spark plugs
Senior Member
Joined: Jun 2004
Posts: 524
I hadn't considered the effect of lengthening the heat transfer path. Thank you for the heads up.
Lacking emprical data other than the "evidence of the glazzies", I still feel that the shrouding does retain more spark plug heat. For one, Mazda started using colder plugs on the trailing side when they went to electronic timing control, which had much more radical timing curves than they could get with the distributors.
Secondly, personal experience. Some time ago, Paul Yaw made a spark plug recommendation on his website. I went out and bought the happy smiley $10 NGK plugs. I do not remember the heat range number but they were nowhere near the 11.5 range. After a couple passes down the test track, I pulled the plugs for a look-see. The ground electrodes were melted a bit on the leading. On the trailing side, the grounds were melted to nubs and the porcelains were missing. Only one of them was still in the trailing hole. It would appear then that the trailing plugs run quite a bit hotter than the leading, yes?
Lacking emprical data other than the "evidence of the glazzies", I still feel that the shrouding does retain more spark plug heat. For one, Mazda started using colder plugs on the trailing side when they went to electronic timing control, which had much more radical timing curves than they could get with the distributors.
Secondly, personal experience. Some time ago, Paul Yaw made a spark plug recommendation on his website. I went out and bought the happy smiley $10 NGK plugs. I do not remember the heat range number but they were nowhere near the 11.5 range. After a couple passes down the test track, I pulled the plugs for a look-see. The ground electrodes were melted a bit on the leading. On the trailing side, the grounds were melted to nubs and the porcelains were missing. Only one of them was still in the trailing hole. It would appear then that the trailing plugs run quite a bit hotter than the leading, yes?
Fabricator
Joined: Jan 2004
Posts: 1,322
From: Central Ohio (Hebron) Zephyrhills Fla.
Originally Posted by heretic' post='843963' date='Nov 4 2006, 01:30 PM
I hadn't considered the effect of lengthening the heat transfer path. Thank you for the heads up.
Lacking emprical data other than the "evidence of the glazzies", I still feel that the shrouding does retain more spark plug heat. For one, Mazda started using colder plugs on the trailing side when they went to electronic timing control, which had much more radical timing curves than they could get with the distributors.
Secondly, personal experience. Some time ago, Paul Yaw made a spark plug recommendation on his website. I went out and bought the happy smiley $10 NGK plugs. I do not remember the heat range number but they were nowhere near the 11.5 range. After a couple passes down the test track, I pulled the plugs for a look-see. The ground electrodes were melted a bit on the leading. On the trailing side, the grounds were melted to nubs and the porcelains were missing. Only one of them was still in the trailing hole. It would appear then that the trailing plugs run quite a bit hotter than the leading, yes?
Yes, obviously too high a heat range, and, or, too lean a mixture or advance for the RPM used. The trailing running a split timing gets more mixture in its little chamber before it fires. The bigger the split, the more it gets. So it is exposed directly to the combustion process. The mixture when lit then reenters the chamber as a jet of fire, instead of just a spark, and that works wonders for liting the bigger charge in the chamber.
This trickery is used to help reduce the unburned hydrocarbons polution problem the rotary is famous for. It does not help power much, and it doesn't hurt it much. Some builders drill out the little hole to about the same size as the leading hole. I never did it and I never saw one with that mod on the dyno, so I cannot comment on the power it might or might not generate.
A housing that has been damaged by too hot a heat range plug, or long time running close to over heated, wil get a tiny crack across the little hole. So long as it cannot be felt, or no surface appearance changes around the crack shows up like the apex seals are stressing the area, there is no need to repair anything.
However if there is evidence of a step or chrome changing color, the surface may be reduced with a stone and the housing reused barring any other problem. The apex seal will tollorate a depression but not a bump.
A housing with radial cracks (in all directions) from the little hole indicates a bigger overheating incident and greater care must be used and extensive inspection of the housing for distortion and so on must be conducted before reuse.
Lynn E. Hanover
Thread Starter
Senior Member
Joined: May 2002
Posts: 22,465
From: California
Originally Posted by Lynn E. Hanover' post='844035' date='Nov 5 2006, 05:03 AM
Yes, obviously too high a heat range, and, or, too lean a mixture or advance for the RPM used. The trailing running a split timing gets more mixture in its little chamber before it fires. The bigger the split, the more it gets. So it is exposed directly to the combustion process. The mixture when lit then reenters the chamber as a jet of fire, instead of just a spark, and that works wonders for liting the bigger charge in the chamber.
This trickery is used to help reduce the unburned hydrocarbons polution problem the rotary is famous for. It does not help power much, and it doesn't hurt it much. Some builders drill out the little hole to about the same size as the leading hole. I never did it and I never saw one with that mod on the dyno, so I cannot comment on the power it might or might not generate.
A housing that has been damaged by too hot a heat range plug, or long time running close to over heated, wil get a tiny crack across the little hole. So long as it cannot be felt, or no surface appearance changes around the crack shows up like the apex seals are stressing the area, there is no need to repair anything.
However if there is evidence of a step or chrome changing color, the surface may be reduced with a stone and the housing reused barring any other problem. The apex seal will tollorate a depression but not a bump.
A housing with radial cracks (in all directions) from the little hole indicates a bigger overheating incident and greater care must be used and extensive inspection of the housing for distortion and so on must be conducted before reuse.
Lynn E. Hanover
i remember one of the first 93-95 engines we tore apart had cracks all over the trailing plug hole...
i guess thats what happens when it runs 12's for 30,000miles with the stock spark plugs!
Senior Member
Joined: Dec 2002
Posts: 686
From: Oblivion
Ok, so now I'm curious as to what holes I should run my 10.5's in.
I will only be using them when I run race gas/higher boost. I will be using a combo of 9's and the 10.5's.
Should I run 9's in the leading, and 10.5's in the trailing or should it be 10.5's in the leading and 9's in the trailing? and why?
I will only be using them when I run race gas/higher boost. I will be using a combo of 9's and the 10.5's.
Should I run 9's in the leading, and 10.5's in the trailing or should it be 10.5's in the leading and 9's in the trailing? and why?
Thread Starter
Senior Member
Joined: May 2002
Posts: 22,465
From: California
Originally Posted by Comitatus' post='844228' date='Nov 6 2006, 11:36 AM
Ok, so now I'm curious as to what holes I should run my 10.5's in.
I will only be using them when I run race gas/higher boost. I will be using a combo of 9's and the 10.5's.
Should I run 9's in the leading, and 10.5's in the trailing or should it be 10.5's in the leading and 9's in the trailing? and why?
10.5's in the trailing, 9's leading, i say
Senior Member
Joined: Dec 2002
Posts: 686
From: Oblivion
Originally Posted by Hyper4mance2k' post='844250' date='Nov 6 2006, 04:44 PM
no need. b9es or b9egv's a around unless you're running more than 15psi. or more than 350rwhp.10.5 are most likely going to foul quickly unless you've got the ingition and proper tuning to prevent it.
Ok, I'm confused...
Are you replying to my question, or just in general to the thread?
If to me, then when I run the 10.5's, I will be running higher than 15psi. Even if I were to run lower than 15psi, I still have more than 350rwhp.
Hence, the reason for 9's and 10.5's as opposed to 9's all around.
Fabricator
Joined: Jan 2004
Posts: 1,322
From: Central Ohio (Hebron) Zephyrhills Fla.
We use the NGK R6725-115 plugs, gapped at .0010". They have a retracted gap and fine wire electrodes. The heat range is ice cold.
This is a fabrication.
We gap the plugs at 0.010" not 0.0010".
That would be ten thousandths of an inch. Not one thousandth of an inch.
Sorry, if you already tried that.
Lynn E. Hanover
This is a fabrication.
We gap the plugs at 0.010" not 0.0010".
That would be ten thousandths of an inch. Not one thousandth of an inch.
Sorry, if you already tried that.
Lynn E. Hanover
Senior Member
Joined: Dec 2002
Posts: 4,107
From: fredneck MD
I have been running a set of 11.5's in the trailing and 10.5s in the leading for a few months, on low boost and crusing around. I guess the plugs havent fouled because of the ign setup?
There is no reason to run these plugs, just what i had sitting around the last time i changed em...
There is no reason to run these plugs, just what i had sitting around the last time i changed em...