John Walker or SteveW...spark plug heat range

[Wil Ferch]

Guys:
The plug for a USA spec 3.2 Carrera is a Bosch WR7DC. The plug for the Euro version is several heat ranges colder... WR4CC.
I have number of mods to my USA-spec 3.2 ( pre-muffler, dual out exhaust, SteveW chip, cup style mod to air box, etc)..that I would think gets me close to Euro spec..if not beyond. I also track the car for DE at the Glen.
Should I use a colder plug? Note that the heat range spread is not quite the full jump from 7 to 4 as indicated before....because the DP indicates an extended tip ( ceramic goes beyond the threads) while CC is not an extended tip...and this could be seen to modify the heat range spread otherwise indicated between 4 and 7. Any ideas here?...and will a colder plug perhaps make the engine run cooler too? An article in Upfixin indicates that it does, using an SC as an example...but I'm not sure.

While on this topic, would a silver ( vs copper) electrode provide a widening of the heat range, regardless if I choose 4 or 7?
---Wil Ferch

[TimT]

Didnt the Euro cars have a higher CR? this may explain the difference in heat ranges for the plugs. From my experience the plug will tell you if it is working properly.

Do a plug cut, check out how the plug looks. I have carbs on both my car so I tend to go for a hotter plug to deal with idle and part throttle mixtures....

Im not sure how much affect the plug will have on overall operating temps. Ive run my car at the glen many times and have different plugs installed.. to many variable to tell if the plugs made a dif in operating temp

[tryan]

typo tim. you might see a doctor and get rid of it. lol

unleaded makes it tough to read the plugs.

[RoninLB]

Originally posted by tryan
unleaded makes it tough to read the plugs.

I eyeball the end 3 threads on the plug

[Plays with cars]

Spark plug heat range should not affect the operating temperature of the engine. The plug heat range is a measure of how quickly combustion chamber temperature disapates from the center electrode of the plug. Low speed fouling and pre-detonation are the bookends that limit your heat range selection. Euro spec cars use a cooler plug because they tend to run their cars harder creating higher combustion temps and their higher compression ratio is more suceptible to pre-detonation. US spec tend to run hotter plugs to prevent low speed fouling. If your typical driving pattern for the car includes stop and go traffic or low speed cruising you may want to keep the higher heat range plugs in it and swap out a cooler range for DE events.

[TimT]

LMAO oops crabs...... meant carbs

[Steve W]

I agree pretty much with what Mark says Wil. Going colder, ie, tip extending farther into combustion chamber doesn't make your car run any cooler, but could cause rough running problems when your engine is cold. Stick with the recommended plugs - I hear some guys are having good performance with the NGK BP6ES.

[Chuck Moreland]

It's common to run a slightly colder plug on the track to avoid detonation caused by high engine temps.

Steve's comments are on, but a correction - longer tip = hotter plug, shorter tip = cooler plug.

[john walker's workshop]

BP6ES for me.

[jmohn]

This reminds me of a question I've meant to ask (sorry if this is hijacking the thread). My car, '78 SC, calls for a Bosch W8DC plug but when I changed them last time (last spring) I found the PO or his mechanic had used W6DC. Both the 6's and the 8's (I just changed this spring) look the same when I removed them (i.e. neither looked over cooked or black or any other problem). Does anyone have any idea why the PO would have used a colder plug. There's no indication it was a track car, in fact just the opposite, not used hard at all.

Jerry M
'78 SC

[beepbeep]

Bosch and NGK plug heat numbers do not corespond to each other and are reciprocal.

I prefer NGK.

B8EGV rocks in 930's...they cost a fortune tough...

[beepbeep]

NGK:

Bosch: (in swedish but you'll get the point)

[jmohn]

I thought the discussion was about heat-ranges not brands. I agree NGK is a good plug, but that has nothing to do with which heat range is optimum, or why someone may wish to use a heat-range other than that recommended for a given engine.

Jerry M
'78 SC

[beepbeep]

Yes, both are good. No, heat numberts cannot be compared for those two brands. Yes, higher compression engines do need colder plugs.

[RoninLB]

Originally posted by jmohn
which heat range is optimum,
Jerry M
'78 SC

I like the coldest I can live with..

and IMO, CIS is forgiving of a colder plug than optimum......Ron

[Argo]

So which are the best NGK's for an '88 with cat pipe, weltmeister chip, 8.5 magnecores (no Beru connectors) and spirited street driving?

BP6RES?

Argo
88 Targa

[CamB]

BP6ES for me.

I'm running BP7ES and (maybe) D7EVX on my twin plug short stroke 3.2. It has S cams and was fouling the BP8ES's that were in there.

I am now worried I've gone too warm because BP8ES was the recommended plug for the early S cars.

Am I ok? I don't hear any detonation, but I'm not that attuned to it.

[Wil Ferch]

There is great info guys here...thanks.
Perhaps this point might be clarified...Yes...Euro cars have higher compression and tend to be driven harder...hence the colder plugs...but if my USA, lower CR car has a SteveW chip that modifies the fuel delivery and goes with much more aggressive timing... is the original Bosch "7" still valid ? I think there are discrete steps along the line from 4 to 7 ( see charts... 7-6-5-4)...so maybe additional spirited driving that I do , along with DE's...would allow a 6 or so? Don't forget, Porsche also knew that as delivered for a USA car, my car had a cat, and there couldn't be any misfiring alowed ( meaning, couldn't deliver the car with a colder plug)...to make sure no unburnt gas or overly rich condition could impact the cat, and result in a glowing, red cat ready for melt-down. Having this piece removed and running a premuffler would also make me think a "6" or so is OK.... no? Is higher CR all there is to running a colder plug, or is timing and such important too?
---Wil Ferch