Plug Cuts

I would be pleased to learn of the Group’s opinion on this subject, and for those who would advocate this procedure, exactly how they would carry it out … and most importantly, how to evaluate the results.

There seems to be two basic streams of thought:

One seems the passionate advocate, the other would say a total irrevolance.

Regards.

huh?

I didn’t want to be the first to say that but can you explain what plug cuts you are refering to :confused: :question:
Brian.

As I seem to remember:

Find a suitable stretch of road (quiet and straight) on a dry day. With the engine at normal temperature, take it up to say 6000 rpm in third and hold it there for 10 seconds. Then in one continuous operation (and very carefully) depress the clutch and turn off ignition (mind any steering lock!), engage neutral and coast to a stop.

The plug can now be removed for analysis.

Yup, that’s the old way. Unfortunately that’s the way John Passini did it back in his day. Kinda makes his insights less relevant and not very useful or reliable. When the only measuring sticks are fuel consumption, types of smoke emitted, seat-of-the-pants-feel and plug cuts chances are you’re going to suck at doing it until you’ve got thousands of hours of practice until the trial and error experience finally kicks in. Good luck! :sunglasses:

I failed miserably at it and with hindsight I realized I was doomed from the start. The fuel supply I was using was changing in it’s vaporization behavoir from tankful to tankful.

Thank gawd the digital air fuel meter that is reasonably priced is now available. :smiley: Anyone with some technical savvy and with proper coaching can do it with one of these units. Of course the plug cut is still necessary but only as the last step in the tuning procedure. To get the plug heat range selection into the self-cleaning temperature range.

Keith,

Thanks for that.

So air/fuel meters are the way to go. A couple of (three) questions then please:

Which would you recommend that might be available this side of the pond?

How are they connected (manifold tappings) ?

What of such things as changes from day to day … eg ambient temperature, humidity etc. Does the old adage (for Webers) still hold true, that a cool/cold but moist air supply is best?

Am new to Elans, but not the twin-cam engine

Regards.

If you’d fill in the personal info a little more I’d know which side of the pond you mean. :confused:

The http://www.innovatemotorsports.com/ units are available world round now. There are also competing brands with similiar pricing available too. However, when you buy the Innovate stuff along with it you get access to Klaus Klatinn’s advice on the forum. He’s about the most knowledgeable guy on technical aspects of combustion I’ve ever heard before. He’s also a Weber guy! Suggest you go and read up on the technology at their website.

Got experience with the twinkcam on the racetrack do we? :smiley:

There’s only one pond, and I like to think I live on the best side (vbg).

Used to envy your weather … but I’m not so sure anymore !

Thanks for the link. Will investigate.

Racetrack experience, sadly no … just a bit of the normal silly stuff on the open road, in my younger days (Cortinas). Now I’m having fun with an Elan … that I never could afford back then!

Regards.

Guys, I’m sorry but I still gotta say, huh? Are you discussing looking at the spark plugs to see how the individual cylinders are functioning? How far does an Elan coast when you turn it off at full chat in third gear? Can’t you just put on the brakes and pull over (on the side of the road?) and then, take the plugs out?

Since the head is a cast from relatively soft, gummy but abrasive aluminum the other downside to doing spark plug cuts is the threads eventually pull out. Helicoil to the rescue! It’s easy to get them cross-threaded too. BTDT :cry: :angry:

I still use that system -----turn the ignition off and dump the clutch as close as possible----at the top of the Andrettii not so straight away at Mosport coast to the pits read the plug —do it on the vee and the sprite and both t. c. motors —works for me —tells what plug is rich or lean–all I want to know ed-- :angry:

It’s interesting, but a completely different language to me :confused:
For the less technical ones amongst us… What is a plug cut?

Thanks

I don’t wish to be rude, but maybe reading the full thread thoroughly might begin to answer your question!

Regards.

Without being rude back, all I can make out by ‘reading thoroughly’ is that it’s something to do with sparkplugs !! A simple answer would have been more helpful.
If you read through the list you will see that I am not the only person who does not understand…

sg booth --you asked a question----- please answer one without the attiude and with the courtesy you would expect ----ed

Okay:

RePost:

“I didn’t want to be the first to say that but can you explain what plug cuts you are refering to”

"As I seem to remember:

Find a suitable stretch of road (quiet and straight) on a dry day. With the engine at normal temperature, take it up to say 6000 rpm in third and hold it there for 10 seconds. Then in one continuous operation (and very carefully) depress the clutch and turn off ignition (mind any steering lock!), engage neutral and coast to a stop.

The plug can now be removed for analysis."

The object of the exercise is to best establish what is happening in the combustion chamber at that precise point in time. Ten seconds or so at those revs, should give a reasonably clean/new plug a chance to ‘take on’ a true colour… obviously such things as points gap, timing etc must be spot-on (and don’t forget to check that the advance curve is correct, and that no air is leaking into the inlet manifold, … etc, etc).

Effectively, you are at the end of the timing/carb balancing/mixture cycle, and are using the “plug cut” to analyse what is happening at these high revs… it gives you a check on how good your setting-up has been.

For analysis try:

ngksparkplugs.com/techinfo/spark_plugs

or:

dansmc.com … click on Index and choose spark plugs.

(hope the links post okay).

In very simple terms, & assuming there are no problems with the carb(s)
themselves, you should then be able to “tweak” individual mixture screws to achieve a good plug colour. BTW, I do mean “tweak”. If you have to make serious adjustments, then either your initial setup was way-out, or something else is afoot.

As an example, this idiot spent half a day setting up his new Elan, fitted a set of NGK BP7es and went off for a test … result: all black … Yipes !!
Whatever I did, I could barely improve the colour.

I used to use these plugs on my Lotus Cortinas, but they were Stage 1/2 road-tuned engines requiring different plug heat settings.

Substituted them for an ‘old’ set of Champion N7YC’s and the colour is MUCH better … without making any other changes. So the correct grade of plug is critical to the engine’s performance. These may well prove not to be the final plugs I use … we’ll see.

As I recall, the higher the plug number, the hotter the plug (Champion), but the reverse is true for NGK.

FWIW (and setting aside the petrol additive question) I intend to use the same type of petrol (Shell Optimax) whenever possible … just to try and eliminate another variable.

Speaking of variables… the Manual states 25 thou as the plug gap.
However, extensive dyno-testing shows that 20 thou gives the most power for a twink.
On the other hand, plug manufacturers say not to bend the earth electrode away from its’ preset gap ('cause electrodes would be out of parallel).

Personally, I intend to stick with my 20 thou, and change plugs more often if needs be.

HTH.

Regards.

Clever,

This all makes perfect sense now. I will have to give it a try.

Thanks
Carl

Sorry if I appeared to be rude… didn’t mean to be (must be getting old and tetchy)…vbg!

Just a further point:

Obviously after the test, you will remove each plug (either one at a time, or all together, whichever). What I’m trying to say is that I think it’s critical that the same plug goes back into the same cylinder each time.

Say for example that whatever you try, No3 is always black. You could then try another (5th) plug. If that were much better, you would suspect that the original plug was faulty. You could test that theory using the suspect plug in another cylinder and compare results.

I once had this problem. It took ages to find the reason. I realised that I might have solved it more quickly if I’d not kept swapping the plugs around.

HTH.

Regards.

“However, extensive dyno-testing shows that 20 thou gives the most power for a twink”

Hmm, i’m running NGK 6 dash 11 's on my Sprint …which are pregapped 1.1mm - 43 thou (Using a Lumenition and their “high energy” coil and it still goes like stink. NGK don’t even supply pregapped plugs less than 0.8mm - 30 thou!

No way am I going back to Champion plugs though - never had anything but trouble with them since the mid 80’s

The 20 thou gap statement wasn’t in any way meant to be a definitive statement… more a chance for feedback. It’s the better part of 30 years since I played with these engines. Things will inevitably have moved on ( much will I hope be for the good).

20 thou was the perceived optimum back then, when running the standard ignition system.

I quote:

A suitable spark plug for the standard and mildy-tuned twin-cam motor is the Champion N9Y. This plug has a wide-enough heat range to enable its’ use in engines up to 135bhp or so. Beyond this, one should use Champion N6Y plugs, and on engines of 145bhp or over, racing plugs such as Champion N57R will be required. When using Champion N9Y or N7Y, the optimum gap has been found by dynamometer testing to be 0.020 inch.

quoted from: Tuning Twin Cam Fords, by David Vizard ( a Speedsport publication here in the UK), published back in '69, republished in '71 and then again in '73). My quoted version is the '73 reprint. The ISBN was 0-85113-007-0.

A different book, which I found in the late eighties, says as follows:

I quote:

Sparking Plugs

Originally, Autolite plugs were used because of the contract with Ford, and because Ford owned that company. Autolite bacame Autocraft, and is now Motorcraft. However, Champion plugs are universally known, and are listed below. Bosch, NGK and Motorcraft equivalents can be cross-referenced if required.

Application Champion Plug Gap

Federal Stromberg N9Y* (N9YC) 0.025 in / 0.6 mm

All others N7Y (N7YC) 0.020-0.023 in
0.55 mm

  • For sustained high speed driving, revert to N7Y.

With electronic ignition:

All types N7Y (N7YC) 0.030-0.035 in / 0.8 mm
or alternatively N6Y (N6YC) same gaps

It goes on to talk briefly about resistive leads, Federal Stromberg variants etc.

This latter quote is from Miles Wilkins’ book, which is listed in the group’s book library… still in print, I believe,…and excellent in MHO.

The above offered in good faith, without warrenty, as-is, etc etc ( just as Microsoft would say)… 'cept I haven’t their money or lawyers.

Regards.