stevieturbo

I dont do diesels, so cant argue one way or another...but I'd be sceptical that they would run a P/R of 1:1 or even close on all but teh most extreme builds...and even then, Id say they are rare.

And if you can show me a cam with overlap on a rotary...I'll be very impressed ! In fact.....

And there are many people with big cams in blowers..and they dont seem to hurt them too much.

rotary1307cc

iTrader: (5)

you didn't know cams in rotaries existed??

ha... i meant that you have to watch your port shape and geometry because that controls your port duration and timing

those things are silly anyway, much better in this world

qqwqeqwrqwqtq

That is assuming that you actually have reversion during overlap in a turbo car or boost loss through the exhaust on a supercharged car.

Maybe the exhaust and intake flow through the engine has enough inertia to where reversion does not happen or is very minimal.

After testing some cams in my old LT1 I found that more overlap equaled more power and extended rpm range (this with backpressure double boost pressure). I think my tests only included from -16 deg overlap to zero overlap however.

Overlap can be good in a supercharged car as well. Even if you do lose some of the mixture out of the exhaust you know that what you're burning isn't contaminated by any residual exhaust.

That being said I still do not run a ton of overlap or duration in most of our forced induction combinations as you can efficiently make plenty of horsepower (1200+++) with a relatively mild cam. Since most of our stuff is street driven I do not like to sacrifice driveability for a marginal amount of horsepower gain.

For example, we have used a 232/232 113lsa cam in many twin 66mm turbo 402 combinations that make 1100+rwhp at around 22psi boost and are still over 1000rwhp at 7,700rpm. These cars drive beautifully with perfect street manners. Would this setup make more power with more cam? It probably would but not by a very big margin. Again, for something street driven why sacrifice driveability and spool time for 20-30hp at the 1100+rwhp level.

We have also done many single 76mm cars that make 900+rwhp with our 225/225 113lsa cam. Would it make more power with a larger cam? In this case I doubt it as the turbo is pretty much maxed out so you would just lose low end driveability.

All these setups still seem very efficient as they are making power at reasonable boost levels and drive great on the street so I just see no reason to go crazy with the cam. With our shop having an emphasis on street driven cars I'm sure I have a different perspective on this than the guys who are strictly building race cars.

engineermike

I agree that once you reach the choke line on the turbo, that's all the power it's going to make, so going with a larger cam wouldn't help the max hp. However, sometimes more cam would improve low-boost power, while sacrificing max power at choke.

For instance, 225/225 would make 900 rwhp at 22 psi boost with the turbo max'd out. Swap to a 230/230 and now it only makes 850 rwhp, but it does so at 20 psi boost. If you want max power on pump gas, you might go 236/236 and make 800 rwhp at 17 psi. And so on... Much like adding displacement on a T4 76mm. You gain power at low boost levels, but lose ultimate hp potential at choke flow. Depends on the goals...

gametech

iTrader: (1)

Why do we have these debates? Buick v6 motors are a close analog to modern GM v8 engines in terms of what is needed for cams to match the intended purpose. There is over 20 years of solid info available at the stroke of a key.

rotary1307cc

iTrader: (5)

true story but what fun would that be?