Bosch WR78 plugs

[terryj]

Having seen discussions on use of these spark plugs I am a bit confused regarding W78, WR78 and WR78X.  I want to try these in a Vitesse 2l Mk2 but don't know which to order.  I note Pete's comments about not ordering plugs with an R in the number but also others have used WR78 satisfactorily.  Green Spark Plug Co. are out of stock of W78 but do have WR78 and there are some on ebay WR78X.  Is there any difference and which would you recommend please?

Terry

[johny]

Not sure what the X means but R indicates this plug (or ones from other manufacturers) has an additional small internal resistance which helps reduce the radio interference generated by the passing of the high voltage current. This obviously causes a voltage drop but how much effect it has on the quality of the spark is the subject of ongoing debate☺️

[Pete Lewis]

this is pretty conclusive  that yes its on a motorbike but some simple comparisons show 

a non resistive managed around 30kv  the resistive plug managed 13kv   its does go on a while but proves the resistor is corking up the HT    A LOT

 

 

 

[johny]

Trouble is ignition and combustion are a complicated subject and of course vary from one engine to the next. I think spark energy and duration come into it not just the voltage generated and then of course one engine might need the best spark possible to achieve maximum combustion efficiency while another can still do the same with less spark...

[terryj]

Thanks Johny and Pete.  The video does indeed show that non-resistance plugs appear to be preferable so I phoned Green Spark Plug Co. to ask when their W78 plugs would be back in stock and was told that they are now obsolete.  They suggested WR78 plugs would still do the job adequately.

 

Terry

[johny]

Resistance plugs seem to be ok for modern engine manufacturers who you'd think would find an alternative if there was a reduction in ignition/combustion efficiency.

Thats not to say they dont make a difference in older design engines but without some controlled testing on each model who's to say....  

[Pete Lewis]

the number i have changed with missfires on R plugs needs two hands to count on, there again  most are NGK and you need to add in problems of 

rich running contaminating the unglazed insulator  which was discussed in the spark plug posting a good while back 

hence suggestions of  bosch W78 which have themselves become rare 

i wouldnt touch anything with an R in the prefix reducing the HT KV by such a large degree cant be beneficial how ever you look at it.

Pete

 

 

 

[Nigel Clark]

I've used Bosch WR78 and NGK BUR6ET multi-electrode plugs successfully in Triumph four and six pot engines for about 15 years. Sorry to contradict, but my experience is that I've had absolutely no problems with these resistive plugs, indeed they've given easier starting, smoother idling and crisper acceleration than the standard non-resistive single electrode plugs. all a little subjective, and merely my experience. If the ignition system is in good condition, I would say resistive plugs are perfectly suitable for our cars.

Nigel

[Pete Lewis]

Nigel  thats good   there's always two sides to a story   ha 

but the test showing such a large reduction in an already weedy HT makes no sense to maybe just me 

 

Pete

[Chris A]

I've been following this discussion just out of idle curiosity.

It seems that the R type plugs may be ok, but there are cases of them not being so. In that case what is the advantage of using them? If the car is equipped with electrical stuff that could suffer from interference then I would say there is a case for considering them. Otherwise do they improve engine performance? This seems far less clear to me.

Them there is the other point raised here, multi electrodes. The case for using them rather than single electrodes does seem to be more in their favour if a) High mileages are done b) getting at the plugs to re-gap them is difficult or a chore.

In the end it comes down to what works for each person/car, as long as the pros and cons are known.

In my case I run my 13/60 on NGK BP6ES and am happy with them, bought from my local car spares specialist so have confidence they are genuine not copies.

[Colin Lindsay]

36 minutes ago, Chris A said:

In the end it comes down to what works for each person/car, as long as the pros and cons are known.

I think I tried about every available version at one time then realised I wasn't doing either the speed or the mileage to justify most of them. In the end I went for standard single terminal plugs, although I was recommended Brisk motorcycle plugs and have bought four to test at some future stage.

[Chris A]

1 hour ago, Colin Lindsay said:

I wasn't doing either the speed or the mileage

So not driving fast, just Briskly then . . . 

[Pete Lewis]

back to basics 

many places only  sell R plugs as the demand is more aimed at moderns than  Non R for older cars and less sales volume 

if its not the specified plug why would you want to  ??   yes upgrades when its "better" but this might work but  R makes no sense 

bit like putting  your finger in the dyke to cork it up 

we need all the spark you can get , why strangle it ???

pete

 

[avivalasvegas]

Anyone know what the X in W78X stands for?

It took me a long time to find a full set of W78 plugs. The last two are currently on their way from Italy. I really hope they live up the forum's hype

[Pete Lewis]

x  was always  the unknown factor  ???

Pete

[terryj]

Thought you may like an update on this.  Originally the engine would rev OK but was woolly and perhaps missing a little at high revs.  All plugs (NGK) were firing and a nice colour brown.  I fitted a new set of WR78 plugs and took the car for a short test drive taking it up to 4500 rpm in the gears and it accelerated and ran beautifully all the way.  So it would seem that one of the old NGK plugs was probably breaking down at high revs.  Certainly the WR78's have made a noticeable improvement.  Thanks for everyone's comments - they were informative and very helpful.

[Chris A]

To confirm if the improvement is really due to the WR78s you should but a new set of NGKs in and take it for a run to compare the results.

[Badwolf]

What about getting a set of everything and doing a comparison report for us all

[Iain T]

On 16/09/2021 at 18:20, johny said:

Not sure what the X means

Johny,

Just read this thread, I believe the X denotes 1.1mm gap which is too wide for our cars. 

Iain 

[Chris A]

1 hour ago, Badwolf said:

What about getting a set of everything and doing a comparison report for us all

There's a good idea, you are a bright spark !

[avivalasvegas]

Pictured are two new Super 4 W78 plugs. No “R” and no “X”.

Anyone know why they have different numbers printed on them?

[Chris A]

At a guess to identify when/where manufactured. Batch number/factory code.

For example the 2 screw on tops are clearly made from different metals so different batches at least.

More importantly, do they work.

[Steve P]

I have run my 2.5 Vitesse on the 3 prong Bosch ones for a couple of years now, does seem smoother on pickup,i am running a standard dizzy atm albeit with an electronic module.Will see what happens when i put the 123 Tune one in.

Steve

[avivalasvegas]

38 minutes ago, Chris A said:

At a guess to identify when/where manufactured. Batch number/factory code.

For example the 2 screw on tops are clearly made from different metals so different batches at least.

More importantly, do they work.

Will find out in a couple weeks when I put them in! Wasn't easy finding these now obsolete W78s.

[Badwolf]

Typical..supply and demand.

Great product but limited market. 

Lasts for ages so limited extra sales

Limited sales means nobody wants them so discontinue them

Eventually wear out so none now available

Next thing cheap oriental rip off so everyone now buys them

They don't work properly so nobody buys anymore

Spare part madness!! KYB shock absorbers anyone?