plug indexing?

Tishabet · 11-03-2003, 02:27 PM

Hello All,
I already did a search on this forum for plug indexing, but the results didn't really answer my questions.
Today I was reading the most current edition of Excellence, and on page 154 there is a question about spark plug changing intervals. The response included a story about the writer (Jim Pasha) trying different plugs in his 1983 944 and using a chassis dyno to find out if there was any difference. He got 132 rwhp using splitfire and Bosch WR7DC, lost "a few" with Champion, and hit 135 with the Bosch WR7DS(!). Then, he says that "indexing" the WR7DS so that the electrode opening faced the exhaust valve got him 139 rwhp with the WR7DS plugs. Whoa! Normally a claim like this would make me rather speculative, but this claim is coming from a writer and magazine that command some respect in the Porsche community.
So OK, I'm guessing that "indexing" means intentionally facing the plug in a particular direction by shimming the plug, but how do you go about doing it? Are there special washers for this application? Do you really think that 4 "easy" hp is possible from this technique? And last but not least, having never had the head off of my car, what's the intake/exhaust valve orientation in each cylinder? Has anyone done this to their 944?

ae1969 · 02:52 PM

Uhmmmm 7 hp out of it..... possibly.

ON a turbo its common practice to use cooler plugs to try an avoid detonation........ I have seen dyno results on using specific gaps for the turbo to maximize horsepower. I believe it was 28 gap was the optimal.

You can buy tiny washers that fit on the plug to index it. So it stops at the right position you want......

SoCal Driver · SoCal Driver's Garage

This is why the multiple ground lugs help. Reduces the chance of ground lug masking.

Tishabet · 11-03-2003, 03:49 PM

Cool, thanks for the info guys. Where would I procure these tiny washers?

gtroth · 11-03-2003, 06:36 PM

perfomanceproducts.com p/n 802062, $15.95 for 30 pcs. Don't know anything about 'em, just happened to see them in their catalog.

Tishabet · 11-03-2003, 07:40 PM

OK, so now that I have the info on where to get all the parts......what is the orientation of the intake/exhaust valve? I suppose I could probably figure it out from the Haynes manual?

shocker1322 · 11-04-2003, 07:35 AM

I just learned about this recently and have never done it, but you want the spark to face the center of the combustion chamber. The easiest way to do this is to mark on the plug where the opening is. Then, with the help of shims, face that to the center of the chamber. This helps with horsepower, mainly at higher rpms, by starting the explosion more in the center of the chamber. A few mm might not seem like a lot, but when you only have 1/1000's of a second to ignite the fuel/air mixture, it helps alot. I just took the head of my car, and you think I would remember what way it should go. I am pretty sure you face the opening toward the right hand side of the car, perpendicular to the fender. I will confirm later. Hope this helps

shocker1322 · 11-04-2003, 01:29 PM

Here (I hope, if it worked) is a picture of my head. Now hopefully your valves do not look like mine, I had a little accident with the timing belt. The bent valves are exhaust and the others are intake. (yes #3 exhaust broke off inside the piston) You are looking from front to back at cylinders 4 to 1. #3 is perfectly indexed, the spark is pointing into the combustion chamber. #2 is twisted slightly, but still close. And #4 is completely backwards. This should be fixed by using some small washers to point the gap inward. And I was correct in saying the gap points to the right side, perpendicular to the fender.

Tishabet · 11-04-2003, 01:49 PM

Thanks for the info! Like they say, a picture is worth a thousand words......hope your valves are looking better nowadays.