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[rsr911]

Originally Posted by StrokerSmoker7.3

It's both the turbo and compression. Banks and ATS and Hypermax all have their turbo kits for these things set to run right around 12 psi. When you turbo an NA motor, you esentially double compression. So you take these motors the are making 21:1 compression the turbo them, your past 40:1. There for if you can lower the compression enough you can safely run 20+ psi. Just a a comparison, a 7.3 PSD is somewhere around 17:1 compression I believe. That's why stock those turbos put out around 20 PSI. If this is wrong, sombody correct me

I'm new to diesels but fairly versed in terms of boost, you are close to correct. In order to double an engines effective compression ratio you need add one atmosphere of boost (14.7 psi or 1 bar). So a 21:1 motor on 12 PSI would be about 38:1 effective compression while the 17:1 motor at 20 PSI is about 40:1 effective. A higher compression motor will be more driveable as it has more off boost power than a lower compression motor. However a lower compression motor can make more overall power due to larger cylinder volume. Cylinder volume and displacement are not one in the same, displacement is a measure of the swept volume, the volume in which the piston travels while cylinder volume is the swept area plus the compression or fixed area which is the combustion chamber. Simply put compression ratio is simplty a function of swept area volume versus combustion chamber volume. Since a lower compression engine has more total cylinder volume it it possible to pack more air/fuel in under a boost condition than a higher compression engine under the same boost. This is one reason among several that boosted engines tend to run lower static compression than their NA counterparts. Then there's dynamic compression but that's a whole nother discertation LOL