cam rpm range and cubic inch

[CGT]

The camshaft is # 1 in the hierarchy in my book. Just look at some of the stock BBC’s from yesterday with the huge square port heads ….say a 1970 LS6.
Peak torque in the 3000’s rpms??…. Peak HP in the 5000’s rpms?? What is wrong with this picture?
Camshaft!

Do you agree that if careful thought and prep were put into the intake and exhaust on that ls6 , paying attention to velocities and csa, even making things smaller, that the peaks would raise with the same cam? I do, and it could be a substantial amount higher with the same cam. Ive definitely seen that. What i have seen is camshafts changing the location of the concentration of tq and hp without altering peaks drastically, within the confines of the rpm range that intake tract was designed for. Although i do feel it would be easier to lower peaks with camshaft than raise them, unless the camshaft was WAY off.

[randy331]

Maybe we should test this.

We could take a stock 350 and change cams out to see how high peak tq/hp rpm can be made at, and then
work on the heads/induction tract only, and see how high the peak tq/hp rpm can be made with the stock cam back in it.

I realize the stock heads would be considered restricted when testing cams, but so would a stock cam when testing head/induction work.

Randy

[Orr89rocz]

I've done a test like this on my stock L98 TPI motor. With stock TPI intake and stock everything else but exhaust/headers, it peaked around 4400 rpm for HP. I switched to a short runner intake and added 1.6 rockers/underdrive pullies. Peaked moved to 5100, kinda flat between 5000-5200 before starting to fall off, and this was with a lean tune.

Granted the 1.6 rockers may have increased duration a tiny bit and definately increased lift, but the rpm range moved.

Same thing can be seen with stock cam only LT1 Gen II sbc's. 3 most popular cams are Lt4 hotcam, CC503 which is the xe276hr 224/230 on a 112, and the cc306 whichs comp's 230/244 112 lsa. Lt4 will peak in the mid 5000 rpm range on stock heads. 503 will peak closer to 5800-6000. CC306 will peak near 6000 but flatline power after that well beyond peak rpm. Throw in a larger cam still, the gm847 which is old crane cams grind 232/242 on a 112, it still peaks around 6000 but also holds power to well beyond peak hp rpm.

After getting stock heads cnc ported or hand ported by one of the LT1 greats, you see huge differences. Same 503 cam will peak alittle higher. CC306 and Gm847 cams will peak closer to 6400-6500 and hold power. Heads needed larger cross sections to pass more flow to allow more rpm.

[CamKing]

Throw in a larger cam still, the gm847 which is old crane cams grind 232/242 on a 112, it still peaks around 6000 but also holds power to well beyond peak hp rpm.

And that's the key.
A given port size will restrict flow, and peak HP RPM, but you can still increase the power beyond peak, by going to a larger cam.
A very popular circle track engine is a 358ci Small block, limited to stock unported heads, and a 500cfm 2bbl carb.
Both the head and the carb are restrictions, and the best you can do is get the peak HP to about 6,500rpm. You only need a cam in the 240@.050" range to make the engine peak at 6,500, but since the engines race to 7,200-7,600, they need a longer duration cam. We run in the 252-256 range, and even though the peak HP rpm stays the same, we make a lot more power beyond peak.

[MrBo]

The camshaft is # 1 in the hierarchy in my book. Just look at some of the stock BBC’s from yesterday with the huge square port heads ….say a 1970 LS6.
Peak torque in the 3000’s rpms??…. Peak HP in the 5000’s rpms?? What is wrong with this picture?
Camshaft!

Do you agree that if careful thought and prep were put into the intake and exhaust on that ls6 , paying attention to velocities and csa, even making things smaller, that the peaks would raise with the same cam? I do, and it could be a substantial amount higher with the same cam. Ive definitely seen that. What i have seen is camshafts changing the location of the concentration of tq and hp without altering peaks drastically, within the confines of the rpm range that intake tract was designed for. Although i do feel it would be easier to lower peaks with camshaft than raise them, unless the camshaft was WAY off.

Yes, I agree to that.
I was just pointing out that a cam swap could have an enormous effect on that engine.
A .900” lift Super Stock roller in that 454ci, with 280 degrees at .050” duration could raise both the HP and torque peaks several thousand rpms all by itself.
It was an oversimplification I suppose.

[CGT]

Maybe we should test this.

We could take a stock 350 and change cams out to see how high peak tq/hp rpm can be made at, and then
work on the heads/induction tract only, and see how high the peak tq/hp rpm can be made with the stock cam back in it.

I realize the stock heads would be considered restricted when testing cams, but so would a stock cam when testing head/induction work.

Randy

That would be some fun testing to do.

[plovett]

Maybe we should test this.

We could take a stock 350 and change cams out to see how high peak tq/hp rpm can be made at, and then
work on the heads/induction tract only, and see how high the peak tq/hp rpm can be made with the stock cam back in it.

I realize the stock heads would be considered restricted when testing cams, but so would a stock cam when testing head/induction work.

Randy

I'm following what you're saying, Randy. It's kind of a "can't see the forest for the trees" type deal. You explain it much better than me. Thanks.

paulie