Head Gastkets - compression?

[Phiber Optic]

first of all could someone briefly explain how compression works in an engine and what it is.

and second i would like to know if adding a high perform. gasket to a stock engine would lower compression, cause i asked this guy at an engine machine shop and he said it doesn't. but i keep thinking i remember seeing it somewhere that if you get a cirtain thickness and material it will lower compression.

(Edited by Phiber Optic at 9:50 pm on June 30, 2001)

[lemonrex]

Compression huh?  Well, compression is how an engine works.  Fuel and oxygen mix together in the cylinders with the pistons close to BDC (bottom dead center).  When the piston moves up the cylinder, the air and fuel are compressed until the sparkplug ignites the mixture and the explosion forces the cylinder back down.  If you raise the compression, the explosion becomes more violent therefore pushing the piston down harder and creating more horsepower.  There are a few different ways this can be accomplished.  One you mentioned with the thinner head gasket.  The most popular and "best" way to do it is to get domed pistons.  

With naturally aspired engines, higher compression is usually better.  One problem is that the explosion can become so violant that it will actually melt the top of the piston.  This is called detonation or pinging.  You don't want your engine to ping.  Turboed and supercharged engines sould keep the compression low as a rule of thumb.  

So there is compression 101.  Any more questions, ask away.

[masta shark]

sorry if this is reapeating what he said, but i didnt read his post :)

the combustion chamber is sealed, and when the piston moves up, it compresses the air and gas, and then ignites it to push the piston downward and create power to the wheels...

if you add a thicker heade gasket, it is going to creat a larger combustion chamber (by moving the head higher and creating more room between the piston and the head)...so it will give you a lower compression ratio

if you add a thinner head gasket, it will increase your compression because the combustion chamber will be smaller and the air and fuel will be comressed into a smaller area


the higher the compression, the more power you end up with...in any motor, higher compression makes more power....but higher compression also creates more stress on internal parts, and more heat inside of the chamber...you also have to consider detonation and  valve clearance.

[Phiber Optic]

since i am going to be running turbo here real soon, i will probably get a thickassed head gasket.

[CRX]

With a turbo thats pushing like 13psi, is like 9.5.1 a good compression ratio, or what? I am thinking now turbo B16 or turbo ZC so I am just seeing what would be a good idea.

[steel]

If you are doing a turbo I dont recommend the B16.  The compression is to high, while the ZC has low compression and can handle more boost.  Try an LS engine, they are suppose to be great for boosting.

[Venom TypeR]

If you are to do a turbo with a b16, do you just get a really thick head gasket?

[steel]

That would help but it is much easier to just start with lower compression.  But hey, there are some who turbo the B16 and I think alot about that.  I also think I would wanna buy some new pistons to lower the compression.

[CRX]

Yeah I am thinking really hard about the Turbo ZC, how involved is a LS swap though?

[5gencivic]

lowering the compression ratio with a thicker headgasket = bad fucking idea.
the reason is that the gasket starts to make a weak point in the motor, a larger gap between the block and the head. a larger spot for the explosion that's happening in your motor to work on. a car that's running a 8.5:1 compression ratio that's using low cr pistons will have a much higher detonation threshold than a car that uses a head gasket to do the same thing. it is not a good idea to do this. you will also run into problems with the timing belt getting over strained over a long period of time because you are asking the belt to stretch a longer distance than it's normally required to. this will also throw off your timing and a few other things that i can't remember right now. please for the love of god do not lower your compression ratio by installing a thicker head gasket or i will personally come over and kick your ass and save your beloved rex from a sever case of owner stupidity...


sorry about that one guys... i was off on a rant... just say no to thicker head gaskets... peace...

[Phiber Optic]

thanx for clearing that up 5gen.

but just as some info, i heard from somewhere that the d15 has a lower compression than the d16. so i figure im not too bad with my 92 hp dx engine :)

[steel]

Plus the D15 also has bigger rods for a stronger bottom end.

[CRX]

Is there any good sites on the LS engine and how to do the LS swap? I am getting very interested in this.