Eight is enough and in this case it's to much IMHO. I'm sure some of the SC guys here, (C5) have gone 700 but eight might be getting out there. 700HP is a bunch on a stock motor's short block. I think I would forge everything, (pistons) and go for it. It's just not worth blowing up everything. One trip to the rev limiter and you could have a basket case on your hands.KillerVette said:With the new z06 at 11:1 compression, is this going to allow for safe turbos and superchargers?? What kind of power should this engine hold? I am not sure of the internals so i was wondering if it could hold 800hp at the crank safely?
Just my opinion....KillerVette said:With the new z06 at 11:1 compression, is this going to allow for safe turbos and superchargers?? What kind of power should this engine hold? I am not sure of the internals so i was wondering if it could hold 800hp at the crank safely?
A true 11:1 static compression ratio is too much for any amount of boost; the compression must be lowered for a forced induction application.MikesZ06 said:As for the 11:1 compression, my guess is that it would work all right for blowers with no more than 6 or 7 lbs of boost.
You may be correct here, but I have seen a number of Procharged Z06's and C5's run a P1 SC at 6-7lbs boost with stock CR and experience no problems, even at the track.SRV said:A true 11:1 static compression ratio is too much for any amount of boost; the compression must be lowered for a forced induction application.
No i mean stock. Ferrari has been engineering their engines and tranny's much like chevy did the new Z06 for a long time. They make them race ready with bullet proof engine's and tranny's. I know of a 355 with all stock internals running like 12 pounds of boost and making 700 hp. It has made 100 passes down the QT on the stock internals clutch and tranny. they are very tough cars. The reliability issues with older Ferraris are with their little things like electronics that are generally made by other people. You rarely see an fcar with a blown engine.KillerVette said:when u say the 355 has a bullit proof engine, do you mean stock? or have they been modified for the turbo.
I agree. It's a huge risk. You have to regulate fuel and timing virtually perfectly so as not to damage the engine. But computers are getting better and making that easier.BIGBOS said:I wouldn't put F.I. on a 11:1 motor, your just asking for problems, if you wanted to truely take advantage of it, drop in some 8:1 boost pistons, change the cam, and put your choice of turbo/supercharger on it, and run 10+ psi on pump gas....
Nice numbers! :cheers:snakecharmer said:On my new motor in the snake, we dropped it to 8:1. No problem, it makes 647 to the tires,
By the same token, you don't want to run low compression just for the sake of low compression, else the motor will be a dog while off boost.so just goes to show you don't NEED high compression on forced induction engines.
Thanks. You are correct, it is a balance. In my stang's case, it has a nasty set of cams, ported intake/heads and a bunch of other goodies that take care of the off-boost issue. We mod motor guys also tend to like big gears that help with that as well.SRV said:Nice numbers! :cheers:
By the same token, you don't want to run low compression just for the sake of low compression, else the motor will be a dog while off boost.
Know your target horsepower, calculate the boost needed to hit the target horsepower, and finally calculate the required compression ratio to run safely without throwing horsepower out the window by running one's compression ratio too low.
Did you have the motor built with a true 11:1 static compression ratio? If so, why did you knowing that you were going to boost it?Zrod said:11:1 CR and 7 lbs boost should be Ok. Been running that set up for a while with no problems. That being said, currently have the car at A&A for forged motor setup (time for more boost!)
What you are describing is a Miller Cycle engine. The problem is, if the effective compression ratio ends up being 11:1 again (same peak compression pressure), then you have not gained any power. It would by definition have exactly the same mass of charge in the cylinder (ideal gas law), and that is assuming the intake charge temperature is lowered to ambient, which is a physical impossibility (would require intercooler with 100% efficiency). In fact, you will have lost some power, because of parasitic supercharger losses.SRV said:Did you have the motor built with a true 11:1 static compression ratio? If so, why did you knowing that you were going to boost it?
The only way I can fathom an 11:1 motor surviving 7 lbs of boost is by changing the cam which affects the engine's dynamic compression ratio. In order for that to work, one must choose a cam that hangs the intake valve open longer after BDC.
In other words, as the piston moves up the bore, the intake valve is still open, allowing the charge to escape past it until the intake valve finally closes. Once closed, only then the engine can start compressing the mixture. And the higher up the bore the piston is before the intake closes, the lower the dynamic compression ratio since the remaining volume above the piston at that point is much smaller.
That is why cam grinders recommend a certain static compression ratio with a particular grind. Since the bigger cams create a lower dynamic compression ratio, one has to 'make up' the lost thermal efficiency with a higher static mechanical compression ratio.
And again, that is why an 8:1 engine is such a dog with a big cam in it; it has a low static compression ratio already, which is made much worse by the cam's effect on dynamic compression ratio.
Needless to say, this discussion doesn't touch on port velocity, etc, from a bigger cam at lower RPM.
Concluding, putting a cam which hangs the intake valve open longer ABDC is one way to 'trick' an engine with a higher static compression ratio to believe it has a lower static compression ratio. This is advantageous for a forced induction engine with a high static compression ratio, and is much cheaper than replacing the pistons: within reason of course.