I' starting an LT1 355 blower motor buildup. Here is what my combo is going to be. Eagle 4340 forged 3.48 inch stroke crank with Eagle 5.7 inch H beam rods, 4 bolt studded mains, studded heads, JE extreme duty 22cc inverted dome pistons with Speedpro rings and Hellfire ring combination. I have got band new bare AFR 210 LT4 heads that I am going to have fully ported (Hopefully AI) with custom HR blower cam matched to the heads, LT4 intake with ASM Monoblade. Here is my issue, the heads right now are 74cc unfinished and will probably be close to 76cc when finished. With the JE piston that I have chosen, their chart shows 7.8 to 1 compression ratio with these heads. I am planning on running about 15 pounds of intercooled boost. This is a pretty low compression ratio, I want to be on the safe side and build the motor to hold more boost than I'm going to give it. My question is, will this low compression ratio hurt my horsepower output (compared to say 8.0 to 8.5 to 1) and will it hurt low end power? I just didn't know if the low compression ratio would kill the streetability?

 

yes, that will hurt power, but you will be very safe. If you don't already have the crankshaft and pistons, then get a 3.75" stroke crank and pistons with the same dish and make a 383. This alone will increase compression to 8.34:1. I have been looking at the Wiseco catalog already today and see that they have -20cc pistons for a 383 that will bump the compression up a little more to about 8.5:1. That is still very safe for plenty of boost.

 

The effect on hp will be quite small. Drops in CR, even at the same boost, have less of an effect on a blower motor than on an NA combo. The reason is somewhat subtle but it is backed up by lots of experience. I have explained the rationale for this in the past and if anyone cares, I can try a search or to re-write what I have posted before.

Rich

If you do an "Advanced Search" in the Forced Induction forum with the keywords "compression ratio" and my username (rskrause) you will find a lot of thereads where this is addressed.

 

Thanks guys, I will do a search and if I can't find it, I'll let you know rkrause. Also, with that low of a compression ratio, how much boost do you think it could take?