Porsche Enthusiasts Club Forum

Hi Folks -

Just to question to how each of us run our motors, what spark plugs do you fit? I have NGK three pins as recommended by some tech chap that said fuel injection motors run 'better' on them, as opposed to a single pin. Have kept will them so far without problems...

Dave
CT 944S2

Hi

I know quite a lot about plugs as I use so many different heat ranges in NGK for my Nitrous system....

For a 928 as a example ....its NOT recommended to use multi electrode plugs...neither triples or quads...

Now a 944 is basically half of a 928 engine....therefore i would never use them in a 944...

When i bought my 928 over a decade ago...it had just been serviced and had a missfire.... new quad plugs which I changed for standard NGK BRR6ES and the miss vanished...

As a general rule on any car... try to stay within the heat range that the manufacturer recommends... the heat range is the number, such as "6" or "7" ...

The difference between a 6 and 7 is around 70 degrees C in operating temperature...i run 7s normally for the road and 9s for high speed runs....

One heat range out will be ok-ish on any car .....more than one range out will cause bad running , and high fuel consumption etc...

All the best Brett

Thanks Brett for your reply - I have also heard that a three pin gives a weaker spark?

Dave

I use NGK Iridium's in mine, as Bret states heat range is important depending on use.....they are single electrode.....a word of warning on Iridium plugs, only use good quality plugs from respected manufacturers. Some make's have been known to have their ceramic centre break up, I had this myself many years ago...also some Dyno's ( the one's that know) won't allow cars to run with Iridium plugs fitted

Pete

Hi Dave

The whole point of a spark plug is to create a spark at a particular time...and of a particular amount of power...

Now one of the problems with multi electrode plugs is that electricity always takes the path of least resistance...

Therefore you dont know which of the three or four electrodes will spark ...and if one electrode is slightly different to the others it may or may not use that one and it may or may not produce the correct amount of power....

You are therefore increasing the risk of a missfire by either 3 or 4 ....

Couple of other things to consider.... our cars and engines were never designed (because of their age) for multi electrode plugs....

Cylinders heads CAN take advantage of multi plugs ..IF they are designed for them...ours are not...

Its also difficult (although not impossible) to set the gap on a multi plug....and anyone who has fitted as many thousands of plugs like myself, knows that no matter what the manufacturer says,,,they do NOT come ready gapped from the box...

So a decent set of feeler gauges is always a good buy...

Regarding the Iridium or Platinum or other esoteric metal tipped plugs....personally I cannot run them as Nitrous doesnt like them lol...

But for a general rule...the same applies as above ...our engines were not designed for them anyway...so dont bother...

So... for your 944 use either 6s or 7s (whichever your manual says) ...by the way Bosch and NGK use a reversed numbering system ...

So a Bosch 7 is exactly the same as an NGK 6..

Hope this helps

All the best Brett

Interesting commentary on multi electrode... On recommendation, I've bought a set of Bosche Super 4 for the 968 which are due to be fitted at next service....

Hi

Here are some pics of what happens when you push a plug too far for its heat range....

This is a plug that I ran for precisely 1/4 mile (Santa Pod) ...

Brand new at start of run...

BUT wrong heat range...was a Ngk 7 and should have been a 9 ...and was running at over 8000 revs...testing my Nitrous...











What those pics mean is that the plug fired too many times and increased the heat drastically, so the earth electrode basically melted as if it had been a 9 it would have taken the heat that me and my Nitrous system forced through it....

I had a slight missfire lol

All the best Brett

In my S2 both engines ran a variety of plugs! The first engine ran Bosch plugs and I think I put those in again ; I bought the car with a poorly cylinder. The second engine ran Nology Silver spark plugs. It was always a hard starter (it would not idle great after being started) and going to Bosch Supers did not really make any difference; the HT leads were new as well. OTOH the battery could have been better and maybe the ICV could have used a clean.

The Turbo came to me with NGKs which it ran very well on. I changed them to Bosch plugs again which it was fine on.

The Clio Sport forum is no different to plugs. Everyone says you should run NGK platinums as specified by Renault (PFR6E-10). They do seem to last a long time however (some have noticed little wear at 70k which is the service interval by Renault!). Mine however came with Bosch Super 4s; probably because a certain European Car Parts website told the previous owner that they would fit and would be cheaper. My car ran fine with them where some had issues from the off, but after 30k they had seen their best:



What I have understood is that Iridium and platinum plugs do not help in giving a fatter spark at all. What they do help with however is a much better spark life and in something that runs LPG this can be the difference between poor running when an oil change is coming up or it running hassle free for a minimum of 40k miles IME.

However it's not that simple and there are so many variables! When I bought my Triumph Stag I bought a set of BP5ES plugs over the stock BP5Es. It always misfired/backfired at 4kRPM under full throttle. I had all sorts of people say it was the carbs or coil etc. One day I went to BP5Es and the problem went away. It was the plugs for sure but IIRC the source of origin was not great for them (they were bought from Halfords in the plastic wrapping). It's the only time I've ever had an issue with NGKs.

For what my sixpeneth is worth. What ever plugs you fit be very careful if buying off the internet, there are plenty of fakes out there. Nuf said.

If I service it, always NGK never had an issue.

I'd agree but with the below proviso.



To be fair, it is the only time I have had an issue with NGKs in any car in my 16 years of tinkering. What I would say is to ensure the NGKs are made in Japan. I think the ones in plastic packaging from Halfords were made in France or somewhere like that.

Personally I always use Bosch in my S2, because they are good-quality and ridiculously cheap if you know how to buy them. At just over £1 each they are changed every 5000 miles, along with the oil and filters.

Many, many cars are running on the wrong plugs - often unknowingly - because people don't realise how important it is to fit the right ones. A spark plug is a complex thing that does a simple job in a very harsh environment and there is a lot of BS spouted about them by many people (including in this thread). My time in automotive diagnostics taught me some simple rules; fit a well-known brand of plug from a reliable source and change them often. Always fit the right ones for the car and, if a car is mis-firing or has running problems, change the oil, filter and plugs and either inspect and thoroughly clean the leads or (better) change them. This will cure 90% of poor running problems. Much the same applies with modern coil-on-plug systems although they are a bit more involved to change.


Oli.

ETA: I use Bosch single-electrode and change them more frequently. There is nothing inherently wrong with the multi-electrode type and they supposedly have a much longer service life. I am always dubious about extended change intervals though and much prefer the cheaper, simpler, single-electrode type and change them frequently.

Care to elaborate?

Vauxhall sell the WR5DC+ model (which is correct for S2's) for around £1 from their trade club scheme, as 'Spark Plug 15'. If you aren't in their trade club scheme then you can buy them for only a fraction more than that on eBay, such as these;

http://www.ebay.co.uk/itm/252015426074? ... EBIDX%3AIT

I've bought from this seller and they are genuine Vauxhall (and hence genuine Bosch) parts, made in Germany.


Oli.

I'm getting some new plugs. NGK BPR6ES and BPR7ES are both ok for the 2.5l 8v engine aren't they? One is just hotter than the other.