924Board.org

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

I don't mean which 9-electrode-triple-iridium-super-duper etc...

Looking at the Haynes, the US turbo uses a WR7DS, the RoW cars use W3DP, and the na's use WR6DS -for Bosch plugs.

Now then-
W = the electrode gap
R = resistor
3/6/7/etc = heat range (lower = colder)
D = plug dimensions
S/P = silver / platinum

I'm wondering a few things from this:

1) Why is the RoW plug 4! heat ranges colder than the US 931? The tuner rule of thumb is something like drop down 1 heat range for every 50hp increase. On top of this, even the na plug is colder than the US 931, this makes absolutely no sense at all...

2) Why doesn't the RoW plug need a resistor? Don't you guys listen to the radio?

3) Why is the RoW plug platinum? SilverSilver is a better conductor than platinum, although platinum lasts longer. I can't imagine why Porsche would choose one for US and another for RoW.

I have heard stories that Porsche used to use unnecessarily cold spark plugs and have only come around within the past 10 years. The W3 seems rediculous. The online shops list the WR6 plugs for both the turbo and na - but I have no idea where they get their info from. Also, the regular "super" copper-core plugs (WR6DC) are considerably cheaper, does anyone use them over the silvers?

-nick

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

FWIW I'm running WR6DP, though I don't have a real explanation other than it's what the German mechanic put in when he rebuilt the head "that last time". Platinum does hold up to heat much better than the other metals used in plugs, and I've always understood that platinum plugs had a longer service life because of this. Not being a chemist or metallurgist I don't know if the slight difference in conductivity is really a factor.

But... the lower the number, the hotter the plug ( http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf )

This question, or a similar one, came up on the Board about a year ago. If I recall, an explanation was offered up that said the fuel composition had something to do with it. Remember, ROW cars were built to use leaded fuel, and the octane ratings are figured differently as well.

I know that none of this is a definitive answer, but it's my $0.02.

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'79 Eurospec 931

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Well I picked up a set of WR6DC copper core plugs to try out ($1.38 versus $5 for platinum). I know they won't last as long, and I'm not sure if the better conduction properties of copper really make any difference. We'll see how they go.

The RoW heat range could certainly be from the fuels available at the time. Sounds as plausible as anything.

PS- NGK's are rated as lower # = hotter. Bosch are opposite, lower # = colder. It's nice how the companies get together to make things more confusing

-nick

Lizard · Posted: Thu Dec 25, 2003 3:41 am Post subject:

I went with the NGK iridiums for the 931, not sure what the heat range I went with was
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3 928s,

numbbers · Posted: Thu Dec 25, 2003 4:29 am Post subject:

I talked to a Bosch service rep a while back, when I was having a problem, and he recommended the WR6DP. He said that regardless of what the owners manual says, the WR6DP is the plug that Bosch recommends for US driving conditions. The silver plug was originally recommended by the factory because the Platinium plug was not available in the US when the factory specs where developed.

I have run both the WR6DP, and the WR7DP over the years, with no apparent differences in performance. But, neither of them seem to last very long. I presently have a set of Champion 3415 Platinium plugs installed based on the recommendation of someone on this board. I have been running them for a few months, and am very happy with the performance. I seem to have better accelleration. I will let you know on the durability.

Has anybody tried indexing their plugs?
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1980 924 Turbo

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

I indexed the plugs a couple of years back on my NA track car and I noticed a change.
Then I forgot about them on the next change.

I will do it again and for the money a good idea. cheap
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

numbbers · Posted: Sat Dec 27, 2003 10:04 am Post subject:

Where do you get the indexing washers?
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1980 924 Turbo

Kenodog · Joined: 25 Jun 2003 Posts: 2651 Location: Vancouver,B.C.

Platinum has a much higher melting point than either silver or copper and is about the best electrical conductor out there.Depleted iridium is close as far as conductivity is concered but is much cheaper than platinum.(Although it is still more expensive than copper and mildly radioactive.We use iridium 192 as a live Gamma source for x-raying off-site industrial components in pulp mills.Nasty stuff.You should hear the Geiger go as the source goes from "shielded" to "exposed".All of the smokers in the field like to think of it as preventitive radiation therapy.)

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1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

SprintStar · Joined: 26 Aug 2003 Posts: 150

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

Yep, that's how they work. I think the guys who go to the extreme by indexing their plugs feel the advantage of a "directed" spark outweighs any disadvantage of the electrode being slightly recessed. The max that they could possibly be "off" is whatever the pitch of the threads are (1.25mm, or 0.05")
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'79 Eurospec 931

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

Any hot rod shop sells them about $12 for set of washers, maybe 12 or more.
I noticed a hp gain although not much. You have to mark the direction of the gapped tip and try to point it toward the incoming gas. You will find that it takes a couple of times threading the plug on and off till you get it right.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

john h · Posted: Tue Feb 17, 2004 10:49 am Post subject:

I've found that NGK B8EVS plugs seem to work best in my 931. I've tried Champion but they a load of crap in NZ - took me 16 plugs to get one set that didn't break down under load.
The Bosch stuff is OK but really expensive comapred to NGK and didin't last any longer.
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Remember a Porsche is not just for Christmas,

if you take it to pieces slowly it can provide anguish all year long!