Plugs for Modified 951S
08-20-2003, 09:22 PM
#16
Race Car
Yeah Adrial I know about the factory manual's recommendations, I figured that was known information.
Chilton's is a universally accepted alternative to factory manuals for many cars like Motor etc. for specifications and labor time guides.
The manual that I'm speaking of list WR6DC as 'standard'.
The guy who gave you plugs that were 5DC with the comment "these are one range colder than the factory standard" must have used the same or similar publication.
Chilton offers detailed front end alignment specs and info not in the factory manuals IIRC.
BTW-Bill, the only thing to watch out for is plug fouling with the colder plug as they may not efficiently burn a borderline rich mixture at idle.
If you soon run into a "cranks but won't start" problem, go straight for the plugs.......they'll be fuel fouled....
Terry S.
Chilton's is a universally accepted alternative to factory manuals for many cars like Motor etc. for specifications and labor time guides.
The manual that I'm speaking of list WR6DC as 'standard'.
The guy who gave you plugs that were 5DC with the comment "these are one range colder than the factory standard" must have used the same or similar publication.
Chilton offers detailed front end alignment specs and info not in the factory manuals IIRC.
BTW-Bill, the only thing to watch out for is plug fouling with the colder plug as they may not efficiently burn a borderline rich mixture at idle.
If you soon run into a "cranks but won't start" problem, go straight for the plugs.......they'll be fuel fouled....
Terry S.
08-20-2003, 09:29 PM
#17
Nordschleife Master
I was thinking that maybe the guy that gave me the plugs screwed up....but maybe not based on what you're saying.
I guess the only way to know for sure is to take a bone stock 951 and run it with 6's for a few thousand miles, then 7's for a few thousand miles and see which plug looks better. Maybe Chilton's knew that so many 951's were modified and decided to just make the 6 the standard plug to make our lives easier?
A too cold plug wouldn't prevent all the fuel from igniting under WOT...would it?
I guess the only way to know for sure is to take a bone stock 951 and run it with 6's for a few thousand miles, then 7's for a few thousand miles and see which plug looks better. Maybe Chilton's knew that so many 951's were modified and decided to just make the 6 the standard plug to make our lives easier?
A too cold plug wouldn't prevent all the fuel from igniting under WOT...would it?
08-20-2003, 09:39 PM
#18
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Terry S,
Thanks for the tip. I will keep that in mind.
I have experienced some hot start issues on very hot days, but I attributed it to my lousy maf that does not have temp compensation. I am constantly adjusting my ARC II to keep the idle mix correct (hot days/cold days). Come to think of it, on a very hot day, after the car has run, the idle mix can become very rich. Thus, hot start issue, which would support your theory of the colder plugs ability to light a rich mix. Interesting how you can magnify problems.
I am waiting for GURU to come out with their plug and play stand alone. Then hopefully it will all go away.
Thanks for the tip. I will keep that in mind.
I have experienced some hot start issues on very hot days, but I attributed it to my lousy maf that does not have temp compensation. I am constantly adjusting my ARC II to keep the idle mix correct (hot days/cold days). Come to think of it, on a very hot day, after the car has run, the idle mix can become very rich. Thus, hot start issue, which would support your theory of the colder plugs ability to light a rich mix. Interesting how you can magnify problems.
I am waiting for GURU to come out with their plug and play stand alone. Then hopefully it will all go away.
08-20-2003, 09:47 PM
#19
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A too cold plug wouldn't prevent all the fuel from igniting under WOT...would it?
Following Terry's logic I would have to say "YES".
You want your mix to be as close to correct at all rpm/load ranges. So if you are running rich at WOT you could have a problem. As a matter of fact, any plug (cold/stock/hot) will have difficulty lighting a very rich mix.
What I am trying to prevent is "Dieseling". The more you compress a mix (high boost) the hotter the gasses get in the combustion chamber. It can get to a point where the heat created by compression, can cause the mix to light itself (like in a diesel motor with no spark plugs). In that condition, a colder plug will not create a "hot spot" in the chamber that can light the mix early (pre-detonation or pinging). Pre-detonation kills engines.
08-20-2003, 10:47 PM
#20
Race Car
Plug checks (more used on street bikes at least by me) are usually done by holding throttle open for a reasonable time in gear and killing the engine while coasting to a stop to not alter the condition of the plugs as they burned under WOT. You can the pull them and inspect each for rich/lean condition. When you purchase new injectors of any real quality they will come with a flow chart defining which injector flowed the most fuel under identical conditions. If you have a questionably/borderline lean cylinder out of four but not extreme enough to warrant a plug range change you can strategically place the injector with the highest flow rate on the lean cylinder. Ironically, given that the # rod bearing has become famous on 951's, it's strange that of the few cars that I've really evaluated plug condition on it's usually #2 that's leanest. It's possible that oil flow limited to the #2 rod could transmit more heat than the others through the connecting rod and piston making that cylinder hotter than the rest but that's only wild speculation.
I used to race a radio control hydroplane (outrigger) on 50% nitromethane with 5% propolene oxide (sp.?) and ultimate performance could only be had with the right choice of "glow plug".....
As an aside- the engine was 15cc, that's .90 of a cubic inch and made 7.2 hp at 25000 rpms......pretty impressive by any standard...
That'd be like a 2.5 liter 951 making 1200hp......... :^)
I used to race a radio control hydroplane (outrigger) on 50% nitromethane with 5% propolene oxide (sp.?) and ultimate performance could only be had with the right choice of "glow plug".....
As an aside- the engine was 15cc, that's .90 of a cubic inch and made 7.2 hp at 25000 rpms......pretty impressive by any standard...
That'd be like a 2.5 liter 951 making 1200hp......... :^)
08-21-2003, 12:54 AM
#21
Race Director
"According to the Porsche factory manuals the WR7DC is the standard 951 plug."
"...after looking over a Chilton's manual today, they list WR6DC as standard so there's some conflicting info there on what the specification is."
Could this be the distinction between the earlier Turbo and later TurboS? Maybe Chilton went with the very latest model and lumped everything else before into that? Similar to how AutoThority 28-pin Stg.2 chips don't distinguish between TurboS and Turbo models; which might explain why the 24-pin APE Stg.2 chip has completely different mapping than the 28-pin.
Maybe we can use say... WR6DC up to 18psi and WR5DC for 18psi+ ???
"but I attributed it to my lousy maf that does not have temp compensation. I am constantly adjusting my ARC II to keep the idle mix correct (hot days/cold days). Come to think of it, on a very hot day, after the car has run, the idle mix can become very rich....
I am waiting for GURU to come out with their plug and play stand alone. Then hopefully it will all go away."
Bill, I'm getting my custom flanges back from the machine shop early next week. You'll have a present in the mail soon after that...
"Plug checks (more used on street bikes at least by me) are usually done by holding throttle open for a reasonable time in gear and killing the engine while coasting to a stop to not alter the condition of the plugs as they burned under WOT. You can the pull them and inspect each for rich/lean condition...
... I used to race a radio control hydroplane (outrigger) on 50% nitromethane with 5% propolene oxide (sp.?) and ultimate performance could only be had with the right choice of "glow plug".....
As an aside- the engine was 15cc, that's .90 of a cubic inch and made 7.2 hp at 25000 rpms......pretty impressive by any standard...
That'd be like a 2.5 liter 951 making 1200hp......... :^)"
I went through A LOT of spark-plugs this way on my motorcycles. The trick is you have to install new plugs for each run in order to keep the contamination from other runs down. And you gotta make sure you pull the clutch at the same time as killing the engine, so you're not pumping air and unburned fuel through the chambers. YUK!!! Tuning Keihin-CV carbs this way is the worse! Amazing how much easier the newer technology, what dyno-tuning and adjusting fuel-maps electronically on the chips can do!
However, I did manage to get 96rwhp@14,000rpm out of a 500cc street-bike! That'd be something like 480rwhp from a 944NA non-turbo!!! heh, heh...
HEY!!! Just thought of something! Motorcycle 10mm plugs.... That'll give us some room to add mondo-huge valves.... hhmm......
"...after looking over a Chilton's manual today, they list WR6DC as standard so there's some conflicting info there on what the specification is."
Could this be the distinction between the earlier Turbo and later TurboS? Maybe Chilton went with the very latest model and lumped everything else before into that? Similar to how AutoThority 28-pin Stg.2 chips don't distinguish between TurboS and Turbo models; which might explain why the 24-pin APE Stg.2 chip has completely different mapping than the 28-pin.
Maybe we can use say... WR6DC up to 18psi and WR5DC for 18psi+ ???
"but I attributed it to my lousy maf that does not have temp compensation. I am constantly adjusting my ARC II to keep the idle mix correct (hot days/cold days). Come to think of it, on a very hot day, after the car has run, the idle mix can become very rich....
I am waiting for GURU to come out with their plug and play stand alone. Then hopefully it will all go away."
Bill, I'm getting my custom flanges back from the machine shop early next week. You'll have a present in the mail soon after that...
"Plug checks (more used on street bikes at least by me) are usually done by holding throttle open for a reasonable time in gear and killing the engine while coasting to a stop to not alter the condition of the plugs as they burned under WOT. You can the pull them and inspect each for rich/lean condition...
... I used to race a radio control hydroplane (outrigger) on 50% nitromethane with 5% propolene oxide (sp.?) and ultimate performance could only be had with the right choice of "glow plug".....
As an aside- the engine was 15cc, that's .90 of a cubic inch and made 7.2 hp at 25000 rpms......pretty impressive by any standard...
That'd be like a 2.5 liter 951 making 1200hp......... :^)"
I went through A LOT of spark-plugs this way on my motorcycles. The trick is you have to install new plugs for each run in order to keep the contamination from other runs down. And you gotta make sure you pull the clutch at the same time as killing the engine, so you're not pumping air and unburned fuel through the chambers. YUK!!! Tuning Keihin-CV carbs this way is the worse! Amazing how much easier the newer technology, what dyno-tuning and adjusting fuel-maps electronically on the chips can do!
However, I did manage to get 96rwhp@14,000rpm out of a 500cc street-bike
! That'd be something like 480rwhp from a 944NA non-turbo!!! heh, heh...HEY!!! Just thought of something! Motorcycle 10mm plugs.... That'll give us some room to add mondo-huge valves.... hhmm......
08-21-2003, 02:03 PM
#23
Race Car
Just to put the final (or not...
) spin on this issue, even the Chilton's manual specs the WR7DC as "standard" plug for the 1989 944 turbo.
The specification page carried on to the next page and I never bothered checking for a difference for the '89 since the '88 listed WR6DC.
The problem there is that Chilton's makes no entry for the '88 S and has one plug listed for all 88' turbos.
It's wierd because you would figure with the later car with more, or to better define, "sustained" boost to redline that they would have opted for the colder plug for the later models. But (and there's always a "but"...) the colder WR6DC may have been used to compensate for hotter inlet air temps due to the tiny size of the K26/6....
Ah shucks, I'm confusing myself now.....
Terry S.
) spin on this issue, even the Chilton's manual specs the WR7DC as "standard" plug for the 1989 944 turbo.The specification page carried on to the next page and I never bothered checking for a difference for the '89 since the '88 listed WR6DC.
The problem there is that Chilton's makes no entry for the '88 S and has one plug listed for all 88' turbos.
It's wierd because you would figure with the later car with more, or to better define, "sustained" boost to redline that they would have opted for the colder plug for the later models. But (and there's always a "but"...
) the colder WR6DC may have been used to compensate for hotter inlet air temps due to the tiny size of the K26/6....Ah shucks, I'm confusing myself now.....
Terry S.
08-21-2003, 09:43 PM
#25
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Bill, I'm getting my custom flanges back from the machine shop early next week. You'll have a present in the mail soon after that
As usual, your "Outside the Box" thinking solves another tough problem. GURU Racing is the best!!
01-08-2005, 11:37 AM
#26
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01-08-2005, 03:35 PM
#27
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FWIW, I recently bought a set of spark plugs for my 951 at the local Porsche dealer and they're Beru Ultra Porsche part number 999.170.156.90
They're "Made in France" and have the numbers 14R - 7DU stamped around the girth. Familiar with Beru spark plug wires, but it's the first time I've ever seen Beru spark plugs. I noticed the U.K. tuner "ProMAX" includes these with some of their 951 upgrade kits, hence this post.
They're "Made in France" and have the numbers 14R - 7DU stamped around the girth. Familiar with Beru spark plug wires, but it's the first time I've ever seen Beru spark plugs. I noticed the U.K. tuner "ProMAX" includes these with some of their 951 upgrade kits, hence this post.
