Spark plugs - I need help

[geoffbeaumont]

What spark gap are you running, then, Nige?

I started out with 1mm gap on a set of champions (don't know the exact spec - but boggo ones) - only lasted a couple of thousand miles, but that was no shock as I swiped them off the old engine and they were due replacing when it died.

Now running NGKs (again, can't remember the model, but the standard ones recommended for the RV8), gapped at 1.3mm. Runs beatifully on petrol and LPG (well it did before the head gasket went...), and no signs of deterioration yet.

Haven't had it really, really, hot though - I've ragged it silly, but only on the road where it's getting plenty of cooling.

[Hybrid_From_Hell]

What spark gap are you running, then, Nige?

I started out with 1mm gap on a set of champions (don't know the exact spec - but boggo ones) - only lasted a couple of thousand miles, but that was no shock as I swiped them off the old engine and they were due replacing when it died.

Now running NGKs (again, can't remember the model, but the standard ones recommended for the RV8), gapped at 1.3mm. Runs beatifully on petrol and LPG (well it did before the head gasket went...), and no signs of deterioration yet.

Haven't had it really, really, hot though - I've ragged it silly, but only on the road where it's getting plenty of cooling.

I have just used the std gap 32 thou .8mm on V8 EFI Std PLugs - BPR6ES

Seems that I should go colder say BPR7ES or even BPR8ES and general advice is to gap up to say 1.1 - 1.3mm

Thoughts ?

Nige

[geoffbeaumont]

I have just used the std gap 32 thou .8mm on V8 EFI Std PLugs - BPR6ES

Seems that I should go colder say BPR7ES or even BPR8ES and general advice is to gap up to say 1.1 - 1.3mm

Thoughts ?

Nige

Gap for EDIS varies for different cars, but 1.3mm seemed to be pretty common - I'd have thought the size of gap possible is going to be largely determined by what the ignition system is capable of driving a decent, reliable spark across, and the EDIS coils pack a great deal more punch than your old ignition (as you found out ).

Of course, someone who actually knows about engines is now going to come along and explain why running a big spark gap on an RV8 is a really, really bad idea

[Hybrid_From_Hell]

Hmmmmmmmmmmmmm

Plug gap I am puzzled over - but RR Platinum plugs have 1.1mm as std with the bosch coils etc, very similar outputs apparently.

I think its Plan A time now

BP7RES poss BP8RES and a 1.1 or 1.2mm mm gap and see.............

Unless I get anymore info ?

Nige

[Bull Bar Cowboy]

BP7RES with a 1.2 / 1.3mm gap …………….. that should do the trick ………….. BP8’s will be harder to procure & may cause other side effects if you go too cold ……. like the tickover can get very, very lumpy.

Ian

[Hybrid_From_Hell]

like the tickover can get very, very lumpy

No worries there Ian - it already is

Will touch up mate in motor factorsd ( ) for a set of "Staff rate" BPR7ES and treat myself to a proper gap reset tool

why is increasing the gap from .8 to 1.2mm going to help ?

Nige

[imspanners]

Bigger gap = larger spark = better bang.

The EDIS is capable of firing across 1mm gaps easily.

For example the EDIS equipped Mondeo 4cyl uses a gap of 1mm

However, the EDIS equipped Mondeo V6 uses 1.3mm gaps...

Run them at 1.1mm and see.

[Diff]

why is increasing the gap from .8 to 1.2mm going to help ?

Nige

Hi Nige, bigger gaps mean bigger sparks, therefore better chance of completely lighting every bit of mixture in the cylinder. BUT the bigger the gap, the more load is placed on the HT ignition system. IF there is an easier path to earth than across the spark plug gap, the spark will take the easier route.

This is why you need decent leads with a high power ignition. The sparks are quite capable of creating microscopic holes in leads, boots etc.

It is harder for the spark to jump the plug gap under different conditions.

For example a weak mixture (which may be present at different revs), An overly rich mixture(particularly in a hot engine, High compression (effective compression is highest at full throttle), and at high temperatures.

In simple terms, under these conditions the air/mixture present between the electrodes does not 'conduct' electricity as well. When this happens, the load on the HT system increases, and the likelyhood of a misfire or damage to the leads etc increases. It is important to note that under these conditions the misfire may not be a total failure to light the mixture, there may simply be poor combustion, which is not detected as a 'hiccup', but rather a tailing off of performance.

So since the conditions within the engine vary at different times, you need the biggest gap which your ignition system can cope with when the conditions within the cylinders are at their least favourable.

I can't remember what the compression ratio on your Eales V8 is, but if it is much higher than the v8s with similar ignition systems you are comparing plug gaps with, you should consider a slightly smaller gap than they have.

By the way if the HT leads have suffered any insulation breakdown as described above, they will always lose power to earth whenever the 'hard to spark' conditions occur in the cylinders. This means they may be working fine most of the time.

Regards,

Diff

[Hybrid_From_Hell]

Ta for the info

Comp is around 10.5 : 1 IIRC.

Leads I am also thinking of redoing, they were cheapliong ones from VWP and are horrible at the plug ends, so was going to make up some "Better" ones now it all works (apart for this prob ), but getting the decent bits is very difficult !

RR 4.6s late bosch HO Coilpack have gap of 1.1mm, so might start there ?

nige

[MogLite]

This is a great thread

Nige - to go back a while P38's changed their ignition system late in 1998

Before the change it was 2x4-way coil packs, and BP6 style plugs - thats what I've got.

After late 1998 - it became the 'Thor' engine ISTR, that had 8 individual coil packs and better MPG ISTR too.

Hope it helps

[Diff]

Ta for the info

Comp is around 10.5 : 1 IIRC.

Leads I am also thinking of redoing, they were cheapliong ones from VWP and are horrible at the plug ends, so was going to make up some "Better" ones now it all works (apart for this prob ), but getting the decent bits is very difficult !

RR 4.6s late bosch HO Coilpack have gap of 1.1mm, so might start there ?

nige

I don't know, but I suspect that RR 4.6 was ony 9:1. If it is, then I would use 1mm gaps, to start with, or Possibly 1.1mm with magnecore leads. Even then I would be careful. Even if the leads stand up to the loads, you are putting extra stress on the coil packs and too bigger gap will hurt performance rather than help it. The coil packs will have a shorter life if they are overloaded. 10.5:1 will put a lot of load on the ignition at full chat on a hot engine.

Regards,

Diff

[Bull Bar Cowboy]

Yeah …………… what Diff said…………. plus,

With a tuned engine running under arduous conditions, the plug heat rating is probably more critical than the gap. The combustion heat is affected in many ways, but the biggest influencers are mixture, with timing & CR plying a significant role. IIRC the biggest influencer on combustion temps is the amount of oxygen in the cylinder payload ………… more oxygen means hotter running ……… so if you want to use BP6 plugs then move to the Alps !

Your engine has alterations made to all of these, with the latest being timing & mixture. I suppose a good way to enforce what Diff has hinted at is the change in mixture that was required due to the more efficient spark system. Remember also, that the ignition system you are now using produces a hotter spark.

Probably under normal road conditions your engine would be fine on the BP6 plug, however, once you get into the slow moving, high load off road situations then the plug nose is getting way too hot and then spark instability occurs ………… in your case this is chronic misfire ……………. have a good look at the plugs for the telltale signs of overheating …………. the centre electrode insulator will be glazed and sometimes cracked, although this can be difficult to see with the naked eye. You may also note deposits on the insulator that look different and are difficult to remove ………. This is referred to as blistering. When the cracking occurs the plug is permanently damaged and will usually randomly misfire. In extreme applications the electrodes melt when you get it wrong.

The actual gap is a bit of a compromise. Small gaps mean a short spark duration and this is associated with the spark being cooler and weaker. Larger gaps mean a longer spark duration and this a associated with a hotter spark, but the down side is that it places more load on the HT system (its probably better described as a significant increase in the HT system duty cycle). However, the larger spark has the effect of igniting the flame front more effectively and it will do so under the very varied conditions of timing, mixture etc.

As a point of interest platinum, iridium, and multi electrodes plugs have no significant performance increase over conventional electrode plugs. There introduction was to significantly increase the service life of the plugs.

After you have gapped the plugs and found the optimum setting………….. and with EDIS that going to be in the 1.1 to 1.3 mm range …………… check the plugs after a few K/miles for abnormal electrode wear. This can occur with widely gapped plugs due to the electrode faces not being quite parallel, however, I wouldn’t have thought that it will apply in your application.

Right, I’ve finished dribbling on the page now …………… I’ll go back to sleep

Ian

[spiffy_lida]

heheh... nice. (i need to find some freakin used hotel matresses )

[imspanners]

Oh, and get yourself some silicone grease.

It's for putting in the rubber section of the plug boot. Stops the spark from tracking down the side of the plug ceramic.

[Hybrid_From_Hell]

Ho hum,

Just picked up 8x BPR7ESs..

and even ordered a gapping tool (sealey VS119) for a few quid to make life easy(ier)

Time will tell.............

Ta for all the input

Nige

[Wattle]

Just to throw my tuppence in.

Years ago when I was into motorbikes, me and 4 mates went to the Elephant Rally in Austria, this is Febuary and it gets very cold (minus 20 - 25 centigrade at night). We were all riding BMW twins, and mine had NGK Platinum plugs fitted. Mine started every morning without fail, but we then had to take my plugs out and fit them into the other 4 bikes to start them up. Once they were warmed up they would run ok on their ordinary plugs.

Impressive!

Phil Watson

[Hybrid_From_Hell]

Phil,

Ta, but at nearly £8 a hit I 1st need to see if I can get it all ok with cheap and cheerfulls.

8x BPR7ESs cost me £11.50 (mates rates) so a plug n a bit

If I have to dump then every 2000 miles that fine, but I may yet have to go BPR8ESs ?

Will also look to get some better leads too

Thats another prob altogether......but I have just got off the phone and now have a cunning plan

Nige

[Diff]

That is an interesting titbit Phil, which reminds me of something I omitted to say earlier.

Platinum, and particularly iridium plugs, although primarily give a longer service life, have another advantage over standard plugs. Because of their thin and highly conductive electrodes (particularly iridium), they do not put such a high load on the HT system compared to standard plugs with the same gap.

This means less fouling, big sparks and less load on the HT system. Obviously you pay through the nose for iridiums and most engines won't see much of a benefit to warrant the cost, though some might.

Regards,

Diff

[geoffbeaumont]

I can't remember what the compression ratio on your Eales V8 is, but if it is much higher than the v8s with similar ignition systems you are comparing plug gaps with, you should consider a slightly smaller gap than they have.

For the record mine's a 3.5 out of '92 disco, completely unmodified apart from the ignition, so I guess it'll be 9.35:1. Definitely not a straight comparison with Nige's Eales

[Jon White]

I'm running the EDIS on mine with the plugs that were in it when I bought the engine 2 years ago - I havnt even checked the gaps on em!

Runs like a sewing machine...

Mines just a carbed ex range rover 9.35:1 V8 with the pulseair removed on twin SU's.

Jon

[FridgeFreezer]

Just shopping for plugs for my (about to get built) 4.6, and this is confusing me. According to Paddocks, they sell these:

Spark Plug RN11YC - V8 Petrol from XA410482 - RANGE ROVER P38A - ERR3799

Which THIS says are equivalent to BPR5ES. I'm ignoring the later platinum ones which cause an acute pain in my wallet

Confusingly they then sell RN9YC and RN12YC side-by-side for the 3.5 EFi with no mention of why you'd want one or the other. Again according to the spark plug site, the RN9YC's are ~=BRP6ES and the RN12YC's are ~=BPR5ES.

So, for a reasonably stock 4.6 and a bone stock 3.5EFi what the hell do I buy?

[Tonk]

So, for a reasonably stock 4.6 and a bone stock 3.5EFi what the hell do I buy?

WD40?

[Diff]

Just shopping for plugs for my (about to get built) 4.6, and this is confusing me. According to Paddocks, they sell these:

Spark Plug RN11YC - V8 Petrol from XA410482 - RANGE ROVER P38A - ERR3799

Which THIS says are equivalent to BPR5ES. I'm ignoring the later platinum ones which cause an acute pain in my wallet

Confusingly they then sell RN9YC and RN12YC side-by-side for the 3.5 EFi with no mention of why you'd want one or the other. Again according to the spark plug site, the RN9YC's are ~=BRP6ES and the RN12YC's are ~=BPR5ES.

So, for a reasonably stock 4.6 and a bone stock 3.5EFi what the hell do I buy?

Don't worry about the Paddocks info, and don't fit Champions. NGKS are better.

You want BPR6ES gapped at .9mm for the 4.6(pre 1999) and the same BPR6ES for the 3.5, but gapped at .8mm.

Assuming you are using the stock ignitions from the donor cars.

Regards,

Diff

[BogMonster]

WD40?

Land Rover fit Champions.

Which probably means they are the cheapest and NGK are better

[FridgeFreezer]

Cheers Diff - seems paddocks only sell "genuine" Champion plugs, no NGK to be found