Plug gap and battery voltage with respect to spark
Turbo Mini Forums

Another query as to plug gap.

I'm going to aim for 35 thou as i've been advised. Anybody done any playing to see what works best?

Would only having just about 12v to my ecu/coil pack cause a poor spark since i'm not currently running an alternator?

Just making sure everything is spot on for the next run on the rollers.

Cheers

I haven't set a plug gap for years, straight out of the packet in to the engine. Never had a problem running an alternator or not.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

im running .6 mm ian ,and yes battery voltage can have a big effect on spark energy ,if youve ever had a car battery gradually go flat ,it acts like a rev limiter that gradually gets lower and lower rpm .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Wil, i'm usually the same as you, straight out the packet into the engine!

It seems like the lower the voltage the less advance i could run at a particular rpm etc. and it would misfire from 4.5k upwards.

I've charged it up and planning on fitting the kubota alternator before the next session.

Iain, do you know the output on these, as I belive it's very low, and when you have a fuel pump, waterpump, and coil pack, are you sure it can cope?? I'm tyring to find out the figures on it, but having no luck at the moment.

Team Racing

My mate with the hillclimb Imp using MS electric fuel and water pumps has no problems upto nearly 9k.

I once measured the current drawn from my battery. At tickover it's 4A so In theory my 18Ah battery should last around 4 hours.

I think my mates Imp had a slightly higher current draw owing to the water pump.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

yeah but i had done a lot of starts with it and was down to 11.9v whilst running (shows on the ECU display on my latop) so wondered if it affected it.

Not sure Jim, but i was kind of hoping to use it as a top up type thing. Those Kubota's must use some electric though, they have lights etc so i'm more than happy it would be enough.

I'll have to do a test once i get it up and running what the output is.

I'm also hoping to use another bigger battery to use as a starter pack.

I would put my ND one on but i sold it like an idiot! lol!

I tried my gaps at 35thou with a dizzy and Aldon ignitor. It misfired like hell, so run 25thou all the time now, never have any trouble.

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but i know with the old wasted spark you can run bigger gaps and its beneficial?

As i say it was my RR operator that recommended 35 thou

All good info on here!

Trial and error is the best, its an easy thing to change! i was at 25 thou and it didnt like it, so i'll try 35 and see if its any different and report back. only thing is i'm changing a lot of variables so wont be able to comment that well.

Far from being frustrating its actually quite interesting!!

bigger gaps are better - IF you can support the voltage needed to jump the gap.

You are running a coil pack design to work at around 14v on less than that - so you peak HT voltages will be lower.

Try closing up your plugs a little and see if the misfire goes.

Alex

AlexF

Iain, The following link may help you.

http://www.spark-plugs.co.uk/pages/technic...s_technical.htm

The NGK code is very useful and the other info is the same.

Thinking about your misfire I suspect the battery voltage is playing a major part as 11.9 vs 13.8 is a substantial drop in primary voltage to the coils. It was occuring at around the point ao max torque and sounded as though it was all the plugs missing as opposed to just one plug.
I suspect Mike will prove correct in recomending the use of non extended nose plugs to avoid detonation at the higher boost pressures. Not to sure about the big gaps though.

At 11.9 volts your battery is operating with the eqivalent of around 40% of a fully charged battery.

One of these might prove useful if you don't want to bother with an alternator and run total loss. You can then use any number of batteries on the rollers.

http://www.demon-tweeks.co.uk/products/Pro...PORT&pcode=AJP3

Best of luck sorting it, It's going to be one quick Mini when it's done.
Regards
Dave

Edited by danboy on 23rd Feb, 2007.

i think it was the major cause Dave to be honest.

Mike's had a lot of mapping experience but not that much turbo i think.

I have a Kubota alternator to go on this next week or so and hopefully this will keep the battery charged up. sure it will enough anyway.

certainly be interesting next time on the rollers with all the niggles sorted out.

oh and btw, after taking a plug out i'm running retracted nose 8's

It may sound like a stupid question but, what are the benefits of larger gaps in the plugs, as long as you get a spark every stoke its needed I can't see how it would make a difference?

Never really thought about it really?

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1/4mile in 13.2sec @ 111 terminal on 15psi

Iain you mention your running an ECU to control the spark?? if so the BATT voltage should be able to run down to around 9v and the battery compensation table in the ECU if it has one should adjust the coil dwell time to compensate for the lower/higher voltages.

What ECU you running ?

Edited by Doodmeister on 23rd Feb, 2007.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

I seriously doubt it!

thats good output for something so small!!

Dood, i'm running emerald so not sure, not seen anything about it.

Robert,
0.6mm is for contact breakers 9v ignition,
mety turbo and any electronic a seri dizzy use 0.9mm plug gap,
regarding larger plus gaps I didn't find improvement using larger than that

Danboy that depend on how saturated you ignition coil is in the first place.

Any ECU worth it's money should have the following IMO

Ignition compensation for battery voltage, gear, air and coolant temperatures

Fueling compensation for battery voltage, gear, air and coolant temperatures

Check out the Omex710 as thats what i'm refering to and planning on using when i get my car back on it's wheels. (Fingers crossed soon)

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.