Hey Guys,

If, theoretically, someone wanted to run without trailing ignition and just buy threaded plugs to plug the trailing spark plug holes with, what would the size/dept/thread width have to be to do it tightly and safely?

I ask because in cases where people upgrade their leading ignition but not their trailing, sometimes they could end up with their leading and trailing plugs doing different things and that can get dangerous. Plus trailing is only for cleaning up your exhaust anyway and doesn't give any power, so I'm sure someone has wanted to do something like an FC Coil leading swap and plug the trailing so they could chuck the trailing spark plug wires and clean up the engine bay a bit.

Jon

 

Interesting...do you really not make 'any' power from the trailing spark plugs?? As in, if you took them out, you wouldn't notice a difference in the power deliverly and how the car runs?
Just curious.

Ryan

 

Two HP on a good day^^

It is basically there to burn whats left of the unburnt gas/oil in the chamber.

 

Just use a couple of old spark plugs to fill the holes. Thats what they were made to do.

 

Yeah, if you're hell-bent on not using the trailing ignition, just take the wires off and leave the plugs in-place.

That said, I don't know why you would. Even a modest 2-3 HP is worth keeping the trailing in operation. Hell, those of us with dual leading spark have three ignition events for every power stroke. I couldn't imagine why you'd go to just one.

 

The idea is that if I've got dual leading spark or MSD, I'm already running multiple ignition events from that and don't really need the trailing to operate.

Let's give an example. Let's say you have an MSD 6AL hooked to your leading plugs (maybe even through a 2nd Gen coil, which would give a multi-spark wasted-spark setup). The 6AL has a limiter, but the trailing which still runs through the distributor cap does not. At the point where you hit your 6AL's limiter (let's say I set it at the 6,800 "where my buzzer goes off" spot), your MSD would be limiting spark but my trailing would not. This would have one of two effects. Either my trailing would be the only plugs firing (if it cuts the spark out completely) or my trailing plugs would be firing at their normal time while the MSD-fired plugs fired at a different time than usual (if it retards spark or something like that).

Either case would be undesirable, though probably not really devastating.

Now say we took my car on the dyno, then on a road trip, and showed that the trailing plugs don't lose enough horsepower to visibly move that line any at all, and I don't lose any gas mileage from it. The sniffer would show my exhaust is dirtier, but with no rat's nest, no air pump, no acv and no cats, that's not exactly one of my priorities. Then say I'm taking the car to a car show and want my engine bay to be as clean and spartan as humanly possible. Extra coil, bracket, and three wires could be removed and the extra spark plugs replaced with very clean-looking caps/bolts.

These are just some hypothetical reasons, but I figure any time you're playing with ignition it's probably easier to eliminate one variable from the mix, especially when you're already trying to deal with two advancing systems, and in the case of some ignition controllers, a split between leading and trailing because they're on their own independent maps.

But honestly does it matter IF I would actually do it or WHY I would actually do it, what if I just wanted the question answered for curiosity's sake?

Because truthfully I'm not running a 6AL, and haven't really decided if I would actually do this, if only for shows. It would certainly get people's heads turning and asking "why"... and "to make you ask questions" is sometimes as good a reason as any

So does anybody know the answer to the original post?

Yes, I know I can just leave a spare set of spark plugs in there. But then it just looks like I forgot to hook something up, not because I purposefully meant for them to not be there.

Jon

 

Jon, I believe it is 14MM X 1.25. But you can call any auto parts place and they can look up the plug number then check their paper catalog for the thread specs. As far as the depth, use the lengt of the seat on the plugs as your reference.

As far as long term effects? Since the trailing side is generally an afterburn it is possible that their may or may not be a undetermined amount of fuel that could lead to excessive build up on the rotor facings. This may have an adverse affect resulting in carbon build up.
But that is all theory.
By running just the leading side you can save the usage of Caps/Rotors since they do not even have to be on the dist to run the 2nd gen leading coil.

 

RPM limiting is a good reason to disable trailing. According to his website, Peejay blew up an engine because the trailing carried up his RPMs despite the limiter of his ignition module.

 

I will try to remove the wires and see if I notice a difference, and possibly take it to the track.
Setup is 6AL firing 2nd gen leading coil.

 

Bump from the dead, I know, but the MSD boxes do not do the dual spark after 3000rpm.

 

This very true. After 3000 RPM....all bets off with multiple spark.. You do still get an intensified spark running the MSD.

This concept of running just the leading intrigues me. I am setting up a street ported nitrous 12a for a buddy of mine. We were gonna disable the trailing because it would be so much easier to do the nitrous timing retard only dealing with the leading.

I wish someone would chime in more.

There was a discussion last year about nitrous and rotaries. I think the consensus was to ditch the trailing when spraying.

 

There's more to sealing a spark plug than the thread size, too... the plug's shoulder serves as a pressure seat, along with the sealing washer. And thermal expansion might be a concern as well; I know it is in design of the plug, though much of that is to prevent cracking of the ceramic insulator.

You'd need a plug with the same diameter, thread pitch, thread length, and shoulder sealing characteristics, and possibly thermal coefficient, as the original plug.

 

FYI.......... http://www.msdignition.com/uploadedF...structions.pdf

 

Brake the white part off and boom!! perfect fit nut!

 

WTF are you talking about????

 

I think he's saying that you can just break off the external insulator & terminal from a regular spark plug, then use the leftover bit as a hole plug.

Might work, might leak (depending on how the ceramic decided to break).

 

Why break it? That's dumb. Leave the spark plug intact.

What's more, breaking the "white part" off still doesn't solve the business end of the plug, inside the chamber. Carbon can supposedly build up and cause preignition. Probably not a problem for NA.

 

Exactly....isn't a sparkplug basically hallow without the ceramic? Why comprimise the integrity of the plug?

 

Carbon build-up in the plug hole could maybe be a problem with any non-functioning hole plug, couldn't it?

They'd not be flush to the inner housing surface, and they'd not be burning deposits off like a functiong plug's supposed to.

Carbon builds up on any c-chamber surface that isn't routinely scraped or blasted clean, seems like.

 

I could see where an argument can be made regarding the loss of the 2-3 hp loss; but I beg to differ on the fact that it is insignificant. First of all it takes less hp for a car to cruise at 60 mph than to get to 60 mph. I recall a study in the 80s using a Chevy Celebrity (one of the most aerodynamic cars ever made). It took 89 hp to get to 60 mph but only 58 hp to cruise at 55 once it was moving, mind you that this was a 3800 pound car. In short the lost trailing hp in a cruising situation translates to a loss of mpg.

 

Hate to be a boner killer....just where did you get this information from??? Did you pull it out of your bunghole???

The Celebrity weighed 2880#. It used a 2.2 litre I-4 (AKA the iron duke) Pontiac sourced engine. This "beast" of an engine made 92 HP Gross.

It would be lucky to muster up 50HP to the ground on a good day. I could see maybe 25 HP to hold a steady 55-60 on this POS Chevy called a Celebrity....not 58.

I do agree with you....With us having only 100HP, we need all the help we can get.

 

According to C&D the Rx-7 take 12hp to maintain 60MPH. 7HP is wind resistance and 5 is rolling resistance on wheels.this is why you can cruise at nearly closed throttle at 3k rpm on the highway.

 

I actually have some spark plugs that I broke the porcelain off of and cut the metal insides down. I was planning on casting them at the lab and make them look pretty. Just haven't gotten around to that yet.

 

All this ignition mumbo jumbo you speak of is way beyond me at 8:30 on a sunday morning, BUT...IIRC, the spark plugs, shifter and wheel studs all have the same diameter and thread pitch. I bet you could just trim down a wheel stud and put a spark plug washer on it, thread it in and remove the hex cap. It might not look too bad.

 

I can totally buy the wind resistance thing... someone did a challange where they were trying to get the MAX MPG out of a car. The winning team basically built a box that was towed behind a truck. Something like a Prius was drivin in the "box"... This took all wind resistance out of the equation. The car got over 100 MPG or something like that.