Turbo Dodge Forums banner
1 - 20 of 22 Posts

· Registered
Joined
·
442 Posts
Discussion Starter · #1 ·
aight this is the usual compression question...

pre oil-140 125 145 130
post -180 235 200 220

all these numbers seem really high for a 8.x to 1 compression motor... but it went way up after i dropped the oil in... possilby the motor wasnt warm enough??

Either way i take it as its time for a rebuild... anyone have opinions?
 

· Registered
Joined
·
4,660 Posts
No rebuild needed yet, I would look to #2 125 and do a leakdown test, might need a head job.
Numbers are not bad for a street engine.
 

· Registered
Joined
·
442 Posts
Discussion Starter · #4 ·
yeah...but like i said i think all then numbers are high... the reason for the test is because it is using oil like crazy and smoking non stop... i had this head on a different motor and i didnt have any problems (unless a valve seal tore or something)... this was a junkyard motor thats has been in the car for like 500 miles... i was hoping it would be ok but the way it is smoking and the fact that the compression went up so high when the oil was added kinda has me worried...
 

· Registered
Joined
·
4,660 Posts
The compression numbers are fine- Like tryingbe said look elsewhere for a problem. Check the turbo for excessive play and also look at the exhaust at the downpipe for oil. How do the spark plugs look? It could be a bad valve guide.
 

· Registered
Joined
·
442 Posts
Discussion Starter · #7 ·
ehhhh the turbo was just rebuilt but i think that might be the problem... it has prob 1/4" of play (total... not to one side)... i guess i was hoping it just wasnt that AGAIN... i guess it is still under warranty but agh... does anyone know why it might be blowing turbo seals? i have the braided line and a filter... the rebuilt turbo has less miles then ive had the motor in for! it is a super 60 i got from a vendor and i blew a seal with prob 1500 miles on it then got it rebuilt and i think it might have just blown another one... i guess i have to get under it and pull the exhaust off to make sure... its just been pretty damn cold to do that kinda stuff...
 

· Registered
Joined
·
4,660 Posts
1/4 inch !!!! DOH! time for a turbo-
 

· Registered
Joined
·
4,660 Posts
I would suggest getting warranty work on it.
 

· Premium Member
Joined
·
9,142 Posts
uh, your 'after oil' numbers seem WAY too high for an 8:1 motor; that kind of psi just isnt possible

the 'before' look normal except the 125 is a bit low, but not so low that I would think it *needed* a re-ring

yeah 1/4" total is A LOT of turbo shaft play and I'm guessing the turbo seals are the source of your oil smoking ; you *could* verify by disconnecting & plugging the oil feed to the turbo.. obviously you wouldnt want to be spooling the turbo up in that configuration

(LOL I just fired up my DSM after a timing belt replacement surprise surprise and there was oil draining from the oil return, which I had forgotten to hook up ! but I was surprised that the flow wasnt really that much.. maybe 1/4 cup in a minute.. apparently the flow thru the turbo isnt *that* much...)
 

· Banned
Joined
·
432 Posts
200 and 220 are more like 9:1CR numbers
Heh, more than that. I had a fresh rebuilt 360 flattop pistons with 9:1 compression doing about 160-170 PSI compression. So 200-220 is atleast 10:1 if not more.

I agree though the compression isn't bad, 130 PSI is usually about when the engine starts to be ''worn'', but actually 100 PSI is minimum spec for the cylinder to be firing according the chrysler.
Did you hold the throttle open while cranking? Did you crank for an equal amount of time on each cylinder? I usually count to about 8 is a relatively but not excessively slow fashion.
 

· Registered
Joined
·
768 Posts
Another way to tell if it wasn't the turbo, is when it's doing it. I.E. Accel or decel (or engine braking).

If it's doing it on decel, then it's probably bad valve guides or seal. If it's accel, then it's probably the rings.

And just because you have good compression doesn't mean that your rings necessarily all good. My honda accord had 150 dead even across all four, but it has stuck/worn oil rings and burns oil like crazy. (500 miles/quart) I'm working on rebuilding it now so hopefully that goes away.

But yeah, if it's burning all of the time, and your turbo has that much play, then that's probably it.
 

· Premium Member
Joined
·
9,142 Posts
Heh, more than that. I had a fresh rebuilt 360 flattop pistons with 9:1 compression doing about 160-170 PSI compression. So 200-220 is atleast 10:1 if not more.
yeah that was my point ... > 200 is really not possible with a turbo motor or even an NA motor .. something in the way the comp test was done is incorrect...

but I think we agree that the turbo is prolly the most likely cause of the oil smoke ...
 

· Registered
Joined
·
3,679 Posts
how much oil did you put in the cylinder for the oil compression test?

And what filter are you talking about with the turbo? "does anyone know why it might be blowing turbo seals? i have the braided line and a filter..."
Tim
 

· Registered
Joined
·
2,028 Posts
Heh, more than that. I had a fresh rebuilt 360 flattop pistons with 9:1 compression doing about 160-170 PSI compression. So 200-220 is atleast 10:1 if not more.
Well my 2.4 with 8.8CR pistons and head/deck slightly resurfaced= 200psi, guessing that its at 9:1, my buddy's same bottom end 2.4 has the same results so I would say that your rings aren't seated or your clearances are huge or did the test when cold?


If the turbo oil feed line is larger than -3an, you should look into a restrictor for it.
 

· Banned
Joined
·
432 Posts
It had about 500 miles on it, hypereutectic pistons and plasma moly rings (did several runs with WOT low RPM while holding the brake pedal to seat the rings). Did with test with throttle wired open, clearances are to spec the engine was bored .030 over and the shop had the pistons to final hone. I'm about 90% sure the engine was warmed up, because I know there's a difference cold or hot.
One thing I don't get is if only 9:1 CR is 200 PSI, and 8:1 is 150, that would mean that a cummins diesel with a compression of 18:1 or better would be pulling 1100+ PSI which they do not, I think it's about half or less that which supports my number results of a 20-30 PSI jump per point of compression.
 

· Premium Member
Joined
·
9,142 Posts
don' forget that we can't directly compare Motor A (2.2 turbo) to Motor B (360) to Motor C (2.4) because the other SIGNIFICANT factor impacting the psi <-> CR relationship is cam timing

e.g., a cam with more overlap will have a lower "psi" reading

thats another reason that a 'leakdown tester' is a much more accurate way to troubleshoot ; I mainly use my old-school push-in compression tester to identify Major problems... like a cylinder thats >20% lower than the rest

and of course as 87dtna infers, the CR <-> psi relationship is not linear
 

· Registered
Joined
·
2,433 Posts
You could get weird reading for many reasons. Guage could be out of whack. Depending on humidity and barometric pressure you will probably get different readings as well. I never look at those numbers and say oh, cylinder #1 is 130 or 135 whatever. The important part is whether or not they're even across the cylinders. Of course if they're all 90 you probably have an issue. You could use 4 different compression guages and get 4 different results.
 
1 - 20 of 22 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top