need help unerstanding compression

[sleepygreen]

i need help understanding compression ratios and how to get them where you want them...like what the hell does 11.1 or watever those numbers mean.

[d112crzy]

http://en.wikipedia.org/wiki/Compression_ratio

[wed3k]

i need help understanding compression ratios and how to get them where you want them...like what the hell does 11.1 or watever those numbers mean.

auto shop pop quiz?

[sleepygreen]

nah no pop quiz...i never took autoshop i learnd to do most of my own DIYs and repairs by just doin it and if i mess up i have no other choice but to fix it...but thankx for the link. that stuff is confusing!!

[flight50]

compression ratios. well you only start getting familiar with them the more you research. it all depends on what you wanna do which will determine a safe ratio for you. for example. stock cb7s are like 8:8. if you want to boost you can keep it here. some go 9:0 up to 9:5. the lower the number when boosting, the more room for error for the tuner. the higher the ratio, more chance to denotate(engine knock). but you get more horsepower. NA you want your numbers higher.that number depends on your motor. i don't know about the stock cb7 range. a h22 is 10:5 stock jdm or usdm is 10 but it also depends on what year the motor is. for street most don't exceed 11:5 but with a near perfect tuner you can go 12-12:5 on pump gas. i am still learning myself on all this but this is what i got out of the years i have been in the game. compression can be changed via pistons, camshaft or head gasket and boring. do them all and you better know what you doing.

[sleepygreen]

so what happends if i get a (bigger?) gasket?

[bruno8747]

so what happends if i get a (bigger?) gasket?

If you get a thicker head gasket compression goes down. But the thicker the head gasket the more the chance of it blowing out.

[sleepygreen]

wow i dunno none of this stuff but thankz i was really thinkin about gettin a thicker gasket...

[Camurai]

i need help understanding compression ratios and how to get them where you want them...like what the hell does 11.1 or watever those numbers mean.

The correct way to list a compression ratio would be something like 8.8:1. It simply means that when the piston is at the bottom of its stroke, the volume inside the cylinder is 8.8 times the size it will be when the piston reaches the top of the stroke. Changing your compression ratio can be a tricky business if you're not fully prepared for any catastrophe that may occur. Using a thicker head gasket to increase your compression ratio, as stated, increases your chance of blowing the gasket, since gasket material has far less strength than metal and will reach a point where it cannot contain the compression of the cylinder. Increasing your compression ratio brings with it the risk of bending valves and detonation, which can hole a piston or burn out exhaust valves. Do a lot of research and consult professionals before fooling around with compression ratios if you want to minimize your risk of destroying your engine.

[MrJinx]

if your looking to go thicker use a copper gasket! That should stop u from blowing your gasket.

[johnl]

Using a thicker head gasket to increase your compression ratio, as stated, increases your chance of blowing the gasket, since gasket material has far less strength than metal and will reach a point where it cannot contain the compression of the cylinder. Increasing your compression ratio brings with it the risk of bending valves and detonation, which can hole a piston or burn out exhaust valves.

Just to avoid confusion from a probable typo, a thicker head gasket will decrease compression, a thinner one will raise it.

I've never heard of higher compression nor detonation causing bent valves, this is caused by the valves hitting the piston or debris being sucked into the motor.

[d112crzy]

I'm sure he meant that valves can be bent with higher compression because usually, higher compression means high piston dome, which means tighter valve to pistons clearances.

That'd be my guess anyways.

[johnl]

Ahh, then Camurai means that careless assembly can cause bent valves...

When fitting higher dome pistons the valve to piston crown clearance should always be checked with plasticene on top of the piston. Place plasticene on top of the pistons then bolt down head using an old head gasket (don't need to torque all the way), rotate the engine several revolutions, the pull the head off and measure the thickness of the valve squashed plasticene to see if it's the clearance is tighter than spec.

[flight50]

if you don't know what your doing you can get it clayed by a professional. its always better to be safe than sorry. but as most upgrades, do your research. that way you know what your getting into and you can troubleshoot better if something fails. educate yourself as best you can because not all shops have dealt with all types of problems.

[Autotek]

Im not a expert at this but From my understanding a low compression piston is usually flat. A high compression piston is dome shaped. So a low compression piston takes more air and fuel to combust. when High compression takes less. So in a turbo application a low compression piston allows enough volume for all the forced air and fuel.