964turbo

hi guys, I test drove my car tonight after I
got the ghl header installed. When I passed 4500
rpm in third, forth gears, the fuel got cut off.
Currently, i have 1 bar spring and cat bypass
along with the new header. Does anybody knows
what is going on? am I getting too much boost
from the 1 bar spring because of the new header?
if it was over boost, should i put the stock
spring back? also should i install a fuel
enchancement device with the header upgrade?

SonnyV

Please read the rely I wrote on the 911turbo.com board for your.

Regards,

Sonny

PeterV

Check that you have grounded the overboost switch. This is located on the top LHS of the intercooler, next to a round orange sensor, which I believe is the transducer that transmits a bost level signal to the boost indicator in the dash.

The overboost switch is normaly set to o/c [open circuit] at around 1.2-1.3 bar, but being a simple mechanical device, its tolerance may be lower and operating at lower boost.

Alternatively your boost may, in fact be higher than you think and the switch is doing its job.

If you short the switch to ground, or better still the cable going to the switch to ground, you now have eliminated at least one variable as to the reason your engine is cutting out.

rgs, peter
93 Turbo 3.6

Turbohead

I had the same problems with those mods,
I tried new OEM overboost Switches (which is supposed be off @1.4 Bar ) which did work on my 87 930, But not on The C2 T.
I finally Went to Carol Supercharging NJ, who made up an adjustable switch kit pre set @ 1.4 bar and no more problems.
Elliot 3.6 Turbo

KeithC2Turto

You are getting more boost than before because of the design of the headers.

Triping the Over Boost switch is telling you you have a problem, so be carful!

I would not bypas the switch unless you have a good mechanical boost gauge plumbed in after the throtle plate so that you can in fact see how much boost you are really pushing now. If you were pushing a true 1 bar before the mod, you could be in the 1.2 bar range based on some of the reports I have seen.

You can also check things on a dyno. Have them plumb in a temparary gauge for the test. The factory manual shows it put in at the supply to the compressor bipass valve off the intercooler but there are other places.

If you are happy with the new boost level you are now getting as a result of you change to headers you will have to modify the overboost switch triger point by doing one or more of the folowing: move the ob switch to after the throtle plate for some isolation , put a surge can on it, or going to a higher value ob switch.

You could bipass it but it could get expensive.

Other wise, you need to recalabrate your wastgate by putting in a lower value spring if you want to run the same boost as before. You could go to a lower spring and install a mechanical or electronic method to adjust it up to the level you want.

Could be that a .8-.9 bar spring might get you close to 1 bar again.

---

I am starting to suspect that a lot of the power gain clamed by header manufacturs is because of the resulting increase boost presure do to there inefficent wastgate exit design. But I am not an expert and that is another story. It calc's out ast going from 1.8 to 2 bar is a 10% increase in boost for about 30+ hp. I think they claim 35 hp.

Good luck.

Keith
91C2T modified w full gutted B&B's

964turbo

Hi Elliot, are you using any fuel enhancement
with your mods? if you are, which one are you
using?

Sameer

964turbo,

I have a 0.9 bar spring and with mods including headers,exhaust,K29 etc.,my boost creeps up closer to 1 bar in higher gears. I dont think your boost should go much higher than 1.1 bar. Does'tn sound correct.

69COU

I was getting the same problem just after a 1 bar spring was added if the outside temp was cold.
My Dyno grapghs were in a earlier posting.
Very quick ( 3 min ) wiring alteration done by G Force cured the problem.

Car goes up to about 1.2bar for a moment then comes back down to 0.9 approx. A look at the graphs shows how machanical boost springs seem to work with a small peak before boost levels off again.

When you get sorted please feedback the difference the Headers made as this may be the next step for me as well.

Cheers

964turbo

I dynoed my car two weeks ago before the header
upgrade, I got 275hp and 288tq with just 1 bar
spring and cat bypass. And I will dyno it again
next week, but I am putting the stock spring
back tommorrow. Sameer, are you sure I am not
exceeding 1.1 bar because I can feel the boost
is much stronger than before. Do you have bypass
the boost switch?

Sameer

964turbo,
Before mods I was just a tad bit above 0.9 bar, now after mods including headers, I'm just a tad bit under 1 bar under full load. It is always betweem 0.9 to 1 bar of boost and never above.

JBH

I get the same response as 69Cou. Up to 1.2 bar for an instant, then back down to 0.9.

With GHL headers/muffler, K29, SC Cams, Tial wastegate, and Andial enrichment I am getting a consistent 393 rwhp. That SAE corrected, at 82F/sea level with no air directed at the intercooler.

I think the solution is an electronic or manual boost control.

JamesE

Sorry to drag the post up from the depths, but I have a few questions. I have recently installed GHL headers on my 91C2T, which already had 1bar spring, K&N, cat bypass, O2 sensor unplugged, and air injectors removed. On a track day at the weekend, I was hitting a sort of soft version of the rev-limiter in 4th and 5th. Is this the over boost problem. The specific question I have is, has any one who has experienced the 'soft rev limiter solved the problem by grounding the overboost switch. The reason for the question is AFAIK, the overboost kills the fuel pumps just like the rev limiter, but my experience is no where near as violent as the rev limiter... Also I get flames out the wastegate exhaust when this problem occurs, which seems to imply the fuel pumps are still running....

Staffan

James, I have been told that you will find "teeth marks on the steering wheel" when the overboost protection kicks in.

I am no expert, but could this be a wastegate problem ?

964turbo

I fixed the problem by replacing the over boost switch. And
today I dyno my car I got 331rwhp and 340 tq with
Ghl header, cat bypass and 1 bar spring. Without any
fuel enrichment I still get about 11 at a/f ratio. And I
set my co at 3%.

Staffan

Great stuff!