2G Compression 180psi with 130k miles- is this normal?

[sean98gsx]

Alright so i did a compression test on my 1998 eclipse gsx and its got 180 all the way across and i was wondering if thats normal, im pulling the head next week and i was thinking maybe ill find some high compression pistons, i really believe ive got a twin disk also, but if i do have a built bottom end why would someone put a built bottom end in with a stock head and cams and a stock radiator and fans, seems senseless to me but a ricer did have my car before i got it, any feedback is appreciated!!!!

 

[Black'95]

Yea, that's normal. My 95 had similar numbers when I did a compression test. How many cranks did it take to get up to that number?

 

[sean98gsx]

It took 4 i think but i wasn't paying that good of attention, also what do you know about twin disks? because when i bought my car the ricer said it had a new act clutch but it had this grinding sound coming from the tranny/clutch area and now its not as loud and ive launched alot since i bought it about a year and a half ago, it grabs at the bottom and its got an aluminum flywheel, i saw the flywheel when i had to refill my transfer case, from what i could see it looked like a pte twin disk but i have never had the tranny off. thanks again.

grinding sound would occur under deceleration the most but ive herd it under slight acceleration.

 

[Black'95]

I can't say much about the twin disc, as I've never had one. However, the grinding noise could be a worn throwout bearing, or input bearing in the tranny. From what I've read, the twin discs can chatter upon engagement, but once they're fully engaged, they should be as quiet as any other clutch. Maybe someone with twin disc experience can chime in, here... Unfortunately, the best way to find out would be to pull the tranny and check. As far as the compression getting that high after 4 strokes, that's excellent!

 

[sean98gsx]

sweet, so do you think that these pistons might not be stock? im pulling the head next week to put studs in but im just curious since its so high.

oh and i looked on your profile, your 60ft is crazy, i wish mine was that good

 

[phunny]

sweet, so do you think that these pistons might not be stock? im pulling the head next week to put studs in but im just curious since its so high.

oh and i looked on your profile, your 60ft is crazy, i wish mine was that good

...No way to tell, we'd just be guessing which is pointless... Hopefully they are but I highly doubt it.

 

[PieEyedPiper]

Normal. At 100k I had compression of 180-180-180-180 and then I began to notice it was reading more like 178-178-178-170. 178 is factory spec, but clearly by 140k cylinder 4 is starting to feel old.

Getting a reading 2 psi above stock does not warrant the thought of forged pistons already being in your car.

 

[Calan]

You know...I don't think I've ever seen a DSM engine that didn't have slightly lower compression on cyl #4, now that I think about it.

 

[sean98gsx]

alright well what are you guys thoughts about the twin disk?

 

[donniekak]

alright well what are you guys thoughts about the twin disk?

I think you should pull the boot on the clutch fork back, and look and tell us.

 

[sean98gsx]

alright i will when i pull the head

 

[Black'95]

I think you should pull the boot on the clutch fork back, and look and tell us.

Son of a!... That's a hell of a good ideer!

sweet, so do you think that these pistons might not be stock? im pulling the head next week to put studs in but im just curious since its so high.

oh and i looked on your profile, your 60ft is crazy, i wish mine was that good

haha, thanks, I got a good launch that time; most of my other 60' times were like 2.2-2.4 seconds. I need to work on my launches bigtime .

Like the other guys said, I'd say you have stock pistons, but you'll find out soon, it sounds like! Good luck with it!

You know...I don't think I've ever seen a DSM engine that didn't have slightly lower compression on cyl #4, now that I think about it.

Any thoughts on why that is? Now I wanna go redo my compression test and see if mine's that way; I can't remember...

 

[PieEyedPiper]

You know...I don't think I've ever seen a DSM engine that didn't have slightly lower compression on cyl #4, now that I think about it.

Son of a!... That's a hell of a good ideer!



haha, thanks, I got a good launch that time; most of my other 60' times were like 2.2-2.4 seconds. I need to work on my launches bigtime .

Like the other guys said, I'd say you have stock pistons, but you'll find out soon, it sounds like! Good luck with it!



Any thoughts on why that is? Now I wanna go redo my compression test and see if mine's that way; I can't remember...

I always test cyl 4 last
I don't think that's it though; decreased cranking power due to battery drain.

 

[sean98gsx]

I think you should pull the boot on the clutch fork back, and look and tell us.

can i do that without pulling the tranny? never pulled my tranny before so im new in that area, thanks for all the help

 

[Black'95]

can i do that without pulling the tranny? never pulled my tranny before so im new in that area, thanks for all the help

Definitely. The boot is on the front of the tranny where the shift fork sticks out to meet the slave cylinder. Just push it aside and shine a flashlight inside to see what you can see!

I always test cyl 4 last
I don't think that's it though; decreased cranking power due to battery drain.

Yea, good thought. I know my battery is getting tired at the end of my test.

 

[MrBoxx]

P.S. Everything I have been taught since day 1 says you really don't want to run a high C/R piston in a forced induction engine. So, no, hopefully your car doesn't have them in the block.

 

[sean98gsx]

well i launched today and i thought id tell you that i have gotten better than i thought, my 60ft is 1.8 but it takes me 8.4 seconds to get to 70mph, 5.7 from 0-60, my cams are raping and i mean raping my power on the top end, here is the log

 

[Bud92gsx]

P.S. Everything I have been taught since day 1 says you really don't want to run a high C/R piston in a forced induction engine. So, no, hopefully your car doesn't have them in the block.

I think he meant higher.. Smart ass

 

[sean98gsx]

i meant like 9 to 1 or something like 8.8 to 1 becouse it sounded high but i guess ill see, what do you guys think of the log, any advice is appreciated!!

 

[sean98gsx]

ok so we removed the head and found some carbon, the pistons are stock but there clean now and so are the valves and the head gasket is in with some ARP studs, we also removed the EGR components and all of the ac components and now when i start it up and in general it feels like i have no balance shafts, idk if EGR affects the way the car feels, i do have polyurethane mounts but its really rough, and my launch control sounds completely different, i like the way it is now, but im kinda worried something isn't right.

thanks for any input.

 

[sean98gsx]

well guys i found out what that roughness was that i liked, it was ma alternator ceasing...

 

[H4G64T]

Just for good measure for someone searching this post in the past, the amount of cranks versus the PSI is not an indication of anything. Doing a compression test is holding the throttle open and cranking until the needle stops. The ending number is all that matters.

 

[400hp93talon]

Just for good measure for someone searching this post in the past, the amount of cranks versus the PSI is not an indication of anything. Doing a compression test is holding the throttle open and cranking until the needle stops. The ending number is all that matters.

I would have to say that a fresh setup is going to produce the numbers faster than a loose/old setup. So yes the faster it gets to max compression the better of shape it is in. So I kind off disagree with you.

 

[H4G64T]

Based on what will literally be a millisecond of difference in time when the car is actually started? Put things in perspective.