HEADGASKET dissertation...
09-24-2002, 06:59 AM
#1
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Thread Starter
HEADGASKET dissertation...
Ok, after seeing several concerns posted about headgaskets:
"The jist was that the widefire was NOT meant to be used in conjunction with the o-ring procedure. A copper gasket was recomended. "
"When we rebuilt the head on my 951 this summer, we did not use a wide fire head gasket. Do you feel that I am going to be taking a significant risk by installing the kit knowing this?"
I figured I'd investigate this phenomenon a little closer. But first, let's compare the differences between the standard headgasket and the wide fire-ring model:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-Compare.jpg" alt=" - " />
As you can see, the wide fire-ring gasket's compression-ring is really only wider on the bottom where it rests on the top of the cylinders. The part on top that's against the head is pretty much the exact same width. Additionally, the really important part, the surface that's facing the combustion chamber, is EXACTLY the same 0.1mm thick (or thin) wall of steel.
Having blown up 2.5 headgaskets in the last TWO years alone, I had enough wasted evidence laying around to examine. So I pulled my three headgasket trophies off the wall and took a closer look at them. The following is my forensic analysis of the situation...
Here's photos of my first headgasket failure; the original 15-year old standard headgasket. Also, I fried my <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=006601" target="_blank">second headgasket</a> (a wide fire-ring) at the <a href="http://www.opentrackchallenge" target="_blank">Open Track Challenge</a> earlier this year:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-FailureCompare.jpg" alt=" - " />
Now from analyzing the failure points and tearing apart the remains, I find there's a dramatic difference in the way these two headgaskets are constructed. The original/standard headgasket uses a rolled & looped compression-ring like what you find used on the crossover pipe flanges and the turbo. The wide fire-ring headgasket on the other hand, has a simple open-ended U-shaped wrap:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-crosssection.gif" alt=" - " />
We actually need to go into WHY a headgasket fails in the first place. Contrary to what you may think, it's not combustion-pressure that 'blows' out a headgasket, but rather it is 'burned' from the intense heat of detonation resulting from too-lean of an air-fuel mixture. If you refer back to the <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=006601" target="_blank">close-up photos of my second headgaket failure</a>, only one of the compression-rings was pushed aside, but all of them were destroyed by being burned. It may just happened coincidentally that the #4 compression-ring was heated up so much, that it melted and was then pushed aside by combustion pressure.
Which brings up an interesting comparison of failure rates and life-expectancy. My wide fire-ring headgasket lasted roughly a year-and-a-half, yet my original headgasket lasted 15-years!!!. I've also known a tuner or two who have blown up several wide fire-ring headgaskets just weeks apart! If you refer to the cross-sectional diagram above, the compression-ring of the standard headgasket completely forms a loop with the ends meeting. This gives it a second barrier to combustion once the first one has been burned through.
So what can we do? One of the first suggestions is to O-ring the head, and/or the block. Here's a comparison of the two methods:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-OringCompare.gif" alt=" - " />
The grooves are typically cut such that the O-ring only protrudes about 0.1-0.2mm above the surface of the head. This then compresses the compression ring somewhat. Cutting a groove opposite the O-ring provides for a second gripping junction. HOWEVER... this only serves to stake and pin the compression ring into place. IT DOES NOTHING to combat the real cause of failure to begin with; the intense heat from detonation due to lean air-fuel ratios. In which case, it doesn't really matter whether there's an O-ring pinching the middle of the compression-ring at all, once the 0.1mm-thick layer facing the combustion chamber is burnt through, that's it!. Again, refer to the <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=006601" target="_blank">close-up photos</a>. O-ringing may have helped keep one compression-ring in place, but most likely the combustion-gasses would've burnt through the fibre center of the gasket anyway even if the top and bottom surfaces of the compression-ring was staked in place. And O-ringing wouldn't have done anything for the other three cylinders that had their compression-rings burnt, yet they stayed in place. That's why high-end tuners like Garrity or Scott Gomes don't even bother with O-ringing a headgasket at all, they just focus their attention on gettting a flat and safe air-fuel ratio and the headgasket will be fine.
Well, what about cooper heagaskets? I believe they solve a completely different problem that what we face. They are for the extreme cases of turbocharging where combustion pressure can and does blow out a headgasket. This occurs in dragsters and high-boost import cars like SupraTTs running 35-45psi of boost. Yes, that's right, 35-45psi of boost. Or the mid-'80s Formulae-1 Turbo-Monsters with 50-55psi of boost even. In these cases, a copper headgasket makes sense.
But putting one on 951 that blew a standard or wide fire-ring headgasket is just masking the real problem and moves the failure to the next weakest link, like your pistons or valves or con-rods. Failure of those components will DEFINITELY be more catastrophic and costly to repair. So if you've blown a headgasket, definitely put your car on the dyno after you've replaced your headgasket and get an air-fuel ratio plot. Make sure it doesn't have a super-rich mid-range that gets dangerously lean in the high-end. Like these popular chips:
<a href="http://boards.rennlist.com/upload/DanWorleyK27Stg2Chips.jpg" target="_blank">AutoThority Stg.2</a> (Dan Worley's)
<a href="http://boards.rennlist.com/upload/Adrial-dyno2low.jpg" target="_blank">AutoThority Stg.2</a> (Adrial's)
<a href="http://www.gururacing.net/images/Dyno020706-TQcompare.jpg" target="_blank">EuroProducts</a> (look at the 'begin AFR' light-blue line)
After examining the after-the-fact data provided by others, I've come to the conclusion that my wide fire-ring headgasket failure was due to an overly-lean high-RPM mixture caused by the AutoThority Stg.2 chips I had @ 15psi. While I hadn't dyno-tested the car, I'm going to assume the my air-fuel ratio looked similar to Dan Worley's and Adrial's above. Combined with 115 degrees-F Nevada desert heat and an idiotic co-driver, this failure was to be expected. Famous quote:
"The car would zip right up to 7000rpm coming out of the corners and there wasn't anything I could do about it!" <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />
"The jist was that the widefire was NOT meant to be used in conjunction with the o-ring procedure. A copper gasket was recomended. "
"When we rebuilt the head on my 951 this summer, we did not use a wide fire head gasket. Do you feel that I am going to be taking a significant risk by installing the kit knowing this?"
I figured I'd investigate this phenomenon a little closer. But first, let's compare the differences between the standard headgasket and the wide fire-ring model:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-Compare.jpg" alt=" - " />
As you can see, the wide fire-ring gasket's compression-ring is really only wider on the bottom where it rests on the top of the cylinders. The part on top that's against the head is pretty much the exact same width. Additionally, the really important part, the surface that's facing the combustion chamber, is EXACTLY the same 0.1mm thick (or thin) wall of steel.
Having blown up 2.5 headgaskets in the last TWO years alone, I had enough wasted evidence laying around to examine. So I pulled my three headgasket trophies off the wall and took a closer look at them. The following is my forensic analysis of the situation...
Here's photos of my first headgasket failure; the original 15-year old standard headgasket. Also, I fried my <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=006601" target="_blank">second headgasket</a> (a wide fire-ring) at the <a href="http://www.opentrackchallenge" target="_blank">Open Track Challenge</a> earlier this year:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-FailureCompare.jpg" alt=" - " />
Now from analyzing the failure points and tearing apart the remains, I find there's a dramatic difference in the way these two headgaskets are constructed. The original/standard headgasket uses a rolled & looped compression-ring like what you find used on the crossover pipe flanges and the turbo. The wide fire-ring headgasket on the other hand, has a simple open-ended U-shaped wrap:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-crosssection.gif" alt=" - " />
We actually need to go into WHY a headgasket fails in the first place. Contrary to what you may think, it's not combustion-pressure that 'blows' out a headgasket, but rather it is 'burned' from the intense heat of detonation resulting from too-lean of an air-fuel mixture. If you refer back to the <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=006601" target="_blank">close-up photos of my second headgaket failure</a>, only one of the compression-rings was pushed aside, but all of them were destroyed by being burned. It may just happened coincidentally that the #4 compression-ring was heated up so much, that it melted and was then pushed aside by combustion pressure.
Which brings up an interesting comparison of failure rates and life-expectancy. My wide fire-ring headgasket lasted roughly a year-and-a-half, yet my original headgasket lasted 15-years!!!. I've also known a tuner or two who have blown up several wide fire-ring headgaskets just weeks apart! If you refer to the cross-sectional diagram above, the compression-ring of the standard headgasket completely forms a loop with the ends meeting. This gives it a second barrier to combustion once the first one has been burned through.
So what can we do? One of the first suggestions is to O-ring the head, and/or the block. Here's a comparison of the two methods:
<img src="http://www.gururacing.net/ImagesMisc/Headgasket-OringCompare.gif" alt=" - " />
The grooves are typically cut such that the O-ring only protrudes about 0.1-0.2mm above the surface of the head. This then compresses the compression ring somewhat. Cutting a groove opposite the O-ring provides for a second gripping junction. HOWEVER... this only serves to stake and pin the compression ring into place. IT DOES NOTHING to combat the real cause of failure to begin with; the intense heat from detonation due to lean air-fuel ratios. In which case, it doesn't really matter whether there's an O-ring pinching the middle of the compression-ring at all, once the 0.1mm-thick layer facing the combustion chamber is burnt through, that's it!. Again, refer to the <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=15&t=006601" target="_blank">close-up photos</a>. O-ringing may have helped keep one compression-ring in place, but most likely the combustion-gasses would've burnt through the fibre center of the gasket anyway even if the top and bottom surfaces of the compression-ring was staked in place. And O-ringing wouldn't have done anything for the other three cylinders that had their compression-rings burnt, yet they stayed in place. That's why high-end tuners like Garrity or Scott Gomes don't even bother with O-ringing a headgasket at all, they just focus their attention on gettting a flat and safe air-fuel ratio and the headgasket will be fine.
Well, what about cooper heagaskets? I believe they solve a completely different problem that what we face. They are for the extreme cases of turbocharging where combustion pressure can and does blow out a headgasket. This occurs in dragsters and high-boost import cars like SupraTTs running 35-45psi of boost. Yes, that's right, 35-45psi of boost. Or the mid-'80s Formulae-1 Turbo-Monsters with 50-55psi of boost even. In these cases, a copper headgasket makes sense.
But putting one on 951 that blew a standard or wide fire-ring headgasket is just masking the real problem and moves the failure to the next weakest link, like your pistons or valves or con-rods. Failure of those components will DEFINITELY be more catastrophic and costly to repair. So if you've blown a headgasket, definitely put your car on the dyno after you've replaced your headgasket and get an air-fuel ratio plot. Make sure it doesn't have a super-rich mid-range that gets dangerously lean in the high-end. Like these popular chips:
<a href="http://boards.rennlist.com/upload/DanWorleyK27Stg2Chips.jpg" target="_blank">AutoThority Stg.2</a> (Dan Worley's)
<a href="http://boards.rennlist.com/upload/Adrial-dyno2low.jpg" target="_blank">AutoThority Stg.2</a> (Adrial's)
<a href="http://www.gururacing.net/images/Dyno020706-TQcompare.jpg" target="_blank">EuroProducts</a> (look at the 'begin AFR' light-blue line)
After examining the after-the-fact data provided by others, I've come to the conclusion that my wide fire-ring headgasket failure was due to an overly-lean high-RPM mixture caused by the AutoThority Stg.2 chips I had @ 15psi. While I hadn't dyno-tested the car, I'm going to assume the my air-fuel ratio looked similar to Dan Worley's and Adrial's above. Combined with 115 degrees-F Nevada desert heat and an idiotic co-driver, this failure was to be expected. Famous quote:
"The car would zip right up to 7000rpm coming out of the corners and there wasn't anything I could do about it!" <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" /> <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />
09-24-2002, 10:10 AM
#2
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I think Danno is right. I have been using 20 - 22 psi all summer on a widefire with no 'O' ring. I have about 2-3% leakdown on all 4.
The fuel curve is safe and I use 100 ocatane if I want to run 22 psi all day.
Alan
The fuel curve is safe and I use 100 ocatane if I want to run 22 psi all day.
Alan
09-24-2002, 10:26 AM
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another case of required reading <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Lean A/F's will cause havock with a lot more than just headgaskets...
Maximum Boost by Mr. Bell isn't too shabby either for those tinkerers (sp?)
Lean A/F's will cause havock with a lot more than just headgaskets...
Maximum Boost by Mr. Bell isn't too shabby either for those tinkerers (sp?)
09-24-2002, 10:36 AM
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Danno, thanks for the post.
But this part is news to me:
[quote]Originally posted by Danno:
<strong>That's why high-end tuners like Garrity or Scott Gomes don't even bother with O-ringing a headgasket at all... </strong><hr></blockquote>
Scott Gomes O-ringed mine - he suggested it fairly strongly.
But this part is news to me:
[quote]Originally posted by Danno:
<strong>That's why high-end tuners like Garrity or Scott Gomes don't even bother with O-ringing a headgasket at all... </strong><hr></blockquote>
Scott Gomes O-ringed mine - he suggested it fairly strongly.
09-24-2002, 10:42 AM
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Nice post Danno, kinda firms up what I felt about chip upgrades, never trusted them to look after the A/F correctly.
Someone I know showed me a blown gasket and burned valve, I asked if the car was chipped and sure enough it was one of the ones you mentioned.
I have heard of 20+ being run on stock gaskets for long periods and no failures. simply by keeping the mixture right.
Thanks for the info.
Someone I know showed me a blown gasket and burned valve, I asked if the car was chipped and sure enough it was one of the ones you mentioned.
I have heard of 20+ being run on stock gaskets for long periods and no failures. simply by keeping the mixture right.
Thanks for the info.
09-24-2002, 10:52 AM
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While I did see some cool looking blocks with BIG grooves in the tops of the cylinder walls at Garrity's shop, I'm pretty sure Danno's meaning is that he uses the O-ringing with copper gaskets to pin the gasket in place for BIG boost motors, not for headgasket longevity on more stock applications.
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09-24-2002, 01:42 PM
#9
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Thanks Danno. As usual you keep adding to my Porsche knowledge <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />
This makes me feel good about my decision to use the factory gasket again. Let's hope I don't screw this one up!
-R.B.
This makes me feel good about my decision to use the factory gasket again. Let's hope I don't screw this one up!
-R.B.
09-24-2002, 01:58 PM
#11
Nordschleife Master
is it safe to run the o2 sensor to the computer if you have a gauge on the line........ or is the difference in voltage so minute that it doesn't affect the signal?
09-24-2002, 02:05 PM
#12
Great post Danno <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />
So in the end, witch gasket should most people use?
Does this mean the wfr gasket blows faster then a stock one under hard detonation? And if it does, do you think it's better to use the wfr gasket to keep the piston and rings from bursting?
It's much cheaper changing the head gasket then the pistons right.
IMO having a head gasket warning you that you are running to lean / to hot is really nice when compared to a blown motor.
So in the end, witch gasket should most people use?
Does this mean the wfr gasket blows faster then a stock one under hard detonation? And if it does, do you think it's better to use the wfr gasket to keep the piston and rings from bursting?
It's much cheaper changing the head gasket then the pistons right.
IMO having a head gasket warning you that you are running to lean / to hot is really nice when compared to a blown motor.
09-24-2002, 02:18 PM
#13
Race Director
Thread Starter
"Great post Danno <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" /> "
Why thank you! <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" /> Ok, I may have been a little cursory with my 'hi-end tuner' remark. The impression I got from them was that O-ringing a wide fire-ring headgasket doesn't do a whole lot. And they both were pushing copper headgaskets. But due to the lower compressibility of a copper headgasket, leaks can occur if you don't have perfectly matching block & head surfaces. Putting in a tongue & groove O-ring will deform the gasket into a 3-D structure to provide a seal in the event there's a gap along the mating surface somewhere. A copper headgasket also requires a special anaerobic sealant as well.
"Danno, what is the voltage range of the A/F meter, 0-1v ?"
Yes, but here's our target range:
When cold, you want to monitor from 0.96-0.99v and when it's fully warmed up, you want to cover 0.81-0.87v. This completely encompasses the too-lean end at about 13.0:1 all the way to too rich at 11.0:1 (under WOT). As you can see, this falls inside the resolution of one or two LEDs on those air-fuel monitor gauges.
You CAN make an air-fuel gauge that uses these types of O2-sensors if you use a micro-controller with 1-millivolt accuracy and program in a look-up table of voltage vs. air-fuel ratio.. But you'd also need to monitor exhaust-gas temperature in order to know how much to shift the table up and down to compensate. Martin Taylor in NZ was going to build one of these units, but I guess there wasn't much interest.
"is it safe to run the o2 sensor to the computer if you have a gauge on the line........ or is the difference in voltage so minute that it doesn't affect the signal?"
It should be fine since the air-fuel monitor gauge (if designed well) will use a high-impedance tap to prevent draining the signal. Although the factory did use a shielded coax cable, so interference may be an issue. So keep the wires to your guage as short as possible.
"So in the end, witch gasket should most people use?"
"So Danno, are you impling you like the factory gasket better? That's what I think I'm reading....."
Well, I think either one would work fine as long as you keep your air-fuel ratio within check. That's because they both have the same thin layer of steel facing the combustion chamber. Although it may appear the standard headgasket has a secondary back wall to the compression-ring once the first one goes. But I'm not sure how strong that rolled overlap is, and combustion pressure may just leak under the compression-ring once the front face goes.
My next headgasket will be a copper one! Now that I've got my air-fuel ratio dialed in (or easily dialed-in), let's turn up the boost !!! <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />
Why thank you! <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" /> Ok, I may have been a little cursory with my 'hi-end tuner' remark. The impression I got from them was that O-ringing a wide fire-ring headgasket doesn't do a whole lot. And they both were pushing copper headgaskets. But due to the lower compressibility of a copper headgasket, leaks can occur if you don't have perfectly matching block & head surfaces. Putting in a tongue & groove O-ring will deform the gasket into a 3-D structure to provide a seal in the event there's a gap along the mating surface somewhere. A copper headgasket also requires a special anaerobic sealant as well.
"Danno, what is the voltage range of the A/F meter, 0-1v ?"
Yes, but here's our target range:
When cold, you want to monitor from 0.96-0.99v and when it's fully warmed up, you want to cover 0.81-0.87v. This completely encompasses the too-lean end at about 13.0:1 all the way to too rich at 11.0:1 (under WOT). As you can see, this falls inside the resolution of one or two LEDs on those air-fuel monitor gauges.
You CAN make an air-fuel gauge that uses these types of O2-sensors if you use a micro-controller with 1-millivolt accuracy and program in a look-up table of voltage vs. air-fuel ratio.. But you'd also need to monitor exhaust-gas temperature in order to know how much to shift the table up and down to compensate. Martin Taylor in NZ was going to build one of these units, but I guess there wasn't much interest.
"is it safe to run the o2 sensor to the computer if you have a gauge on the line........ or is the difference in voltage so minute that it doesn't affect the signal?"
It should be fine since the air-fuel monitor gauge (if designed well) will use a high-impedance tap to prevent draining the signal. Although the factory did use a shielded coax cable, so interference may be an issue. So keep the wires to your guage as short as possible.
"So in the end, witch gasket should most people use?"
"So Danno, are you impling you like the factory gasket better? That's what I think I'm reading....."
Well, I think either one would work fine as long as you keep your air-fuel ratio within check. That's because they both have the same thin layer of steel facing the combustion chamber. Although it may appear the standard headgasket has a secondary back wall to the compression-ring once the first one goes. But I'm not sure how strong that rolled overlap is, and combustion pressure may just leak under the compression-ring once the front face goes.
My next headgasket will be a copper one! Now that I've got my air-fuel ratio dialed in (or easily dialed-in), let's turn up the boost !!! <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />
09-24-2002, 02:32 PM
#14
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I've been running 19psi with stock injectors, stock air flow meter, stock turbo, stock pressure regulator for close to a year now on pump gas. So far no problems, and according to my A/F gauge the mixture is dead on but we know they're not very accurate. I've been meaning to get the bastard on a dyno with an exaust analyzer, and hopefully that'll still happen and I'll make sure to let you know of the results...
PS: This is running the much hated Europroducts chips... Ofcourse the car has many other mods, but no fuel/ignition controllers.
Ahmet
PS: This is running the much hated Europroducts chips... Ofcourse the car has many other mods, but no fuel/ignition controllers.
Ahmet
09-24-2002, 03:58 PM
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Danno,
The first dyno sheet (Woorleys) doesn't look like it gets to a too lean condition. His stays under 13 all the way to 6500 rpm. Adrials looks like it crosses the 13:1 threshold and the last one looks like it would if the rpms kept going up. All look to be too rich just before heading lean.
So 13:1 is too lean and 11:1 is too rich. In addition it looks like it is tough to accurately monitor the AF ratio due to temp variations. What is a guy to do? Are there any "good" chips out there? Do you have to go to a stand alone system to set this up correctly? I want it run well but don't want to put the dyno guys kids through school doing it. Any suggestions? It really looks as though this issue has not been well adressed by chip makers, why?
The first dyno sheet (Woorleys) doesn't look like it gets to a too lean condition. His stays under 13 all the way to 6500 rpm. Adrials looks like it crosses the 13:1 threshold and the last one looks like it would if the rpms kept going up. All look to be too rich just before heading lean.
So 13:1 is too lean and 11:1 is too rich. In addition it looks like it is tough to accurately monitor the AF ratio due to temp variations. What is a guy to do? Are there any "good" chips out there? Do you have to go to a stand alone system to set this up correctly? I want it run well but don't want to put the dyno guys kids through school doing it. Any suggestions? It really looks as though this issue has not been well adressed by chip makers, why?