Is my stock compression a bit to low to handle a turbo??

[jermzfree]

I have an 02 busa w/ 26k on it. I have a rcc stage 1 kit with plans of running 6lbs of boost. Before having the turbo installed I had a dyno to get a baseline hp. It was a little low (139hp). I checked the compression on the cylinders, and they range from 180-182psi. I also ran a leak down test, which showed no sighns of valve or head gasket problems. Should I proceed with the install? or is the turbo going to cause a lot of blow by past the cylinders?

 

[SKnight]

Your power is down by about 30 if it was stone stock for the pre turbo test. I don't have my GenI manual handy but for a GenII the spec is 199-256 normal, 142 lower limit so you're most likely good since the GenII has more compression ratio. If you're wanting to check the rings, do a wet compression test. Run the compression as is and note the numbers. Then put a teaspoon or so of engine oil down into the cylinder. Spin it over a few times, screw the tester back in and recheck. The oil seals up the rings, a slight increase is normal but if it changes more than 10PSI then you have some getting by the rings. The bigger the change, the more blowby you have.

If you have blowby then yes a turbo will make it worse.

Before I installed the turbo I'd sort out why it's low on power. No need compounding a problem or selling yourself short.

 

[GNBRETT]

wat kinda dyno and wat was ur torque readout? who dynoed it?

 

[jermzfree]

wat kinda dyno and wat was ur torque readout? who dynoed it?

The torque reading was around 90lbs. Mike from Quick Cycles preformed the dyno. Ill try the wet compression test today and see what changes.
Thanks.

 

[POWERHOUSE]

I have an 02 busa w/ 26k on it. I have a rcc stage 1 kit with plans of running 6lbs of boost. Before having the turbo installed I had a dyno to get a baseline hp. It was a little low (139hp). I checked the compression on the cylinders, and they range from 180-182psi. I also ran a leak down test, which showed no sighns of valve or head gasket problems. Should I proceed with the install? or is the turbo going to cause a lot of blow by past the cylinders?

When you did the leak down test, you had a certain amount of "leak", which you were able to hear. What was the percentage of leak for each cylinder? If you didn't hear air in the exhaust or through the throttle bodies, then the valves are good as you say. All of your leak is through the rings, which is normal. Anything from 0-5% is ideal, anything under 10% is still good. Over that, you have a top end in your future. In any case, at 26K I would install a new cam chain along with your turbo.

 

[jermzfree]

When you did the leak down test, you had a certain amount of "leak", which you were able to hear. What was the percentage of leak for each cylinder? If you didn't hear air in the exhaust or through the throttle bodies, then the valves are good as you say. All of your leak is through the rings, which is normal. Anything from 0-5% is ideal, anything under 10% is still good. Over that, you have a top end in your future. In any case, at 26K I would install a new cam chain along with your turbo.

Well it looks like a new top end is in the works. The leak down test read 15% leakage as best as I could tell, had a hard time keeping the needle steady to get an accurate reading. All cylinders read between 180-182psi on compression. When I added a little oil the compression jumped to 240psi. I a little bumed :unhappy: Really wanted to slap that turbo on and hang on for dear life. I have plans for getting the gears cut, heavy duty head studs, valve work, cam chain, and anything else that looks worn. I don't plan on dropping the compression because I plan on keeping the boost at 6lbs, and I still want that low end torque for the windy roads. If anyone has advice on engine mods it is greatly appreciated!
Thanks.