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Maximum safe compression ratio for premium pump gas.

  
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Maximum safe compression ratio for premium pump gas.

 
Pontiacman8 Pontiacman8
Moderator | Posts: 5779 | Joined: 02/08
Posted: 12/17/13
06:43 AM

9.5:1CR static is max on premium pump gas with iron heads on a Pontiac engine, any more and you will have detonation issues this is fact.
You may here about fixes like if you run a trick cam one with more duration it will allow you to run a higher C.R.  or adjusting the timing down or even using a adjustable vacuum advance and turning the vacuum advance way down is a fix but these are nothing but band aids and will not solve the problem at all the only way to prevent detonation is to run the proper octane that a engine requires.




An engine detonates when cylinder pressure is too high for the detonation
resisting chemicals, (octane) to work. If, you were not meeting the octane
requirement with a stock cam, when you install a bigger duration cam
and build more cylinder pressure, you'll be worse off than before.
Why because a larger duration cam will fill the cylinder with more air and fuel on each filling cycle making more cylinder pressure.  

Of course depending on how much more duration you have will
directly relate to what RPM it takes for the extra pressure to happen.
So the Half an answer that is correct from  (how ever tells you a trick cam will fix detonation problems) is, yes, at idle, or below 2000 - 2500 rpm the cylinder pressure is lower than a stock cam.
So as long as you can never put your foot into it, you're fine.


There are not any magic tricks when it comes to meeting the octane requirement for any engine.
You simply must!

Maximum safe limits on premium pump gas are as follows
9.5:1CR with iron heads
10.5:1CR with aluminum

Why can you run more compression with aluminum heads, because Aluminum dissipates heat quicker plain and simple.  
Engine builder,self taught auto body guy.
Horsepower sells engines and torque wins races

Pontiacman8
Pontiacman8
Pontiacman8