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Post  tom a hawk on March 20th 2019, 9:54 pm

AFR build with 545 motor: what compression with a 270- 580 lift cam, forged crank and pistons.
the 2 different head combos Im looking at would put me at either 10.65-1 or 11.6-1. will be a street/ srtip 68 hunderbird on pump gas. whats the limit for compression on 93 octane with that cam? Im tempted to push it and go with the higher compression, but Im to cheap to buy race fuel

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Post  rmcomprandy on March 20th 2019, 10:42 pm

tom a hawk wrote:AFR build with 545 motor: what compression with a 270- 580 lift cam, forged crank and pistons.
the 2 different head combos  Im looking at would put me at either  10.65-1 or 11.6-1. will be a street/ srtip   68 Thunderbird on pump gas. whats the limit for compression on 93 octane with that cam?  Im tempted to push it and go with the higher compression, but Im to cheap to buy race fuel

What final compression you can use will depend greatly upon the engine temperature and under-hood temperature.

At 180 degrees engine temp with 100 degree air temp would make 11/1 difficult to control detonation; hotter or colder ... you can make your decision from there.

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Post  68galaxie on March 21st 2019, 9:49 am

The power gained using 11.6:1 CR will be lost when you dial back ignition timing to run pump fuel.
Even the 10.65:1 may be too much with the short duration cam.
Not sure what your converter stall will be? A higher stall converter will help avoid low rpm high load detonation.

Like Randy says cool engine/air temps will help.
Also pay close attention to quench distance.

For me 10.65 would be my limit if using pump gas (and tight quench)
Pump 93 isn't always consistent.
Doesn't take much detonation to cost alot of $$.
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Post  gt350hr on March 21st 2019, 11:26 am

Go with the 10.65 combination. "Years down the road" you will be much happier you did. With that many cubic inches you will still have a powerhouse of an engine.

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Post  Lem Evans on March 21st 2019, 11:29 am

10.65 in my opinion.

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Post  tom a hawk on March 21st 2019, 4:18 pm

10.6 it is thank you guys

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