compression ratio

[steve_ram]

What is the safe maximum compression ratio for my Ford 302, using the current fuel available?.
I'm using a mild 268 degree cam with +40 pistons and I intend to change to alloy heads.

Thanks Steve

[JamesP]

Given a few discussions on this forum re compression ratios I believe the consensus is that if you go over 9.5CR you'll need to run on Super Unleaded, the Ally heads complicate the matter as many experts believe that you can run between 0.5 - 1 CR higher on same fuel before detonation as the heads run cooler. The shorter cam also will increase the 'Dynamic' compression ratio as the intake valve closes earlier.

Have a look at the attached excel file, I built this to give me an idea of what comperssion ratio I'd be getting and by putting in your cam specs it'll give you an idea of the dynamic compression to be expected as well. Reference points given are for a small block chevy as per David Vizard books but should be similar for your engine.

For reference I'm building a 383 SBC with AFR Ally heads with about a 10.2CR, I'm going to use the Edelbrock ProFlo RPM Multipoint Fuel Injection which may also help in reducing detonation due to better atomisation of the fuel in comparison to a carb.

My hope is to run on Standard unleaded but will go up to Super if get detonation or the performance is significantly better.

Hope this helps

James

'Every journey begins with one small step'

[steve_ram]

thank you James, just what i was looking for.

steve.