First off does compression make your gas mileage wrose and how much if so? Going from a 10.1 xcompression piston to a 13. 1 compression pistosn how much of a increase in power would you see? Percentage wise? Such as getting a victor jr. package frlom edelbrock with 12.1 pistosn make aorund 525 horses If 10.1 what would i make? What would be the stock compression with these heads?

Compression is probably the single most important factor in building a motor. If you plan on running crazy compression pistons/heads you'll need to run race fuel all the time. Is this car for race use only? Cause with that high of compression it should be

provided you have the timing and fuel quality to take advantage of it.

Increasing it will increase gasmileage b/c the engine is more efficient.

jcb is totally right. CC did a article on the power increases in compression. Using 91 octane on all pulls on there Mopar 440, they gained about 20 horse each point and trigged that number right on 3.5, but the high end jumps (11:1 -12:1) they were gaining much more, like 5 percent. The mag is still on the stands until, flip, flip, there- last page!, Oh! till Jan. 1st!!! It is the big block shootout one. Good Luck!

Basically its gonna be a toy i drive in town every once in a while.

Unfortunately i liv eina small town and the race fuel tanks have all been recently disposed of.

What kind of octane rating do i need to have to use 13:1 compression pistons?


Also what kind of gas mileage woudl i be expecting from a carburated 350 with all victor jr. parts and some headers and exhaust

town and highway

Also would i need to modify anyhitng to fit 13:1 pistons so that there is clearence?

Oh i forgot if i used the stock pistons what woudl be the compression ratio estimated at since i think the combustion chambers on the victor jr.s are like 76cc?

Or is this a bad idea

70 cc my bad

piston to head clearance, and piston to valve clearance.

ps. today is my birthday.

Vette-eater,
I like that. But there are some pretty mean Vettes out there.
(See below)


I wouldn't suggest such a high compression ratio on a daily driven car. It would be expensive to keep race gas in it all the time. If it's a street/strip car, there are better ways to get horsepower than having to live with such a high compression ratio.

Yes, going to a carburetor will help get the revs, and the horsepower up. But I'd suggest a hydraulic roller cam if you don't already have one. Go as big as you can get away with, if you have a smog test.

I'd suggest stroking your 350 to a 383, or go to a 400-based engine. That's the mouse that thinks it's a rat. Then see if you can get away with a true dual exhaust, or at least an excellent flowing single exhaust.

On my 355 when it was carbureted, I was averaging 16 to 17 mpg on the highway. Plus it would outpull a healthy 5.7 liter L98 C4 Corvette. That's with 10:1 compression.

I yanked it out of my Corvette to get ready for the big block, and stuck it in my IROC with the tuned port installed.

For a 13:1 engine you'll probably need a minimum of 100 octane fuel and 112-114 would be prefered.

High compression in a gasoline street engine isn't a good choice. Even the muscle cars of the late 60's only peaked to around 12:1. High compression will also build a lot of heat. A better cooling system needs to be used to get the heat out of the engine.

Stock pistons will have problems with that kind of compression ratio. Forged pistons should be used.

You could solve your octane problems by converting your fuel system to propane or alcohol/methonal. Both fuels work well in high compresion ratio engines and alcohol runs cool. In a street engine it may actually run too cool and cause other problems.

If you plan on any street driving, stick to a max of around 10:1 and put premium pump gas in it.