Spark Plug Advice

[Mikey37027]

I am sorting-out my 1972 911T and I am a newb, so I need some advice. I am going to swap-out my ignition wire set and spark plugs. The engine has been upgraded to Webers and S-cams. What spark plug do you guys recommend with that set-up? Currently it is running with Bosch W7DC. I don't think these are available. The PO mentioned he always ran with a hotter spark plug. Thanks.

[James Brown]

Sounds good, run a little hotter just plain old copper Bosh plugs, no fancy double unobtainum-platinum gimmick plugs. The $2.00 ones are the best.

[moneymanager]

I've long preferred NGK's to Bosch... there's an equivalent number available. I believe they easily meet Mr. Brown's $2 test.

[Rot 911]

Ngk bpr6es

[moneymanager]

Perfect. Gap to .045" if you have an MSD.

[James Brown]

Sometimes the cheaper things in life are better, beer and champagne exempted. Ngk's are good also. Larger gap with the 6AL is a good thing.

[JohnJL]

Originally Posted by Rot 911

Ngk bpr6es

Same

[Mikey37027]

Would this be the current Bosch W-7-DSR-M14 eq? I was going through the old parts for the car and they were running a 5.

[James Brown]

Remember Bosch and NGK are backwards on heat range. Forgot witch is witch.

[spuggy]

Originally Posted by James Brown

Remember Bosch and NGK are backwards on heat range. Forgot witch is witch.

Bosch W3DPO is a factory-fitted platinum plug for the 930. Frosty. Cold enough for sustained track use.

The colder the plug, the crisper/better the throttle response. Also, it removes more heat from the combustion chamber.

The downside is that a cold plug is more likely to foul if you're not getting the tip hot enough (the flame path cleans it off). W3DPOs don't foul around town even with typical over-rich 930 mixtures thanks to their platinum construction - but they're $15. Each.

[911s55]

NGK BP6ES or BP7ES depending on your climate, lower number is a hotter plug opposite of Bosch. I use BP6ES in the Seattle area with 40-85 degree temps, and I use OEM Beru plug wires on my carbureuted 2.7. Also fuel grade/octane rating that you use is very important to the whole ignition performance.

David

[Flieger]

I am not sure if "removing heat from the combustion chamber" is precisely the correct term. The heat range grades how much heat the part of the spark plug insulator which sticks out into the combustion chamber retains between combustion cycles. I do not think the ceramic insulator conducts heat well enough to remove an appreciable amount of heat from the combustion chamber's metal walls/cylinder head itself- that is the job of the cooling fins and air flow. The less insulator sticks out, the less is exposed to the flames, and the less heat is retained. This reduces the risk that the air-fuel mixture will pre-ignite on the hot plug. It will not burn off the carbon at low loads, though.

[enjefriy]

Originally Posted by Flieger

I am not sure if "removing heat from the combustion chamber" is precisely the correct term. The heat range grades how much heat the part of the spark plug insulator which sticks out into the combustion chamber retains between combustion cycles. I do not think the ceramic insulator conducts heat well enough to remove an appreciable amount of heat from the combustion chamber's metal walls/cylinder head itself- that is the job of the cooling fins and air flow. The less insulator sticks out, the less is exposed to the flames, and the less heat is retained. This reduces the risk that the air-fuel mixture will pre-ignite on the hot plug. It will not burn off the carbon at low loads, though.

sounds logical to me.
Would the ambient temperature be a factor for selection.
I know engine compression is, but whether the temp of the day makes it relevant too.
My rationale is that the bentley states the WR7 as the plug to use
Porsche singapore supplies WR5 for my 82 911sc.
So a colder WR5 was supplied here in asia.
I did have a go at fitting a WR7 sometime back just to read the plug, and actually found it was nicer looking. In a sence that the WR5 looked more carbon fowled compared to the WR5.

Noting that i do not track the car (no tracks here), is it reasonable the WR7 would be fine for me based on the plug reading.

[Mikey37027]

I am using a 91 octane fuel (can't find non-ethanol here in Middle TN). We have hot summers here, so would use the NGK BP7ES.

[Flieger]

Originally Posted by enjefriy

sounds logical to me.
Would the ambient temperature be a factor for selection.
I know engine compression is, but whether the temp of the day makes it relevant too.
My rationale is that the bentley states the WR7 as the plug to use
Porsche singapore supplies WR5 for my 82 911sc.
So a colder WR5 was supplied here in asia.
I did have a go at fitting a WR7 sometime back just to read the plug, and actually found it was nicer looking. In a sence that the WR5 looked more carbon fowled compared to the WR5.

Noting that i do not track the car (no tracks here), is it reasonable the WR7 would be fine for me based on the plug reading.

The ambient temperature fluctuations are nothing compared to the heat of the combustion chamber so starting with warm air will not make the flame any hotter. What higher ambient temperatures can do is reduce air density, causing the car to run rich (cooler) or to run at a lower power (also cooler). Singapore I would imagine is lower in altitude and much more humid. The higher barometric pressure would increase the compression and heat, but I am not sure how the humidity would effect things. Less air and more water, so cooler temps? It seems like a lot would balance out.

930s had boost so they had hotter temps and needed colder plugs. However, the buyers of street 930s were not as "sporting" as Porsche thought and drove at slow speed, low load, no boost. This lead to plug fouling and so Porsche spec'ed a hotter plug for street use but still recommended the colder plug for racing.

[moneymanager]

I've always run the coldest plug I could that didn't foul. Started with NGK 5's which worked fine. Tried 6's, they working fine too. Plan to change to 7's next time to see if they will work.

[Flieger]

Originally Posted by moneymanager

I've always run the coldest plug I could that didn't foul. Started with NGK 5's which worked fine. Tried 6's, they working fine too. Plan to change to 7's next time to see if they will work.

That is the best way to go. You do not want pre-ignition. Fouling is not as bad as the engine damage from detonation.