New DP, low boost

[Shimy87]

well as usual I was wrong, thought I was super careful about exhaust leak avoidance but.....wired puck closed and to the floor only 15 lbs boost. will be pulling cross over and headers and seeing if I can find any leaking areas? must be a pretty bad leak to cause this??

[Scoobum]

Stupid question...but are you running a larger than stock crossover pipe?

[Scoobum]

I'll take shit from all corners on this...but I don't give a fuck. I use an RJC turbo gasket and Felpro header gaskets. Yeah, I know. Never came from the factory with gaskets. My take is this. After a million heating/cooling cycles...shit warps. The Felpro header gaskets are hooked on the ends...and are easily removed and replaced. They don't last forever. Change mine once a year. Use a stock crossover pipe...a larger diameter will decrease velocity. Use new proper exhaust studs and nuts for the crossover pipe. I put my finger around the lip of the crossover when tightening to assure the pipe mates to the header evenly all the way around.

[Steve Wood]

No need to pull stuff off. Pour some top engine cleaner into the throttle body while running at 1500 rpm or so and look for smoke coming out of leaks. Tranny fluid will make smoke too.

Most common leaks are under the turbo, crossover pipe joints, and backside of #3\5 header welds
  Also warped flanges will leak between the header and head

[Shimy87]

I also use the felpro header gaskets with the same reasoning, they are both new. I also use a stock crossover. I put it on the same way as Scoob. I was going to tear into it and remembered Steve had told me about the "dump in the cleaner" trick. I did find one small leak on the drivers side header to crossover pipe, but that's the only one I can find with the smoke trick. Then when I found it I could see a pencil eraser size carbon mark it was leaving on the connection flange. Could that one small leak cause this?
Thanks again guys!!

[gusszgs]

If he's got header leaks that are that bad that it will only boost to 15lbs with a HD actuator wouldn't these leaks be audible?

[Scoobum]

The data Murphster has been putting up running a stock engine and turbo to its limit may shed some light on this. That back pressure that stock turbo is encountering is insane...at only 22 PSI. Shimy has a slightly larger than stock turbo...with a stock engine. That little turbo needs all the help it can get to overcome the back pressure...so any exhaust leak at all will be a killer.

Norbs pushed a stock turbo to 30 PSI...and it ate itself. The back pressure at 30 PSI must have been nuts...from what I've seen from the data at 22 PSI.

I don't think the puck is sealing either.

[Scoobum]

With stock heads and IC, I'm betting Shimys turbo is all in at 24 PSI.

[good2win22]

Just going to throw this out there about exhaust leaks.


 When I was trying to diagnose my rpm issue, I wired my puck open. 6262 with a precision .63 housing from 3k rpm to 5100 rpm and it made 11 pounds boost in a high gear pull.  There's something to be said for increasing compression and not having any leaks prior to the turbine housing. 

[Be4u]

Great thread!

[nocooler]

Check the cold side for leaks as well - I blew a weld on an intercooler once, but I was loud enough to hear, but I was limited to 15psi or so.

[Shimy87]

well I found 4 leaks on the cross over pipe, none in the header areas and no cracks in the header. cleaned everything up good and put back together very carefully with new gasket and also used high temp silicone in the crossover connections. Waiting til tomorrow to fire it up and see if we made any progress.

[Steve Wood]

Be sure your O2s are 800 or less at full throttle as well.  An overly rich a/f will not spool up either

[Shimy87]

Thanks...going off of memory but I think during my last testing they were in the 812-820 area...I will have to pull some fuel.

[Scoobum]

Erics low gear fueling is notoriously rich.