I too have an overboost situation. I have a 1986 Turbo (CIS), SC cams, Kokeln IC, K27-HF, GHL headers,non-cat muffler, 46mm Tial wastegate (1bar boost spring), and a modified fuel head. Not until I installed the K27-HF, GHL headers and tial wastegate did I experience overboost. I initially experienced overboost at around 4200 RPM. I then installed a .5bar boost spring and the overboost moved to around 5400 RPM. Last, Stephen suggested that I remove the wastegate dump pipe. I did an intitial set of test runs seeme to have positive results (I am still pegging my stock boost gauge during the run). I would, however, like to find a better solution as I am concerned that when I install my HKS EVC 5 elecdtronic boost controller, that I will be right back in the same situation. I expect to be in an overboost situation again since the electronic boost controller will prevent the premature bleed-off of pressure that occurs with a solely mechanical wastegate device.

Since I now know that there are a number of other individuals in the same situation I would appreciate hearing from those that find solutions to this problem.

Thanks,
David

 

The solution is to remove the 1 5/8 pipe and replace it with a 1 3/4 ID pipe. Also, if you can weld it so that it is more in-line with the airflow you'll be better off. Or at least that is what a few people have done to resolve it.

Brian

 

I do get boost creeps with my 0.9 bar spring to a max of just under 1 bar under very heavy load on high end which I think is ok.

 

Brian,

I did see the posts regarding having a large wastegate pipe, but would certainly like to see photos of a corrected pipe (both larger pipe and angled for better flow) and find out how much they paid to have it done.

Thanks,
David

 

Sameer, you are one of the lucky ones to not have this boost creep problem.

 

Sameer,

How does your configuration differ from mine (see earlier message for details)? When you have tested for overboost, have you been flooring it all the way to red line without letting up on the gas at all? I have always been able to get mine to red line without overboosting, but could only get there by backing off the throttle slightly when I got to the point where I knew it was going to overboost and then continue up the RPM range at a slower pace from there. However, since I removed the wastegate dump pipe, I can go all the way up to redline without backing off the gas (it is a bit louder without the dump pipe).

David

 

I solved the problem by doing exactly what Brian said. 2" dump pipe... I think it was a couple of hundred in parts plus a few hours labour.

I've since scrapped the GHL headers completely. They just don't flow enough for this motor (3.6 EFI 600hp potential). The heat keeps backing up into the engine. The color of the metal gets darker and darker as you get closer to the turbo, where they are just black! The secondary tubing seems to be too small. The primaries flow into a secondary that is almost the same size.

B&B seems to use a much larger secondary. But I've ordered a custom set from Powerhaus for almost the same price. Hindsight is always 20/20.