I just helped a friend build a very stout 4.3 V6 for his 1993 GMC Typhoon. After some issues with a faulty "Knock off" MSD distributor and a crappy fuel pressure gauge we have the new combo timed and running. Here's where the problem shows up: He can't build any boost; the highest he's revved the engine so far is 3500 rpm's and foot braked it to 2200-2400 NO boost. The Build details...
Engine:
1992 SyTy block with 2 bolt mains with the Nodular iron main caps. Fully studded and bored .030 and hone fit to the pistons w/.007 clearance
Speed Pro -21cc forged pistons
Eagle H-beam rods 5.70" with the large big end to work with the 4.3 crank.
Total Seal file fit rings set at .028/.028/.017
Rotating assembly fully balanced
Standard volume oil pump
Comp Cams #422 HR cam set up for boost. .500/.510 @0.050 215/220 adv 270/276 LSA 114 ICL 110 Comp timing set fully degreed. New #853 lifters

Heads:
1998 Vortec Heads w/ Proflow 1.94/1.50 stainless valves Fully ported by HeadFlowInc. on both the Intake and Exhaust with chamber work and polishing.
Comp Cams #924 dual springs setup @1.750 160# on the seat raw. Screw in studs/plates Comp Cams 1.52 roller tip rockers.
Hardened one-piece pushrods 7.200"

Induction:
LT-1 throttle body with air foil bolted to a RENZ FAB fabricated upper plenum.
SyTy lower intake fully ported by HeadFlowInc matching the intake ports to the Felpro #1203 gaskets.
70# injectors
Syclone fuel rail setup with adjustable fuel pressure regulator. Fuel Pressure is set to 42#
New Walbro 255L fuel pump with a "Hotwire Kit"

Turbo:
Turbonetics 62-1 62mm with a .63 Hot side
SyTy exhaust manifolds and crossover setup with a TIAL 38mm WG mounted to the crossover pipe 10# spring.
Aftermarket Water to air Inter-cooler with a dual fan assisted factory coolant cooler below the core support.
Forge BOV not sure the size but IIRC 10# spring.

Tune:
Custom burned chip from Turbo Tweak with two tunes #1 92 octane #2 92 octane with Meth injection

I'm convinced it has to be a bad WG because I had him unhook the line to the BOV an it made no difference at all. The engine runs great but the Turbo isn't making even a single pound of boost! Where should we look? Need more info just ask we are an open book nothing to hide. JD

He has a Scan Master 3 setup, manual boost controller, Innovate Wide Band, Boost gauge, and EGT setup.

Video:

 

take off the bov, block the pipe . drive it and floor it in a high gear and take it to 4000 rpm .see what happens . i can hear the turbo spooling as you rev it , it may just need a bit more revs and load to show boost than 2400.

if it then has boost , put bov back on and try again .

make sure your wastegate is shut and has pre load on the spring .

good luck
robert.

 

What Robert said: it may just need a bit more revs and load to show boost than 2400.
"He can't build any boost; the highest he's revved the engine so far is 3500 rpm's and foot braked it to 2200-2400 NO boost"
Free rev = zip/no boost.
Foot brake to 2400, likely not enuf load to spool it.

What Robert said: it may just need a bit more revs and load to show boost than 2400.

 

I'll text him the suggestions ASAP! It's just very odd because two things have changed, the footbrake which use to hold to 2800+ rpm now barely holds 2300-2400 rpm and when it was stock he could boost launch at 14 psi! Thanks I'll update the results JD

 

Where is your boost gauge attached? Remember, boost is actually a measurement of restriction, with all the porting that was done, there may not be anywhere near as much restriction as one might normally expect.....

 

It's always been under load either footbraking on driving to try and get boost. The Stock baby Mitsubishi turbo would boost launch at 2800+ rpm 14 psi so it at least use to make boost down low. He selected the 62/63 Turbo so it wouldn't be too big but now he's wondering if maybe it is to big. I'm still betting on the WG or BOV being the cause. The owner is babying the engine because he doesn't want to hurt anything before he gets everything worked out which is why he's not revving the engine very high. On his first time driving the new combo he felt something was wrong by it not building any boost and took it back home.
Thanks for the feedback it all helps! JD

 

The boost gauge is connected on the firewall side of the fabricated upper plenum; it has it's own port there. It's true the heads are flowing way more than stock and he now has a larger camshaft with a larger turbo too! You can see all the port work on the HeadFlowInc youtube channel check out the videos https://www.youtube.com/user/HeadFlowInc/videos. Thanks Rick!

 

"The Stock baby Mitsubishi turbo would boost launch at 2800+ rpm 14 psi so it at least use to make boost down low. He selected the 62/63 Turbo so it wouldn't be too big but now he's wondering if maybe it is to big."
Apples to oranges.........

 

Very true!

 

I would be checking the wastegate to start. Make sure the valve seat is in it. Make sure the blowoff/bypass is closed. That thing should make boost no problem.

 

I'm texting everyones suggestions! I wish I had time to run down and work on it in person. Thanks! JD

 

Why is it so loud in the video? Does he have a big pre-turbo exhaust leak??

A couple of notes here. The cam and head changes will drop the low rpm torque, that is why he can't fot brake as high as before. These will also move the RPM required to get hte turbo pumping.

Like everyone else has said, Check that there is a seat in the WG, make sure it's sealed off. Make sur ethe BOV isn't open when trying to test for boosties.

 

Tell him to put his purse down and stand on it in high gear for a few seconds. It's probably not going to build boost without a lot of load an a lot of throttle.

 

agreed.....give 'er the berries for a bit....lol

 

It's loud because of the "Up Dump" sounding off like a big diesel truck. I sent him everyones suggestions hopefully he can find the problem. JD

 

UPDATE:
What would cause the 90 degree coupler coming out of the intercooler to collapse shut when the engine is revved? He noticed when he revved the engine the one coupler literally "Sucked" shut! How can a charge pipe that is suppose to be under pressure not vacuum?! Confused... JD

 

Because the engine is pulling more volume than the turbo puts out on a free rev....

 

Video showing the charge pipe coupler collapsing.
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OK, we have verified:
WG has no leaks and passes all the TIAL tests.
There are no leaks at any of the exhaust manifold and cross over connections.
The BOV is sealed tight evident by the engine sucking the charge pipe elbow closed.

The only thing left is the ebay water to air inter-cooler as the cause of the restriction. Basically the engine is sucking on the charge pipe and it's collapsing like a cheap drinking straw. This makes no sense on a Turbo application, the only thing left in the system is the Inter-cooler it has to be the restriction. I bet Richard $20 if he bypassed the cooler he would see boost; currently he is trying to find a piece of pipe to put my theory to the test... tic toc we will find out soon!

 

NAILED IT! The "Craptastic" Ebay inter-cooler was the problem! Either it was to small or there has to be a manufacturing/assembly error inside because it was literally restricting boost all together. Richard fabricated a straight 2 1/2" pipe to by-pass the inter-cooler and BINGO he was seeing 10-15# of boost maintaining the self-imposed rpm limit of 3500 rpm's. They took the Typhoon on a 35-40 mile cruise logging the air/fuel and boost numbers. He said it was only getting roughly 10# of boost on the footbrake at 2400 rpm's. It's to be expected with all the changes we made building the new combo we traded low speed power for a Greatly improved Mid range and Top end charge.
Bigger camshaft
Heavily ported Vortecs
Larger Turbo

I think he will be happy with the results once he feels comfortable turning it up! Below 3500 rpm's I'd imagine it does feel sluggish compared to stock but from 3500-6000 rpm's is where double the factory rating happens! Be patient with him as he gets confidence in the build and verifies the tune up. He said it was showing good air/fuel in the 10.8-11.5 under boost and cruising was high 13's.... Not too bad so far we are both thrilled to finally have BOOST! JD