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Spark plugs - I need help

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Plugs prob

I have found today the eales V8 Mit EDIS 8 unit is fairly waterpoof, I say this cos I hit the ford at 2.6 foot deep flat out 2nd gear, water over boonet in through vents and into Lap :i-m_so_happy::hysterical:


I was at an event, had to recover a dead RR, used kenetic strop loads of revs and engine got hot and when I say hot not silly hot just hotter than normal moving to the "I'll keep an eye on this" Hot

As it was under very heavy load and got hot - a £$^&* Misfire


But these were new, they had done only 27 miles pre this new misfire, but once the engine has cooled down considerably the misfire went, I have had this before, worse, the misfire finally did not go away, a change of plugs saw it gone, so I know its a plugs issue.


I need some ideas, the one I have in my mind is to try the late V8 disco 2 plugs, these have same thread and reach but differeing heat values and seem to be there to cope with a wasted high output ignition

For those who are unaware the spec of the engine is

John Eales Built 4.5 V8 Rover EFI

High compression pistions with valve cut outs

Big valve heads, ali rods, balanced and tweaked generally

High Lift long duration cam, rhodes bleed down lifters

EFI is a flapper system, Jag injectors and AFM

ECU adjustable, set at plus 30.5% fuelling

EDIS 8 plus Megajolt system,

Plugs are NGK BP6RES

Thoughts and ideas to think of, a few knowledgeable mates have said go for BP7RES or even higher BP8RES

One of the probs is with a wasted spark system the plugs are being asked to fire twice as often as a std V8, plus the engine revs to 7,000 RPM, plus the heat this generates etc etc etc

I have a mate who is going to hunt at work for a set of the bosch Disco 2 V8 plugs, but anyone here have any thoughts ??? (and no, a diesel refit is not a thought ta everso :P )


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i had a problem much like this on my last engine (crossbolter 4.0, blueprinted, CR at 10.4:1 etc etc)

always got it when i ran on lpg as the flame was so much hotter- i went to BP7s which helped for a while, then went wrong again. Finally went for BP7 platinums which, whilst v v v v expensive, were perfect and sorted out any of the ignition problems i had.

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Disco 2s are platinum too I think and have a needle rather than a matchstick size tip, also MUCH Bigger gap and are rated at around a 6 rather than a 8....

Intersting ta for the info...hope theres a skip load more to come from forumeers :rolleyes:


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Are you gonna do anything about the loose nut behind the wheel?

The extra heat was probably from the sweat popping out of me :)

I had my head out of the RR and was saying the RR owner "do you wanna get in and do thisssssss arghhhhh ". A few moments later it was ok, we'd stopped, travelled about 3 foot back and 6 foot right, least not much sand came in the window.. I'll get the pictures off the wifes phone later..

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I woulndnt bother going to platinum or iriduim plugs in a N/A motor ,i would only consider them in a blown motor.Cost is the real down fall BUT they do last ALOT LONGER than std plugs and with the ignition system you are running you could EASYLY use 1.1mm+ gap.This in turn would give better running etc.


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Look forward to the pics, F me you were dead in a dreadfull area, :lol:



I think some of the platinum data is longer service intervals, but, bear in mind a wasted spark system at 6,000+ rpm means the plug is actaully doing 12,000 RPM and the heat build up too....

There has to be an answer, and this has to be something others have come across.

Apparently if you shove BP6RESs in a disco 2 you'll have a dead motor very quickly - WHY ??? thats what I wnat to know, then I am onto something !


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So if you want the best type of plug for your motor Nige just stick it on the dyno and put a few differant sets of plugs through it,you WILL see some supprising figures!!!

If you want to go the whole hog i guess some NGK race 7 plugs would do the job,the electrode is a thin sliver of iriduim,they are designed this way so if the plug does over heat and fail the electrode will not cause any damage to the internals.

Forget all the gimicky type plugs like like splitfires etc we tested every concivable plug on the market in different engine configureations from Subaru WRC engine,Honda touring car,Toyota v6 SR2 car etc and EVERY time we went back to GOOD QUALITY plugs from either NGK or DENSO.

If you are having probs with water still with the wasted spark just try and run the gap narrower with the sort of engine you are running i.e not that high revving etc you wont see any differance other than it should help when water is in contact with the H/T components.


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NGK race 7 plugs

Wots the part numbers for these then ?

I think I may be onto something with the disco 2 plugs, hopefully matey can produce a secondhand set of opnes to try and see.

Dragging a completely dead RR 400 yards up and down huge snady hills and drops takes some horsepower and generated some heat I can say, the underbonnet temp was huge !

I have never really understood the spitfire / 4 prong plusg thingy, and I have removed many and repalced with std NGKs and seen them run better.

I think its a combo of heat and RPM x 2 thats causing this prob.....

If I did "give it large" (which I might have) then thats 7000 rpm (14,000 fires per plug) and that may just be too much for a run of the mill NGK BP6RES 32 thou gap and red hot too :huh:

Ta for the input keeop it coming


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Nige thats not hot mate,Slap on a turbo map some anti-lag and your egt will be up atleast 300 degrees :o

I will have a word for you in the morning see what i can lay my hands on ( they might still be warm :ph34r: )

What is the thread length on the current pugs you are useing?????


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You may find this useful.

It suggests using cooler range spark plugs (eg BP7RES or BP8RES).

The reason incorrect spark plugs shut down Disco2 is resistance. If the wrong plugs are fitted an electro-magnetic field can be produced which works its way back to the ECU, often frying them, or causing them to shut down. :blink:

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Plugs overheating and the insulation breaking down used to be a common problem associated with engine tuning …. particularly the BLMC series ‘A’ & ‘B’ engines.

Hotter engine = cooler plugs……………. for general running your engine should be fine on BP7’s ……… and open up the plug gap to beyond 1mm (go for 1.2 as a start). Remember also, that your new ignition system is producing more heat at the spark …….this has probably accentuated the problem………….. probably the BP6’s were giving borderline performance on the conventional ignition.

Yes, platinum plugs are more heat resistant, but their real bonus comes in the ability for them to perform over many thousands of miles without human intervention……….but you pay dearly for the privilege. Stick with a cooler conventional plug (BP7) and bin them every 6K.


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Thoughts then on fitting the Disco 2 V8 plugs then ?

Big gap, thin electrode, similar ignition system and coils to megajolt, platinum, .......

and erm free :D

I think the chances are a good match ?

Thoughts ?


As long as the heat range is similer and the nose putrusion is the same then give it a go just listen out for MR DET.


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Can a kind soul who has a late 4.6 RR P38 advise on spark plugs used please pref a makers part number not a LR one please ?

Have been doing some reasearch, ......getting mixed answers for the GEMS P38 plugs ?


useful link to website here, have PMd it to White90 who I am sure will add to the already useful thread in the tech forum on plugs


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Been down to see mate who works at a motor factors, luckily he had a spare NGK plug booklet, been a studying :

RR & disco 1 / 2 3.9 AND 4.0 (to 1998) 4.2 AND 4.6 (to 1998) BPR6E OR BPR6ES


RR 4.0 1999 and 3.9 disco 1999 and 4.0 2002 onwards have the different PFR6N-11

delving into the specs :

B 14mm

P Projected centre Electrode

R Resistor

6 6 on heat scale of 2 - 12

E Thread 19mm

S Std copper core gapped 32 thou = .8mm


P Platinum

F 14mm

R Resistor

6 same heat value

N "Special" unknown what ?

11 1.1mm gap

Whats the difference on these latee models ignition wise please esp as it seems a pre 99 RR 4.6 has what I have now and a post 99 has completely differing plugs and what so different on a 3.9 Disco 99 on vs pre 99 re the same plug difference ???



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You seen the price of the platinum tipped plugs then???? That'll be the main difference.

Basically the main reason for going to platinum tipped plugs is it allows the service intervals to be increased as the tips dont erode. Service interval for most platinum tipped plugs is around 70k miles. Remember that on alot of late model motors its virtualy an engine out job to change the plugs - you dont wanna be doing that every 12k miles!

Otherwise the only other difference is the large electrode gap as the later models ran coil packs which gives a bigger spark and hence allows a large plug gap and hence better running.

Putting the expensive late ones in wont help you as they're still the same heat rating. You'd need to run 7 heat rating plugs anyway.

All that taxpayers money wasted.............bluddy students!


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Hmmmmmmmmmmmmmmmm :huh:

Had a long (and very useful) chat with NGK technical a short while ago.

After explaining the prob, he was able to tell me that the Platinum plugs fitted to the Late RR etc, were done for 2 reasosn, 1st that the later plugs are higher qulaity, and are "Better" than BPR^ESs, but also for durability etc.

So, maybe that 2nd hand set might get a try yet :lol:

BUT, he also pointed out that I probably want a 7 or even colder 8 type plug, and that the Late RR plugs are 6s....

He then went to suggest a plug for the engine, made me gulp a bit :


These are Iridium Fine tip 7 (colder) plugs, .....be interested in forumeers thoughts as to :

1. WHY these he thinks are so good ?

2. And generally thoughts on the suggestion ?


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