Thread: what do you guy think the highest compresson i can run on pump gas

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Whats the highest compresson i can run on pump gas, or with octane booster,
on a 383 chevy=
on a 350 chevy=

Cast iron heads or aluminum heads?

what type of octane booster are we talking about.... the cheesy of the counter crap that will do nothing, or something real like touluene, doesn't matter what displacement the engine is either, the only things that matter are the metal you use in the motor, and the cam grind

I have no clue, but my guess is 12to1

As Blackroc alluded to, you can run another full point of static compression ratio with aluminum heads over cast iron heads.

The limit on scr will be determined by cylinder pressure (intake closing point on the cam), head material, combustion chamber and piston crown shape and size, total ignition timing and advance curve, spark plug heat range and indexing of the ground strap, thermostat opening point, inlet air temperature, air/fuel ratio, your elevation above sea level (air density), squish (distance from the piston crown to the underside of the cylinder head with the piston at TDC), rear gear (lugging the motor with a tall gear will allow detonation to occur easier than a short gear), whether or not there are any hot spots in the chamber/cylinder and whether or not you're polluting the incoming charge with an EGR or PCV system.

With everything optimized, it's possible to operate at a little over 11:1 with iron heads on premium pump gas with no octane booster.

my response sounded a little less quality as Techs, so i'll just leave his to do the talking

cast heads

What's your goal? What do you want the car to do?

Originally Posted by frankgomez65

Whats the highest compresson i can run on pump gas, or with octane booster,
on a 383 chevy=
on a 350 chevy=

It all depends on the cam specs as more duration will bleed off compression due to overlap. You have to figure dynamic compression ratio rather than static compression. DCR of 8:1 is about maximum with iron heads and 8.5:1 with aluminum heads. DCR takes into consideration your cam specs and is a much more reliable guide to building an engine. For a very thorough explanation of DCR, go here: http://www.chevytalk.org/fusionbb/sh...php?tid/92966/.

Another bad thing on high compression besides today's dismal fuel is that high compression makes more heat... On a street car that will be idling around in stop and go traffic high cylinder temps leads to high operating temps and overheated engines which can cause a lot of very expensive damage. Optimizing the compression may be best left to race cars and sticking with compression in the 9 to 9.5 range could be better. I like to spec my engine components for building torque which IMO is a much more beneficial for street use.....

I thought it would be a cake walk to run pump premium 91 octane in my 10.6:1 motor but I've found I can't put in any more timing than 32* spark lead without detonation (lightly peppered plugs)... This is on an aluminum headed, high altitude motor (carefully prepped pistons and chambers, too!) that should tolerate highest compression... it runs just fine but it runs a whole lot better with higher octane and 36-40*

Just a word of caution, you may be able to get away with 11:1 on premium but you'll have to compromise in many ways to get there...

Two cents,
-Chris

9.5:1 on 93 Octane Max

I run 10.6:1 compression in my 383 and have no problems if I run 91/92 octane. In fact, I had to fill it with 89 octane in a pinch two weeks ago, and still no pinging. My DCR is 8.46:1 which is getting close to the 8.5 edge. But with AFR heads, less timing is more, and 32 degrees total made the most hp and torque. I originally wanted to run a CC XE-274 cam but it put the DCR at 8.67. But the Magnum 280 cam put me under 8.5. I am very happy with my engine combination.

I ran 92 octane in a 11.3:1 350 +.030, nasty solid cam, iron heads ported and polished.

I had to index the plugs to get rid of pinging.

IMO a water injector would get you over the hump, and they are not too expensive nor are they a pain to keep up.

Kitz

what is index the plugs mean.
and 32 degrees mean