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Trying to figure out what fuel a friend is going to need to run with a new engine we are putting together. Mopar 493 stroker, trick flow 240 heads, straub hyd roller. Static compression ratio is 11.82:1, DCR using Keith Black calculator (add 15 degrees to intake closing point @ .050" lift), comes out to 9.607:1.
 

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I feel there are way too many variables to narrow a specific fuel octane needed based on compression ratio.

I have built for myself 11:1 and 12:1 SBC 350" engines with GM iron heads with chambers in the mid 50cc area.
Ran them with very small cams 260H comp a nd 270H comp which was 224 @.050" on the 12:1 It had 245PSI cranking pressure.

They ran fine on 91 octane with 38-41 timing.

I feel a variable is how well the heads fill the cylinder.
Longer stroke can fill the cylinder more.
Buddy had a 427" small block chevy with 10:1 and aluminum heads and No idea what cam but it was much larger than the 270H comp magnum I ran in my 12: 1 350.

I tweaked and tweaked on that 427 to try and make it run right... it just would not ,, it had a vibration in it at low speed and just would not run well at any rpm with any amount of advance.

I said lets try some 110 racing fuel..
That did it... the engine smoothed out and ran excellent .. idle got way smooth also..
Then we decided to cut it 50/50 with 91 octane... it liked that just as well also.

That 427 only had 185PSI cranking pressure.
I have no idea what size chambers or surface texture was in that 427.. but i do know what my 350's had.

SO the cranking pressure means nothing and compression means nothing at least for comparing these 2 different engines.

Give it some 110 and see if it likes it and then cut it 50-50 and see if it likes it.. then cut it some more and more.

Or try 91 and see what happens.. that is about what it boils down to.. try and see.

My Honda V65magna at 10.5:1 was quickest with 87 octane 91 octane it was .2 slower.
Same thing happened with my buddies Yamaha V-Max. You just never know.
 

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Intake valve closing point, piston velocity, quench, fuel emulsion, chamber shape/ material and ignition advance have more influence on detonation than CR.
 

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Intake valve closing point, piston velocity, quench, fuel emulsion, chamber shape/ material and ignition advance have more influence on detonation than CR.
I run a 12.0 to 1 540 on 91 octane with no issues, but I drive around town with the DA at 7000 feet, which makes a big difference on detination. But I agree with bradley, quench and chamber shape are biggies.
 
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