compression....too high?

[MojoMan]

I just put my second det motor in my 96 240se and I did a compression test on it and noticed it to be way outta range from where the stock one is supposed to be. Correct me if Im wrong but the red top is supposed to be around 156 give or take a few yadayadayada. My last one seemed to always be around 160 or so across the board. Well the #1 is 200 2nd is 165 3rd is 155 and the forth is 195. Either the owner before me changed the pistons out for higher compression(stupid) or the head gaskets been changed to a thinner one or the head was milled but then you might encounter valve clearance problems. Maybe valves but not likely. None of this sounds likely if you ask me. Whos got an idea? Ive gotta do a leak down test and check the oil for water because I just put it in and ran it for fifteen minutes so Im going over every angle. So if anyones got a red top for sell with just a head and block they want to get rid of then pm me. Thats how I got this motor(just head and block). I bought it from a friend but it was never in his car and it was was the full set up before he tore it apart for me. :help

[themadscientist]

Or you have a lot of carbon deposits in the combustion chambers and on the piston tops which will raise compression.

[Dori Dori]

:withstup

Try doing a carbon flush on your motor to clean it out.

[MojoMan]

Thanks guys. I hadn't thought of that yet. Do you think it would really create that much carbon? and who knows what the best fuel treatment stuff is?

[dreamsOfSkylines]

do a search on here for seafoam or a thread called "my car runs like new, here is what i did" (something like that)

[martin]

Be aware of what a carbon flush does... it losens the carbon on the top of the pistions and cumbustion chambers, and hopefully it falls off.

Yeah OK, that's what you want right?

Maybe... think about where it's going to go - out the exhaust, which does what? Drives the turbo!

If you really have enough carbon on 1 & 4 pistons to raise the compression 35-40 points I don't think i'd want it going through my turbo.

Better off to pull the head and do it the old fashioned way. You alos might find that teh problem is that the head gasket is starting to go between 2 & 3 which ius why they are lower than 1 &4. In which case you might have high compression pistons in there. Are you sure this isn't a SR20 motor ie. not DET?

-Martin.

[pampadori]

how are you checking compression? you should have the engine warmed up, unhook the fuel injectors and keep the throttle floored. try it again. 50pts off from one cyl to the other is extreme. shaun

[MojoMan]

how are you checking compression? you should have the engine warmed up, unhook the fuel injectors and keep the throttle floored. try it again. 50pts off from one cyl to the other is extreme. shaun

Thats exactly what I did. And I had thought of it being a de not a det but I have to go back and look at the stamp on the head and block. Ive looked at the cam, valves and rocker arms and everything looks like its supposed to be but we'll see. any other opinions?

[pampadori]

well,sr20det compressiong is to be 156psi, minimum of 128psisr20de is around 174 as a high.

[MojoMan]

Thats what Iv'e read I just wanted to clarify. Do you think that carbon buildup would cause this?

[pampadori]

it is possible. but do you hear any ping or anything when it is revved up? i would just say screw it. maybe a valve isn't opening? remove the valve cover and look for a rocker that might have jumped off. take the head off if you want to do a headgasket, and then inspect for carbon. shaun