924Board.org

JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

Did a search but want to get everyone's updated opinions--

Time to swap spark plugs, was running a non-resistor NGK copper plug for about 3K miles, but I am told that the W6DS or W6DC is the correct plug (non-resistor) for the '82 931. Any other recommendations from what people have experienced? Car is running 9-11psi, if that matters.

I have also been told that the 924 uses solid-core ignition wires, not the "new" interference-reducting wound wires...the car came with a Jacobs ignitions system, so the previous owner had the correct wound wires to function with the Jacobs. I have since switched to new Kingsbourne solid-core wires, and the Jacobs is in a box collecting dust. Is this still correct? Should I go back to the OEM-type Bosch wires? What is their construction?

Coils. The now-removed Jacobs system is known to overwork a stock coil, and is only recommended for use with a higher-powered coil (Bosch Blue, Nology, Jacobs, MSD, etc.). This is still the original stock coil since it left the factory, and reading old posts I am seeing symptoms of a bad/misfiring coil at higher rpm. I am planning on sticking with the stock ignition system (unless I do MegaSquirt and coilpacks, but that is for much later). Is the stock/OEM Bosch coil sufficient, or due to the fact that I am running doube the stock boost and will often see track/autocross time should I go with a Bosch Blue (or other hp coil....I have access to Pertronix Flame Throwers for very little $$)??

Also-- my factory 931 manual supplement shows in ALL of its photos the negative coil plug-connector (2 wires with big white plastic plug) on the passenger side, and the double-wire with single connector on the driver side. I'll have to look at which is which, but on my car it seems they are reversed, though apparently correctly connected at #1 and #15. Could it be that it is an incorrect coil for use with the DITC of the later 931's?

Thanks,

-JamesW
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'82 924 Turbo (not stock) - soon returning home?
www.AffordableRacingData.com

JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

Oh-Kay, updates after speaking with some local shops that have had extensive experience on one of their own shop 931 racecars back in the day......

81-82 931 MUST use the OEM or equivalent coil, as its windings are specific to work with the DITC system...they have tried the Blue and other coils and usually only created problems. Picked one up for $40 today (Bosch 00041).

Same deal with spark plugs, only they had been using the W5DC when running 0.7 bar on their car, same as mine. I did manage to pick up a set of four W5DC as well as another set of the original-spec W6DC for comparison.

The stock wires are solid-core with built-in resistors at each end, so instead of running resistance based on wire lenght on a spiro-wound wire, Bosch put resistors at each end of the wire to be around 5K ohms. This is just what he told me, I haven't put my Kingsbourne wires on an ohmmeter yet to see what is what.

I will install both tonight and see what is up, either way this stuff needed to be replaced so I am not worried that I am "throwing parts at the car" to fix problems...its still an old car with worn-out stuff.

Thoughts? Comments?

-JW
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'82 924 Turbo (not stock) - soon returning home?
www.AffordableRacingData.com

John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

Only to concur. The stock system specified resistance wires AND resistor plugs: wR6xx or wR7xx.
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

Smoothie · Posted: Wed Sep 21, 2005 11:06 pm Post subject:

JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

Got a chance to run the car hard this morning.

It pulls strongly and revs cleanly, and instead of cutting out or having a "soft limiter" at 4K rpm like before, it will pull to about 5200rpm before it behaves the same way, but now the revs will still climb beyond that but still sputters and misfires. Think this is still from that air gap between the plugs and the wires?

I need to get it on a dyno soon and see what the A/F ratio is doing, but on the stationary and no-load revving the numbers look good on an exhaust gas analyser.

-JamesW
_________________
'82 924 Turbo (not stock) - soon returning home?
www.AffordableRacingData.com

Smoothie · Posted: Thu Sep 22, 2005 6:23 am Post subject:

Both sets of metal-shrouded-connector wires that've been on my car have had spring wire clips that grab onto the threaded end of the plug (with the screw-on tip removed), so I'm not seeing how you're ending up with an air gap. You don't see a small clip way up inside each connector? -Or is it there, but too wide open to make good contact?
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

JamesWilson · Joined: 10 Jun 2005 Posts: 132 Location: San Diego, CA

That little wire clip is, IMO, not sufficient to carry enough spark. So there is still an effective gap there, as the "regular style" would have full metal hookup from the wire to the plug. I dunno, this is just my opinion and the symptoms that are occuring.

-JamesW
_________________
'82 924 Turbo (not stock) - soon returning home?
www.AffordableRacingData.com

John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

The Turbo Manual Vol 4 shows resistor plugs. The Service Information Model 81 spec section indicates resistor plug for USA; some other places non-resistor.

For a stock system I suspect resistor plug vs non wouldn't be too big a deal so long as you don't at the same time use the wrong (non-resistor) wires. A total circuit resistance variance between 5 to 10Kohm isn't such a big deal. From 5-10k to zero is a big deal. The tolerance on resistance variation is pretty broad.

Either wire end attachment style is fine and more than adequate. Just have to match.
_________________
John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

numbbers · Posted: Mon Sep 26, 2005 9:19 am Post subject:

OK, my '80 Owners Manual calls for WR7DS. I usually run a WR7DP, because the silver plugs are too expensive.

What is the difference in a WR7, and a WR6 or WR5? Which is the coldest? Also, since I run 17 PSI of boost, what is the theory for higher boost, a hotter plug, or a colder plug?
_________________
1980 924 Turbo

Smoothie · Posted: Mon Sep 26, 2005 9:32 am Post subject:

Comparing a W8DC to a W6DC -

W8DC -
insulator tip length - longer
tendency to preignite - greater
plug-fouling tendency - less
temperature response - hotter

W6DC -
insulator tip length - shorter
tendency to preignite - less
plug-fouling tendency - greater
temperature response - colder
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

john h · Posted: Mon Sep 26, 2005 2:09 pm Post subject:

I’ve played with plugs and leads on my 924 GT replica many years ago and found that it ran best with eth standard Porsche leads and NGK plugs – Currently I run the latest NGK plugs – BR8H1X which run really well.

I've found chapion plugs are junk and shouldn't be used in teh turbo, Bosch are too expensive in NZ to use, whereas teh NGK are quite resonable priced. I then recycle the old NGK in my old Suzuki bike (once they done a few race meetings in the GT)

In the past I’ve found if you don’t run plugs and leads with the correct resistance the DITC unit gets a bit of interference from eth ignition system at high revs and causes misfires. Bit like a cell phone going off near you computer speakers – enough to be noticeable but not enough to create major problems

Do a search on spark plugs as this has been covered quite a few times before.
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Racing · Joined: 27 Apr 2004 Posts: 374

James.
Try this.
Take the plugs out n close the gap to 0,5mm or there abouts.
Be careful so they can manage a regap to OEM specs.
What that leads to is an easier path for the igniting current to follow.
Very common on tricked out boosted cars.

If that remedies the problem OR moves it around..seek out ignition sys for faults.
If it does nothing..look elsewhere.

Note.
I´ve seen the trigger wheels inside the distributor come lose after yrs of use.
When it happends,it´ll produce all kinds of havoc.
Easy enough to check.
Take cap off.
Get rid of rotor and plastic seal-if still present.
Grab trigger wheel with a cloth and a pair of pliers-whiggle back n forth radially.
If ANY relative movement can be felt/seen between the trigger wheel n the axleyoke..
Dismantle time.
1/There is sort of a yoke that carries the sheet metal trigger wheel on the dist axle.This yoke is fixed by a small pin.Be wary when taking apart.
Problem tho..is that over the yrs some schmuck might have bent one of the trigger wheel arms making the arm come in contact with something solid within the dist.
If arms are bent..that´s a surefire telltale.
None the less...the trigger wheel is merely pressed to the yoke..
If the trigger wheel is lose..just suffix it with a tack weld or similar.

Phasing is important in that case.

Best way really is to drill a 1/4" hole in the dist cap and take out the strobe light.(Don´t worry bout the hole...it´ll work just as fine)
Adjust timing per OEM specs.
Use strobe to check into hole...and make sure that the rotor is facing the outlet post for No1 cyl when at proper revs(approx 3 grand)
If not..twist trigger wheel around,reset timing asf...until it does.
Then stop engine and tackweld trigger wheel in place.

numbbers · Posted: Tue Sep 27, 2005 8:41 am Post subject:

Thanks smoothie, so the higher the number, the hotter the plug. Maybe I will try WR5DP's if I can find them. But, with that cold of a plug, the engine may load up around town.
_________________
1980 924 Turbo

Smoothie · Posted: Tue Sep 27, 2005 10:15 am Post subject:

I just remembered I had this - it's right at or beyond the limit of readability, but - http://pg.photos.yahoo.com/ph/smoothies931pics/detail?.dir=341f&.dnm=5bbd.jpg&.src=ph
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox