Stock Turbo Boost drop 1st & 2nd???

[STF420@comcast.]

Hi, I have a problem I can't seem to figure it out. At low RPM it builds boost fine then the boost falls off as RPM increases. I can get 19lbs in 1st & 2nd but by the end of the gear it is down to almost 16lbs. When it shifts into 3rd it goes to 20 to 21lbs and holds pretty good. The car runs good 12.30's @ 108.5mph. (Stock turbo, KB Big Boy, Ported iron heads, 3000 PAT's LK-up, Tho I have not locked during a run yet. KB Hi-LO Pro chip, Slicks, Ford Super coupe injecters, Wastegate housing fender dump.) I have tried bleeder valve. Grainger valve. I can't seem to get high boost to hold in the lower gears without getting way high (TO HIGH) in the upper gears. Am I running out of Turbo (Not enough CFM?) Any help would be appreciated.

Thanks, Mike

 

[QUIP'6']

check for header or any type of exhaust leak

 

[STF420@comcast.]

Hi, Thanks for the reply

I am leaning towards an exhaust leak but I can't see or hear any. I put a very thin coat of HI-Temp RTV on every flange and cross-over joint. I have the larger wastegate hole about 15/16" to 1". with good alighnment 1/16" to 1/8" puck contact all around. I did try running the car with the wastegate disconnected and at the very top of 2nd gear I would get 5 - 6lbs boost. Then I removed the turbo exhaust housing and ported and contoured the inlet around the wg hole (Inside only, did not touch the puck face side) I contoured the inlet of the turbo to the wg hole. I went for another run and it would only build about 3lbs at the top of 2nd. (with WG disconnected) Allthough this mod should help with boost creep not the problem i am having.


Thanks, Mike

 

[STF420@comcast.]

Update

Hi,

Update:

Installed ALKY. Same boost problem but went 12.20's @ 110mph. There was an engine noise so pulled motor to just check it over everything was fine (bearings and lifters). I installed a Completely stock heads including springs mileage unknown w/stock big neck stock intercooler. Now boost stays rock steady 22 to 22.5lbs. No creep, No drop, No spike. But I could only got a 12.40's @ 106.8mph. Seems like the heads were just flowing more air than the turbo could keep up with? I did try a TA60 with the ported head setup and the boost held fine. With first time out minimal tune time. The car went 11.70's best ET with 1 run netting 117mph.

T.I.A. Mike