Sparkplugs for a race motor

[stownsen914]

Looks like the sparkplug landscape has changed a bit since the last time I bought them. I have used Bosch W3CS and W3DPO in the past. They appear to be limited availability now. I've seen lots of references to people using NGK plugs in 911s. I want non-resistor plugs, and it seems those are getting harder to find. A few options.

NGK:
B9EA or B9ES - I've read the NGK naming convention, but the difference isn't clear.
B9EG - fine wire tip

Bosch:
I see a reference to F3CS, not clear if it is still available
W3CS - available anymore?
Other options?

For the 12mm second sparkplug on my heads, the options I can find are NGK D9EA and DP9EA (more projected tip).

Anyone using Champion plugs? They make a C57 and C59 that are close to a Bosch 3 heat range. An engine builder recommended them to me for a 968 race engine. Can't say I've ever heard of people putting Champion plugs in a 911.

[winders]

The heads on my race engine use 12mm plugs in both plug holes. I use NGK DCPR9EIX plugs.

Bosch doesn't seem to make the good racing plugs any more. I wanted to use their XR2CS plugs but they stopped making them in 9/2017

[stownsen914]

Originally Posted by winders

The heads on my race engine use 12mm plugs in both plug holes. I use NGK DCPR9EIX plugs.

Bosch doesn't seem to make the good racing plugs any more. I wanted to use their XR2CS plugs but they stopped making them in 9/2017

Thanks for sharing that. Did you go with resistor plugs as a preference, or because that's what is available?

[winders]

More due to availability...but several engine builders suggested them.

[Walt Fricke]

Scott - 9s are a pretty cold plug, if I recall right and NGK hasn't changed their conventions in the last 10 years, aren't they? But if you use them, they must be right for whatever motor you have them in. High compression or high EGTs or both call for these? Or maybe they aren't as cold as I thought they were?

One part # NGK can come with the screw on tip, and another (I got mine at a motorcycle shop) only came with the threaded rod. Since my wires had ends to snap over the screw on part, I had to salvage them from the old plugs. That might be the difference in numbers here.

[stownsen914]

Walt - NGK 9 heat range is equivalent to a Bosch 3. I've been using 3's as long as I can remember for the race engines. Curious to hear if others are using different.

[Walt Fricke]

My 2.8 engine and track car have been sidelined for about 7 years now. I see from my notes that I had run 9s, but switched to 8s - B8ES top, D8EA bottom. So much for memory. I had a set of 10s once, but realized those were too cold. That must have been what I was thinking of.

[winders]

Yes, NGK 9's are cold. But I am running a 12.5:1 compression ratio in an engine that will rev to 8000 RPM and has a high specific output. I'd rather have the plug be 1 level too cold that 1 level too hot. Yes, the engine does not idle well until the heads get some heat in them.

After the engines first race weekend I will pull a few plugs to see how they look.

[Walt Fricke]

I shifted at 7,600 unless stretching, as that was the optimum upshift point based on gears and torque curve. If the curve were higher at that end, I'd happily have shifted up to 8. But my
CR was "only" about 10.6.
I built an engine for 12, but had problems unrelated to compression and now don't want to buy $8-10 per gallon fuel, though maybe I should - you can't take it with you, but the glory of winning goes on forever maybe? I always believed the 2.8 RSR had the usual 10.3 or 6 or what Porsche said, but have just recently seen an assertion that the factory cars ran 12s!

[smokintr6]

I've been on a Denso spark plug binge for a few years. I don't remember what is in my standard 964 3.6 engine, but I think they're a "regular" denso iridium. That engine doesn't seem to need anything special. I have a 944 turbo running E60 blend, 20 psi boost 400 torque and 409 wheel HP. That combination seemed to be a struggle for the stock ignition system until I switched to the Denso Iridium Racing plugs.

https://www.denso.com/global/en/products-and-services/automotive-service-parts-and-accessories/plug/iridiumracing/productlist.html

The web site almost looks like a scam, but the best prices I've found on the denso iridium racing plugs was at www.sparkplugs.com . Definitely a money is no object spark plug. I'm running the IW01-31 on the 944. No trouble with self cleaning for street driving.

[r lane]

Heat ranges are about how fast or slow a sparkplug transfers its heat into the head. I assume we are looking for balance in temperature, just not sure how that is determined other than research that spark plug mfgs have done. On the subject of CR and the price of fuel. I have a track motor, 10.5-1, shift at 7500. My fuel choice is 93 or 110. Would you risk 93 octane in a 10.5-1 track motor. Bob

[smokintr6]

Originally Posted by r lane

Heat ranges are about how fast or slow a sparkplug transfers its heat into the head. I assume we are looking for balance in temperature, just not sure how that is determined other than research that spark plug mfgs have done. On the subject of CR and the price of fuel. I have a track motor, 10.5-1, shift at 7500. My fuel choice is 93 or 110. Would you risk 93 octane in a 10.5-1 track motor. Bob

If it's a single plug engine, common wisdom would suggest you need the 110 octane. Lots of factors to consider, including what fuel the ignition map is tuned for. If your car was set up on 110, and you throw 93 in it, you're going to have a bad day, no matter what plugs you have. Pure speculation on my part (without knowing your full setup) is there is almost certainly a tune that someone could develop on the dyno for that engine on 93. Then when you're on the track you could put a few gallons of 110 in with each tank of 93 to add a little margin of safety. I used to have a 12:1 twin plug race engine. I always mixed the fuel down with 93. Never ran straight 110 in it.

[r lane]

I was thinking of the mix and also wondering if it was linier, as in a gal of 110 and a gal of 93, does it make 101.5. My engine is twin plugged, MFI, crank fire and I think I have the max advance set at 28*. Been thinking of knock sensors to see if that would be informative.

[smokintr6]

Originally Posted by r lane

I was thinking of the mix and also wondering if it was linier, as in a gal of 110 and a gal of 93, does it make 101.5. My engine is twin plugged, MFI, crank fire and I think I have the max advance set at 28*. Been thinking of knock sensors to see if that would be informative.

It's somewhat linear to my understanding of it. It's been a minute since i've looked at a twin plug timing chart, but 28* sounds pretty aggressive. Off the cuff, I think the stock 964 timing is around 18*. I looked into knock sensors years ago, and it seemed like the valves and top end on an aircooled 911 engine made enough noise that the systems had a hard time separating valve noise from knock. Maybe they're more efficient now?

I've given up on race gas, and changed all my efforts over to playing with E85. That stuff is basically free, and its probably cheap enough to be worth hauling around to the track with you.

[stownsen914]

I have my twin plug 3.5 at 26 degrees total advance. 28 is possible, but you'll want to make sure you're not knocking.