How much boost can a 951's engine handle? Just had a head gasket go and the P.O. of my car put an aftermarket chip in there, and was trying to evaluate that as a possible cause.

 

I ran 18psi on k26/6 for a long time.
If it was running lean that could be an issue - what chips/boost?
Was it pinging at all or were you having any other issues?

 

Overheating -- one of the fans was broken. But I'm not sure if the overheating was the cause or the effect of the head leaking and losing coolant, etc...

 

Not sure exactly how much boost it's set for, but I can get up to the 2 bar end of the stock boost gauge under full accel. I think I got the overboost protection once, as well.

 

How long were you driving it after you think the gasket blew?
Was it overheating for a while before you had an issue?
Overheating = bad.

 

Not sure...it was overheating, so then I took it in to the shop, fan was broken and very little coolant, so fan was fixed and coolant restocked, and it continued to run through coolant, so I took it back and they found a bad head. I'm told there's no permanent damage, but i want to make sure it doesn't happen again. If it was the fan that broke and I let it get too hot, then that's one thing, but if a chip causing too much boost led to the overheating/loss of coolant and the resulting temperature fluctuations (not ameliorated by the fan switch breaking and causing more severe overheating), then I want to turn the boost down.

 

Is there a boost controller in the car, or is it still using the stock cycling valve?
Do you know what brand of chips they are?

The only way to raise boost in a car with the cycling valve still in place is with a jetted banjo bolt - a restricter in the bolt that holds the line from the hard pipe to the cycling valve - it makes the cyclic valve see less air to make it hold slightly higher boost. But these still don't raise boost to dangerous levels when used with the right chip.

If your car does have a boost controller and you have no boost gauge other than stock, then you might have an issue...

 

I *think* it's a KLR chip. The P.O. was a chief tech at a Porsche dealership, so I'm doubtful that this is it, but I'm trying to cover my bases.

No boost controller.

 

The KLR is one of the computer boxes - along with the DME.
It is possible that the additional boost could be a cause, but I believe it is unlikely.
If it were running too hot I would point my finger towards possible causes of overheating...

 

Thanks for the input...any other opinions? Likely will give the P.O. a ring to get my facts straight on the chip.

 

chip would most likely make it run rich. I would say if your fan was junk and it was getting hot, that would be the cause. Running too hot can warp the head slightly and blow the gasket out esp when coupled w/ boost pressure.

 

That isn't accurate, The Welt chips, for example, raise the boost to ~1bar, by reprograming the KLR chip. It still uses the cycling valve and no boost controller. The boost of ~1bar is the max that can be achieved by this method, since the KLR is capable of sensing a higher boost. But again this is hardly a dangerous boost level if everything else is ok.

 

It's probably good to 40 PSI at least once.

lol, IIRC I think it was Lart who was running at 21..

 

I have the Weltmeister kit and just tested the boost pressure with a precision gauge. It would spike to 1.1 bar gauge pressure then come back down to 1 bar gauge pressure.

After you get the car running again maybe you should dyno it and have them trend boost pressure to see where you are.

Lou

 

Isn't Lart running water injection too though? That'll make a huge difference to the boost you can run.

Most people seem to go with 16-18 on aftermarket chips. I think only Danno (Guru chips) was the only one saying 18 and just about all the other ones suggest 16 unless you put race gas in. Of course you could spend a huge amount of time tuning it and run 26-30 like Special Tool does, but he's a bit different then most.