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Discussion Starter #1
Sorry this is rather lengthy.
I just finished my installing my on3 kit on my 95 cobra.

While apart, I took the heads to the machine shop to have them surfaced and a valve jobbed. I installed some engine works mls head gaskets with arp head bolts. I used felpro 1250 intake gaskets for the intake and other than that it is all stock.

The first time I took it out I babied it shifting at about 4k and hitting 8lbs like it should. I went back home and everything checked good i took it back out and ran it harder and past 4500 the boost kept creeping hitting 15lbs. A/f was around 10.8 to 11.2 at wot and base timing set at 10.

My problem (other than boost creeping) is that everytime I hit boost it pushes water out of the overflow tank and starts over heating. I replaced the cap today because it was bad. I just want peoples opinion on what could be wrong or if my suspensions are right and its popped a head gasket already. and btw if I drive without hitting boost it does not overflow or get hot and there is not water in the oil.
 

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Sounds like you're lifting the heads. 15 psi is a lot for stock heads. The decks are too thin for that. Fix the boost creep and lower the boost, and keep it lower. Then replace the gaskets again.
 

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when i first got mine going it would do the same. i ended up still having air in my cooling system. i just took off the radiator cap and let it idle for 20 mins and kept topping it off as needed.
 

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Discussion Starter #4
thanks for the quick replies

10secgoal: Thats what i was afraid of. I have read that the gt40s are bad to lift. Its only seen 15 lbs once and since then I have not let the boost get that high again. The highest I let it get was 12 and still pushes water even if it only sees 8. Is that still to much and what gaskets do you suggest?

chevyguy15: I though that at first so I did just what you said and test drove it again. It still overflowed and got hot.
 

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Boost is getting into the cooling system. Either blown head gasket or lifting the heads. Either way, time for new head gaskets. Fix the creep so this doesn't happen again.

How are you controlling timing? Chip?
 

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Discussion Starter #6
Yes I have a chip from on3 he said since the car was bone stock that it would be pretty close leaning on the safe side.

Any tips on fixing the boost creep?
 

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Either bad placement of the wg or a bad wg. Being that its on3, id say both
 

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Discussion Starter #11
Can you point me in a direction on what to check for the wastegate?

Also, what head gaskets should I go back with? I know this is a deep subject and has been covered extensively I just dont want this to happen again. Its my daily driver.
 

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I relocated my wg to control boost better, and so far so good. I have a Tial now and I plumbed it in at the merge before the turbo flange. Then I recirculated it into the downpipe which i might add was a TOTAL PITA!!! That stainless they use is some hard stuff. Ate 2 of my cobalt bits. But it is so much quieter now and my boost doesn't go beyond 12 unless I want it to. Cost about 400 bucks for the new wg and the stainless 1.5" pipe and getting my buddy to weld it all up but it was money well spent.
 

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not currently, my camera was destroyed by my 19 month old. We call her hurricane Grace. When I get a new one and a free moment i'll take some pics of it. Right now the car's torn apart getting ready for a 4r70 swap. It's gonna be a few weeks.
 

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PM me if you want guidance. Ive been through it all. I have even tougher heads to seal...Went through about 4 different sets of head gaskets now I have the "Good" ones...
 

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Discussion Starter #17
mw95gt I sent a PM but my sent box still says 0. Am I doing something wrong? I'm new to all the forum stuff sorry.
 

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we had the same issues lately on a stock bloc set-up. my tuner recomend against mls on stock block, he sez dech is too thin, 7/16 bolt not enuff to compress mls right. he also sez standard replacement gasket have no problem at 12 psi, maybe a bit more. we are swaping gasket next week.
 

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Discussion Starter #19
Update: I tore the top end apart and checked everything out. It all looked good except for one spot on the gasket. The heads and block were straight. I replaced the head gaskets with 9333pt1s and went back with arp studs instead of bolts. I torqued the studs to 85 on the bottom row and 95 top(arp tech suggested ). Also while I had it apart I relocated my wastegate to the passanger side of the crossover tube. Once I got it all back together and running I backed the base timing back from 10 to 7 for a little more safety till I can get it tuned. So far I have had no more boost creep. It stays right around the 6-8lb range and I have not had it overheat and push water out. Thanks guys for all the help
 

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Just 2 days ago a friend took his GT40p turbo’d setup to Alternative auto in the Detroit area for a tune…and guess what happened after moderate boost (8psi) on the 4th pull. You guessed it, the heads lifted and pressurized the coolant. After the pull (was only able to take it to 4k rpm) everything was back to normal. His only option now is to tear it back apart (this was a completely freshened/machined short block & heads setup) and throw some cometics on it or to rent an Isky O-ring tool and o-ring the block (with 9333's).

Anyways, good luck....and hopefully they don't lift for you again.
 
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