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And87mnr
09-30-2004, 06:57 PM
I've been having a problem with my 87 GN. Unusually low boost. I have TA-49 turbo (just rebuilt last week with new impeller). 3" downpipe, 2 1/2" exhaust, 42.5lb. fuel inj, high flow fuel pump, AFP regulator, champion ported iron heads, .425 lift cam, bored .20 over, O-ringed block with copper head gaskets cold air intake, 3000 stall converter, CAS V-4 intercooler, JE forged pistons, Red Armstrong street/strip chip.

The problem is that the max boost I get is about 14-15 lbs. I’ve tried adjusting the wastegate actuator, checking all turbo/intercooler hoses and clamps and vacuum lines to no avail. I was curious if anybody had any suggestions I would really appreciate it.
Thanks

Turbo2nr
09-30-2004, 07:14 PM
Do you have a BOV? Is car slow to spool, or just the lack of high boost? Checked the puck to wastegate hole, to make sure it is a good seal? Crack in turbine housing? It has happened to me with a turbine housing custom cast in Australia for a WRX with a Garrett GT. (very uncommon for US turbine housings) A more common mistake is to install the "t" with the wrong side going to wastegate accuator. If you look closely, there is a small metered oriface that has to be on the line going to the accuator, I think (check somewhere in this web site for the proper location) if you have it screwed up, or reversed, about 15psi is max, no matter how hard you try to adjust stuff. Too much boost will be going to accuator and opening it up early. Thats my guess, and i'm sticking with it.

And87mnr
09-30-2004, 07:36 PM
I do not have a BOV, it is quick to spool, the turbine housing is not cracked, and the puck seals great. The "Y" of the wastegate actuator vacuum line is facing towards the line coming from the turbo compressor outlet. I'm not sure what else it could be but I appreciate the suggestions.

Keller
09-30-2004, 09:59 PM
Do you have an adjustable wastegate?

Could be a wastegate hose set from GM with a "Y" that has a restrictor of the wrong size. There was a batch like this, and there is some info in the archives that adresses this.

Try this: Pull the wastegate hose off the wategate actuator diapragm. Then go for a drive and *carefullly* get into boost. It should head for the moon, with no wastegate control...be careful!! But you should get over stock levels, easily. Be sure to let off as it climbs over 15...this is only a test.

If it doesn't, the problem may be elsewhere.

Turbo2nr
10-01-2004, 06:29 AM
I do not have a BOV, it is quick to spool, the turbine housing is not cracked, and the puck seals great. The "Y" of the wastegate actuator vacuum line is facing towards the line coming from the turbo compressor outlet. I'm not sure what else it could be but I appreciate the suggestions.

The side that is important is the line going to the wastegate accuator! That line needs to have the restrictor in it! Double check it. ;)

Keller
10-01-2004, 12:52 PM
Silly question, but (1) are you reading boost off the stock gauge? If not, then where is the aftermarket gauge line plumbed in?

Once got a call from a local guy who has owned several GNs and TTAs, but doesn't know one end of a wrench from the other. He had his latest Gn worked over by an expert head porter, renown for his capabilities on the 455 cars. The car ran OK, but kept blowing head gaskets. He was on his 3rd set! He was looking for help.

I came over with my scan tool. Of course, he did not have one. :nono: We set out for a lonely stretch of highway. I manned the co-pilot's seat, plugged in my Turbolink setup, and had him punch it. Felt pretty strong, but the knock was so severe, it sounded like the Rockettes doing a tap-dance number. Boost was only showing some sub-15 number on the aftermarket gauge, which was his chief complaint. The O2 numbers looked a little lean on the scan tool, but not severely.

Hmm... :confused:

Back at base, I peeked in the engine compartment. Everyting looked OK at first. He'd been cranking on his wastegate rod looking for more boost. So it was as short as could be. Boost was still showing 12-13 PSI. He had a Volt Booster plumbed in, looking for more juice to the fuel pump to stop blowing gaskets. Then...I saw where his boost gauge had been plumbed in. Just past a restrictor in the EGR line routing. He claims the head porting guy had hooked up the gauge for him.

Temporarily removed the Volt Booster and put the gauge plumbing in that line. Let the EGR pass straight through again.

We took the car out again. He rolled into the boost. I was watching the gauge and the knock count on Turbolink. The boost guage started going up...5..10..15..20.. :eek: I was screaming for him to get out of it as it was heading further north and the knock count was going up like the national debt.

I think we found his problem. Might this be yours?

And87mnr
10-01-2004, 05:21 PM
Thank you for all the suggestions. I found the problem. To answer all of your questions I am not using the stock gauge (option U52..not really much of a boost gauge just a red and orange light ) . I am using a VDO boost gauge. Everything is plummed properly. I did double check the "Y" restrictor and it was correct. The problem was my stupidity. Being tired and rushing to put the turbo back in a month ago, I somehow had the vac lines from the accuator and housing going to the heater bypass vac lines :o.