Valve guides and the CAT bypass....
05-11-2012, 11:57 PM
#1
Racer
Thread Starter
Valve guides and the CAT bypass....
Having one of the few 993 misfortunes of crappy OEM valve guides that face inevitable demise, there is a theory floating around that a CAT bypass left in the long term, can prolong the life of the OEM valve guides because of the release of excess heat.
What do you guys think?
What do you guys think?
05-12-2012, 02:05 AM
#2
Track Day
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More likely was that the long standing 911 valve guide wear issue was made worse by Porsche, when they decreased the valve stem diameter when they introduced the 993.
Excessive heat doesn't help, hence removing the engine cover to allow clearer flow of air isn't a bad idea, but ultimately the smaller valve stem is the reason 993 guides would be more prown to wear than 964 guides.
Excessive heat doesn't help, hence removing the engine cover to allow clearer flow of air isn't a bad idea, but ultimately the smaller valve stem is the reason 993 guides would be more prown to wear than 964 guides.
05-12-2012, 03:03 AM
#3
RL Technical Advisor
Hi,
Since we've been doing our machine work here in-house since 1978 and have done well over several thousand heads since then, we've had a unique opportunity to do detailed forensics on all these things to determine wear points and causes of premature failures.
FWIW,...the 8mm 993 guides do not wear any more than their predecessors; 964, Carrera 3.2, or SC guides, and thats even considering the 993 engine's hard-chrome plated valve stems.
The root causes are multifold:
1) OEM material that's soft.
2) Poor & inconsistent fitment at the factory which is a QC problem.
3) Excess heat that accelerates wear.
Although I do not recommend removing the cat(s) on many cars, it certainly reduces EGT's and that does help reduce valve & guide operating temps. It will not help whatsoever if they came fitted too loosely from the factory and that's been a real issue.
The real fix is to use a more durable guide material (we make our own phosphorus-bronze ones) and ensure proper clearances so the valves remain centered on the seats, cool properly, and manage oil control.
Since we've been doing our machine work here in-house since 1978 and have done well over several thousand heads since then, we've had a unique opportunity to do detailed forensics on all these things to determine wear points and causes of premature failures.
FWIW,...the 8mm 993 guides do not wear any more than their predecessors; 964, Carrera 3.2, or SC guides, and thats even considering the 993 engine's hard-chrome plated valve stems.
The root causes are multifold:
1) OEM material that's soft.
2) Poor & inconsistent fitment at the factory which is a QC problem.
3) Excess heat that accelerates wear.
Although I do not recommend removing the cat(s) on many cars, it certainly reduces EGT's and that does help reduce valve & guide operating temps. It will not help whatsoever if they came fitted too loosely from the factory and that's been a real issue.
The real fix is to use a more durable guide material (we make our own phosphorus-bronze ones) and ensure proper clearances so the valves remain centered on the seats, cool properly, and manage oil control.
05-12-2012, 06:02 PM
#5
Drifting
Hi,
Since we've been doing our machine work here in-house since 1978 and have done well over several thousand heads since then, we've had a unique opportunity to do detailed forensics on all these things to determine wear points and causes of premature failures.
FWIW,...the 8mm 993 guides do not wear any more than their predecessors; 964, Carrera 3.2, or SC guides, and thats even considering the 993 engine's hard-chrome plated valve stems.
The root causes are multifold:
1) OEM material that's soft.
2) Poor & inconsistent fitment at the factory which is a QC problem.
3) Excess heat that accelerates wear.
Although I do not recommend removing the cat(s) on many cars, it certainly reduces EGT's and that does help reduce valve & guide operating temps. It will not help whatsoever if they came fitted too loosely from the factory and that's been a real issue.
The real fix is to use a more durable guide material (we make our own phosphorus-bronze ones) and ensure proper clearances so the valves remain centered on the seats, cool properly, and manage oil control.
Since we've been doing our machine work here in-house since 1978 and have done well over several thousand heads since then, we've had a unique opportunity to do detailed forensics on all these things to determine wear points and causes of premature failures.
FWIW,...the 8mm 993 guides do not wear any more than their predecessors; 964, Carrera 3.2, or SC guides, and thats even considering the 993 engine's hard-chrome plated valve stems.
The root causes are multifold:
1) OEM material that's soft.
2) Poor & inconsistent fitment at the factory which is a QC problem.
3) Excess heat that accelerates wear.
Although I do not recommend removing the cat(s) on many cars, it certainly reduces EGT's and that does help reduce valve & guide operating temps. It will not help whatsoever if they came fitted too loosely from the factory and that's been a real issue.
The real fix is to use a more durable guide material (we make our own phosphorus-bronze ones) and ensure proper clearances so the valves remain centered on the seats, cool properly, and manage oil control.
Would running a 100-cell sport cat help at all? I would be reluctant to do a full bypass in conjunction with my incoming Fister IIIs due to the decrease in back pressure (recall that I'm not a race car driver yet
) and the possibility of the exhaust being too loud / obnoxious.Thanks in advance
05-12-2012, 08:08 PM
#6
RL Technical Advisor
Steve,
Would running a 100-cell sport cat help at all? I would be reluctant to do a full bypass in conjunction with my incoming Fister IIIs due to the decrease in back pressure (recall that I'm not a race car driver yet) and the possibility of the exhaust being too loud / obnoxious.
Thanks in advance
Would running a 100-cell sport cat help at all? I would be reluctant to do a full bypass in conjunction with my incoming Fister IIIs due to the decrease in back pressure (recall that I'm not a race car driver yet
) and the possibility of the exhaust being too loud / obnoxious.Thanks in advance
Further, many 100-cell cats do not actually work very well and Check Engine Light issues are not uncommon.
05-13-2012, 03:37 PM
#7
Drifting
Nossir, no gains insofar as durability is concerned. Bypasses on these cars typically reduce mid-range torque which runs counterintuitive for maximizing performance. The tradeoff is a net loss unless you have RS cams (or better) and close-ratio gears.
Further, many 100-cell cats do not actually work very well and Check Engine Light issues are not uncommon.
Further, many 100-cell cats do not actually work very well and Check Engine Light issues are not uncommon.
