Anthony DiBernardo

I recently noticed a rough spot at about 3000 rpm. The first thing I did was to pull the plugs. They had not been changed in a while and were grey with mild carbon buildup. All were more or less consitent with eachother. I opted to go one step hotter in my next platinum plug. At my local stores, I was unable to get any Bosch plugs. Now the car runs much worse. I was inspecting the spark plug wires connections at the ditributer while the engine was running and was shocked by one of the wires at the base. I dont think the car is running on all cylinders now. I suspect this problem runs deeper than crappy new plugs. Is it as simple as new spark plug wires? Or do I need a new distributer? Any responses will be appreciated.

theiceman

Did you do the plugs one at a time or could you have swapt some wires by accident, believe me it is easy to do. Cap and rotors are pretty cheap parts really and should be considered PM when replacing plugs anyway. But I would definitely start with iring order and connection quality

TonyG

First off, the Platinum plug stuff is junk.

Get NGK BP 6ES. Gap at .030"

Install new spark plug wires, distributor cap and rotor.

Do that, then if you still have a problem let us know.

Here's a couple of links so you can price shop for the parts (all of these places can drop ship you the parts next day).

www.aaaforeignautoparts.com
www.placeforparts.com
www.ontrackautoparts.com
www.onlineparts4imports.com

TonyG

Peter Zimmermann

Anthony: As others have said, Bosch Platinum plugs(Turbo W3DPO excepted) are junk. Not knowing what year your car is, here are the recommendations for plugs:
1978/79: W8DC Bosch
1980-83: W5DC Bosch
This is not from my mouth,this is what the manufacturer wants in the car. Use a .028" gap, check every plug before installation. NGKs are OK, and a reasonable substitute as long as the heat range is cross-referenced correctly, but I've always preferred Bosch.

Regarding getting shocked, without seeing your car I can't tell what's going on. There are basically two possibilities:
1. You have loose resistors (the short, hard piece at the end of the wire that plugs into the distributor cap). You can gently work with those to pull them out of the cap, along with the wire (don't pull on the wire!). When loose each resistor can be screwed back onto its wire to make it tighter.
2. If your wires are visually cracked, both near the distributor and at the plug connectors, you should buy a new wire set. The set will come with the correct braiding, new plug connectors, and new connectors at the distrib end. They will be assembled and ready to install. There are others on this forum who endorse some types of aftermarket wires, I don't. My recommendation is to buy a set of factory wires through whatever source you can find them. If you don't know the car's history a new cap & rotor is not a bad idea.
Good luck with it,
Pete

TonyG

Pete & Anthony,

While Porsche specifies the Bosch plug, I can tell you from much experience that the NGK plug is a better plug.

In back-to-back dyno testing, on a dyno, there was a substantial difference when using the NGK plugs.

On my previous 500Hp 944 turbo, the difference was 10 hp, back-to-back, on the same dyno, on the same day, and the dyno chart was much smoother on the top end.

On the 911SC, there was no appreciable Hp gain, but the charts were definitely smoother on the top end as well.

My findings were the result of a friend that owns a Honda race shop, where I was performing the dyno testing. He suggested the NGK. I did not believe him when he told me it would smooth out the top end. After laughing at him, and making my usual jokes about Honda guys, he handed me a set of used Honda NGK's. The bolt head was smaller, but the reach and threads were the same so I tried them. I repeated the test 3 times switching the NGK plugs with the factory Bosch plugs, and an aftermarket Bosch platinum plug. Same results every time.

I wish I had an explantion for the difference.

All I know is that they do make a noticable difference, and as a result are the only plugs that I will run on the air cooled 911 engines as well as the 944 turbos.


TonyG

Steve Weiner-Rennsport Systems

Hi:

There is no question that NGK makes excellent plugs and I recommend them interchangably with Bosch Copper or Silvers.

Everyone has different experiences and there are few hard & fast rules about what plug is best in each engine. Factors that affect which plugs are optimal are combustion chamber shape & design, plug position, plug angles, extended or normal tip configuration, heat range, and A/F ratios.

Further, plug gaps also make a big difference. If one has sufficient ignition voltage & current, one can open the gaps to .040-.045 to pick up better drivability and more HP. Porsche OEM ignitions do not sustain those wide gaps and must run something in the .028-.030 range to avoid a high RPM miss.

I'd also mention that Bosch Platinum plugs have really been the source of all kinds of misfires and stumbles and we'll not use them in ANY motor. Anyone making comparisons between Platinums and anyother type of plug can and will find more performance,...

One last note,....making comparisons between each manufacturer's heat ranges are not precise relationships and sometimes one needs to try different ones to find the optimal heat range for each engine and how its being used. This is especially important with turbocharged or high-compression engines.

TonyG

Steve Weiner-Rennsport Systems

The comparisions I made, on the dyno, were with a standard Bosch plug (per the manual) and a Bosch platinum plug, and a standard NGK plug.

In all 3 cases, the NGK plug was superior.

TonyG

Anthony DiBernardo

I would like to thank everyone for their input. I think I will install the NGK plugs and get a new cap and rotor and wires. I will report the results.

emac

Tony
I had a problem just like yours. I changed the wires, plugs, cap, rotor and it was still there at just about 3k. I was going nuts and when I was just about ready to give up I had my hand around the coil, with the engine off. and one of the small wires that connected to the positive side of the coil fell out of the spade. What was happening was it was shorting out around 3k and a two cent spade cured my problem. I hope this is the case with you.

Ernie 81 SC

e911

Steve,

What do you suggest for a 83 EURO SC. If my memory is correct, Wayne's book recommdends a different plug than the US models. I remember seraching for them a few years ago and ending up using NGK 2611 B9ES. I don't have my research with me , but would appreciate any comments / suggestions.

Earl

Peter Zimmermann

Earl: Good job! The factory recommended plug for your car is the WR3CC Bosch. The "R" is mentioned in some tech info, ignored in others. It's meaning is the plug has a suppression resistor. The "3" is the heat range, which is quite cold. The first "C" indicates a 19mm thread reach with a normal electrode. So, drop the "R" and you have a W3CC - an almost perfect cross reference to your B9ES. (I have no idea what 2611 means). With heat ranges you have to remember that as Bosch numbers increase the plug gets hotter, with NGK the opposite is true.

So not to be misunderstood, this thread has been one of specific information about specific models (911 SC) of 911s. For the right application I love NGK plugs, but during my career, that has spanned more than 30 years, working mostly on 911 automobiles, almost always 5 days a week, I discovered that NGKs certainly have their place. I had great success using NGKs in 1969 - 1973 MFI cars, especially Es and Ss. Those cars came to life with a set of BP ("P" = projected electrode) 8ESs. As the car's aged, we found it helpful if we went one heat range hotter, to BP7ESs. If the car was used primarily to commute with, or it had gotten pretty tired, we switched to BP6ESs, with a warning in writing on the invoice that if they were going to go to Vegas we had to go with a colder plug. With the NGKs MFI adjustments were more precise - no dyno needed. It's amazing how good a butt-dyno can be. As Steve W. says, it's all about combustion chamber ccs, plug gap, compression ratios and many other control factors. I've seen results more than 10 hp apart with like plugs, and if every plug is not gapped accurately the results can be even greater. With CIS cars being precise is the key - from cam timing to plug gap to deck height. Tony's findings are largely unimportant (there is not nearly enough info here to make a complete analysis), a different car tested on that same dyno the next day might have produced a couple more ponies with a different set of Bosch plugs. By the way, Earl, your car is about half a point higher in compression than its comparable USA model, that's why Porsche went with a colder plug. They also must have found something during testing that required a normal, vs projected, electrode.

Ernie: We've seen the same problem, that you had, with customer cars. For what it's worth, it's a rare one.

Pete

Steve Weiner-Rennsport Systems

Earl:

IMHO, the B9ES plugs are far too cold for your SC unless you are driving for miles at top speed.

I would use the projected-nose NGK BP7ES for all around street driving.