dholling13

I just took the car out for a few runs, and mashed the gas in 3rd gear and the boost pressure didn't surge over (bear in mind this is an analog gauge) 15.5 psi's. As it turns out, the boost creep is in the mid-range and as the rpm's continue to rise after 4.7k or so, the boost pressure levels itself out and never surges like I was afraid of!!!

Before this last test run, the boost pressure just kept rising and rising and I was scared to over-boost the car. But since changing the spring, I guess my problem is solved. So all of you cat bypass pipe owners, if you go with a set of headers, make sure you lower your boost pressure. In conclusion, I have a tial gate with a .7 bar spring, b&b headers, and both cats removed. The car sees one bar of boost with this set up...

Megatron-UK

Would going with a ball and spring type boost controller or electronic controller not be easier in this sort of case? They're trivial to turn down the boost if spikes are seen - much cheaper than a wastegate and changing springs of different strength.

dholling13

Yes, I agree they would be, and I went that route to begin with. We installed a .7 bar spring and manual controller with the notion that we could dial the boost in. But, the car saw almost 1 bar with out any help from the controller. In the future a .5 bar spring would be the way to go with a controller... However, Profec's and other digital controllers are a completely different beast to install.

NineMeister

My educated guess is that the wastegate take-off pipe from the header, right under the turbo flange, is welded on at less than 90 degrees . This causes the exhaust flow to prioritise the turbo rather than the wastegate, hence the overboost. A simple solution, rather than replacing the pipe at the correct angle, would be to cut out the lower section of the joint and weld in a fillet piece cut from a section of 1 3/4 pipe. We have done this in the past to rectify the same issue on GHL headers as well.

dholling13

Do you have to remove the headers to do this?

NineMeister

Yes, there is cutting and welding involved so the lhs header section will need to be removed. Unfortunately I cannot find a photo of the modification we did to the GHL headers that had the same fault.

Miles965uk

maybe take the boost reading from downstream of the trottle, the same hose that goes into the EZ69 and then see what boost you are getting.

dholling13

This is directed at Colin,

I looked under the car, and you are right about the wastegate pipe not meeting the headers at a true 90 degree point. I plan on changing my turbo to a high flow unit in the next few weeks, when the shop does this I'll have them pull the left side header and add more diameter to the wastegate pipe weld. Thanks for the input. I'll post pictures in February.

If anyones' interested in my stock k27, I'll let it go for $400. It works great as it has caused my car to over boost over and over again

Drew

Staffan

Yes, this is where you should start I think.
It looks like you measure boost at the IC and that your pressure switch is at the stock location (at the IC). From my experience the pressure in the IC and manifold could differ in certain situations (perhaps due to a not perfect working BOV), creating spikes in the IC triggering the pressure switch.

My EZ69 is connected to the manifold (but I am not sure all cars get there pressure for the EZ69 from the same place), I put a T-connection at this hose where I measure boost. At the same hose I have another T-connection where a stock pressure switch is mounted. So my boost gauge and pressure switch reacts on true manifold pressure, not IC pressure. Before having this setup my pressure switch could kill the engine in middle of corners at the track, very scary indeed.

It could of course be other explanations for your overboost such as problems with the BOV, wastegate and header construction but by comparing IC pressure and manifold pressure you could outrule problems with a pressure spikes in the IC.

dholling13

Miles,

How did you mount a boost kill or pressure switch in the manifold? Could you shoot me some pictures?

Drew

cobalt

Like others have said i am not so sure this is your problem. I have the same design headers on my car and I have absolutely no issues with over-boosting so why should the design work on my car and not yours. I am also running a HF K27 and 1 bar spring and I have the same andial gage.

I think your problem lies elsewhere

dholling13

Anthony,

The car hasn't over-boosted since we installed the .7 bar spring, but I am curious to see what other c2 turbo owners have experienced or what ideas they may have. Do you have a cat or muffler bolted up to your high flow?

Drew

cobalt

I do have a cat but no muffler. This may be what is keeping my car in check but I know of others that are not running cats with mufflers that are not having issues.

Miles965uk

Drew,
The pressure switch Staffan is on about is the fuel cut off switch, which should cut the fuel pumps if boost goes above 1.2-1.4bar (ish). I gather this isnt your issue.
Your intercooler boost pressure will show higher than manifold, due to the throttle blocking flow etc. So you may not be getting the correct reading- i.e a too high of one. Besides as Staffan says its more accurate to have it at the manifold as your timing etc is done with this to.
That T-piece you have coming from the left of the IC I assume that is going to your boost guage? If so disconnect that and put the T-peice inbetween the black pipe that comes out of the EZ, which is just up on the left from the IC, you will see a black pipe that goes into the manifold. Hook it up there and see what pressures you get.

Also if you think its the WG how about take the thing completely off and drive it to see how much boost youll get- that will eliminate that.

JamesE

I had a problem with GHL's (as refered to by Colin), not sure whether it was the increase in pipe diameter or alterations to the angle, but it fixed the problem.