high compression pistons, compression test

[Ajax]

Theoretically, will a compression test yield results that correspond to the percentage increase in compression ratio?Example:9.5:1-10.5:1 is approximately a 10.5% increase.would this then yield a compression test increase of 10.5%- theoretically?

I'm testing because my KA which is supposed to have 10.5:1 pistons is only getting 170 peak on the compression test. I'll be retesting this weekend just to make sure I did everything right.

Does anyone have actual compression test figures for a high compression KA?
Modified by Ajax at 12:50 PM 6/16/2006

[TheOne]

i believe it should be higher because when my friend tested his after shaving his cylinder head(was warped) his compression test bumped to 210.

170 is about right for a stock ka.

[Ajax]

I know it should be higher, but will it be a percentage increase equal to that of the ratio increase?And stock compression test results is what I'm worried about. I spent a lot of money to get this thing rebuilt and I have waited a hell of a long time. So by the old adage "quick, cheap, good, pick two" I should have one hell of a quality engine... And if things aren't built the way they were supposed to be, then I'm going to be suing this mechanic.

[sunnys14]

is your engine warmed up before doing the compression test?

[pregmantis]

Do you have an aftermarket cam? That could change compression readings.

[DjPantsSpecR]

yeah he SHOULD have a set of JWT cams, but that has yet to be determined.

and these should be Arias pistons (10.5:1) so around 170 is a very piss-poor result. DId you do the tests again last night Dave? It wouldnt be hard to swap cams really quick to get a reading on stock cams, i could pull that off in about an hour.

It very possible the huge overlap of the JWTs is causing a problem. Just for reference purposes i believe Chezedik was building something with SOHC pistons and he had some serious compression test number crunching before he wanted to run it. I think he was getting ****ty compression with 248/248 cams, but then once he put some oil in the cyl and got outrageous compression results like you claim of over 210.

i wouldnt put it past your mechanic to either have reglular pistons in there, or maybe he did a ****ty job putting in the rings or honing the cyl. It could be a lot of things, but i guess the next step is to see if the cams are causing the problem, so that might be a good thing to edit into your topic post

call me Dave, if tomorrow is good i got all day before like 5. today i got all day except i'll probably be bull****ting with my friends. But s14 2510s is the cat with the header for sale, so maybe he'll chime in too

[Bigvinnie]

It very possible the huge overlap of the JWTs is causing a problem.

I don't believe the term you want to use is overlap, since most overlap occurs during high rev. I believe that the duration of the cams is the correct term to use when checking for the compression. I highly doubt that the JWT cams would throw off the compression very much, just probably a few minor points, but nothing too significant that would read 170.Could be something like what you said as far as oil being added and ran through the engine.If he is using a stock ecu though it would be really easy to hook up a wide band o2 and a sniffer, then run it through a smog check. NOX emissions should run higher than normal if he has 10.5:1 pistons. If he is on the stock injection he should be running pretty lean under load.

[DjPantsSpecR]

i dont think you are saying what you meant to say. overlap occurs if you are cranking the motor around at 10 rpm by hand, not just at high revs. overlap is good for high revs, but it doesnt just suddenly appear. perhaps this is a case of semantics, but a set of JWT N/A cam gears does have a lot of duration, now they also have a lot of overlap too. So actually they are two seperate occurances, as you could have a bunch of overlap and a short duration (if you were a moron with adj cam gears or something ridiculous, just an example). So who knows, the bottom line is, i agree the cams shouldnt affect compression results too much. If you had to sacrifice compression for bumpsticks, you'd be pissed off at your investment. The cams shouldn't lower compression significantly, bottom line.

Now, with that said, me and Ajax already figured this one out, and no one would ever have come up with the answer, because it is infact ridiculous. I'm not at liberty to say at this point, however

[s14 2510's]

I need the header gone I bought a stand up 650 jetski for $40 and it needs top end. 150 the header is yours. I just re ceramic painted it so it would not start to rust. Is ajax dave from were you interned? Or is there more than one dave in mn. LOL

[Ajax]

different daveNow, is the header for an s14? because I believe that is the model I have now which is causing the problem with my steering. I need a header for s13.

For everyone's info OBX header for s14 (I'm pretty sure its for that model as it had 2 bungs for O2 sensors) will interfere with the steering on an s13. At first I thought it was just from a poorly cutoff bung, but it turns out if the engine is seated correctly (say with new motor mounts that you can't move around with your fingers) the secondary tube from cylinders 1 & 4 will rub against the linkage making it very dangerous to drive as it locks the steering. You can muscle it through, but I can't imagine this to be good for the steering.

[DjPantsSpecR]

the header is for s13, and it is on an s13, right phil? your s14 doesnt have anything in it right? Anyway, you told me earlier that you weren't sure if it was the DC sports or the OBX, maybe its my poor memory but is that true?

either way, when and wherever this header deal goes down, can my driveshaft be involved. I'm sure Dave would't mind grabbing it. Additionally, i'd like to discuss what happens with the s14 header, Dave.

[s14 2510's]

Both my s13 and s14 are gutted down to wiper motor and power steering right now. I am in the middle of under engine blacking the engine bay in my s13. And yes the header is a dc header and yes I ran it in my s13 with no problem. I was told it was for a s13 when I bought it. I still have your drive shaft. Kinda camping on the grass u know. Someone local wanted the header as his manifold is leaking but first to come up with the money gets it. EMail me at [email protected] if you want to discuss more about payment ect....