Will these spark plugs fit?

[seaandmoor]

I've looked through the workshop manual but no help with specifications.

I'm looking to buy Denso Iridium IW22 spark plugs for a 130 big valve 1558 lotus (1973) According to the manufacturer these Denso plugs have...

Thread diameter 14mm
Thread reach 19mm
Seat - Flat
Hex size - 21mm
Tip - projected

Can anyone tell me if they will fit in place of the old N7Y plugs please?
Thanks

[martinbrowning]

Hi there,

The physical dimensions that you have given match my NGK BP7ES plugs, which I have in my 1972 S130 Twinc, so they should fit ok. Couldn't comment on the performance characteristics of the plugs though.

regards

Martin B

[leifanten]

The NGK BP7 work fine, why try something more exotic?

[seaandmoor]

Thanks Martin and Lief.

I've been reading up on the design of these plugs and the shape of the sparking 'pin' and ground are different as is the shape of the ceramic such that it should provide a better spark and a better shape to form an initial 'ball of flame' to give a better burn on the firing of the mixture in the cylinder. Plus it is a slightly hotter plug and eliminates any tendancy to wet foul the plugs.
As Martin says they will fit, Santa will bring me some and I'll fit them after Christmas.
... unless anyone knows any different.
Cheers.

[pereirac]

NGK actually quote an Iridium version of their BP7ES plug for the Elan, BPR7EIX

http://www.ngksparkplugs.com/part_finde ... esults.asp

I seem to remember reading that resistive plugs required different plug leads??

Carl

[bcmc33]

I seem to remember reading that resistive plugs required different plug leads??

Carl,

I use resistive plugs - so I need to know more about the leads. I will try to check it out.

FWIW, a friend now uses Iridium plugs in his Sprint and says he noticed a significant improvement in performance.

[seaandmoor]

Brian, do let me know what you find out about the plug leads.

I use resistive plugs (with additional shrouds) on another engine because it is fitted with latest Megasquirt EFI with wideband, trigger wheel and coil packs etc and if you don't cut out ALL interferences from plugs/unscreened cables and wires together with ALL the small potential differences (as in millivolts) caused by different earthing points then it just simply won't work or at best is very erratic. I just assumed that all plug cables these days were resistive/screened... I await to be informed!

[bcmc33]

It appears that when using any sort of electronic systems in a vehicle resistor (resistive) plugs should be used. I asked NGK about the leads and this was their answer:

Both part numbers you have mentioned are resisted plugs and can be used
with or without resisted ignition leads.

A plugs internal resistor is purely there to reduce the inherent
electrical noise produced by spark ignition. As long as the ignition
system is in good condition there should no issue using resistor plugs and
resisted leads.

The conclusion is that even if you're only using the simplest form of electronic ignition - resistor plugs should be used.

I currently use BPR7ES plugs in my fuel injected Sprint and plan to go to BPR7EIX as I am told by a number of Lotus users that they perform much better, so with the NGK answer, I guess I don't need to change the leads.

[seaandmoor]

Hi Brian,
Hmm, I don't think they have answered the question at all..

and can be used with or without resistive ignition leads.

there should no issue using resistive plugs and
resistive leads.

Basically they are saying that resistive leads CAN be used and NO ISSUES.
CAN be used implies that they are not necessary... so what's the point of making resistive leads???
To my mind there must be some applications where the resistive leads MUST/CAN ONLY be used otherwise there would be no reason for them to be made; just in the same way that resistive plugs aren't made for no reason.
I'd be interested to hear what they say on that if you have a hotline direct to their techie.
In view of the sensitivity of EFI/EDIS systems to outside interference I'm going to get a set of resistive leads.
Regards,

[bcmc33]

Hi Brian,
Hmm, I don't think they have answered the question at all..

and can be used with or without resistive ignition leads.

there should no issue using resistive plugs and
resistive leads.

Basically they are saying that resistive leads CAN be used and NO ISSUES.
CAN be used implies that they are not necessary... so what's the point of making resistive leads???
To my mind there must be some applications where the resistive leads MUST/CAN ONLY be used otherwise there would be no reason for them to be made; just in the same way that resistive plugs aren't made for no reason.
I'd be interested to hear what they say on that if you have a hotline direct to their techie.
In view of the sensitivity of EFI/EDIS systems to outside interference I'm going to get a set of resistive leads.
Regards,

To my mind the answer was perfect. As NGK make big money from the sale of their resistive leads, and as my question was a perfect invitation for NGK to make a sales pitch, I take the view that what their techie said indicated that the resistive leads are not really necessary, only the plugs. On reflection, it makes sense as the 'electrical noise' starts and ends at the plug. The NGK sales brochures for the Iridium plugs makes no reference to the need for resistive plug leads.

However, I've checked and I am using plug leads with "built-in supression" from the EDIS coil - so perhaps they are of the resistive type.

[Paul Chapman]

For what its worth I have been running a set of NGK BPR7ES ( gapped to 0.030" ) fitted to a set of standard leads for a while now and they have produced what appears to be a smoother engine performance and I have noted no other problems.

[seaandmoor]

Well there are a few people who seem to be pleased with the plugs and mine are on the way.

However, I believe you have emphasised my point Brian - the tech guy says resistive leads aren't necessary... so why then would anybody buy them?
Also how do NGK make big money from producing resistive leads? Surely you can't sell a product, or even give it away, if it is superflous to requirements. Or can you??

So if I can pose my last question: who is buying them but more importantly for what reason? Is there any circumstances known where ONLY resistive leads will do? Just curious now.
I called at local motor factors for a fuse to-day but they didn't understand the question.
Regards all,

[andyelan]

Hi Everyone

All this seems very clear to me unless I'm missing somthing.

Here in the UK (and I assume in other countries too) it's a requirement by law that ignition systems are suspressed. Traditionally, with points/coil ignition systems, this would be done by adding resistance to the plug lead, either by resistive plug caps or resistive leads themselves. More recently resistives plugs have become available. Now I will admit that I don't know much about these but I always assumed they were simply an alternative to suspressing the plug leads. Don't forget, however, its the motor industry who are calling the shots here. If one manufacture chooses to fits resistive plug leads to his cars but another does not, then NGK will have on option but to cover both cases if they want to keep their market share.

My understanding of NGKs reply is simply that if you choose to use fit resistive plugs then resistive leads aren't necessary, however, if your car already has resistive leads, then fitting resistive plugs as well won't cause any problems

Andy

[bcmc33]

My understanding of NGKs reply is simply that if you choose to use fit resistive plugs then resistive leads aren't necessary, however, if your car already has resistive leads, then fitting resistive plugs as well won't cause any problems

Andy

That's how I understood it, Andy.

[seaandmoor]

I feel an experiment coming on.
It doesn't matter on the Lotus because I was really just opting for the plugs because I considered that the shape and size of the +ve 'pin' and earth 'strap' and ceramic 'nose' would give a better ignition of the fuel air mixture and better burn and being slightly hotter would keep the plugs cleaner etc. I can perhaps see if there is any noticeable reduction in interference on the radio although it is pretty good already.

However, on my other car (again originally manufactured with old distributor etc) I subsequently fitted a distributorless ignition and leads taken from 8 coil packs. When plugged into a laptop interference was clearly seen as a significant issue. After some searching a change to resistive plugs cured the issue and it now runs far better than would ever be possible with an old distibutor.
What I could do is to check the existing leads to see if there are any markings first.
If not I could get some new leads that I know are resistive and then put back in the old non resistive plugs. If there is no interference then one only needs either leads or plugs that are resistive (but not both). If there is interference then resistive plugs are the essential part.

Hellooo - anyone still there? I think I hear snores Zzzzz. I know - I think I deserve it!