Lowering C/R

[T66]

Guys, please bare with me and my questions (we are about 15 years behind you guys). In order to lower C/R which is not suitable for forced induction, why couldn’t I use a 2mm copper gasket when boosting say between 12 and 15 psi’s? That would lower the C/R to a more boost able scenario?

[Polygon]

That is a cheap and unreliable way to lower C/R in my opinion. To me that is like cutting your springs to lower the car. It does the job but it isn't reliable or safe. The best way to lower your compression would be to buy the appropriate pistons.

However, I sure there are some that will disagree with me.

[drdisque]

a 2mm gasket isn't going to make a whole hell of a lot of difference either way (either in reliability or in compression ratio)

[Schister66]

you're basically saying that you could get a thicker headgasket to lower the cr....that would work, but there is going to be a lot of stress on that piece. You'll be more likely to blow the hg and then have to spend money to replace that and ultimately lower the cr the right way....just do it right the first time!!

[T66]

Originally Posted by Schister66

you're basically saying that you could get a thicker headgasket to lower the cr....that would work, but there is going to be a lot of stress on that piece. You'll be more likely to blow the hg and then have to spend money to replace that and ultimately lower the cr the right way....just do it right the first time!!

Point taken.

[CBFryman]

if you have room make your combustion chamber bigger

[T66]

Originally Posted by CBFryman

if you have room make your combustion chamber bigger

Easier to put in forged internals.

[T66]

Just for interest sake, how much will a C/R drop (10:0:1) if one should put in a 2mm copper gasket?

[beyondloadedSE]

Originally Posted by T66

Just for interest sake, how much will a C/R drop (10:0:1) if one should put in a 2mm copper gasket?

maybe a couple tenths, which doesnt even put it close to an ideal compression ratio for boost.

If you want to lower the compression, do it right and get some forged pistons made.

[drdisque]

we'd have to know the bore to know how much the gasket would change c/r

[Schister66]

unless you're planning to go really big you don't NEED to lower the cr....people boost GSR's like mine all day at a 10.2:1 cr w/o problems. If you're looking for some serious power, you'll have to use forged internals!

[CBFryman]

Originally Posted by T66

Easier to put in forged internals.

its as easy as a port and polish. ive seen it done one briggs 5hp motors..notmally you would make the CR higher and the only head work you would do is rounding off any sharp points and maybe a port on the intake and port and polish on the exaust, however when burning Nitro mixtures in a sprint kart its best to keep the CR around OE or go lower to prevent over heating since its an air cooled motor.

you really do learn a lot of tricks from messing around with performance gokarts and talking with organized racers (not the 8 year olds )

[curtis73]

I would examine the current setup and figure out how many more CCs you need to get the compression ratio you need and work from there. These guys are right, just a thick copper gasket would be an invitation to failure. If you just wanted to lower CR without boost, it would be a good idea to an extent, but copper isn't the best for boost if its too thick.

Polishing chambers is a good way to add a few CCs as well as reduce detonation danger. A strongly cut valve job will add a few CCs, but at the expense of wasting material for future valve work and possibly custom valvetrain components.

Take a look at some aftermarket gaskets and their compressed thicknesses. Sometimes just choosing between a superior composite style FelPro or Reinz gasket can net you a few CCs without having to resort to using copper.

I might consider calculating out how much a carefully chosen composite gasket, a chamber polish (since it not only gets you a few CCs, it may make it possible to get your target boost with a touch more compression than normal), a heavy-cut valve job for a few CCs, and consider gasoline octane rating and ignition curves. If you do all the math on those changes you might find enough of a CR drop to get boost that you can live with.

[T66]

Thank you all so much for the advice. No copper gasket, will do it the proper way.

Christie.

[Schister66]

what are you turboing....what size turbo.....and what are your power goals???