if a leakdown test indicates blowby then that means that boost is blowing by? usually w/ cam gears we'd want to retard the exhaust gear right? so if we did a leakdown test, saw a lot of blowby, then retarded the cam gears, did it again and saw less blow by , that would be a good thing correct? albeit, retarding too much can be a bad thing, but a few degrees could do some good stuff. Would this be a nice way to tune ? or is it like playing w/ fire....

 

I thought a leakdown test would just show the condition of your rings.

 

beats me, turbolude said it, i was just wondering if i could get away w/ retarding some gears w/o going to the 185/hr dyno!

 

a leak down test is a more advanced form of doing a compression test. What you do is remove all the spark plugs, then you pressurize the cylinder with air. From that, you can tell by sound where the leakage is occuring. If you hear a hissing from the intake, then the intake valves are bent. If you hear it from the exhaust, then exhaust valves are bent. If you hear it coming from the breather, then valve guides/seals are worn. Coming from the dipstick is ring blowby. Feel free to correct me if I am wrong on this, it's late and I've had a few

 

Just curiuos, why do people recomend using stock rings? I need to know for future reference when I rebuild my block because I was going to get OEM rings and cast pistons.

art

 

I thought the problem was the location of the ring lands of oem pistons, not the rings themself.

 

When performing the leak down test must each cylinder be at TDC before pressurizing?

 

I think it's the actual material of the stock rings that are favorable. The chrome, moly rings are harder and take longer to seat, and wear the cylinder more. A cast ring, or the less hard ring would seat easily, the finished hone doesn't have to be a 3 stage process (assuming the bore is still good). Arturbo, are you going to use aftermarket cast pistons? I am looking for a low expansion set of pistons also, I think the newer forgings are less expansive, but not as good as cast alum. I think there are gapless or total seal piston rings in different materials, you may want to check on those over the stock, but if you do a little searching, stock rings are pretty cheap.......

 

a leak down test is more accurate than a compression test...it allows you to see the leakage from each cylinder...leakage is not good...and like vaportrail was saying you can kinda figure out what your problem is by checking the radiator, exuast, intake, and dipstick...i picked up my friends leak test today, so ill post my results tonight...

 

It is the ring lands that break. This is a section of the piston, not the rings themselves. onefastb18c has made over 400hp using stock rings, but he used forged pistons - as any good turbo motor should.

 

Do the leak down test, then if it is a high percentage put some oil in the cylinder. If the percentage changes drastically, it is a ring sealing problem. If the percentage of leak is still the same, it is the valves......

 

I did the leak down test and am very happy and suprised at the same time. Less than 5% leakage in every cylinder. The only air comming out was from the crankcase which means there is some ring land wear. but that is expected after 105,000 miles.


[Modified by Turbolude, 1:27 PM 7/25/2001]

 

My mistake.. The ringlands are what breaks, and not the rings themselves...Thanks again John and everyone..

art