Just got a built gsr motor tuned and running 2 months ago, compression tests at this time warm were 175 +/- 10 PSI across all 4. Now i'm reading roughly 150 +/- 10 PSI on a warm engine at WOT. Overall motor still pulls hard, burns no oil, cam gears are in time, head gasket seems good. Any input, maybe ring wear? ... seems like aggressive ring wear to me.

81.5mm dart sleeved block, cp 9:1 pistons.

 

Were both tests done with all plus removed with the throttle wide open?

and was the car up to operating temp? not just coolant temp but oil temp as well... oil temp is more important to determine "operating temp" than coolant temp

 

All plugs were removed, oil temp was fine (just got back from a drive). I'm about to put a bit of oil in the cyls to check the rings

 

Put oil in cylinders, results were all between 180-200 PSI. So an increase of roughly 30 across all 4.

Even if the rings are going, is there any risk of engine damage from just driving. I mean motor still pulls and if anything ill change oil more often from increased blow-by.

 

I've never compression tested a motor where compression numbers didn't increase from adding oil, regardless of ring condition.

is the motor smoking or making any kind of noises? It's hard to say what "normal" compression should be on a 9:1 motor as no 2 motors will ever read the same but 150 is a little on the low side.

does the car have cams in it? sometimes a cam with high duration/overlap can cause low compression numbers, also if the mechanical timing is off or if there is an issue with valve sealing/valve seats that can also cause low compression.

Compression will always be higher when the motor was just built as the rings haven't had time to seat. it's normal to see compression come down a bit over time on a fresh build.

you should be more concerned about leakdown numbers. on a recently built motor you shouldn't see more than a few percent in each cylinder.

 

i would go to the leakdown test before i worried about anything. one of my friends back in the day had about 160 psi compression in his 9:1 motor and it made 598whp and ran mid 10's.

can you borrow a different compression tester? just for the hell of it

 

Readjust valves and try again.

 

Thanks for the input everyone.
Motor has gsr cams (gsr motor if i didn't mention already). I'll try to grab a leak down tester and see what the results are.

 

?
Seems backward

 

Depends on the build. I've had it go either way. Mostly p2w and ring gap dependant

 

ok speaking of, what piston to wall was used on this motor. those cp's seem to tend to need a bit more than other pistons, like .004 and up rather than .0035

what kind of power is this motor making?

 

I don't know clearances, bought motor from a previous owner. Makes 300 whp, 270 wtq. I plan do change the headgasket in 2 months. During that time I'll check clearances.

 

I have the same issue

 

I'm getting 195 on all 4 after 1015 miles. 9:1 cp.pistons Manley h beams b18c. Stock sleeves Anyone have noise between idle and 1500 rpms? I've check valve adjustment. Twice. Piston slap? So.annoying.

 

How long does the noise last?

 

Doesn't burn any oil runs great minus that noise. Definitely gets quiter with temperature.but still there.

 

From minute it starts but you cant hear it at first because cold start idle is at above 1500rpms, once it comes down in rpm.you start to hear it.great oil pressure 80psi cold start once full warm idle 14psi. If you lightly throttle it you can hear up to 1500rpms after that noise is gone. Makes me wanna go tighter on valve adjustment but I know its spot on. P2W .0035 for the cp pistons. Motor is current n/a in process of about to turbocharge it. But this noise worries me more or less annoys me any help would be great apprecaited. Supertech valve train titanium retainers turbo valve springs, super tech valves, stock gsr cams.skunk 2 bee hive lost motion springs. Just to give you idea of what's done to it.

 

After it warms up, does the noise go away or is it all the time from 1500 and below? May sound out there but, it could be something loose in the exhaust. I have some janky hangers right now and get a funny clatter/vibration 2k and under. Lol! Scared the hell out of me until I discovered what it was.

 

Any results?