Hybrid96EK

First off, all leakdown results were obtained with the car at operating temperature. The leakdown tester SEEMS to be in good shape. Completely blocked off it shows 0% like it should. I have no other reasons to suspect an issue with it.

I can do a leakdown on the engine and get 25% or so. Seems high. If I rotate the piston some past TDC either BTDC or ATDC, the results change considerably to little. Sometimes I can get things down to 10%, other times the readings go up even higher. The car uses 0 oil, none. Seems to make decent power (dead even with a 00 Bullet Mustang GT at 8psi), doesn't smoke, no coolant loss, etc. This is with Vitara Pistons (YCPS) and the supplied rings that come with them. FJT custom length I beams, stock headgasket, etc. Compression results are all good 175-180 across. I even tried adding oil to the cylinder to see if the leakdown results would improve, it did nothing whatsoever for the results. Anyone have any ideas that would help explain the erratic results. I find it hard to believe there is that much leakdown with the way the car performs for the amount of boost I am running.

amimaxima

can you hear it leaking from anywhere?

Hybrid96EK

Yes, it appears to be clearly coming from the crankcase.. As I rotate the piston I can head it get louder/quieter as the results change. Just seems odd to me that the results can vary so widely. I mean, I could come back and test the same piston in the same spot and get completely different results. If the rings WERE worn this badly, it would not make any sense that its not smoking, down a lot on power, etc. Engine has about 1,500 miles on it, so its realatively new as well.

got wide

im wondering why you are worried or testing for leak down if there is nothing wrong and everything else tests good? any way leak down results should be measured at tdc. when you move btdc or atdc your starting to release tention on the valves which could effect your results, even though you might not hear it leaking out the valves. im not too familiar with the vitara piston set up or what you have the rings gapped at but the piston material and design (forged, cast, hyper) and ring material and gap will all have an affect on blow by.

are these pistons a little "looser" than stock? and what kinda pcv system are you running? if its the stock pcv you wouldnt see any smoke from the blow by and probably not from a catch can/breather set up either until hi rpm/ hi boost, my blow by isnt evident until about 15psi

also make sure you check the orings on the tester. ive seen an engine almost get condemed until someone noticed a tiny slit in the o ring but it still showed 0 when the valve was closed

are all cylinders close to each other when they are at tdc? if so i wouldnt worry. 25%is a little high but it could be cuz of the setup if the clearances are looser than stock.

jewjew bean

I experienced the same thing you did on a 351W with 117k. I'm not sure why it does.

I would lose almost 50 psi through the rings but if I rotate the crank, it would seal up to about 4-6%. I put the motor back in my truck and it runs fine. doesn't burn any oil.

Hybrid96EK

I like to keep an eye on how things are doing with my engine. So I will periodically run a leakdown, compression test and inspect the plugs. If something was going wrong, I would rather catch it sooner then later. Waiting for a complete failure could get expensive. I have never had this 'problem' before with leakdown tests, but then again I have also never used these pistons before either! I had the block bored to set the piston to cylinder wall clearance correctly, so its not like these things are slapping around in there. The ring gaps were all measured also prior to assembly and everything was in spec. Since its not using oil, not smoking, and seems to make good power for the low boost level I am just going to leave the damn thing alone.

shortyz21

doesnt heat expand the pistons and help seal them?

got wide

well i cant argue with that, and i should probably follow your lead.

why do people use these pistons (whats the advantage)? if they are forged as opposed to our stock cast pistons they will expand differently. so even if they were honed to the stock clearance they might still be a loose which isnt really bad for a boosted app.

but i still say if they are all equal you should be ok

jewjew bean

yes it does. even with low milage new cars, when they first start and drive away, many times I'll notice blue smoke out the tail pipe

Hybrid96EK

Compression results are good like I said, the leakdown is what varies. And it varies much more then I would think it should. It must be the way the rings are sitting in the grooves is all I can think of. I removed the valve cover and verified that the valves were no opened, so I know thats not the explanation. The only other thing I can think of is the valves are bent. Since the valves are designed to rotate some with actuaction, perhaps its causing the valve to seat slightly better in different positions and thus effecting the leakdown. I don't head air escaping into the intake manifold, but I have not removed either manifold to be 100% sure either. It doesn't take much of a leak to throw off the test a good 15-20%. Since the car runs quite well as is, I am not too heavily concerned with the results. Just wanted to see if someone else had any insight.

jewjew bean

in my experience, exhaust valves are usually the culprit to most leaks. I suggest removing the wastegate anytime you do a leakdown. however, I doubt that they are causing what you are describiing

Hybrid96EK

Internally gated turbo, so I can't exactly remove it Eventually I plan to pull the exhaust manifold and inspect the valves at that time.