All Small Six Max Compression Ratio for Pump?

[StarDiero75]

Howdy Guys,

With the new aussie 2V coming, I gotta plan what kind of compression ratio I want. I had a guy at work telling me since the head breathes better I should be able to run up to 10.5:1. That sounds really high. Can I run higher than the 9.3 I'm currently rolling with on my log head?

Thanks,
Ryan

 

[drag-200stang]

I could be wrong, but that makes no sense to me. I would think that would make the effective comp. higher and you would have to deal with that.

 

[gb500]

Look up a dynamic compression calculator and plug your numbers in.

Some recommendations in tech pages on this site for DYNAMIC comp ratios to aim for.

Static & Dynamic Compression Ratios

If your building a performance motor, one of your first thoughts was probably 'How high should my Compression Ratio (C/R) be?" If so, you need to know the difference between Static Compression and Dynamic Compression, as Static compression is...

fordsix.com

The 2v chamber ain't too great a shape plus its cast iron (not alloy)plus need your quench set up properly for higher comp ratios plus need good octane plus etc etc

 

[xctasy]

He's right. Static compression is irrelevant. Anytime you add a Cam with 68 degrees exhaust timing like most 264 or 274 Clay Smith or Schneider cams have, you have to go to a 13% higher static compression or 10.2:1...jist to maintain your original Effective Compression.

Our 1970-1972 M code based Phase 1, 2,3 and 4V 351 Cleveland's with 340 to 390 gross hp ran on 10.7 to 10.2 compression ratios and 185 psi cold cranking compressions on four star 97 octane, but they can take 94 octane because they used K code style 310 or 300 degree at lash cams reground to a 228 to 240 degree 50 thou exhaust valve lift. This lowered the effective compression to the same Effective compression as a stock 256 cam 2V 351C with 193 degrees at 50 thou lift. The exhaust closing event, if it's set 5 to 10 degrees more at lash or at 50 thou lift than the intake, will allow you to get your Effective compression below 8.5:1, and that will allow you to run on 89 octane if you don't polish the intakes port too much.

Again, it's exhaust closing duration before top dead centre that governs octane demand. The red numbers here

"https://fordsix.com/threads/effective-compression-calculations-installment-one.5518/"

 

[drag-200stang]

The guy at work said that because the head flows more, that he can run more comp. with no talk of cam change..I say if the head flows more, that the compression that the engine sees will be more because of more air trapped than the poor flow head with less air to compress.