Strange Compression

[srumel]

Hey all. I've been an avid reader of the forums for the past three years or so, first time asking a question. This is something that has been bugging me for the past couple of years. I replaced my beat to hell stock 1g long block with a jdm (14b). When i received the motor I was rather suprised at its condition. Clean, of course; but a few things caught my eye. One, the exhaust manifold stud nuts were brand spanking new as well as the washers. Two, the tps and isc sensors were chipped at the connector. Three, after installing the motor it was taken to a local mechanic just for a precautionary once over. They informed me that the motor looked great and that it appeared that the head had been pulled recently, which brings me to my question. My compression, ever since i received the motor, has registered a wopping 180psi across all four cylinders with a minor two psi deviation in cylinder number three. I figured it was simply carbon build-up so I ran Sea-Foam through it on a number of different occasions. Still nothing. Could these abnormally high (while uniform) compression readings be due to A) the head was shaved while being rebuilt B) just some stubborn carbon that won't dislodge (doesn't knock much) or C) the previous owner of the engine installed aftermarket pistons? Any responses would be appreciated. Thanks.

 

[blackbyrd]

hmm, i would say some headwork was done. 180 is great! I'm getting a jdm in a couple weeks i hope i get that lucky. Hows the condition on the turbo? Does it appear that someone was racing out this engine?

 

[JayRolla]

You may have 8.5:1 pistons or higher. I think the 2g's, which have higher compression pistons, should have around 180 compression. You should be ok man.

 

[kenamond]

You may have 8.5:1 pistons or higher. I think the 2g's, which have higher compression pistons, should have around 180 compression. You should be ok man.

2g "perfect" compression is 178psi. Close enough .

Probably overly cautious, but did you do a wet compression test just to make sure it's not a higher CR designed for race gas but with worn rings? I know, I know, I doubt it, too, but it's a (paranoid) thought - what are the odds all rings would wear that equally, blah blah.

 

[bushy]

A decked head would cause higher compression.

Other than that, it could be stubborn carbon still stuck on there.

 

[srumel]

wow, quick responses. so basically there is no way to confirm any of my suspicions without pulling the head? if i remeber correctly i could make out a few numbers/letters when peering down the spark plug well. are there any specific identification numbers i should look for, assuming they are stock 1g pistons? oh and about the milled head possibility...wouldn't it be a little too coincidental for my compression numbers to be nearly identical to those of motors with 2g pistons? is there a specific height the deck should measure unmilled? sorry for all the questions at once, just brainstorming.

 

[srumel]

oh and to the turbo question. the turbo (good ol' 14b) is in perfect shape, no shaft play whatsoever. and to the ring comment, the motor doesn't lose an ounce of oil from what i can tell (between oil changes, i check the level religiously.)

 

[PRESSURIZED]

I just got a JDM 6 bolt and it too clocked 180psi. across the board.

I think these motors are different.

 

[srumel]

Hrm, PRESSURIZED might be one to something. I wonder if the numbers/letters stamped on the pistons could help us solve this mystery.

 

[srumel]

This thread seems to support this theory.
http://www.dsmtuners.com/forums/showthread.php?t=89574&page=2&highlight=jdm+motor+compression
8.5:1 you say?

 

[Dream On]

Wow, that's pretty good. I wouldn't pull the head or anything to check though, everything sounds to be in great shape.