Are race ignition leads necessary?.... Discuss

Competition engines and ancillaries - general discussion
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Snakeman
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Are race ignition leads necessary?.... Discuss

Post by Snakeman »

Hi Guy & the world!

I have a stage II 2.0L TC which is fuel injected, the details of which are posted elsewhere on this site.

A recent discussion with other parties have prompted the question about ignition leads. Now we all know that if you ask a supplier of 'big fat race spark plug leads' if race leads are really required or not, they will almost certainly respond with a resouding YES. But why?

If normal OE leads can cope with all manner of conditions then why are 'Race Spec' ones better for racing?

It seems to me that unless you are running a super high compression ratio where the ignition KV's will be sygnificantly higher then there is little risk of arcing or spark degridation from OEM leads. Or have I missed something?

Geoff W
Fahrell
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Re: Are race ignition leads necessary?.... Discuss

Post by Fahrell »

Snakeman wrote:Hi Guy & the world!

It seems to me that unless you are running a super high compression ratio where the ignition KV's will be sygnificantly higher then there is little risk of arcing or spark degridation from OEM leads. Or have I missed something?
Good question, Geoff. It seems that you have answered your own question above.

the use of high compression/high turbo pressure/Rich mixture/wider spark plug gap plus a spark amplifier (a good one) normally generates HT leaks across the entire system from the coil to the spark plug.

The manufacturer of the spark amplifier I use says that we have to increase isolation of cables (leads?), external porcelain of spark plugs and remove any metal near cables, distributor, coil etc... using HT tape and/or crystal silicone tubing. He says It's mandatory... And he doesn't recommend all the frizz about "race" cables, suppressive, etc... He recommends the original one plus aditional isolation.


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Guy Croft
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Post by Guy Croft »

I have run many different types of HT lead and wouldn't ever waste my time looking for a performance difference between them - if they in good condition - ie: matched rated resistance quote by manufacturer.

I certainly regard the robustness of HT leads as being of over-riding importance, having fixed more than I can count, even new ones.. leads that don't separate when you try to pull them off, (or need pliers - ergo BMW, which are a total fright to work with) leading to torn knuckles etc.

Does anyone make super-strong leads? Would make a nice magazine article 'HT lead rip test..'

You know about engines and you're no fool Geoff! But there are plenty of fools out there. Those who will hang or bolt almost anything on engine in an attempt to make it go faster (or make look faster/shinier) and avoid really difficult tuning work inside the actual motor.
This of course is why there is so much 'guff' written on the internet about turbochargers eg. The supreme 'bolt-on' mod. Ho ho. Not to detract from informed observation regarding plug lead performance I'll just say that as far as I'm concerned 'high performance' plug leads (and several other things so far discussed on my site) rather falls into the er, sorry, 'snake oil' category!!

GC
Snakeman
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Post by Snakeman »

OK I have trawled the Google web and found some reference to electromagnetic interference (EMI) from spark plug wires causing erroneous signals to be sent to engine management systems in the same manner as RFI (radio frequency interference) can cause unwanted signals to be heard on a radio receiver.

There are also claims that engine driveability problems ranging from intermittent missing to a dramatic loss of power can result when engine management computers receive signals from sensors that have been altered by EMI radiating from spark plug wires. Mmmm..

As I said earlier a good set of standard leads should be perfectly capable of achieving the same result. The only sensor on my injection system that might be sensitive to EMI is the crank sensor which already has a shielded cable, and the ECU is tucked away from in the passenger compartment. I guess if one was to tie wrap the ECU to the ignition cables then maybe‚¦

Guy, I like your connection between race leads and Snake oil. I remain un-convinced that race leads make any improvement over a good set of standard leads. That is unless someone can persuade me otherwise?

Geoff W
Guy Croft
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Post by Guy Croft »

Yes, I hear the FI harness/system rumours too.

'resistive plugs must be used because some spark plugs can interfere with the throttle potentiometer signal..' etc etc.

With some systems, I suppose, there will be a disclaimer on the box (like the ones on many food products - incl peanut packets, 'may contain traces of nuts') that reads:

'Caution. May not work if fitted to an engine.'


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Julian
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Post by Julian »

We had a little discussion on this last month (viewtopic.php?t=436&highlight=). The concensus from pretty much everyone is that the overriding factor (as already mentioned) is the quality of construction and the longevity of the component.

Anything that claims to improve performance by fitting a different lead is only likely to work if the leads being replaced have degraded which does happen over time. More importantly most replacement leads are made to a poor standard and likely to degrade very quickly by comparison.

The answer is to rely on the quality of OEM leads - as already suggested - or on finding someone that works to an even higher standard.
Chris H
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Post by Chris H »

resistance checks on HT leads can be hit and miss, a small break in a decent HT lead will mean infinite resistance but it will happily fire the plug under all conditions.

OEM I have found tend to be the best.

Magnecor the supposed best of the best of the best - sir! The quality is awfull lately, they pull apart and unwind. Carbon core wrapped with silver wire for suppression.

OE gear is the best.

This is a bit of a dodgy method but I have foudn it can work wonders. OE leads after a while can get stiff, option is replace, however, in a few cases i have fouund chucking it in the washing machine (no seriously) and on a 90 degree wash, gets them not only clean but supple again!

I can think of 2 cars (1.4 ohc renault and a 1.8 zetec) where you could see the lead arcing out in the dark, the leads were stiff, in the washign machine, leads were flexible again and no more tracking, missfires gone.

Doesn't always work and if the mrs catches you then it can be awkward. Bit like when she comes home and the ovens on and theres a cylinder head in it.

EMI and RF interference is very real, you just need to have the radio on and run with unsupressed HT leads or non resistive plugs and you can hear it!
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