b18c block, honed .25 over, balanced/blueprinted, JDM ITR .25mm overbored pistons, b16 head, skunk2 valvetrain (stage 2 cams)... my compression numbers were 170 all the way across, and my leakdown test was under 10% on all 4 cylinders... my compression numbers should be ATLEAST over 200... my piston rings are fine, the leakdown test showed everything was ok..

where the hell could i be losing so much compression???? could it possibly be because the block may have accidentally been honed too big, like to .5 over instead of .25, and the pistons are too small for the block??? any input would be great, thanks

edit: forgot to mention, i lost 2 quarts of oil in under 3,000 miles...

 

did you block the throttle wide open when you did the compression test? the reason i ask is i didnt one time and my #'s were low , then i blocked it wide open and the #'s came up alot.

 

the shop did the tests so im assuming they did it all right..

 

If there are no variation (170 in all 4) between the 4 cylinders, I wouldn't worry about it. Atmospheric Pressure may play a role in your compression numbers also.....are you at sea level or above (how much)?

For the burning oil issue, where was your leakage coming from in each cylinder?

 

1. im nearly at sea level. 2. there was no oil leakage in the cylinders.


im going to worry about the 170's, because im definitely not making the power that i should be... turbo'd cars usually make 170 and n/a's make 220+... im not making any power..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lke2drvgsr &raquo;</TD></TR><TR><TD CLASS="quote">1. im nearly at sea level. 2. there was no oil leakage in the cylinders.


im going to worry about the 170's, because im definitely not making the power that i should be... turbo'd cars usually make 170 and n/a's make 220+... im not making any power..</TD></TR></TABLE>You said you are losing a couple quarts of oil and and there are 10% leakage in all four cylinders via the leakdown test.....where are they coming from? You can find out if it's the rings, valve seals, etc. from that (considering that the oil did not leak externally).

 

i thought anything below 10% is normal, no leaks.. ill call them n ask them if they heard anything...

 

10% Leakdown sucks...find out where its going.

PS: If that 170PSI was with the throttle open, your below 9:1 CR.

How many cranks???

Suprdave

 

9:1 cr? damn, time to start boostin

ill call the shop tomorrow, see if they listened to where its comin from.. and ask 'em if the throttle was open when doing the compression test. thanks for the replies

 

Prolly like 8.7:1...I woudlnt start boosting...seems like the motor in hurt.

Who did the machine work?

 

i was jokin bout the boosting lol

apg did the motorwork

 

when they did the leakdown test and got all the numbers under 10% they said its near impossible to hear where it's coming out. if it were like 20-30% or so then it's easier to hear.

they also said for the compression test that whether its WOT or not, it doesn't really affect the test that much..

 

Nicked some valves maybe?

Can't the cam timing being way off effect a compression check?

 

does anyone know the equation to how you know what numbers you should be pushing? what goes into finding the psi? thanks

can anyone confirm that cam timing affects the compression?

my car has never been tuned before and im sure the timing is off..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lke2drvgsr &raquo;</TD></TR><TR><TD CLASS="quote">when they did the leakdown test and got all the numbers under 10% they said its near impossible to hear where it's coming out. if it were like 20-30% or so then it's easier to hear.

they also said for the compression test that whether its WOT or not, it doesn't really affect the test that much..</TD></TR></TABLE>Sounds like your mechanic doesn't know what he's talking about if he said he can't hear 10% leakage.

I almost forgot that valve timing affects your compression also&lt;---That just might be it! Check your timing belt, it might be a couple of degrees "retarded." This causes low compression in all cylinders. Check to see if your TDC on the crank line up exactly with TDC on the cam(s).
Good Luck.

 

i'm wondering, how exactly does cam timing affect compression?

thanks for the help, it's much appreciated, and i'll definitely look into this as soon as possible

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lke2drvgsr &raquo;</TD></TR><TR><TD CLASS="quote">
apg did the motorwork</TD></TR></TABLE>

That might be your issue...

 

Get some oil and put a small amount into each cylinder then run the compression test. This will determine things such as the rings or valve seals to be at fault. (Compression test should be done with all spark plugs out of engine, throttle plate at W.O.T., and 4-5 cranks (rotations) of engine, also remove fuel pump and ignition fuses. The fuel may still be put into the engine during your compression test and washing all of the oil off of the cylinder walls which aids in the sealing of your rings to the cylinder wall. (That is why you add small amount of oil to cylinder to prevent that problem)
After that have a vaccum gauge ready and hook it up to good intake manifold vacuum source. Start the car. See what it reads. This will determine if you have sticking valves, etc. etc. where your problem lays......hopefully.
I cant remember what the exact readings on the vacuum gauge will tell you. I think a helms manual will tell what the readings mean, from a fluctuating reading, to what level of vacuum it is pulling while running.
If your cylinders were hones or bored too large to some degree, you could have piston slap.