boost dropping off problem, can't figure it out.
 

my car is starting to frustrate me now. I should have never changed the way it was because it worked great.

First I tried a 76 R DBB turbo. Would spool great upto 6 psi by 3700, then would struggle to get to 10 psi by redline in 4th gear. Could get it to 12 with some passengers in the car. That was with the waste gate getting no open signal and all pressure diverted to the top port on it to hold it closed.

I switched back to a 67 turbo. Now the damn thing will boost to 10 psi by 3500, but as the rpms increase boost falls back to 5-7. It also will not make full boost in 2nd gear like it use to.

I pressurized the piping tonight and found a leak at the BOV on the flange, had it re-welded and it's better. Still have the same issue. I disconnected the top port and plugged the line to it so it was only running off the spring and pressure to the port that opens it. It would go to 3 psi and then drop to 1.5 by redline! (my pressures are lower due to the drop in the i/c).

The only real change to the entire setup has been the addition of 2 dynomax 3" bullets after the turbo to make it quiet. The entire exhaust system after the turbo is about 5' long with the waste gate plumbed back into it after the 1st muffler. I wouldn't think that this would cause any issues since it's pretty much a short high flowing exhaust.

Anyone have some suggestions. The car also does not have any audible exhaust leaks.

anyone?

BOV leak ??

Incorrect wastegate control plumbing ??

Waste gate has been re-plumbed to it's simplist form, turbo outlet to wastegate control input, one line to give it pressure. I'll be pulling it off tonight to check for any problems with it.

I'll probably plumb the outlet of the turbo to the top port of the gate just to see if it will keep boost from dropping of at high rpm. Just gotta make sure boost doesn't spike too high since it's like having no wastegate on the car.

you should be getting your vacum signal from up front. if your taking it from the turbo it doesn't know about the loss accross the intercooler.

also have you tried not routing the wastegate into the exhaust to see if it makes a difference. I was told it can have a negative effect sometimes. (something easy to try at least)

also try unbolting the exhaust from the turbo so see what effect it has.

as an aside, how the heck did you get 2 bullets in ? did you do one right off the turbo, then do a 90 then another ? I assume you meant 5' not 5" exhaust system right? otherwise those are some TINY mufflers :jest:

Yeah, I meant 5'. It's setup exactly how you describe it, muffler, 90, muffler.

I'm going to be unbolting the exhaust tonight to try it. The more I think about it the more I'm pointing my finger at the exhaust.

When the 76 turbo was on the car and it had trouble making more than 6 psi without rediculously high load, the maf readings would barely change. I was able to get upto 11 psi sometimes in 4th gear at like 5.5k, but the maf readings would stay the same as 8 psi. It was making more boost, but would not make any more power.

I'm hoping its the exhaust cause my problems would be fixed. I'm alos hoping it's not cause I really like it :p

check the tune, that was my problem. i woul only build like 6-7 psi then it would fall to like 2-3. had it tuned and wam it worked.

maybe the mufflers are restrictive. Don't fix it unless its broke!

Thats what i'm now hoping, if not, back to the drawing board. I so wish I would have never touched the setup. It was working sooooo good.

112 LSA cam , maybe ?

Bullet mufflers, though?

It would be a shame if it turns out to be the exhaust, you can barely hear it. Would make it very easy to sneak up on unsuspecting Cobras.

Ok, went through some paces tonight.

Here is the list of things that were tried or fixed
Exhaust after turbo removed... boost dropped
checked for exhaust leaks before turbo... none found
Found a decent sized exhaust leak from the waste gate... fixed, boost dropped
pulled wastegate off and examined... boost dropped
replaced wastegate spring with slightly stiffer one... boost dropped
visual inspection of silicone couplers... no probs, boost dropped
ran turbo outlet to wastegate port (spring only, no 2nd stage)... boost dropped

disconnected wastegate and put pressure to top port... Hella boost! 12psi done very carefully and it would have done a lot more. Tried from 4.5k where it would normally drop.

The next step is to pull the valve covers, back off the rockers on the intake valves and pressurize the entire system again. This will let is find all leaks upto the valve.

Very frustrating problem... :bang:

still sounds like a wastegate plumbing or actual wastegate problem.

If the turbocharger is capable of making the boost with the wastegate closed/blocked off, then the problem isnt with the turbo, engne or elsewhere.
Its most likely something to do with your wastegate or how its plumbed up.

agreed

Turbo outlet nipple to bottom port on wastegate... I've tried simplifying it.
Will probably be looking for boost leaks again tonight.

Pressurized the entire system again last night upto 10 psi.

Found a good sized leak coming from the egr crap. I have it blocked off, but the o-rings are shot. So I'll be replacing those. I've also got an issue with my BOV not sealing well to the flange which is an issue too, but not as much as the EGR issue. I'm pretty sure the car has always had these two leaks though.

EGR is an easy fix, BOV flange is gonna be a little tougher though.

how do you pressurize your system?
you have me wanting to do this now.
seems like a good thing to do to make sure your getting everything out of the system.

Just lose the BOV then, Its not really needed.

Wont that put a lot of stress on the turbo when you let off?