Compression with the blower??

[GEARS]

Alright.... I have my HT3.4 in pieces as I am in the process of supercharging it. It has the Crane H260-2 cam, with Comp 1.6:1 roller rockers, with 1.5" really longtubes, and some pretty intense exhaust head porting on the iron bricks.

I want to run this motor with about 6 psi of boost at 5000 rpm, right now it has 9:1 compression.... I could get the heads decked 0.010" and that would raise the compression to about 9.25:1..... Do you guys think that would be safe to run with the setup I am running???

[DefEddie]

9.0:1 + 6psi = 12.67:1 effective CR
9.25:1 + 6psi = 13.03 effective CR
That what your looking for?

[ForcedFirebird]

9.0:1 + 6psi = 12.67:1 effective CR
9.25:1 + 6psi = 13.03 effective CR
That what your looking for?

That's a rough measurement, in a running engine the compression is dynamic and based on cam specs. That cam has some decent overlap. ~.1:1 difference compression on a charged engine is negligible.

[DefEddie]

That's why I said effective ratio,not dynamic.

[GEARS]

I think I am going to see if they can only resurface 0.005", which will still bring it up to 9.16:1.... but I think with 6 psi of boost, having a custom tune and the water/alky kit will make for some reliable power......... I HOPE!!!

[SappySE107]

a good tune is all you need with 6 psi on that compression.

[GEARS]

Ya I used a few online calculators, and I come up with 12.36:1 Dynamic compression with the use of the 3.622 bore, 3.307 stroke, 5.7" rods, 9.16:1 static N/A compression, and 29* ABDC on the intake side of the cam.

Tune and water!!!! And we should be safe....

[Mars]

It'll be more than safe, don't lose any sleep over it.

[ForcedFirebird]

Ya I used a few online calculators, and I come up with 12.36:1 Dynamic compression with the use of the 3.622 bore, 3.307 stroke, 5.7" rods, 9.16:1 static N/A compression, and 29* ABDC on the intake side of the cam.

Tune and water!!!! And we should be safe....

It'll be more than safe, don't lose any sleep over it.

Mars is right. We have boosted 9.6:1 with no issues, even at double digits guage pressure - according to those dynamic/effective calculators we were seeing 18+:1 which is no way supposed to run on pump gas, but guess what?

Those calculators have been outdated and proven wrong on many occasions, take them with a grain of salt. Cylinder pressures are far more complicated to calculate than taking a valve closing event, or adding compression to boost pressures etc. You need an in depth program with lots of inputs to understand the cylinder filling and cam dynamics. I used to hand calc everything, but Dynomation does it for me now in seconds. It's all about trapped mass and airspeed.

tuning, tuning, tuning, tuning, I can't express that enough. There's 10.5:1 and 8psi cars running around with pump gas and living to tell about it. The lower compression just allows you to be less accurate with your fueling and timing.