View Single Post
356-930 356-930 is offline
Acceleration Junkie
 
Join Date: Aug 2007
Location: Laguna Beach, CA
Posts: 263
Garage
Alan:
Theoretically, with your exhaust outlet capped the only leak path for air to escape a pressurized intake system would be past the valves and rings and that path is miniscule in a good engine. Thus, given the volume of the intake system, i.e. turbo feed pipe, turbo, turbo outlet pipe, intercooler, intake manifold, power brake boost line, distributor vac/retard and pressure gage lines etc., I’d guestimate a 930 engine charged to 15-psi should hold for hours before it drops even 1-psi.
You note, “My compressor could only produce about 5 psi running flat out before I pulled the motor.” Are you saying your turbo (compressor) boosted to a max 5 psi? If so, less than half what it should be capable of with a stock wastegate. A turbo can flow a whoollee bunch more air than the ¼” airline you have on your test setup. It was doing a good job keeping up with a huge leak.
Unless I’m missing something here, you’ve still got a huge leak.
It’s going to be a process of elimination. Pull the intercooler and plug all the accessory lines/ports coming off the intake manifold. (Some of the 930 vac control valves are designed to vent the intake to atmosphere is certain cases. Perhaps one is open all the time?) Pressurize the throttle body– it and the intake manifold and any open cylinders should hold 15 psi for a long time. If ok, start adding back the accessory lines and accessories, test the intercooler, hoses etc.
I recommend you test the integrity of the intercooler by itself. It’s basically a radiator and many a radiator leaks only under pressure and the higher the pressure, the greater the leak. It may have no appreciable leak under vacuum so you wouldn’t notice it at idle or no/low engine load.
Old 04-16-2008, 05:45 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)