Boost Leak Checking Clarification Needed

[Onefast99gsx]

Having been into DSM's for 5 years now, I feel stupid for even asking this but I'm not finding consistant information. The vfaq doesn't state anything about it. Some say to put #1 at TDC. I found a report that someone puts theirs at 10* ATDC and even another person who puts his at 30* ATDC.

Last night I borrowed the neighbors air comp to do some checking. Couldn't finish because the dam belt blew on the air comp. I put #1 at TDC and I couldn't even get a rise out of the boost gauge. So.. I cranked the motor clockwise about 4 teeth on the cam gears. I got the boost gauge to rise to 10psi but it would fall within seconds.

So because I'm really unclear on where to have the pistons during the test, I don't know if I have boost leaks or the if the valves aren't in the right position to even perform the test.

I have HKS 272's if that makes any difference.


Thanks for any help.

[Shane@DBPerformance]

Just keep air flowing through the system and listen for leaks.

[Onefast99gsx]

Thanks Shane. It would be nice if i could go find one of those air nozzles that clamps on the the filler nozzle. Then i can diagnose better without having to hold the hose on using up an arm. Of course, have the regulator set to a safe psi level.

[JiggahMan]

Have a friend hold it there. I hate leak testing, but it sounds like you're losing a fair amount of boost.

[s1ngletracker]

It doesnt matter where the pistons are, and unless your cylinders have terrible leakdown the loss past the rings or valves will be pretty much negligable compared to the leaks you probably have in the charge piping.

Think about it... Since when are all your valves open at once?

[Onefast99gsx]

Thanks for the input quys. I plan to resume my leak testing tonight. I found some leaking at the BOV the other night. There is some orings in it that appear to have expanded over time, maybe with heat. It's about 4 years old. They are sending new ones.

[Pushit2.0]

Originally Posted by s1ngletracker

Think about it... Since when are all your valves open at once?

This would come down to how much overlap your cams have, Turbo cars will have low over lap but intake and exhaust valves are open at the same time. This will happen as the piston is coming up on the exhaust stroke and as its coming down for the intake stroke, over lap will be in degrees of crank rotation as it comes to TDC and away from it, ie 10deg of overlap.

As said befor keep the pressure there and feel/listen for leaks. Home Depot should sell the proper fittings to hook your aircompressor up.

~John

[s1ngletracker]

how much overlap does 272s have?

[Pushit2.0]

Off topic but what I have found on the unpossible internet is.

HKS 272/272 cams for a 4g63

Overlap 8deg.
Intake duration 218deg
Exhaust duration 218deg
@1mm lift

Based on Max lift of Intake 10.3mm
Max lift or exhaust 9.8mm

Intake valve opens 6deg BTDC
valve closes 32deg ABDC

Exhaust valve opens 36deg BBDC
valve closes 2deg ATDC
@1mm lift

~John
with out a cam card, or a degreed set of 272's it looks right to me.

[Onefast99gsx]

Thanks John for that info. Helpful.

Well last night I spent a good couple of hours doing an extensive test. I got out the automotive stethiscope to probe around. Other than the bubbling in the oil pan, I have 3 leaks.

1) BISS screw on the TB (very minor leak)
2) TurboXS BOV (Junk!, I would never buy one again. They are sending new orings but i'm doubtful that it will help. I may JB weld the fittings where it all leaks)

3) Compressor housing cover where it meets with the backplate. I know this PTE to4e cover has an oring and the bolts are tight. Still leaks though. This 50 trim isn't all that old, less than 2 years.

What do you guys recommend for fixing that compr. cover leak?

Thanks.

[Pushit2.0]

Try RTV.

~John