KwikistZ

I'm pretty sure I'm right on this, but tha cam has the most effect on the rev range right? So...what about the cam makes the engine rev higher? Just whatever you can tell me, thanks!

SKeTchy

rskrause

Do you mean the rev range where it makes max hp or do you mean what is the limit on how high a given combo can rev?

A typical SBC will run out of air and stop making power long before it will break anything, if that's what you mean. That's why you can see people with stock shortblocks but upgraded cam, valvetrain, and heads revving to up to ~7K where a stock motor runs out of breath at less than 6K. To get really high revs, not only does it need to breathe well, but the rotating parts need to upgraded to be stronger and lighter to allow high revs without self destructing. Valve float becomes an as the revs rise and the cam gets bigger. So better valve train components are needed to get high revs.

Rich Krause

KwikistZ

Lets make an example...say I have a stock LT1....and I want it to rev to around 6500-7000 or so. How would I go about doing that? I'm not sure where the stock LT1's power is at, I forgot, but lets say we try to get the power around 6000-6200. See what I'm asking now? Basically, how do you make your engine rev higher....heh, ok, I'm done....

SKeTchy

racer7088

You have to create a situation where the airflow in the engine peaks there (6500-7000 rpm) with the heads and intake and cam you choose.

KwikistZ

Well, is there a way to take a stock LT1 cam and rev it that high? Or maybe get a custom grind that is tame like the LT1 cam but revvs higher?

SKeTchy

rskrause

There are people running cams like the CC306 with stock heads and revving in that range. There would sure be a lot more power with better heads in that circumstance, but it does supposedly make power up to that point even with stock heads. I never seen this myself though, as it would be pretty unusuall to install a big cam with stock heads. The rest of the valvetrain does need to be upgraded to allow this though.

Still not sure exactly what you are trying to accomplish, or is it just curiousity?

Rich Krause

GUMP

You can make huge improvements with cam, headers, and tuning. The stock LT1 heads are lot better than most people think.


Daren

Fast Caddie

Rich, I have a few graphs comparing various dynos from LT1 setups (basically took an average over many people's dyno graphs to get a rough idea). One graph plots the hp and tq curves of full bolt-on LT1s, CC305 and LT headers, and CC306 and LTs. All three represent M6s and stock heads. There's barely a difference between the 305 and 306 on stock heads from 3000-5000, with the 305 making much more low end torque and the 306 making an avg of 10rwhp more after 5000. If you'd like to see some let me know.

Apparently, stock LT1 heads don't flow enough to make much more than 340rwhp... no matter how big of a cam you use or how high you rev it. And interestingly enough, i've never seen a stock headed NA LT1 hit peak hp after 6200rpm.....even with "huge" cams they all seem to peak at or near 6K. Must be the absolute choke point of the stockers.

I guess what i'm saying is that it's pointless to rev an engine much over what the heads allow. Get bigger ports either with porting or by buying new castings such as AFRs, then get a cam that'll peak up there and rev it till your heart's content. Or until you hit the 7K rpm limit by the computer. With bigger ports you can take advantage of big cams by revving higher and still make power. Take Jim's car or Mindgame's car for example... they use big cams with stokers. But they also have non-LT1 heads that'll flow like the stockers can only dream of. And it's kind of wierd how both make peak hp at around 6500rpm even though they took very different routes to making 550+rwhp on pump gas.

Big ports + good intake + big cam = higher revving engine

GUMP

It's all a matter of what your application is. It is not that hard to make 400 rwhp with stock heads, intake, and throttle body. It's all a matter of matching the cam to the heads. My Stocker motors make peak HP at about 6800 rpm with factory lift and stamped rockers, etc.
Yes they are race only motors and run on race gas only. I just wanted to point out that if set up correctly stock LT1 heads make good power.

Daren

95grandsport

other variables also like: stroke, rod ratio, and all together OPTISPARK which will distort high res signals at higher RPM's which can extremely limit power above say 6200.

KwikistZ

What I was thinking about doing is making a mild cammed high rev motor...and I wanted to do this so that if you're cruising around town, you have the driveablity of a stock car. Then, when you hit the strip...or run into someone on the highway you just get the revvs up higher for the power. Now, you can get the big lopy cams and what not, but that sacrifices the whole driveability/mileage aspect of a street car. Basically what I'm looking for is relativly mild motor down low, then wakes the hell up in the upperz. You guys get it now? I know, I suck at explaining things...sorry...hope this clears it up!

SKeTchy

Fast Caddie

Just to be sure, when i say "stock" heads I mean unported or otherwise untouched. Ported stock castings can sure make power.... 400+ NA rwhp on the stock bottom end is something those 2V 4.6s can't come close to claiming. Not sure about the cobras, but i'm sure even they'll have problems hitting that much. It's hard to tell since most of them go either N20 or SC after they do all the bolt-ons.

Well, your cam will dictate your rev potential. That CC306 cam will peak around 6K rpm on stock heads.... you open the heads up and that cam will peak out a few hundred rpm higher since the stock heads choke it, if not close to the mid-6K range. If you want a medium cam such as the CC305, hotcam, XE218 or XE224 with ported heads you'll still end up with and engine that peaks close to 6K or a tad bit over. To rev higher than that and still make usable power, you MUST have the combo of high-flowing heads (relative to displacement) and a large cam (again, relative to displacement). I say relative to displacement cause more of it will "tame" larger ports and cams.

A 350 LT1 with, say, LT4 heads ported out to about 205-210CCs and flowing near 300cfm and a cam such as the CC306 or larger will be a HIGH revving sob.

Just to give some perspective (keep in mind stock displacement), stock LT1 castings have 170CC intake ports (flow around 210cfm intake) and top out around 340 rwhp with a fairly nice torque curve. Stock LT4s are 190-195CC (flow around 240cfm intake) and one member here with them paired along with a CC306 and LT headers dynoed about 380rwhp. Fully ported stockers and a CC306 will get you near 400rwhp (with a fairly biased torque/hp curve towards the higher rpms, weaker low end torque). LT4s around 20 or more rwhp on top of that.

GUMP

In my post above I was talking about 170cc stock heads. Believe me, I have just a tiny bit of experience with them.

Daren

rskrause

Thanks for the info. I believe that more than what I have heard from others. Note that I said "supposedly", as I am somewhat skeptical about the claims I have seen for cams like the CC306 and stock heads. Now, I am even more skeptical.

I think you have the best answer so far, but when I re-read the original post, I see he was trying to ask a "why" question. Here's the answer. A cam with more duration/lift allows more time for the intake charge to enter the cylinder, so it has the potential to make more hp than a smaller cam, if the other components can support the airflow. As the revs increase, the engine needs more air to fill the more rapidly filling and emtying cylinders. With a small cam, the airflow limit may be the cam itself, so at a certain rpm, it no more air can flow and more revs won't make any more power. Make the cam bigger, and something else will be the limits (heads, intake, exhaust).

Of course, overlap plays into as well as duration. The effect of overlap is more complex, but basically, more overlap will tend to make more peak power, but the curve will be narrower, ie "peakier". If you change nothing else but the overlap, I don't think it will have a large effect on the rpm at which peak power occurs. I am willing to be corrected/educated on that statement though.

It's early, I hope that what I just typed is coherent.

Rich Krause

Injuneer

Just use nitrous. A lot easier, and not a lot of risk at lower levels.

Do you have some hard facts on the high res pulse signal issue? At least two cases I'm personaly familiar with have not encountered this problem, or any evidence of it, revving well into the 7,000rpm range. That's using the Opti optical module to feed an aftermarket ECU, and includes one application producing over 1,100HP.