Ok guys, need a little help picking out a cam for my new engine that I am currently building.

The stats:
-383 with 10.7:1 compression
-Looking to get my Dynamic compression about 8.2-8.4 area
-AFR 195cc Eliminator heads
-1.52 Roller Rockers
-Hyd. Roller cam
-Holley Stealthram
-32 lb/hr flow matched injectors
-Deburred/Polished runners
-58mm Throttle body
-Speed Density
-Edge 3000 stall
-700r4 with shift kit
-3.73 gears
-Also have long tube headers, custom exhaust.

Ok now...what cam....I am looking at a 230/236 Comp XE on a 112 lsa, 224/230 XFI lobes on a 112 lsa, or building a custom cam on LSK lobes possibly a 226/232 cam.

Nothing radical, this is for my truck that I would like to drive daily if I wanted too. Shift around 6000 rpms would be about right. I can tune the engine via Ostrich.

 

Summit Catalog # CCA-08-503-8 has the following specs:

Duration @ 0.050 Intake Exhaust
224.0 230.0
Lift 0.503 Int. 0.510 Ex.
Lobe Seperation 112 degrees.

It's a hydraulic roller that would sound nice in your set up. A.F.R. heads usually like when there's about 6 degrees difference, so this cam is also ideal. Using 1.6 rockers would allow you to get more lift as well. A custom cam would probably be better, but this set up will do the job in the 1800-5800 rpm band in a 350, so expect the power to peak earlier in a 383. Hope this helps.

 

I know of someone with the Holley Stealthram in almost the same 383 combo and he said it peaks about 5500 rpm. The rockers as listed above will be 1.52 b/c I already have them is the main reason. I've looked custom but since I'm not looking for every hp possible, then a custom cam picked out by me or a shelf unit wouldn't be bad. Thanks for your input. Anyone else!

 

Going up for anyone else....any reason not to go with the 230/236?

 

So great to hear of someone who wants to upgrade who actually has a target for their upgrade. My mention of this is your concern for the DCR. I think, or believe, you are on the correct track with your inquiry. I believe if you contace the cam manufacturer, they can give you the proper advice for your combination. 'Hi mr. cam mfgr. I am looking for 8.2 DCR with my 10.7 (calculated) SCR, what is your recomendation, oh and by the way I am wanting to shift at 'x' and have intake runners 'x' length, thx mr. cam mfgr.'
I do not mean to sound insulting, no insult intended at all, I applaud you for such an insightful inquiry. In fact I had been looking to start a thread on this very subject because I do not know enough about the subject to give the answer you need. The question I have had for quite some time has been 'how much DCR is possible with 91-93 octane, and a good tune obviously'. If you or anyone else has any kn. about any of this please help.
Good luck in your search.
There are a few guys/gals on this board who are using 10+ SCR effectively on the street without going to extremes with race gas. A friend of mine told me that if I was going to get into the need for 93+ octane, then just go for 12/1 + SCR, build around it and forget it (emission laws in individual cases excepted).
I could, and probably will in the future, ramble on a little more in this sujbject at a later date, with the hope that the real genius among us will speak up and enlighten us with the necessary facts about how much DCR is possible for the street.

Off to reflect on how to approach this subject, and not hijak your thread.
Luck to you.

 

I've read many cam selection items and compression target zones. Most say, you want the DCR to be between 8-8.5:1. Anything over 8.4:1....you start needing race fuel or lower you timing severly. With aluminium heads, they say around 10.5:1 is ok with premium fuel and with cast iron heads....not above 10:1. Again...all stuff I've read.

 

I'm running 10.75:1 compression ratio with a 8.5:1 dcr. This is with a quench of .035" . I consider this to be on the edge with 91 octane but no problems so far. If you want to run 87 octane I would drop the dcr to no more than 8.0:1 with a tight quench. This is on aluminum heads.

You have very good heads. To get full use of the heads I would shoot for high lift and use 1.6rr. I like the XFI series of cams if you limit the rpm to 6000 they are great. If going higher on the rpm's I would use the LSK lobes.

By the way Comp Cams said I should not go higher than 10.75:1 compression ratio on my XFI 268 cam. I took them to their word.

 

How about Crane Power Max Hydraulic Roller # 270-119831 with 284/294 dur and .509/.528 lift. The power band is from 2000 to 6200 with engines with compression up to 10.7:1

 

I have looked at that cam but I feel that it has a little bit too much intake vs. exhaust split for my heads plus I haven't seen much success with that cam. I could be wrong on that one just haven't seen many people use it.
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I have 93 octane where I live so that's why I want the DCR about 8.3 to keep it just a little more relative in case I drive it and have to fuel up somewhere that only has 91 or less octane or in case of bad fuel. I feel that's important for a DD is the bad fuel story. I would like too use the XFI cam with my 1.52 rockers but I've heard and been told not too bad its a little radical for a DD. I've been looking at the XFI 224/230 lobes pretty hard and put it on a 112 lsa or just an Xtreme Energy 230/236 on a .510/.520 lift on a 112-113 lsa.

 

YenkoST
Great stuff here. I agree whole heartedly with 1989Transam about what his reccomendations are with the comp grind. If that cam gives youwhat you are looking for, for DCR then mission accomplished.
On a personal note, since I am a new poster here, I would liketo ask a couple of questions (without the hijak of course). What material were you reading, and where can I get it. DCR is connected to the closing point of the intake valve, and does not change through the rev range. My question about 8.5 DCR, is, what is the cranking psi?
A real indepth discussion of this would be really helpful for many of those who want to learn more about this subject.
(OPINION, OPINION, WARNING)
I am not sure what 'too radical" means, Probably too much overlap without enough SCR, Or too much compression and not enough overlap (late closing point of IV). I would bet someone could, with a properly designed piston/chamber combination (no dome to screw with flame issues of the chamber) run 12+ on pump with properly designed cam combination and still have great low end torque and drivability without the detonation.
???
I am glad to hear of some well thought out opinions of some of these combinations.

 

When I say radical, I mean too much cam for the low end power curve and stop/go traffic. DCR is relative to the compression vs. cam specs for the most part as I understand it. Take a 383 engine for example with a 218/224 cam with 9.5:1 compression. The cranking psi is about 200 psi or at least my old engine was. Take a bigger 230/236 cam, the psi might be 180 psi now.

 

You are correct relating the DCR to the cam specs. I DO believe that you can run 230 236 duration and still have reasonable SCR, hopefully in the 200psi cranking range, and still have great low end performance. I think (may be wrong) the only problem which may be encountered still has to do with the I.V. closing point. I agree with you on the 218/228 cam with 9.5 comp resulting in 200+ cranking psi. Will make for some spunky driving. You may be looking at the quench distance clearance. Do you know how close you may be?
I too have been poking around on some sites looking for 'the' definitive answer for the 'how much SCR can I run safely on pump gas' question. I have, as of yet, not found the definitive answer. I know there have been some blanket statements which state that 9.5 w/iron heads, and 10. w/al heads seems to be the conventional wisdom.
I am not so sure.
Yes, a cam with very little overlap ie 305 peanut cam with 9.5 comp. will give some peppy performance with a tpi, a tight converter, and a 2:7x gear will be a little fun-for a while-but the fun factor has no rpm's, hence hi et's and low mph in the1/4.
The mistake many seem to make with larger duration higher overlap cams, is the failure to raise SCR and therefore lower DCR. Which is my question from above (or statement), I would bet that we could run 12:+ if we could get long enough duration and overlap and - here's the kicker - control the Intake Valve closing point.
Now I feel old, I used to run l-88's in the past, 427, 12:1, outrageousely large cam, 850 carb, etc you get the point. At idle I believe that the DCR was pretty low due to the LONG duration HIGH overlap lazy ramped GM cams. They ran great but needed the hi comp to restore cylinder pressure and run the rpm's up.
With the TPI's we are limited in the RPM department, so who do we get the most out of what we have to work with. One more question, conventional wisdom with the tuned system 'requires' that 112-114 lsa's are necessary. Is this true with higher compression ratios? Not sure of this. All I know is 'watch the I.V. closing point', which can be alleviated (addressed?) with narrower lsa's. Some food for further discussion and possible education from others more informed than I am. Keep this up.

 

Oh, Forgot one thing, a 230/236 112 cam will quite possibly give you just under 200cranking psi with the cam degreed in properly, again if you know where the closing point of the I.V. is. But the DCR may not quite be in the 8's, but close.

 

yes you could run a SCR of 12+ on pump gas but for street driving it would be horrible it would have to live above 4K to move the car a manual tranny would be out of the question after 10 minutes of stop and go traffic you would be pushing it home... couldnt see an auto being any more fun well maybe on the strip but not the street

 

Good Reply, Let me clarify your point for my understanding. What I hear you saying is that the high DCR, 12.+ and above would be sluggish at a lower rpm, usually due to long overlap cams which typically are tuned to run at higher rpms. Typically you are correct. High DCR means you can use larger overlap cams which bleed off compression at lower rpm's, and the engine can use the higher rpm's to make their power, with corresponding induction and final gear ratio. I understand this concept. Look at the 60's and into the 70's performance engines, before the smog police became a force and forced the manufacturers to adopt a more accurate targeting of performance combinations. It is 'easy' to raise the comp. and install a large overlap cam, and zing the engine into the stratosphere -great drag strip stuff- still works today, but the question may be "how do I get an engine to perform with a lower rpm engine with somewhat of an extended rpm. For example the ls1 engine has a cranking pressure of around 200 psi. the cam it uses has a wide lsa. the rest of the components, well designed heads, 10:1 DCR, .5ish lift cam, 200, or so duration all makes for a smooth idle. Some of the larger performance cams for this engine still offer a reasonable idle. I am not trying to compare apples to oranges, but some of the physics are the same as many other engines. The one who designes the engine is still trying to deal with the same physics. We still cannot get past the 'size does matter' issue, and 1.3 hp/ci is still difficult to accomplish in any engine, but it becomes easier when you alr allowed to aim for a higher rpm. We still have to come to grips with 1. how much DCR can I get away with, 2. the cam plays a major role (with pistons) in how to reach the desired DCR. larger cam overlap means the need for a higher SCR. Ijust do not know how high is too high. When I said 12:1+ I was alsothinking of 200psi cranking pressure, what cam specs (different for different sized engines) will give us the desired outcome?

 

but probably the main advantages of the LS engine will be the aluminum heads and block and pretty sure they also have reverse flow cooling and displacement
the heads,block and cooling help the engine run that compression with out detonation and the displacment will help tame that cam


the cranking psi is set by the DCR changing the DCR will always effect cranking psi

in turn all you would be doing would be moving the peak numbers up in the rpms which would again be putting you out of the realm of streetability

 

Only the LT1 series have reverse cooling and can run an additional .5 dcr.

My XFI268 cam has very good street manners and power down low. Just ask my tires. Also my gas milage is up with my latest motor.

When changing cams your dcr will most likely change. Keep an eye on it and shoot for the 8.3 dcr you want. That will help keep the torque up in the lower ranges.

Also don't forget the quench. Very important to keep detonation under control.

 

Definately. I'm looking at a .041 gasket. The block might be decked....got to check with my machinist to see what he says but it looks very nice. Heads are 65cc chambers and I believe my pistons are 5cc but could be 3.4cc. I need to verify that last part as that's my only unknown but its one or the other. One will give me 10.52 SCR and the other 10.76.

I need to find some ABDC numbers on these different cams so I can figure the DCR with these different cams. I figure I will need about 54-55 ABDC on my cams to have 8.3 DCR.

What's the ABDC on the 268XFI cam? Thanks.

 

All this tech makes me happy.
If what 1989GTATransAm is saying is true, and that running a DCR of 8-8:5 is completely possible with todays gas, just think what may be possible with E-85. That comp cam is really a fine piece, the newest technology in lobes for efi engines. YenkoST these xfi cams are great cams. Please post, if you know, what the seat timing at close is, and how many degrees after bdc.
Thanks a bunch, keep the quench tight.

 

Well, I went with the 224/230 XFI cam on a 112 lsa. The lift will be .544/.540 with my 1.52 rockers. I'll keep y'all posted on it. Comp said it will peak to 5700 at would need to be shifted about 6k. Which is perfect for what I intend to do right now.

 

280XFI:
IVO 31
IVC 69
EVO 81
EVC 27

I'm only running about 7.5DCR (10:1 static) with this cam, AFR 190 heads, .038 quench, TPI. It'll run on 87 most days but with 91 there are no issues.

 

Being a noob on this board, I am really appreciating an in depth discussion on the real essentials which will help most any engine.
If I may, I wish to get a little bit of a 'rule of thumb' on this issue. I am hearing that those of you who are in the know are saying that an SCR of around 10-10.8:1 will work if the SCR is kept around 8-8.5:1, with a reasonable tune of course, without resorting to exotic race fuel.
The nest thing I would like to know, is how do I get the TPI intaKE TO FLOW in the 260-280 range? and to boot (as if this is not complicated enough), get ready, Is there a formula as to how much cfm the intake should be capable of in order to feed the capabilities of the cyl. head. Ie. if the head can flow 250-260, what MUST the intake runner flow in order to not choke or underflow the head???
Just some food for discussion.
THX

 

well if the head can flow 250 intake then the intake will need to flow atleast that much...

 

With the losses of the rest of the intake track probably even more. This would be from the airfilter to the intake manifold.

 

Yup. . . At least the same. Just not sure how much more in the intake is necessary to allow the heads to work most efficiently. Not having any way to flow an intake (much less a head), I am not sure how much more an intake should be able to flow. My real question is, what can the TPI intake be made to flow in order to feed the head.

 

There is a problem, With the TPI set up from the air filters through the plenum what do they get? 600-700 cfm at the most? with mods to the whole tract perhaps? What can be done other than the usual filters, Maf work (wether descreening applies or not) foil, porting plenum, and some kind of ram air mod.

 

From what I've found reading around and looking at different setups, 11.5:1 SCR is the max you'd want to take a pump gas motor.

For a standard SBC 8.4 DCR is probably tops, my LT1's SCR is 11.6:1 and DCR is 9.15 iirc, of course it has reverse cooling.

 

"There is a problem, With the TPI set up from the air filters through the plenum what do they get? 600-700 cfm at the most? with mods to the whole tract perhaps? What can be done other than the usual filters, Maf work (wether descreening applies or not) foil, porting plenum, and some kind of ram air mod."

Yes all the parts have to be upgraded. An upgraded cold air intake, bigger throttle body. For the rest we will have to see what BBK comes up with. I just hope it can easily be opened up for the higher horsepower motors.

That is the problem with the Edelbrock TPI intake. It takes a lot of work to open it up where it should be for the higher horse power motors. If Edelbrock changed the design a little it would make life easier.

This is where BBK has a chance to shine with the correct design. I hope they let us critique it. One is to have the intake runner track look like a funnel. The end that meets the head can be cast to be the size of stock heads. But leave enough material so it can be easily opened up. Also make sure the runner entry point into the heads is straight with the head runner and not at and angle like the stock one and the Edelbrock.

OOPS! sorry for getting off track with the original post.

 

Hmmm. . . YenkoST got this started with a question about wether or not a cam would work for his engine. I hope he is not offended with the 'legs' and the direction this has taken. Should this be taken to another thread for protocol, or should we (I) drop this. In any case, I have learned, and I love to learn, and want to continue to learn in order to apply this to my next engine. THX all.
I look at the lsx intakes, and see what the engineers did for the entry point of the intake, a direct shot pretty much at the IV. and the truck intakes set up more for torque. FAST LSX a bigger version of the factory intake design for larger engines, and high rpm. The mention of the BBK intake is reasonably exciting, but has anyone done any research into the marine intakes?
OOPS, off topic again, sorry.

 

Well....no one was really helpful in a decision for a cam so I picked the cam down one size and made it aggressive. I'm just glad to see this thread take-off somehow.

 

You are much better off with a size to small than a size to large of a cam. The heads you have are the most important thing and they are good ones. I would seriously consider 1.6rr with those heads.

 

Yea I know. But the 1.52s is what I have so I will stick with those for the time being. If I upgrade the cam then I'll think about it at a later date. Right now, its more of a money reason. But at least I already have roller rockers.

 

Ok, camshaft cam this week. Specs are the XFI 224/230 lobes with .538/.541 lift on 1.5s. BTDC - 4, ABDC - 40, BBDC - 51, ATDC - (-1). So, overlap looks to be 3 degrees with the HSR loves hardly any overlap and the DCR from the cam will put me about 7.9:1 but its ok, I'll just up the timing to compensate for it. At least I have a good running engine. All of this is on a 112 with 4 degrees advanced built in.

 

I didn't know the HSR liked little overlap or I would have taken that into consideration with my custom cam. Do you know any engine builders with some HSR experience? It seems that most engine builders I talk to have never seen or heard of the Stealth Ram let alone ground a cam for it. When I took mine in to get ported the guy looked at it funny and said he'd never worked with one before and he builds lots and lots of small blocks. He did however think the runner length and shape is going to make it produce a nice amount of torque along with some nice power over 6k RPM. The only thing he said negative was that there really isn't much of a transition from the plenum down into the runners but that is one of the reasons I took it to him in the first place as I had him round off the sharp edges on the beginning of the runners. I'm going to Austin tomorrow to pick up my heads, ported HSR, and custom cam. I haven't seen the cam card yet but my engine builder quoted me over the phone that it was 230/236 .589/.598 112+4 on XFI lobes. My target SCR is 11:1 so that I end up around 8.7:1 DCR. I'm probably pushing the limits of what the 7730 ECM can probably make run well (thankfully I know a guy with LOTS of tuning experince with this ECM) but I want to make over 400rwhp on a NA 350.

 

I have been told this from custom cam designers who have experience with teh HSR system. Plus, from my last engine from the HSR, I got a little experience about what it likes. The reason for the little overlap is b/c the intake runners flow so durn good and its a straight to the head design I was told so with not like its making turns like a SuperRam/TPI/carb dual plan design.

Oh and I miss calculated my DCR....its 8.8.
The 230/236 XFI lobes on 1.6 rockers is like .576/.570 lift I think unless your going with 1.7s. Either way, that thing should sound great! I was hoping more cam for my 383 but I think its going to work great.....dyno desktep shows a peak hp of about 5700-5800.

 

I was actually given a choice of a more conservative 228/232 cam as well but my engine builder/head porter STRONGLY recommended the 230/236, saying if it was his car that would be his choice (along with 11:1 SCR). Speaking of overlap, I read an interesting article about heads with strong flowing exhaust ports and 6 degrees of duration split causing overscavenging of the cylinder and asked if a 232/234 cam was possible (my new heads have an excellent E/I ratio) but was told the GEN I lobes don't work that way. I wonder if a cam like that would work very well with the HSR? Probably so. I think the intake runner of the Stealth Ram is a good design for velocity as well as quantity. It is funny that some people on this site claim the HSR is not a "performance intake" when it is producing some really nice power curves on even the mildest 350s. The lift on my cam is using 1.6s as I'm not using the 280XFI that has the .576/.570 lift, but the lobes are from the same "family". I was set on a 280XFI at one point but was convinced to go with a custom grind by several of my friends. I'm sure your 383 will run hard with a 224/230 and be EXTREMELY "streetable" at the same time as I know of many 350s running great with them. A 230/236 cam would have been as tame as 224/230 cam in a 350 and made a little more up top power but seeing as you have a truck I think you made a good choice with a nod towards low end to mid range power. I'll share my cam specs and revised head flowsheets after I get everything picked up.

 

yenko i would have to say 8.8 would be to high for cast heads but AL it is defenitly pushing the limits what is your quench at?

it is just me but i wouldnt want to be running a truck on the ragged edge all the time

 

Yea, I agree. Its kinda funny, I've seen some people with the 230/236 XFI in a 383 claim around 390rwhp in their sig. Thanks, Comp and everyone said a 230/236 would be fine but in my truck I went a little conservative.

 

i know you went conservative that is what caused the 8.8 DCR the intake valve is closing to soon and making to much preassure it could be a problem on pump gas

 

Well, my truck doesn't tow, haul, or anything. Its my baby and I do drive it everyday but also like to have fun with it. Yes, the DCR is not what I was hoping for but I can live with it.....in a few months it won't be my daily driver anymore so I don't really care....part of the reason I was looking into the 230/236 cams. I'll put a high flow water pump on it to help cool it a little better. The quench is not severe at all. I'll have .015 or .010, need to measure once the block comes back from teh machine shop from getting bored and honed from the piston to deck and .041 from the gasket. So, .051-.056.

I don't think I'll have too much trouble b/c I've seen custom cams from Camshaft innovation and Cam Motion with roughly the same ABDC numbers with 10.5:1 compression.

I was aiming for .045 quench and 10.5:1 compression with 8.3:1 DCR but I have around .051 quench, 10.7:1, and 8.8:1 DCR. I have 93 octane in these parts and I can tune it so I can lower the timing if need be. Should be fun either way.

 

With the amount of compression you'll have and the low end power from the 383 with a 224/230 cam your throttle response should be really kick *** and should really get your truck moving off the line.

 

I believe you are right....should be very stout. The old combination was a flat tappet 218/224 cam on XE lobes, 9.5:1 compression, and stock converter. So, that was fun to drive, I can't wait to drive this one.