11:1 CR and Supercharging

[Route666]

Hi guys, I was just wondering whether, since the 5.0 Cammer engine (when it is released) will have 11:1 CR, would it withstand 10 psi of centrifugal supercharger boost with 9.3:1 pistons in it?

Since I would have to change the pistons, I'd go for the best I could find, and the rings as well, and while I'm at it, probably the rods and crank... but my question is really about detonation. Since this engine is designed to run 11:1 CR, I would think it would handle around 9:1 CR with 10 psi of boost without detonating, when used in a 3400lb car.

 

[Vanride69]

so long as you fully intend to install low compression pistons, you should be fine. most cars can handle about 12.0:1 CR before detonation. And if you are upgrading the internals, you should be fine. Good rule of thumb is this: http://www.holley.com/HiOctn/TechServ/TechInfo/SCTech.html
scroll down to about half way and you will see a beautiful chart with all the info you need on S/C'ing a N/A engine and the basic amounts of boost at a given CR. hope this helps!

 

[Route666]

so with 9:1 CR, only 4psi of boost???? I've seen sites that say stock engines can handle from 6 - 9 psi of boost. I thought I could go higher than 4psi.

 

[Booyah]

Originally posted by Route666
so with 9:1 CR, only 4psi of boost???? I've seen sites that say stock engines can handle from 6 - 9 psi of boost. I thought I could go higher than 4psi.

Without pulling timing yes. It's based on trying to stay as close to stock timing without detonation on 92 octane.

 

[Route666]

ok, so if I went to 8.5 psi, it would handle more boost obviously, but I'm just worried about what will happen to low-rpm performance with the centrifugal blower, since it won't boost all that much low down.

Would it be better, with the centrifugal pump, to:

A: Stay at 9:1CR and retard timing a little.

or

B: Put it at 8.5:1CR and keep the timing.

Keep in mind the no boost at low rpm factor of the centrifugal.

 

[Booyah]

Originally posted by Route666
ok, so if I went to 8.5 psi, it would handle more boost obviously, but I'm just worried about what will happen to low-rpm performance with the centrifugal blower, since it won't boost all that much low down.

Would it be better, with the centrifugal pump, to:

A: Stay at 9:1CR and retard timing a little.

or

B: Put it at 8.5:1CR and keep the timing.

Keep in mind the no boost at low rpm factor of the centrifugal.

Well personally I wouldn't go lower than 9.1:1 ratio. On my '98 Cobra I noticed no difference in low rpm performance from dropping my CR from 9.85:1 to 9.1 when I had the motor rebuilt. And I only lost 10 rwhp from the drop, that's because I didn't have to pull nearly as much timing at the higher rpms. But if you were to go with 8.5 CR I would go with a positive displacement blower or a proper sized turbo. We were discussing this in another thread here

 

[Route666]

okay cool thanks, another site I asked this same sort of question on they said turbo as well, I don't like turbos all that much, the plumbing, the heat, the noise. Plus I'd rather keep higher compression.

 

[Poisonous Mods]

Route...see good place to be at for ur answers :beer:

Aint nothing wrong with Turbo's....Yes more worked involved but boost is boost.

 

[Route666]

Yeh thanks for the direction over here

and everyone, thanks for the info, its been more than helpful.

I've done some more calculations, and am thinking I only need 8psi max, for the horsepower I want, which would be above 650 mustangs (horsies) at the engine, and with jet hot LFC on the gearbox gears and diff gears, drivetrain loss will be slightly reduced.

Sorry guys, I'm not mad keep on turbos, if I went with turbos I'd have to go all out and use two small turbos, and make it an insane twin turbo beast, but then it wouldnt be too driveable on the road, and may guzzle a little more fuel than I need

:burnout:
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