Head gasket triva - Pics
04-23-2007, 03:21 AM
#16
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Originally Posted by KuHL 951
Personally I wouldn't use the OE studs twice on a Turbo. They are designed to stretch once only and shouldn't be used again. You might get away with it on a NA, but not a 951. Is there any chance that the HG had blown before making this one the 3rd time they were torqued? You just can't get the same clamping pressure to prevent head lift under boost unless you use studs like ARP or Raceware designed for reuse. Needless to say, buy new studs for the repairs. You also might look into the Lindsey Racing steam vent kit to prevent that hot spot on #4.
Hosrom is dead on with the AFR.
04-23-2007, 03:29 AM
#17
hum...can't talk from personal experience, but a very well-known tuner recommends not going over 11.8:1 ratio at WOT...yes you can go higher but you have no safety margin. personally, i'll be following his recommendations 
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04-23-2007, 03:51 AM
#18
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Originally Posted by 9fitty1
I disagree. I have re-used the stock studs and nuts multiple times on 951s with no problems at all. A good friend of mine works at a highly respected Porsche Speed Shop and he has re-used the factory studs and nuts as well on countless headgasket jobs, no problems. I do understand the theory behind it and would not advise re-using on a highly modded motor, but in practice all has been well. I'd also like to mention that most of the cars that go through my buddy's shop live at the track.
Hosrom is dead on with the AFR.
Hosrom is dead on with the AFR.
Me too I am currently using my old studs and nuts up to 23psi.
04-23-2007, 06:57 AM
#19
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I put a rebuilt head on my '86 951 and reused the factory studs. That was almost 2 years ago. Since then I've done about 10 autox's and 4 DE's and been daily driving the car at 15psi, hitting full boost daily. No problems so far.
When tightening the head nuts I went slightly tighter than the factory manual dictates.
When tightening the head nuts I went slightly tighter than the factory manual dictates.
04-23-2007, 08:36 AM
#20
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I re-used the factory studs twice, the first time i removed the head gasket, there was a wide fire gasket in there, meaning somone replaced the head as well, so that's three times.
Special tool re-used his four times, and that is not including what the PO (or the person before him) replaced it.
Porsche was right to go for stretch type studs, unless you have a track car pushing timing and boost, the aftermarket studs would be a better choice.
Now, when replacing the head gasket, it would be better to replace the nuts and washers, as well as to get a die kit and chase the threads on the studs. A lot of crap came off the studs when i did that, no matter how i got the threads cleaned up, the die got rid of so much dirt/crap you can't see.
Rich: Do you mind telling me what was the torque you put on the head?
Special tool re-used his four times, and that is not including what the PO (or the person before him) replaced it.
Porsche was right to go for stretch type studs, unless you have a track car pushing timing and boost, the aftermarket studs would be a better choice.
Now, when replacing the head gasket, it would be better to replace the nuts and washers, as well as to get a die kit and chase the threads on the studs. A lot of crap came off the studs when i did that, no matter how i got the threads cleaned up, the die got rid of so much dirt/crap you can't see.
Rich: Do you mind telling me what was the torque you put on the head?
04-23-2007, 10:13 AM
#22
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What boost level were you running? What octane?
Regardless 12.5 AFR at WOT/boost is a bit lean, 11.8:1 is where you want to run.
Regardless 12.5 AFR at WOT/boost is a bit lean, 11.8:1 is where you want to run.
04-23-2007, 10:33 AM
#23
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Originally Posted by lart951
I have heard different reasons of why the #4 cyl fails, many said head desing, anothers claim air bubble is trapped in the back of the head and ultimately some think that it's a flaw in certain series of blocks. I blew 3 head gaskets months apart each on my 1st engine in my current 951, in the last blown headgasket I replaced the WF HG with the cometic MLS and in less than a month I had broken a ring thus damaging my block beyond repair. I never ran more than 17psi in my previous setup. I strongly believe that my block was flawed, Chris White a well known builder among listers said once that he believed that certain blocks might have been flawed by factory by a certain factor that remain a mistery until today, in another words certain blocks are cursed.
To put my previous setup into contrast I use 21psi daily for the last 3 years, I have ran up to 23psi and my a/f ratio has gone as high as 13:1 for a second but I also used 10-20% xylene depending upon boost level. But I have a different block and head also.
To put my previous setup into contrast I use 21psi daily for the last 3 years, I have ran up to 23psi and my a/f ratio has gone as high as 13:1 for a second but I also used 10-20% xylene depending upon boost level. But I have a different block and head also.
We had discussed this at length awhile back and no 4 is is the hottest running cylinder, there is serious heat buildup there . your other engine last because you are not running straight 93 octane. If adjusted correctly you will not have any issues, a good start is to lower the normal operating water temp . By running the engine at 11.5 this has the same effect of lower the combustion temperature , the key is to get the operating temps down as 93 is very susceptible to knock with the higher temperatures ...
As you discovered going to a harder gasket will not solve the problem. I have never seen the need for better than stock gaskets if combustion is properly controlled, i would prefer to O-ring the block
04-23-2007, 10:37 AM
#24
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Originally Posted by Chris White
The original poster did not note what boost level he was running....time to 'fess up!
04-23-2007, 10:58 AM
#25
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David, with the version of the software you are running you should not exceed 15psi on 93 oct. If you want to run 16psi, you should (at least) use FQS 4-7 to pull some timing out.
04-23-2007, 11:34 AM
#27
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Originally Posted by 9fitty1
I disagree. I have re-used the stock studs and nuts multiple times on 951s with no problems at all. A good friend of mine works at a highly respected Porsche Speed Shop and he has re-used the factory studs and nuts as well on countless headgasket jobs, no problems. I do understand the theory behind it and would not advise re-using on a highly modded motor, but in practice all has been well. I'd also like to mention that most of the cars that go through my buddy's shop live at the track.
Hosrom is dead on with the AFR.
Hosrom is dead on with the AFR.
This has been an interesting topic. I noticed my #4 had the worst carbon build by far but no HG issues. I was hoping for a better condition on the spare motor I'm refreshing. Unfortunately for only 91K miles it's got issues that I wouldn't have expected from a car that ran well before it crashed.
04-23-2007, 01:37 PM
#28
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The Lindsey Racing steam vent kit addresses the problem with the number 4 cylinder. Here is a link to the page that explains it LR steam vent
I built a 2.8L with a lindsey racing super 75 turbo, I RE-USED the stock head studs. I went to the track ran it at 23psi hand hammered on it for two days in the summer heat, nothing happened. I have the LR steam vent kit, wether or not nothing happened because of the steam vent is up to you, but for me the chance it might help was worth the 39$.
I built a 2.8L with a lindsey racing super 75 turbo, I RE-USED the stock head studs. I went to the track ran it at 23psi hand hammered on it for two days in the summer heat, nothing happened. I have the LR steam vent kit, wether or not nothing happened because of the steam vent is up to you, but for me the chance it might help was worth the 39$.
04-23-2007, 03:00 PM
#29
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Originally Posted by Tms951
The Lindsey Racing steam vent kit addresses the problem with the number 4 cylinder. Here is a link to the page that explains it LR steam vent
I built a 2.8L with a lindsey racing super 75 turbo, I RE-USED the stock head studs. I went to the track ran it at 23psi hand hammered on it for two days in the summer heat, nothing happened. I have the LR steam vent kit, wether or not nothing happened because of the steam vent is up to you, but for me the chance it might help was worth the 39$.
I built a 2.8L with a lindsey racing super 75 turbo, I RE-USED the stock head studs. I went to the track ran it at 23psi hand hammered on it for two days in the summer heat, nothing happened. I have the LR steam vent kit, wether or not nothing happened because of the steam vent is up to you, but for me the chance it might help was worth the 39$.
A little off topic but how do you like that Super 75 on your 2.8L? Any dyno charts? Im about to pull the trigger on a Super 61 but I would be interested to hear what 1 more person has to say about a Super 75 on a 2.8L.
04-23-2007, 03:16 PM
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Originally Posted by Andial951
Thanks for the heads up on the steam vent kit.
A little off topic but how do you like that Super 75 on your 2.8L? Any dyno charts? Im about to pull the trigger on a Super 61 but I would be interested to hear what 1 more person has to say about a Super 75 on a 2.8L.
A little off topic but how do you like that Super 75 on your 2.8L? Any dyno charts? Im about to pull the trigger on a Super 61 but I would be interested to hear what 1 more person has to say about a Super 75 on a 2.8L.