M Danger

Hmmmm, I cant help but try and guess at this so...

As to the Blown HG and low boost.
I have heard of the Double walled cross over pipe collapesed , as i have heard they can do,... and caused too much pack pressure blowing the HG and keeping the boost low afterwards???

M Danger

anyone?

2bridges

sound unlikely to me. Excess backpressure would cause low power and reduced boost, but would force exhaust back into combustion charge and power would brop.... but I don;t think it would cause a spike or increase in comustion pressures

Duke

Excessive backpressure can result in spiking.

M Danger

Even if it happened under full boost? The PPO said the Blown HG and low boost happened at the same time

2bridges

I guess I am not familiar with the "colapsing" issue you speak of, but for it to creat a combustion spike, I would think is would have to be very significant backpressure change.

Wouldn't the vaccum/backpressure/CV safety - relationship should still be in check in event of backpressure change. As such I question how anything but a large change in backpressure could spike combustion pressures enough to blow head gasket....... just doesn't wash to me

M Danger

well it was just one idea, trying to figure out why the combo of low boost and Blown HG

2bridges

Good thought I think. is CV removed?

ehall

It would contribute to backpreasure, which in turn will increase EGT's and heating. It will definitely effect power, and the excess heat could potentially exascerbate a weak situation. I don't know that it would be the only direct cause but it could be a good piece of the puzzle. Are you running an aftermarket chip, boost controller, or other modifications from stock? If so, these mods, without proper tuning and monitoring can add up to a further unstable situation as you air/fuel ratio may also be off. There are a number of variables, but do get rid of that old exhaust. BTW, it may just be a clogged catalytic converter. I'd be surprised if it was the exhaust tubing itself. A clogged cat really kills power and creates a HELL of a lot of heat.

M Danger

Ok heres the deal on it, 3" turbo back, k29-8 turbo, Guru chips, Tial 38mm WG, EBC, boost and A/F meter
Doesnt apper to have any kind of exhaust leak, I think the CV is good, most all New Vac lines. WG works fine

ehall

Were these guru chips programmed for the k29/8. You might want to do a search on guro and a guy named Danno.
Do you still have the original cat on this exhaust or was the cat removed and /or replaced? What did you A/F meter read when the head gasket blew? An exhaust leak as opposed to an exhaust collapse or clog is comparatively a good thing, depending on whether or not it is after the turbo.
Based on your list, there are a lage number of potential places to start. By and large it is usually a problem with the interaction of the total system. BTW isn't the lag on the k29/8 pretty significant on a 2.5L engine?

ehall

BTW shouldn't the cv be bypassed with the combo that you are running? EBC, chips

M Danger

all this was done BY the PPO, Im trying to fix it, supposedly Danno did program the chips for it.

I just im trying to not have to go through every single thing just to find it was just a tiny like problem.

Like the time my other 951 simply had the plugs gapped to small

SchnellerUmsetzer

The DME has a saftey that would prevent such stuff if the car is still stock. Porsche Workshop manuel Section 28 Page 30!

Bill

What does the failure in the head gasket look like? Is the sealing ring burned through? This would indicate lean AFR/excessive combustion temps. Like ehall says, excessive back pressure can and will increase combustion temps.

A head gasket can also fail from poor head to block seal. If you see an "oval or egg shape" ring in the head gasket, you lost your torque on the head gasket. If you loose the clamping force (or torque) on your headgasket, the combustion pressure will "push" out the seal ring causing the failure. You can loose head stud torque over time with the continual heat cycling of the engine. You can loose torque if the head or block mating surface warps. For a head gasket to hold up to the high combustion pressues in a turbo motor, it needs to be "clamped down" properly. This is the purpose of a o-ringed head, to provide additional clamping force to the head gasket combustion seal rings.

You say that your turbo was not producing boost, so it does not make sence that there would be an overboost condition. And as SchnellerUmsetzer noted, the factory did a pretty good job providing for overboost protection. Over boost could also push the seal ring "oval or egg shaped" though.

Inspect the head gasket carefully for your clues.

Also remember, low boost and a failed head gasket CAN be totally independent issues that have no impact on each other. So fixing your head gasket issue could possibly not solve your boost issue, and vice versa.