TR2/3/3A spark plugs for TR2-4

[willeng]

I noticed a post that asked about spark plugs for the TR2-4 engines & the mention of NGK BP6ES.

Being a race engine builder i have tested many spark plugs. It is true that the BP6ES works nicely--up to a point.

The biggest problem using the long reach plugs like the BP6ES is that the end of the plug protrudes to far into the chamber protruding out past the thread in the head itself.
This in turn has a dramatic effect on the cooling of the spark plug which can only be cooled by the incoming air/fuel charge & the contact surface of the thread in the head. If the plug protrudes past the length of the thread it will not cool sufficiently & at higher rpm levels the end of the plug can glow red with the extra heat & poor cooling contact area. If you have a look at how the plugs fit into the head you will notice there is not much metal around the plug thread for cooling as is.

As you can imagine the last thing we need is the fresh fuel/air charge to come into contact with an already glowing hot spark plug & many unwanted things can & will result. Pre ignition & lead fouling, pinging etc.

For this reason we use the NGK-B8HS exclusively in our engines--short reach & the plug cooling is great. Road cars may need to go to one step hotter than the B8HS

Hope this helps

 

[piman]

Hello Willeng,

the idea of the extended reach spark plug is that it stays cleaner due to being in the combustion heat and helps in that the heat range is wider because of this.
Racing engines are different and road cars will not benefit from plugs that suit a hard driven racing engine, even allowing for the grade change. I certainly do not remember any plug fouling\detaonation problems with using standard (in my case Champion) plugs for very many years. I do remember before extended nose plugs were commonplace (that rather dates me a bit) that regular cleaning was required. That was also the days when racing cars started on soft plugs and switched to hard plugs once warmed up.

Alec

 

[willeng]

Gday Piman,

The first part of your reply, is basically what i was refering to:
""the idea of the extended reach spark plug is that it stays cleaner due to being in the combustion heat and helps in that the heat range is wider because of this.""

Being more in the combustion heat we have found to be the problem.

You are correct in that theres not much you can do to a road engine that will show signs of trouble because of the low state of tune. On the other hand a high revving Triumph race engine--to 7000rpm is a very sensitive animal, especially with the old bathtub designed combustion chambers.

If, like you mention that fouling was common place with the short reach plugs, there was obviously causes for this as you will agree. Seldom is it a case of the plug itself unless the wrong plug or a faulty one or ignition system problems exist, plug fouling problems are normally associated with oil burning, wrong mixtures, wrong heat range etc.

Years ago an old car sales yard trick was to actualy extend the plug out of the chamber to get it out of the burning oil etc so when they went to sell dubious cars to customers they wouldn't foul the plugs with the test drive.
I have found many old oil burners with extra washers under the plug seat for this very reason.

Horses for courses though, as you'll agree in the long run it is better to eleviated the "cause" of the problems rather than to create others with quick fixes.

Long reach plugs are a problem for racing applications in these engines we have found. It is the electrode ground on the plug tip that is the problem, all interesting stuff though.

Thanks for the reply

Willeng

 

[piman]

Hello Willeng,

Yes, I do agree with what you say and in the times I was refering to I don't know if the fuel was so good and also people tended to have much older cars than is normal now so worn engines would contribute.

Alec