did you ever follow up on this? One of the thread contributors received his spec the other day and I'm keen to do an analysis between those suggested for you earlier and what you might get from Jones.
Even if you're not ready to pull the trigger, it would be interesting to know.
He said, It should make around 410 ft/lbs of torque, and 390 hp. With the short seat duration (264/268@.006") it should have about 16-17" of vacuum, if that's not enough, we can go to a 112 LSA.
Based on my research I think I would stick to the 112 lsa to ease tuning and streetability.
I like the look of that cam, relatively low duration, but with pretty significant lift. It seems he requires the lifters to be used with his cam though, not sure why that would be. I thought as long as hydro roller lifters are in good shape they can be re-used, is this true or not???
I'm still considering it against these other cams:
Good to see you back.
Nice spread sheet although you forgot one critical element. The duration at "lash" will define the lobe's intensity when compared to the .050" numbers.
Most but not all hydraulic rollers are measured at the valve at .006". Comp is measured this way. There are some exceptions though and GM I believe is one of them. I don't recall how they calculate their advertised duration.
That said, I think you'll find in all cases that the Jones lobes are the quickest. This provides that tight seat to seat number that helps keeping the compression pressure up but the .050" values are such that the cylinder has enough time to fill and evacuate.
The seat to seat numbers also define the overlap area. That will play a large part in the cam's character and tunability.
The next and more pressing quandry is heads! I think given the disucssion here and elsewhere, I just need to bite the bullet slowly buy the parts as I can afford them and do all the install at once this fall after the AutoX season is over.
Since the heads are the bigger ticket item, I figure I should make a point of using that 10% off summit discount on the heads, but that means I have 2 days to place the order.
I was all but set on getting the AFR 195 Enforcer heads, but since I have been hearing about the benefits of a 180 head for autox and streetability I am still entertaining the option of the Brodix IK180 heads. I actually spoke to someone at both AFR and Brodix yesterday. Nice conversations with both. Brodix also offers an IK 200 head if I decide I like the Brodix offering better but want higher flow.
Both Heads:
- Made from same material
- As cast runners and combustion chamber
-All head machining done in USA
Benefit AFR:
- offer angled plugs, this is a great benefit for third gens with shorty headers, right?
- Runner volume between 180 and 200, advertisements say their geometry reduces the losses from the low lift low rpm range often seen with other 195/200 cc heads.
- 8mm valve stems VS Brodix (11/32"?) Allows more flow?
Benefit Brodix:
- Heads Made in USA (AFR uses Chinese castings but seems to have pretty good quality control compared to cheaper Chinese head castings.)
- 180s Seems to have slightly better flow at intermediate lift, but looses out at high lift.
- No steam holes machined on heads, could be a point of crack initiation on the AFR head, or so the Bordix guy says...
I graphed the flow numbers below to compare, this makes the AFR 195 look like it is leading in my choice process...
Granted, this should be taken with a grain of salt because flow benches may not tell the whole power story...
Which heads did you specify with the Jones cam recommendation form? That spec would be a major contributor to how he designed your cam.
That is a valid point, I said my plan was to go with the AFR 195's. I think I'm still leaning that way, unless someone can convince me the 180 cc heads are really going to work that much better than the 195's.
A couple of things come to mind as I re-read the thread.
What's your objective/performance wise? 350 CID and how much RPM? Cruiser or racer?
I went back to Mike for a engine spec revision as I wanted to change how I'll use the car. He obliged with a different cam spec. If I were thinking of different heads it's certain that I would re-visit with him.
Speaking of heads, that takes us back to my questions above.
Personally, I'm in the smaller port category. I've had a 7000 RPM, AFR 195 headed 350 and drove it hard. It also ate parts along the way. 7k isn't as easy as you might think if any measure of longevity is taken into account. Valvetrain parts aren't necessarily cheap. But that's where the 195's shine. Or less RPM but more cubes.
There are benefits to a smaller port although it's not cut and dried really. The general consensus is that the smaller port might be more efficient at low RPM cylinder filling but some larger ports do a better job down low compared to smaller heads. It depends.
Do you have flow numbers and other specs for each?
My 357 has (slightly) reworked aftermarket iron heads that started out at 170 cc. Maybe 175 now? CFM @ .500" is ~255. Plenty for peak HP at 6200 and the Jones cam spec'd is said to peak there and carry to 6500 and change. I'm thinking this will be spot on.
By the way, he spec'd:
Going in to his online lobe profile index and the 72360 intake lobe is 280° at .006". The 73360 is 284°. What Mike said he does is pull a profile from his catalogue and then tweak it to suit. He sent it to me as 280/284, 232/236.
I went with his lifters for a couple of reasons. He guarantees country of origin which is US and the slow bleed rate is a racer's friend. Plus it's his cam and his lifter recommendation so I was in. If you've original equipment GM roller lifters there is internet evidence that they kind if give up beyond 6k. I witnessed it. There are those though that say no problemo.
At 350ish ci, "lower" rpm range, I don't know if you'd see any difference. My disclaimer to that statement is that you never know without testing. I went with 180s and a HSR, port match is nearly identical with both parts being untouched so I think I made a good choice. But I'm also not spinning more than 5600 with a 355. I doubt I would be losing anything if I had gotten the 195s and had room to 'grow' if I chose to do so. My combination is done so the 180s were set.
Also note, I think if you get a Jones cam, they make sure you use their roller lifters. I got a recommendation that was very similar to my current cam. I would have/should have but they never responded back to emails or calls when I tried to order. I'm guessing I'm just the odd exception, I doubt they have bad customer service when they make recommendations quickly.
Last edited by aliceempire; 03-29-2024 at 05:39 PM.
At 350. I got a recommendation that was very similar to my current cam. I would have/should have but they never responded back to emails or calls when I tried to order. I'm guessing I'm just the odd exception, I doubt they have bad customer service when they make recommendations quickly.
Not sure how long ago your email correspondence was with Jones but a few months back the server that provides their internet services was hacked. Their email was messed up as a result. He also has a couple of email addresses IIRC. One for tech info which is where the cam form goes. The other is day to day which is where I followed up with him.
A couple of things come to mind as I re-read the thread.
What's your objective/performance wise? 350 CID and how much RPM? Cruiser or racer?
I went back to Mike for a engine spec revision as I wanted to change how I'll use the car. He obliged with a different cam spec. If I were thinking of different heads it's certain that I would re-visit with him.
Speaking of heads, that takes us back to my questions above.
Personally, I'm in the smaller port category. I've had a 7000 RPM, AFR 195 headed 350 and drove it hard. It also ate parts along the way. 7k isn't as easy as you might think if any measure of longevity is taken into account. Valvetrain parts aren't necessarily cheap. But that's where the 195's shine. Or less RPM but more cubes.
There are benefits to a smaller port although it's not cut and dried really. The general consensus is that the smaller port might be more efficient at low RPM cylinder filling but some larger ports do a better job down low compared to smaller heads. It depends.
Do you have flow numbers and other specs for each?
I am autocrossing the car, about an event a month over the warmer months. I also plan to do some time trial type track events, so only a couple laps at a time. I do though, drive the car on road on nice summer days and sometimes the 45 min to my work, which involves urban and country roads and highways.
I DO WANT something that sounds moderately racy and lopey to a point, but I don't want it dying at stop lights, or while idling. I am currently running the original 700r4 which I have put the complete re-programing kit in, corvette servo, and have upped my shift point up to about 5500, could go a bit further, but do not plan on spinning the motor up past 6k rpm. I do not want to deal with the issues associated with very high revving engines. I'm also running a 2600 rpm stall 9.5" lockup converter. Still have the stock 3.23 posi rear as well, though I would like to go up to something like 3.42, but it seems like a lot of work for a small difference. Ran the calculations and 3.73 gears sounded like too much for highway cruising...
The guy at Brodix explained that the difference between the 180 and 195(200) heads would amount to about 10 more ft-lbs of torque for the 180s at about peak tq (maybe 3200 rpm), but the 195 (200) heads would give that up in exchange for maybe 5 more HP at top end (maybe 5400-5500 rpm).
Does this sound right to you guys? I'm also wondering for autox if I would be able to use the extra 10 ft-lbs with the amount of traction I will have, or if going with the larger heads for the few extra HP would actually yield better lap times??? I do lock the trans into 2nd which means it will shift between 1st and 2nd as it sees fit, with the mechanically programmed shift point of 5500 rpm currently...
Lastly, I have read in a number of places that having angled plugs is a HUGE benefit with the 1.75 SLP shorty headers I have, if this is critical, only the AFR offering has angled plugs... Unfortunately, my budget is restricting me to the as cast heads too, so keep that in mind for flow numbers and such. The as cast 195's seem to flow very similarly to the CNC'ed 180 AFR heads...
@skinny z I included all the flow information with the graph above, was there different flow info you were asking about?
If it were me, I'd go with the smaller cylinder head.
Seeing as you intend to keep the revs below 6k, the benefit of the larger port isn't likely to be realized. I'd say your autocrossing would be better served with more torque rather than out and out HP. That's my thinking anyway.
In the cylinder head spec department, I've measured mine (as best I could) to determine port volume but just as importantly, the minimum cross sectional area. This is typically at the pushrod pinch (in a SBC anyway) although it could be at the valve seat throat. But it gives a good indication of air speed relative to CFM. The faster the air, up to a point, the more inertia it has to aid in cylinder filling. That's were the torque bump comes from as I understand it.
The valve job too has a significant impact on VE. Better and /or different profiles impact the flow at the seat in different ways. It's really difficult to do a valid comparison though as you'd need all of the heads in question tested on the same bench. In that case about all you could do is the old YouTube search for somebody like Eric Weingartner. He has a kajillion SBC heads tests with great data as a result.
This is why I'm keen to see what my little ports (~175-180 cc) and MCSA of 1.90 sq. in. will do for drag racing a 357 at 6000-6500. If my science is right I will have maximized the potential of that particular package which also includes small diameter headers at 1-5/8" and a dual plane intake with 750n CFM vacuum secondary carb.
Whatever you decide on for heads, if it's not the spec you provided to Jones Cams, get another recommendation. You could ask too that if you keep the revs to a certain point (and he could tell you what that point is) that you may be able to reuse your current lifters. That said, for the dollars involved it's cheap insurance with new lifters. Don't forget a valve spring recommendation. Mike and I discussed that and I went with his PAC 1218 suggestion.
Regarding your rear gear, as an example, I've a 700R4 that's been thoroughly modified. That includes your upgrades plus quite a bit more. Presently using a 10" TCI lockup converter. With my 3.73 rear gear and a 26" tire, 75 MPH sees 2500 RPM locked up in O.D. Seems like a highway cruising sweet spot. I've managed to tune it to 20+ MPG(US) in it's worn out and over-cammed version. I expect better with a fresher tighter engine and shorter cam.
As for the angled plug vs your header question, I can't say I'll be of any help there. I've got Hedman 1-5/8" long tube headers and other than needing more than one kind of tool for plug removal, (a 5/8" offset box end wrench is super handy in a couple of cases) the straight plugs have plenty of clearance. This included the plug boot to header gap as well. I've never had the need for a larger primary pipe other than a few seasons running the 350 out to 7000 on track days. I've dialed it back since then and the small pipes should be better suited.
CHP tested all 5 of the Iron Eagles at one point. The 200cc and even 215cc on a 350 made more torque everywhere than the 165cc and 180cc on a 10:1 350 with a mild cam. It was not until they went to 230cc ports that the low-speed torque output suffered. Even then the 230cc heads had the highest average torque under 4,000 rpm. I swapped from iron vortecs to 200cc aluminum heads on a 9.6:1 L31 with a small 218/228 @ 0.050 roller cam and saw improved torque everywhere. Intake runner size does not make a huge difference in torque. The difference in average tq was single digit numbers from 165cc to 230cc. Also found it interesting that the larger head ports actually made HP peak at a lower rpm.
I would have liked to see a little more head specific information such as valve sizes, valve job and MCSA between all of those. Chamber volume too.
That said, I think what I'm seeing is that the 180 cc was at or near the top in average TQ and peak TQ.
AVG TQ 372 381 377 382 381 (up 4 lb. ft.)
From 2600
To 6000 rpm
The differences are small though. I'd like to see the full test.
Thanks for that.
I think Weingartner did some port volume vs engine testing recently. I'll have to have a look for it.
As opposed to peak torque, it would be helpful if there were dyno graph overlays of the torque curves. That might be more telling than the peak numbers posted above. Like, what's happening at highway cruise RPM's when it's not WOT?
"Overall graphs often do not show enough detail to give you a clear picture of the results. Rather than create a graph of the entire power curve, we decided to produce just the curve from 4,500 rpm up through peak horsepower"
^That is an odd perspective. Graphs often don't show enough detail? So...cut a bunch of data out, and that's...better? Whatever. I want to see the whole thing, since when driving a street car...you use, the whole thing.
"Overall graphs often do not show enough detail to give you a clear picture of the results. Rather than create a graph of the entire power curve, we decided to produce just the curve from 4,500 rpm up through peak horsepower"
^That is an odd perspective. Graphs often don't show enough detail? So...cut a bunch of data out, and that's...better? Whatever. I want to see the whole thing, since when driving a street car...you use, the whole thing.
Most folks are after the big numbers. As in peak. Every once in a while though you'll get a dyno run that was pulled down to 2500 or so. But again, these are almost always WOT deals. It would be interesting to see some part throttle / light load runs such as would be seen while cruising on the highway.
Most folks are after the big numbers. As in peak. Every once in a while though you'll get a dyno run that was pulled down to 2500 or so. But again, these are almost always WOT deals. It would be interesting to see some part throttle / light load runs such as would be seen while cruising on the highway.
I pulled mine down to 1,000 rpm on the chassis dyno tuning it. Also drove it for a year with the 200cc aluminum heads. Coasting around town, I was often under 1,500 rpm never noticed any lack of throttle response of off-idle torque. I feel port fuel injection makes it even harder to kill off throttle response and off-idle torque with the larger head ports. If it were a carb the larger ports may have caused some fuel to drop out of suspension when the throttle is opened at low rpm. I never noticed any loss off off-idle part throttle torque in my case, then again the aluminum heads tolerated a much quicker advance curve without running into detonation compared to the iron vortecs on 91 pump gas. With the timing coming in sooner, it was more responsive all around. At low rpm, 1,000-2,500 ,there was a fairly substantial gain, up to about 20 ft/lbs in places, midrange was about the same and over 4,500 the 200cc ports took off even with a fairly mild cam. A lot of it likely from timing curve, but a gain none the less that was not possible running iron vortecs.
Holdener did some testing a few years ago on 3 different engines as well. All WOT testing, but the results mimicked what was seen by the CHP Dart testing. Some of his head choices were as cast and CNC ported versions of the same castings. I find it interesting that the larger ports lost a little midrange in his testing, but actually made more power on both ends of the curve. Makes me wonder if starting out with say a 165cc as cast and porting it, keeping a 180cc or so runner would show the same benifits down low and add to the midrange. I need to do some digging and see if he has tested a multi point injected engine with the only thing being changed being the heads. Like a 5.3L with 706/862 heads swapped to a 245cc head or something. That would provide some data to how an MPFI engine reacts to a larger port.
I pulled mine down to 1,000 rpm on the chassis dyno tuning it. Also drove it for a year with the 200cc aluminum heads. Coasting around town, I was often under 1,500 rpm never noticed any lack of throttle response of off-idle torque. I feel port fuel injection makes it even harder to kill off throttle response and off-idle torque with the larger head ports. If it were a carb the larger ports may have caused some fuel to drop out of suspension when the throttle is opened at low rpm. I never noticed any loss off off-idle part throttle torque in my case, then again the aluminum heads tolerated a much quicker advance curve without running into detonation compared to the iron vortecs on 91 pump gas. With the timing coming in sooner, it was more responsive all around. At low rpm, 1,000-2,500 ,there was a fairly substantial gain, up to about 20 ft/lbs in places, midrange was about the same and over 4,500 the 200cc ports took off even with a fairly mild cam. A lot of it likely from timing curve, but a gain none the less that was not possible running iron vortecs.
I'm hopeful of getting to a chassis dyno with my new setup. I know though I doubt I'll explore the part throttle side of things as dyno time is expensive and I'm looking for the WOT numbers so as to generate a decent profile for some further simulations. I might give a go at part throttle and 2500 RPM as that's where I spend most of highway time. That bit of info and working through the timing there (I've approached 50° advance with a very lean 16:1 cruise) would pay dividends on an extended (and planned) cross country tour. Just once. It does rattle there however but nothing was damaged during the last tear down. Not sure if the dyno operator would be obliging but they shouldn't care really.
That said, I'm in a transition where I think most of attention will be at the track and the street will only be occasionally. But I do like to drive. Fuel has just gotten so damned expensive that it kind of kills the hobby.
Holdener did some testing a few years ago on 3 different engines as well. All WOT testing, but the results mimicked what was seen by the CHP Dart testing. Some of his head choices were as cast and CNC ported versions of the same castings. I find it interesting that the larger ports lost a little midrange in his testing, but actually made more power on both ends of the curve. Makes me wonder if starting out with say a 165cc as cast and porting it, keeping a 180cc or so runner would show the same benifits down low and add to the midrange. I need to do some digging and see if he has tested a multi point injected engine with the only thing being changed being the heads. Like a 5.3L with 706/862 heads swapped to a 245cc head or something. That would provide some data to how an MPFI engine reacts to a larger port.
01-04-2024, 04:35 PM
