i want lower compression

i want a lower compression ratio i guess i could have said? what would be the advantage of that vs the base gasket?( im in uncharted territory for me thanks

You don't want a lower compression ratio, you want lower cylinder pressure

Think of it like this, if you have a 13:1 compression ratio, but the intake valve don't close until the piston is half way up on the compression stroke, how much actual compression (cylinder pressure) are you going to have?
Not much because you have effectively cut your compression ratio in half, since you just forced half the air in the cylinder back out the intake. Valve timing controls cylinder pressure, hence Jay's suggestion about cam timing.

Believe it or not, the maximum effective compression ratio is around 8:1 on gasoline, that's a cylinder pressure of around 200 psi. Above that detonation creeps in and starts munching on your pistons

Now you say "Hold on there a minute steel, how are the Nascar boys getting away with running 16-17:1 compression ratios then?".

The Nascar boys are forced to run restrictor plates between the carb and intake manifold to restrict the amount of air getting to the cylinders, thus reducing the effective compression ratio to somewhere around 9-10:1. And that's on their high tech race fuel, not pump gas.


Gets complicated when you start modifying things, don't it?


To answer your original question, if the 12.5:1 pistons are going in the early style (not the 998cc late style) 1000 motor, then using a J head ought to drop the compression ratio down to around 10-10.5:1 or so. Jay can tell you for certain if that will work.

Probably the best answer is to sell those pistons to someone else and get the proper pistons for your motor.

A word of caution, Dont use the octane booster, it doesent mix completly with the gas, ie you can get more or less than the advertised amout of boost,
I knocked a hole in a piston once using the crap, never again,

BSKZ650 wrote:

A word of caution, Dont use the octane booster, it doesent mix completly with the gas, ie you can get more or less than the advertised amout of boost,
I knocked a hole in a piston once using the crap, never again,

Were you using this stuff (Octane Supreme 130) or one of the other phoney boosters? I use this and it seems to mix perfectly in gas. This is the only additive with tetraethyl lead, which is what was sdded to gas to boost octane before lead was banned.

At $20.00 a quart, $4.00 per gallon for gas, and two quarts per 4 gallons to boost the octane enough for 12.5:1 compression (their figures, not mine), figure about $56.00 per 4 1/2 gallon tank.

Good Gawd Almighty!! :woohoo:

steell wrote:

At $20.00 a quart, $4.00 per gallon for gas, and two quarts per 4 gallons to boost the octane enough for 12.5:1 compression (their figures, not mine), figure about $56.00 per 4 1/2 gallon tank.

Good Gawd Almighty!! :woohoo:

Here's the octane boost ratio:

6.0- Ounces OS-130 to 1 gallon/fuel……..11.0 point octane increase

That would mean to get to about 103 octane, you need 6 ounces per gallon which is 6/32 ($4) = 75 cents per gallon to treat the fuel which would be $3.38 for a 4.5 gallon tank.

Back in the 60's, we ran some pretty jacked up hot rods on 102 octane so I'm thinking you can crank the compression up pretty high and still run it. Some of those were running 10.5 or 11 to one as I recall.

BTW, you can also reduce the octane requirement and increase HP by using water vapor injection. We ran that in the old turbocharged Corvair engines.

I based my statement on the following info from the second link you posted.

18- Ounces OS-130 to 1 gallon/fuel……..16.0 point octane increase

Octane is in full points. eg; 93 octane to 101 octane by adding 3 oz. / gallon fuel

COMPRESSION RATIO CHART

Engine Octane Needed

Compression Ratio Min. Max.

8:1 87 92

9:1 89 96

10:1 92 100

11:1 96 102

12:1 100 108

So 16 oz per gallon for a 12.5:1 compression ratio sounds reasonable based on the above info.

If you were talking about the 11:5:1 compression ratios of the Chevy's back in the 60's, keep in mind that they ran lots of valve overlap to blow the mixture back into the intake and lower effective compression pressures.

I had one of those hot rodded Corvair turbos, a 65 Corsa, took it to Germany in 78 and blew away Porches with it

steell wrote:

I had one of those hot rodded Corvair turbos, a 65 Corsa, took it to Germany in 78 and blew away Porches with it

My buddy's was a 66 turbo Corvair. It had high comp heads, headers, water injection, two barrel carb on the intake side. That thing would pull 7k revs before you knew it. I think the speedo went up to 140, we buried it off the end of the dial. It kept burning valves because the heat in the cylinder was more than an air-cooled engine could deal with.

This is one option, I have the same dilemma on the 1000R when I start on that project.