Boost Spike = Blown Head Gasket

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DAVID C

Member
Joined
May 24, 2001
Hopefully you guys can help me figure out why I overboosted and give me recomendations. First here's my setup:
'86 GN, 112k, virgin motor. New PTE 60 Turbo w/hd wg actuator, new Turbo Tweak 60# injectors and TT alky chip set for 22# boost. Home made single nozzle meth/alky kit. 3 1/2" maf and translator, TH 3 1/2" downpipe w/internal wastegate, into stock exhaust (no cat). Cold air kit, big neck stock ic, Stage Right brake, stock converter for now. New kirban valve springs, stock unported heads and cam at this point. Hot wired fuel pump. Scanmaster.
It's been running rock steady 22# on the street with 93 octane, 50/50 water/meth spray and stock exhaust. Zero knock retard.
1st run at the track, uncapped dump tube, sprayed 100% Meth. Glanced at the boost gauge at near the end of the 1/4 mile....Pegged past 27psi!!!:mad:
I hit return road and felt it skipping. Scanmaster showed 13.4 KR.
Why the overboost? Chip problem? Solenoid? What should I do to correct it, besides pay more attention. I'm going to install my Caspers audible knock alarm. But I really need to figure out why the high boost. wastegate actuator is backed off about as far as possible and still have it seal.
It blew out the head gasket fire ring on #3 at the top into the crankcase. It never pushed to coolant :cool: Compression test showed 150+ on all, except #3, which was zero.
Also, I'm not sure if I'm going to do both gaskets, port the heads, roller cam install, maybe even pull the motor to change the converter and make the whole project easier. Goal is low 11's or quicker.
Searches show only confusion on headgasket choices. I think I'm going with the stock GM graphites it had. It looked great except for the clean tear from the boost. What's another 2 grand at this point. :rolleyes:
Sorry for the long post. Wanted to get it all out there. All suggestions are appreciated, especially on the overboost issue. Don't want to pull this bitch more than once. Thanks
 
Easy one. You opened the exhaust dump.....
Install a proper high flowing exhaust system, keep the dump closed or remove it completely, and lower the boost back down. Your chip may not be programmed for enough fuel at that boost level.
 
Are you sure your home made alky kit is working properly ? There are guys running that much boost on alky with no problems.
 
My alky kit has been working fine. It sprays at 10psi. I have a pressure switch plumbed into the nozzle line that lights the "Power Injection" light in the instrument cluster when the line pressure hits about 40 psi. This way if the pump fails, I'll know (probably too late). I need to add a LED near the boost gauge to make it easier to monitor. I have no idea how high the boost actually got. my 25# gauge will display to about 27#s. I may have had 30+. My big concern is why did I have such high boost.
 
You would think it would I recently ran my car with the exhaust open and it seemed stronger but the boost stayed the same as with the system closed 18 psi. Do you have a boost controller ?
 
Seen it many times, you have to turn up the wastegate a lot to get to the 22 psi you have been seeing...Get rid of the junk exhaust or keep you dump pipe open and it will take many less turns on the actuator to make 22 psi.

You see the wastegate system has no way to know how much boost you are running, it's all just pressures and springs...If you make a large change in airflow (opening dump, when your exhaust system is real restrictive) then the car will make boost easier and you will have to retune.
 
Slow91z said:
Seen it many times, you have to turn up the wastegate a lot to get to the 22 psi you have been seeing...Get rid of the junk exhaust or keep you dump pipe open and it will take many less turns on the actuator to make 22 psi.

You see the wastegate system has no way to know how much boost you are running, it's all just pressures and springs...If you make a large change in airflow (opening dump, when your exhaust system is real restrictive) then the car will make boost easier and you will have to retune.
Click to expand...

I don't have the wastegate turned up to get 22 psi... Just the opposite. It barely has pressure on the puck. I wonder if I should go back to my non-hd wastegate actuator.:confused: I agree the junk exhaust has to go. Hate to chuck it. It looks new and adds to the sleeper look. Kinda nice being quiet too.
 
Did I miss the part where you state that you ported the waste gate hole of the turbo?? If you did not port the hole then there is the reason for the extra boost.
 
DAVID C said:
Didn't port the the wastegate hole. Always have in the past. Should I?
Click to expand...

when you have the exhaust hooked up there is more back pressure after the turbo. Therfore it needs more exhaust gas through it to keep it spinning. (do to drag/resistance/whatever you wantto call it) If you lower the backpressure the waste gate should keep your boost the same at it's reference point. However, in order to do so it needs to pass less exhaust gas through the turbine. If the gate can't flow that gas it's going to make more boost.
 
jpratt said:
Yep you should. Less back pressure will allow more air flow, now you need better waste control by enlarging the hole.
Click to expand...

X3! Porting that hole is almost a requirement at this point in the new turbo/internally wastegated downpipes. Happened to me as soon as I bolted up my new turbo. Before the porting i was making 24 psi at part throttle now i can adjust it as low as 15 psi with the HD actuator and an RJC 3" dp.
 
Oh yeah if you are making that much boost you for sure need to port the hole...That's WAY high for not having much tension on the wastegate...Assuming you don't have any problems with your wastegate lines (split, blown off, I have even seen them plugged up with debris).
 
DAVID C said:
Shouldn't the system control the boost even with the free flowing dump tube? :confused:
Click to expand...


NOPE. The only time positive control can happen is with a "closed loop" elecronic boost controller.

Close loop meaning....... Something that uses a map sensor, and adjusts the boost control signal to the solenoid(s) to maintain boost level.
 
All the wastegate lines are new and clamped with tiny tie wraps. None blew off. That was the first thing I checked. I'll definately port that wastegate hole. The old stock turbo struggled to make 20-21 psi with the dump pipe. I should have known enough to port this one. I didn't because it was brand new. I didn't know if it was goin to work out. If I ported it, I couldn't send it back. Plus I needed the carbon ring from the puck to port it properly. Thanks
 
When i bought my new turbo from Hartline, Holly emailed me precise directions on how to do this. Easiest way is to use a little grease on the puck. Reinstall the downpipe, make alignment marks so the downpipe is on exactly the same after the porting as before. Close the puck a couple times to create the mark, pull the downpipe and go to town! i ported it while it was still on the car. used a small shop vac to keep the majority of the debris down and the rest blew out when i fired up the car. everything works great now! Good Luck with it!
 
If you intend to stay at those boost levels, and from the sound of it you are, I would go back with a stronger headgasket for sure. I know some likes to have a FUSE in their motors, but the stock head gaskets will and do fail prematurely.
 
You set up your boost around one amount of exhaust backpressure, then upcapped it freeing up apparently 5psi at full load. It's actually the reason you probably bought the Dump, to free up backpressure on the turbos exhaust wheel.

It totally sucks you blew a headgasket, but porting the wastegate wouldn't have done jack in this situation, your catback system is very restrictive and it's too bad you didn't test your "Track Tune" on the street somewhere safe.

Don't throw Cometics on there unless you send off the heads to get looked at, it'll bite you in the ass, believe me.
 
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