11 to 1 on pump gas

dgc333 said

The issue with that article is its not overlap that effects cranking pressure it's how long the intake valve stays open past bottom dead center. Exhaust/Intake overlap occurs when the piston is transitioning from moving up the cylinder to going down.

Cranking pressure and the dynamic compression ratio is created after the intake closes on the compression stroke. Pressure does not start to be captured in the cylinder until the intake is closed (the exhaust was closed long before BDC). When you look at cam catalogs as the intake duration gets bigger the recommended static compression ratio goes up, this is to ensure that adequate pressure is captured in the cylinder for good low/mid rpm response.

Click to expand...

Thank you. There is a great deal of false in formation in the article by "Steve" and your answer is finally a voice of reason. It is when the intake valve closes that the compression begins to build in the engine. The overlap does not bleed cylinder pressure. There is generally a loss of cylinder pressure with a cam of greater overlap because those cams likely have a longer intake duration and therefore it is of neccessity that the intake closes later causing a loss of dynamic compression.

I have personally run 11.9:1 compression on 91 octane with factory 906 iron heads, .160" quench, the distributor locked at 38 degrees and there was no detonation. You have to be smarter than your cylinder head design, compression ratio and fuel type.

I don't believe I would run the OP's engine at 11:1. If you have to ask if you can run 11:1 on pump gas you probably don't have the expertise to attempt the task. The problem with having to ask on the forum is that many answers will be given by those who don't have the knowledge to answer correctly. We read false information, assume it to be the truth and repeat it.