Compression too high ?

[lewis15498]

correct me if im wrong here...

he is leaking coolant into cylinders... coolant is now in clyinders... coolant doesnt compress like air...comression increases...theretically it makes sense, but that would mean he was getting coolant in all clyinders

I had this problem reading compression of like 180 psi in my 2 stroke jet ski motor when it was only supposed to have 115 psi, cuz i got water in the engine...it also got water in my new compression tester and fucked it up...luckily autozone gave me another one.

 

[easternguy2005]

There's some badass formula on wikipedia that had me stumped. Just having the PSI results won't solve the equation.

Here's an example of how it is supposed to be done -

http://www.chevyhiperformance.com/techarticles/46778_engine_compression_guide/index.html


There's a "coosh" zone I keep hearing about which is .04 on the top so the explosion is efficient as well.

Most people are coming in with the same numbers lower than this. Haven't seen anyone trying to pull higher compression and lower boost.

 

[easternguy2005]

Lewis1548-
I am confident a little oil/coolant crud got in even after I mopped up the deck around the spark plugs when I pulled them out but this gasket didn't leak coolant in. It blew compression out to the water jacket.

Also I had all the plugs out and spinning the motor - If there was any coolant in there I would have seen it blowing out everywhere. Each cylinder was tested 3 revolutions. Twice per cylinder. I got this early before there was a easy escape path for the compression and I think that's why the differential isn't that great.


Here's another way to measure compression ratio

http://www.geocities.com/reliopoulos/upgrade/3-12-p05.html


You can be sure I'm going to do a compression test before starting it...and then after a few runs.

 

[wiseco7mgt]

I don't understand your pictures.Is the first pic on the left the after and the second the before.That block is bloody mess no offense, there's no way i'd fit a gasket to a surface like that. I'd personally get it machined along with the head, then do the appropriate measurements for a mhg. It's just not worth putting it back together only to find it leaks again straightaway and haveing to do the whole job over imo.

 

[easternguy2005]

Pic with glass is while it is being lapped. Pic after is the rear #6 cleaned. There's plenty of staining. Can't imagine lapping this thing to remove leftover carbon stains. I definitely could be wrong.

 

[wiseco7mgt]

From what i can see between cylinder 6 and the coolant port there is corrosion in the block, doesn't look like just a stain.

 

[easternguy2005]

yeah looked at it close today - that's not a stain. There's still a gap there between the fire ring and the coolant area. Back to lapping the block...

 

[IJ.]

It's going to be smooth but not flat/true....

 

[easternguy2005]

I agree that it won't be perfect flat and true. Last I measured it wasn't perfect and the pitting isn't making things any better that's for sure. I'm willing to give it a try using the more forgiving composite gasket with the ARP studs although the odds are against long term success.
If it (when it) fails I'll definitely pull the engine out this time and get the block and head done properly with a correctly sized MHG. That's when I pull the supra wallet out and find qualified experts to prepare the surfaces rather than my sorry ass attempts.

Yeah and I know I'm being stubborn and stupid. It's definitely not my career path.

I can aspire though....like this guy professional guy in Spain.

http://www.lancerregister.com/showthread.php?t=224101

He is the guru....


Also added a pic of one of the drilled out dowels.

 

[jdub]

As long as you know, if the block deck is not straight, it is very unlikely even a composite HG will seal. Hate to see you do all that work just to have to re-do it

 

[wiseco7mgt]

Well at least your not under any illusion about it, so ill tell you a few dodgy things that may or may not help.Cover up all the holes on the top of the block, clean the surface down with turps or carby cleaner.Then get some copper spray and apply a couple of coats until it dries fairly well and torque that bitch down.You may get lucky but it wont last long either way.

 

[easternguy2005]

All back together. Started and ran till warm, crappy idle at warm maybe vacuum lines(choking me it's so rich in the garage with the door open) . Then after it was warm did a compression check. Still getting those "low" numbers on 1 and 6.
Ok there is more. Altitude matters too. I live 5 miles from the ocean and there isn't a mountain for 50 miles. Looking at other numbers I've seen and this chart

Compression Test Altitude Compensation Factors
Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773


A compression reading of about 150 psi at sea level would measure less in the mountains. At an elevation of 6000 feet, the expected reading would be 150 psi X .8359 = 125 psi. The cylinders would be reading low if compared to sea level measurements, yet perfectly fine at this altitude.



In the "supra statistics" section I saw - 142PSI
In the "compression test section" I saw - 165 PSI
(coincidentally he is also higher in #1. #2 and #6)

Here we see the 150 to 160 PSI range
http://www.supramania.com/forums/showthread.php?t=85560


Japan is a mountainous area (think Mt Fuji) and is above sea level
http://www.askasia.org/teachers/maps/map.php?no=61


So at 4500 feet of altitude my compression would look normal.

If anyone has more on this I would appreciate it. I had a freakin' dream that I did a compression test and and it went past the gauge max...and I said to myself "this ain't good".....LOL and was afraid the gauge would blow up.

 

[easternguy2005]

She's running for the last few hundred miles nice and smooth. One day this summer I'm going to take this on vacation to the mountains and do a compression test just to find out what the heck the deal is with compression.

 

[easternguy2005]

One day didn't come. Back in the garage with BHG today. No question about it - tomorrow morning the engine is coming out to get it properly machined and have it measured. Cometic of proper size.

This shit has gotten real old. real real old.