Howard Coleman

iTrader: (6)

AR3934X 8 heat range
AR3933X 9
AR3932X 10
AR3931X 11

i have the 9s and 10s. we are currently finishing the tune off the spring at 15 psi and 9s are in the motor. no issues so far. after taking a look at them we will probably switch them out for 10s as we raise the boost.

as to resistor/non-resistor, we will just have to see how it goes.

here's some info from the Roush site... price from Jack is $4.99

"Designed Specifically for racing applications. New cooler running sidewire providing improved durability and less risk of pre-ignition. New Yttrium-Enhanced alloy enables up to 8% reduction in sidewire temperature. Cut back ground electrode providing improved ignitability Anti corrosive Nickle plating."

i became interested in the plug after Lance Nist suggested them for my app. Lance is a key person behind the Mercury coil which now is marketed re-labeled by a growing number of vendors. he indicated i would probably not need the 11 as the plugs tend to run cold.

just to re-iterate, w re to ignition, as well as other areas, i am just doing my own thing. my previous ignition, two Jacobs FC3000 amps, two magnificent MSD 8253 coils had zero problems firing a 9.0 AFR at 21 psi. (w 6725 plugs/Magnecor wires).

Lance just got me interested in inductive. if it works it is a lower cost alternative, has less items to malfunction and you don't have to hunt around to find a place for a CDI module(s).

four compact coils, around 70 each, and $5 plugs (perhaps)

so we are doing some R&D here and it remains to be determined as to how it will work.

fun

howard

T-7

Spark plugs heat range is dependent on mainly combustion chamber tempters and varies for different geographical location, colder climate may not require much colder that one or two points over stock and a hotter climate may use a wider range of colder plugs. If the engine is setup correctly and tune correctly then it is easier to read and choose plugs.
Heat is the biggest killer in any engine and you want to manage that first, proper intake charge tempts and engine coolant temps, excessively rich mixtures and too lean mixtures well also affect what happens with the plugs .

C. Ludwig

iTrader: (27)

You talk as if you're inventing something. You're just getting on a train that left the shed several years ago.

tony94s4

iTrader: (1)

Only 9 heat range comes up searching, where can i get colder ones?

Howard Coleman

iTrader: (6)

i was able to get 9 and 10s thru NAPA. they did not have them in Wisconsin and they came directly from Detroit... another friend bought them off the Roush site. i believe sparkplugs.com lists them.

howard

cewrx7r1

iTrader: (2)

From the other Chuck:

First I mixed adjectives about using WI with plugs. The old brain fades sometimes. Since WI cools more, you can go .5 to 1 hotter plug instead of colder.

I use to run the non resistor B9/10EGVs years ago until HKS said not do it with the twin power. But that was only up to around 370 whp. Did not have any problems with EMF interference.

I went to R6725-9/10 plugs about 8 years ago when I tried some used ones and experienced how much better the engine ran. Then I switched to the newer R7420-9/10 two years ago. Not having to use the thin wall socket was another bonus.

I have two sets and swap between them about every 6 months with a good non sand media blast cleaning.

ALPSTA

iTrader: (3)

I have a GTX35R and meth/water injection (my goal is 400-450whp). Planning to run 15psi daily and go up to 18-20psi for racing. The plugs I buy should NOT require a special socket, SHOULD be suitable for both slow daily driving and racing (low and high boost) and not foul all the time.

I think NGK 7420 in 10 or 10.5 will do the job. Is there much difference between 10 and 10.5? Which one is less likely to fail on me and perform at the same time?

PS. My ignition system is almost stock except the HKS Twin Power.

sleeper7

Little update. The v-power plugs worked great up to a hp limit. Around 550 I started to melt the grounding strap. Had to look close to noticed but they started to melt.

SO went back to the 2396 5$ 19mm reach plugs leading. V-power plugs for trailing, No issues so far. HP range in the 650 so far.

Friday night I was getting a tad misfire in the higher rpms with the rich tune and 2396 plugs. Broke down and gave the high dollar plugs a try. Left the tune alone. Made a pass and still had the misfire. Leaned the fuel out and the misfire went away. Did not notice any idle improvements or power increase. Pulling the high dollars plugs and reinstalling the cheapies. 140+mph

Still on the stock turboII coils, four trailing ones.

Friends FD that was tuned on the high dollar plugs and tuned rich. Was fouling the high dollar plugs in 4/5 weeks of daily driving. Ask him to give the V-power plugs a try. It's been 8 weeks on the same plugs and says the car drive today as good as when the plugs were new. He's a happy camper. Yes I know if the tune was better he could have continued to use the $ plugs as a daily driver. V-power plugs take less energy to fire and fires hotter because there grounding stapp is nickel. But cant take the heat in a "higher" hp rotary.

Rub20B

anyone has an opinon on the new NGK R7440A plugs? They are sold on RHDJapan site for RX-8 application and come in 9-10-11 heat range. funny is that they have the 10 heat range in T and L, would the length be different??

gxl90rx7

iTrader: (1)

ive been using NGK R6712-9 and -10. they are true surface discharge for really consistent spark. i have noticed with deep dish, semi-surface discharge (like the factory BUR9EQ), the spark has more ways to discharge, which is better for fouling, but not for spark consistency. duration and output will jump around, based on where the spark bridges the gap

Speed of light

iTrader: (8)

^^^ yep. I think GXL is right on the money here. I've visibly witnessed this phenomenon while test firing plugs in a pressure chamber. When BUR9's are brand new they seem ok; however, in very short order they start to wear at the firing end and the spark likes to move way down inside the plug which seems to shroud it from the chamber.

Another similar, interesting and important effect I've noticed is that the cold type plugs the rotary requires don't do large gaps very well. In fact, if you open gaps past approx .035", the plugs will start to quasi-surface discharge preferring to follow the nose insulator's surface once chamber pressure is applied. This is in large part due to the rather short insulator noses on these very cold plug designs--they become the path of least resistance--as the discharge would rather follow a [longer] surface than jump a [shorter] gap, to a point. All brands of plugs I tested exhibited this behavior--but primarily in the coldest ranges; i.e., the ones we use (tests included NGK, Autolite, Champion and AC). And New or used plugs or even fine wire tipped plugs did NOT make any apparent difference. (This was a surprising result as I was expecting the fine wire plugs to show an improvement.) If you want to run large .050+ gaps you apparently need to run Hotter plugs with a long insulator nose (not really an option for us), stock plugs or perhaps do a real surface discharge plug; there may be others that work, but I haven't found them yet.

In any event, I've had good luck with the conventional style Autolites (and the NGK V-power plugs) set to ~.025" gap; I've pushed the Autolites pretty hard and have never seen evidence of a problem with either the porcelain or the ground strap.

The hypothesis that I advance is that as the spark moves down inside the plug and/or onto the nose insulator's surface, it becomes effectively more shrouded, cooler and delays flame front travel into the chamber which, for all intents and purposes, "retards" the timing and may slow the overall burn rate as well. This offers one possible explanation for poor or inconsistent power--and that which occurs without an apparent misfire (may also produce high egts too).

Given some thought, one may see where it possibly has other tuning implications as well. This is, of course, solely conjecture on my part, but if a motor were tuned to say, the ragged edge, while using well worn plugs, what might happen if fresh set of "good" plugs were installed on that same tune? Would there be enough of a performance difference to potentially put the engine in peril? I don't know. Just some food for thought....

Ciclovnz

iTrader: (6)

I have a peripheral engine, GT42, four barrel, premix, aem smart coil, microtech, the engine and check we have on for any failure b10es and am using two burn engine lit, it could be happening? It will be the lack of intonation? Buy a R6725 105 to try but if not go to burn again

gxl90rx7

iTrader: (1)

as far as resistor plugs.. i did some testing a while back with a spectrum analyzer. Even with an 3k wire, the non-resistor plug would emit so much EMI, it would reset the micorcontroller i was using to generate the coil trigger signal, even at idle speeds. No problems using resistor plugs, even with a solid core wire. It was difficult to quantify on the analyzer because the noise was just all over the place, but the plug definitely causes more EMI. i am not sure what affect having the plug sealed off in the housing does, it may naturally shield some of that EMI, but i have not tested that. I believe the higher EMI may be caused by the high-frequency signals reflecting off the plug and back up the wire to the coil, but just a theory. but it seems if you want to lower your spark resistance, you will get better results to do it in the wire, not the plug

Howard Coleman

iTrader: (6)

just finished talking w Autolite.

it may be that the AR3932 has the same problem that the V power plugs have which is a melting ground strap above 550.

it also may not be the case as the motor was around 1650 F EGT and perhaps should have been tuned a bit more rich on E63. the ground strap showed signs of starting to melt. no harm to the motor. (BTW, not my car but is an engine i buit)

there does exist an Autolite 3931 which is a colder (11) plug... about 100 F colder.

it just seems it isn't available...

according to my Autolite guy they have 1180 of them sitting in the warehouse.

probably because in order to get them you need to add a dash 02 to the PN.

if you are interested, NAPA is a good bet

AR3931-02

in this particular situation we are going to clean up a few items and richen it up a bit to get the EGTs down.

i will be ordering some of the 31s for myself.

howard

Howard Coleman

iTrader: (6)

our motors provide, perhaps, the most challenging test for sparkplugs.

in my conversation w the Autolite tech guy yesterday i mentioned that a 600 rwhp rotary makes 8.6 (flywheel) hp per cubic inch... there was a long silence on the other end and the guy pretty much said that the number was in the area that he had not seen.

this all creates huge combustion chamber pressure and heat.

when i lost my fuel pump fuse my engine went lean in 3rd gear. after pulling one of the lead plugs (AR3932) i noticed a significant part of the porcelain was missing.

late yesterday i received an email from an engine customer that did two days on track at wide open Brainerd Int'l.

"The car performed beautifully this weekend at BIR. Only issue I ran into was at around 5-6k rpm the ignition would start to break up. We discovered it was due to the spark plugs, the Autolites. So I swapped out to a new set and still had the issue. Luckily I made some FD friends at the track and he had a used set of NGK race "wire" plugs that we threw in and that solved the issue. Just wanted to let you know and give you an update."

i spoke w him last night and he said that he was running the AR3932s gapped at .023 on E85 w a GT3574 off the spring (14-15) and after they pulled the 3932s noticed that the majority of the porcelain was missing from one lead plug!

while he didn't mention the "D" word (detonation) he did say the car was "missing" and the plug swap fixed it and that the motor was fine etc...

as of last night and my concerns re the porcelain i will no longer run Autolite plugs. they were originally a recommendation to me from Lance Nist/PanteraEFI. Autolite makes great plugs, IMO, but i conclude they don't fit our highly stressed motors.

howard