Low boost??? Help diagnosing??

[golfaddicted]

Well I went for my first ride on my Apex since boosting it with a Bender rear mount. It seems to pull really hard, but it is only getting a tad over 6lbs of boost on the high setting and about 4.5/5 lbs on low boost. I made a fixture and attached it to the intake on the turbo and attached shop air. I couldn't find any leaks. I sprayed all of the joints and they seem to be sealed well. The kit is used, but I was told it was making boost when pulled. There isn't any side play on the compressor wheel. What else can I do to diagnose the problem. Thanks
Greg

 

[mbarryracing]

Greg,

You need to check the exhaust side for leaks, not the intake side. If you have a loss of back pressure (exhaust leak) it will not build as much boost.
If you had a leak on the intake side, the turbo would compensate for that with overboosting and you'd never know until the bearings smoked. You did yourself good by checking you have no leaks in the induction side.

If no leaks in the exhaust, then you only need to adjust the linkage from the boost control diaphram on the compressor housing to the wastegate lever. You'll have to pop the seat off. Use shop air to blow into the diaphram to extend the linkage to get it off easier. The rod is threaded so you'll want to turn it in to create more pre-load.

If you have not lowered the compression in the engine, don't crank it over 8lbs on pump gas to be safe. I suggest you put a call into Justin at Full Power for more insight.

Mory

 

[BigDog05]

Do you have a flex pipe where the exhaust pipe and the turbo inlet pipe hook together?

I was getting erratic boost reading last season and when I looked real close you could see where the pipe was sliding when the sled would flex.

Justin put a flex pipe in that location for me.

 

[mbarryracing]

Yes, that is one of his own FPP designs that can be retro fit to the Bender systems. Good suggestion!

 

[golfaddicted]

Thanks a bunch guys.

I don't have a flex joint on that connection yet, but I do plan on it. I did talk to Justin before the install. He had lots of good advice. I plan on getting his updates.
How bad of a leak on the exhaust side will cause this much boost loss? I ran the sled with the skid off and didn't see any exhaust leaks. Is there another way to check this?
I did stack 3 stock head gaskets and torqued to Ted's specs. I only plan on running it to 8lbs for a little while while a get it dialed and then gradually go up to about 10 or 11psi. The problem that concerned me was it was making a solid 4-5 lbs on the low setting but only a tad over 6 at the hight setting. I assumed from reading all the posts that it should be a 4psi jump with the switch. The previous owner of the kit said the turbo was set up for 8psi. I should've verified before installing, but I didn't. There were several leaks in the line going from the wastegate to the hi/lo switch. I fixed them. Could that be where he was getting the extra boost?
I'm going to try it again tonight when I get home from work. While I was sleeping, I remembered that I didn't tighten down the boost tube that goes to the boost gauge. It is a used gauge with a used compression sleeve. It may have been making the 8 lbs and the gauge not reading it. I'll update tonight.
Again thanks and sorry for the book!

 

[BigDog05]

It doesn't take much of a leak on the exhaust side to cut the boost down. Mine would be fine for 10-15 miles set on 10 lbs and then it would just drop to 5-6 lbs for a couple of miles.

The pipe was sliding about 1 inch, and on a stand it was fine, I think it had to do with the sled flexing. I really did not see it until Justin told me what to look for at the end of the season.

 

[golfaddicted]

Update

I couldn't wait till after work. I just went and tried it just tightening up the fitting on the boost gauge. I now hit 8lbs of boost. BUT... I get 8psi whether the switch is on high or low boost. Could the switch be bad. Stuck open?
How would you bench test this?

 

[mbarryracing]

I think that a leak in the line to the switch would bleed off the boost sense / pressure signal to the wastegate diaphram, make more boost? I'm not positive.

Remember that as boost goes up, so does the exhaust pressure and it might not leak enough at low boost, but start leaking enough to not build your big boost. Same goes for pressure and your gauge...

Same boost? You might have a leaking "fast / too fast" switch, then.

 

[BigDog05]

There is a bleed hole in the switch. Take the hose off back near the turbo and and put a little compressed air thru the line to the switch. In low boost position you will not hear any air being released thru the bleed hole. On high boost position you will hear air thru the bleed hole.

Once you find the problem, call Ted and get a Halmann Pro manual boost control and throw that switch on your work bench.

This is a pretty good controller for the price.

 

[mbarryracing]

is that a dial type? I saw a purple one with a knob on Wolfes sled.

 

[BigDog05]

Picture of controller.

http://turboaddictionparts.com/catalog/ ... cts_id=282

 

[mbarryracing]

Yup, that's the one! Nice, but $$$.

 

[golfaddicted]

Well...

I got in touch with the installer for the guy I bought the kit from. Apparently the "fast/too fast" switch failed on him last year and he has been leaving it at the boost it was set at. Didn't bother replacing it or fixing it. That makes me feel better. This is an easy fix. I'll order a new boost controller. It will probably take a couple of days to get used the insane power it has at only 8lbs. We'll see how long it take to want more power...
Thanks guys for helping work through this. I really appreciate the input.

 

[mbarryracing]

Cool!

 

[rxrider]

The Hallman's MBCs works just fine, and you will want more boost right away, it's that addictive Good luck on your turboed ride.