Lose of power on my motor and was wondering which one would be better to do first , i dont have either in my tool box at present time. Thanks

 

Compression test first.Then do a leak down.
Have you done any other testing?

 

No testing yet just a lose of 17rwhp on the dyno, It been to cold to work outside here, so when the weather changes for the better I'll get a chance to do some testing/guessing.

 

The compression tester will be alot cheaper than the leakdown so if you can find the problem with the compression tester you could save some $ and if you can't find it well then you'll end up with both a leakdown tester and a compression tester...

 

How many miles on the valve springs?

 

can you tell me what each test does, fairly new to this. I went from 431 rwhp to 380 rwhp. the TA smokes now. So what would the compression test tell me vs what does the leak down test tell you? Additional info, the 431 rwhp dyno was done when I dah the heads/cam/headers plus extras done. the 380 hp was done after a new spec 3 clutch and moser 12 bolt with 4.56's and 315 nitto's vs stock wheels/tires on the original dyno. I did put about 15,000 miles on the car between dyno's and maybe 30 trips down the track on stock clutch/rear end before swithing to the spec/moser. any ideas on what is causing the loss of power? I believe it is in the heads (GTP stage II) and hope its not in the pistons? which test will tell what?

 

Compression test will tell you if your compression is good. Leakdown can identify exactly where the problem lies whether it be a pad piston/rings/ringland, intake valve exhaust valve and even a head gasket.

 

valvesprings are 02 ls6 springs and have about400 to 500 miles on them .

 

Well I did a compression test This morning and all the cylinders were Between 165 and 175 so THe problem doesnt seem to be there. Man this is totally pissing me off now, Dam its leaving me to beleive that something might have been messed up after I brought it back to get some IDLE work done. I have new valvesprings and Ti retainers and hardened pushrods and a (New TCI3800 converter on the way)waiting to go in , but I dont see that fixing anything either, Here are the dyno graphs , if anyone has clue.

Bad dyno
good dyno

 

Compression test didnt show me anything. Leakdown showed I had three cylinders between 22-25% (rest were 5-7%). Rings or Bore was the location. Tore it apart and found some scuffed cylinders...rings not sealing. Probably from broken rocker/spring debris.

Rebuilding right now.

 

I don't understand how the leak down can tell you exactly what is wrong. Doesn't a leak down test just tell you if a cylinder holds compression.

 

With the leakdown you can hear what the problem is. At TDC all your valves should be shut and this is where you inject the air. If it is leaking into the crankcase its a ring/piston issue. If its leaking into the Intake its the intake valve, If its leaking into the exhaust its the exhaust valve and if you see bubbles in your coolant than its a head gasket. Its a pretty cool test to be honest. It honed in on my piston troubles before I even had the engine apart. The good part of this is you can narrow it down to what cylinder and what part either valves, rings, gaskets etc so you know exactly how much work will be involved before you start and you know exactly where to look.

 

So let me get this straight if all my compression readings are good wouldnt that rule out bad rings, or is there something im missing .

 

I think that would rule out compression rings but not the oil control rings. I am not positive on this one so hopefully somebody else chimes in.