Supercharger

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Scampin around

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would 10.5 to 1 compression be too high o super charge? Would you need to build bottom or would it be strong enough stock?
 
10.5 would be pretty much the edge of too high w/o supercharging, and if we're talking a 225, You'd need a custom piston & modded chamber to generate a proper squish
distance to push that & beyond.....unless You've got really special gas pumps.............
 
I believe approx. 3 psi of boost is about 1 point of compression. So yes, 10.5 CR is too much. 65'
 
The rule of thumb for naturally aspirated stockish cam compression I've always heard is move the decimal point to the right for the octane.
9:1=91 octane
10:1=100 octane
Heard this would allow max spark advance in most motors.

Dunno how correct, but that's what I heard.

Most blower motors run lower compression, not higher.
 
run e-85 if available. many guys running higher than "normal" compression with a lot of boost, also dynamic compression is really something to look at as well when determining octane of fuel
 
Static compression is used all too often and many times is inaccurate in an of itself. I.e. I bought 10.5:1 pistons so I have a 10.5:1 engine. not necessarily. Even the factory ratings aren't always 100% right.

Now add the camshaft. Now you get into cranking compression. Most Na guys run bigger overlap and tighter centerline angles on their cams. This is the exact opposite of a forced induction grind.

Last you need to look at the head materials and the head design. Aluminum will allow more compression and chamber design plays into it as well. Being it's a slant, you obviously have iron heads.


So before I made a call to whomever you are going to buy your SC from, I'd know my cam specs, my true static compression and my cranking compression.
 
just do it
then when/if it blows, you can put a V8 in there

stir.gif
 
The rule of thumb for naturally aspirated stockish cam compression I've always heard is move the decimal point to the right for the octane.
9:1=91 octane
10:1=100 octane
Heard this would allow max spark advance in most motors.

Dunno how correct, but that's what I heard.

Most blower motors run lower compression, not higher.
That's a terrible rule of thumb, and there are tons of 10:1 engines running around on 93-94 pump gas w/o any issues. There is no "rule of thumb" because the amount of
variables that affect suitability are nearly endless. From head and block materials,design,cooling system quality & effectiveness, spark plug location & cooling, quench vs.
no quench vs squish vs the terrible zone in between, piston design, intake system fuel distribution variation,....................it doesn't end there but You get the idea.
 
That's a terrible rule of thumb, and there are tons of 10:1 engines running around on 93-94 pump gas w/o any issues. There is no "rule of thumb" because the amount of
variables that affect suitability are nearly endless. From head and block materials,design,cooling system quality & effectiveness, spark plug location & cooling, quench vs.
no quench vs squish vs the terrible zone in between, piston design, intake system fuel distribution variation,....................it doesn't end there but You get the idea.

Agreed there's room for improvement on all the fronts you mention, but I would say that rule of thumb is, as I heard it, the starting point.

That said, the Quad 4 was still in production when I heard that....
 
Agreed there's room for improvement on all the fronts you mention, but I would say that rule of thumb is, as I heard it, the starting point.

That said, the Quad 4 was still in production when I heard that....
LOL! Oye!. OK, I'll take a sec. to shake those memories off,...........ahh, all better!
Well, what I'm getting at is take My stock over 140K '87 Dak, 1st year 3.9L V-6 w/a carb. Has the heart-shaped chambers a la "302" 'teener heads and stock squeeze of
9:1, runs on 87 pump all day even with a sure buildup of carbon & associated hot-spot & squeeze increases due to the mileage, even tho' the heads are iron the fast-burn
design makes that rule of thumb way off, Al-u-minimum would be able to go another whole point higher...10:1 w/o battin' an eye.....

AHHHHH!!!! Quad 4, AHHHHHH Coil Castle Flashback!!! AHHHHHH!!!
 
That's a terrible rule of thumb, and there are tons of 10:1 engines running around on 93-94 pump gas w/o any issues.

:thumbsup:

10:1 with eddy heads, 160psi cranking compression. Premium pump gas only.
 
The rule of thumb for naturally aspirated stockish cam compression I've always heard is move the decimal point to the right for the octane.
9:1=91 octane
10:1=100 octane
Heard this would allow max spark advance in most motors.

Dunno how correct, but that's what I heard.

Most blower motors run lower compression, not higher.

that's not a good or correct rule at all.

the Chevy Cobalt SS has 10 to 1 and a Blower on it, there are way to many variables for a general rule like that.
chamber design, piston design, piston material, head material, cam choice are just a few things that skew that rule.

I had/have a 493 big block I am running almost 11 to 1 on pump gas, no pinging no pre ignition works great.
 
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