Chris Prack

OK so it finally happened. Last Friday at VIR during the last run session of the day I burned a valve coming onto the front straight. It was obvious to everyone in the paddock that something had happened to my car due to the terrible way that it sounded as it went past at 125 or so and I got out of it.

After tearing it apart the following Monday and finding a sizable chunk of #1 exhaust valve missing, I am now concerned about the condition of my turbine in my turbo. I have not removed it for inspection yet but am fearing/expecting the worst.

So having said that, what is the consensus for an inexpensive, almost stock turbo? I remember seeing something posted about one in particular but am too lazy to dig through the achieves and find the old posts.

Thanks in advance.

Oddjob

Chris,

I burned the #4 exhaust valve on an 89 Turbo about 5 years ago at a track event (was very impressed how fast the car would still go on only 3 cylinders).

Had the same fear about the burned piece of valve blowing out the turbine vanes, so also fearing the worst I pulled the turbo to check.

Nothing wrong with it. The molten metal most likely stuck to some part of the cross over pipe before entering the housing. I had about 90k miles on the car, so sent the turbo off for a precautionary rebuild since it was out of the car.

Definitely worth pulling the turbo to check, but dont spend any money getting a replacement until you know for sure the vanes are damaged.

TonyG

The turbo is OK. Seen it many times. The piece that you see missing wasn't that big when it finally exited. The pieces are much smaller than what you see missing.

Put in new exhaust valves, shim the springs properly, double check for burned lifters, and put her back together with a new full metal 3 piece jacket head gasket.

The question is why did you burn a valve?

And ... what are you gonna do about it? :-)

Chris Prack

I am not buying anything right now. I had originally said I was just going to put it back together and see what happens. It's not like I will create any extra work for myself by doing so. With the exception of the intake there really are not any overlapping components between the head and the turbo so we will see.

I am mostly sure that the valve burned due to worn guides. They are not worn they are smoked. I should have had the head done last December when it was apart last but got impatient and slammed it together and let it eat. A few on this board know me personally and as far as I am concerned it will either go or blow. It has taken it 9 months, 10k miles and 12 track days to blow so I am fine with that. BTW I had used a stock head gasket not even a wide fire and the gasket is totally fine around the fire ring. The valve started to cut the head on the stem past the burnt spot. It was like a blow torch. I got pretty lucky all in all, no damage to the cylinder or head and possibly the turbo is OK as well. The head is at my machine shop and I am replacing all of the guides and valves, intake and exhaust, the springs nd retainers also. I have a new wide fire head gasket and timed valve which I found to be broken as well. I guess it could have contributed to the valve issue but I'm not too sure on this as it didn't feel like it was over boosting...........which reminds me that I had an issue with what felt like the overboost protection kicking in at WOT but if I cycled the key with my foot all the way in it it would run just fine.............ran four track days like that, maybe one too many...........

TonyG

You can pay now or you can pay later..... but as they say... "you will pay...". It's just a question of when.

Do you not have a real boost gauge, a/f gauge (preferrably a wide band 02 setup), or EGT gauge?

If not, then you have no idea of what is going on in there.

Chris White

I have done the burnt valve thing before – my theory is that the typical burnt valve failure is due to a small piece of the usual carbon build up braking loose and ending up between the valve face and seat. This holds the valve open a very small amount creating a very high velocity and high temp leak. Very much like an Acetylene torch!
Carbon build up on the valve heads is pretty much a typical condition due to the rich mixtures run. Carbon also makes for hot spots which are great starting points for melting things.
I know the exhaust temps are typically quite high (1600+ ) on the 951 (I have seen 1700 on my car many times….remember that aluminum starts melting in the 14000 range!)

This is a good example of a popular theory being incorrect – many folks think that running too rich does not have any serious drawbacks. The associated carbon build up is a bad thing! If you are going to run it hard make sure that the mixtures are right where they should be, between 12-1 and 12.5-1