Does cutting the groud electrode back on a plug really give a noticable performance increase or should I file this procedure along with the air foil/tornado swirlley thingie?
If this procedure is valid, where can I find documentation on the steps to perform the operation?

Thanks,

 

While I haven't done it myself...I have read that there are some gains to be had in performing this mod. Although I do not believe the gains to be substantial.

 

Do a search, a week ago some asked the same question, and someone posted a link with the answer. it did make a difference.

 

65Z01 has the procedure on his website. As far as worthiness, he swears by it, and it is interesting to observe that on the Bosch +4s, the outer electrodes do not meet over the center electrode like normal plugs. :seeya :cheers:

 

Thanks jmrl98, I tried to locate the other thread but i couldnt find it.

 

Just thought you might like to know - the motorcraft racing plugs are already cut-back.

Sorry, I meant Autolite racing plugs.

Just my .02


[Modified by 85vet, 10:52 PM 1/29/2003]

 

Could someone please post pics of this *mod*? From what I am picturing, I can't think of any reason why this should be done, and can think of a bunch why it shouldn't.

 

There's a sketch on my site.

 

I see all kinds of issues with the experimentation process here, and the only potential gain would be from having two sharp edges near each other, but the life of the plug is HUGELY diminished, and the performance of the plug will fall in the crapper right along with the lifespan. Also, screwing with the gap on the plug isn't a good idea anyway...it requires higher voltage output from your ignition system, will impose a lower limit on your rpms as controlled by the ingnition (when the system can't produce enough voltage fast enough and the engine will no longer accelerate because the ignition can't provide enough voltage to arc every time), and it hurts the lifespan of the plugs due to the accompanying change in geometry of the plug when you bend the ground electrode.

 

Anyone have before/after dyno results with cut-back plugs? I know people swear by it, but I'm curious to see the numbers... :)

 

Re: Spark plug circumcision (C44ever)

Sounds painful!

 

Helmet or anteater? :jester

 

Well, here goes another perfectly good thread into the gutter! :bb :jester :cheers:

 

Cut-back spark plugs are a throwback to the early sixties when we used to cut back the spark plug's ground electrode to expose more of the spark to the air-fuel mixture in the combustion chamber just like the real racers that used J-gap spark plugs from Champion for racing. Besides cutting back the ground electrode, we used to close the gap from .035" to .028" to lower the voltage requirements to jump the gap thus ensuring adequate spark above 5800 rpm for our high compression (11:1) small blocks. (Transistorized ignition systems were still a couple of years away so most of us used dual-point distributors to increase the dwell time for our high performance ignition coils. Retaining the stock gap almost guaranteed a high rpm misfire!) :eek:

Given the current availability of multiple-spark ignition systems, better spark plugs, and the relatively mild compression engines that most of us use today, the use of cut-back spark plugs is passe in street machines. :sleep:

If you do want to use cut-back spark plugs, remember to index the plug such that the open gap is facing the intake valve to maximize the exposure of the air-fuel mixture to the spark. How much more HP/torque this will give you than simply indexing your current plugs is debatable if you are using slant plug heads. On straight plug heads, I have seen a 5 HP increase above 6000 rpm on my blueprinted 1970 LT-1 engine (11.25:1 compression). YMMV! :)