never figured out where that post was, but stumbled across this picture so posting it up

Renesis NGK R7440 Iridium on left and REW NGK R7420 Iridium on the right with thicker ground strap


https://cimg6.ibsrv.net/gimg/www.rx7...51ba09668.jpeg
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not to mention that the Renesis version costs 2x -3x more, most likely due to smaller quantities produced/purchased …
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after 200 miles break in and a few brief trips to low teens boost w my G40-1150 i pulled my plugs to take a peek...
leads were NGK 10s and the trail were the new side gap R6601s 10s.

my rears were just a bit more lean looking which supports my rear knock readings which were slightly higher than the front. i will add a bit more fuel to the rear rotor.

i decided to switch from 10s to 11s so we will see how that goes. all of our rotor housings have raised areas around the two spark plug bosses and the close on the exhaust port. the colder the plug the less the rise and the less wear on the apex seals.

i swapped Densos into the leads. take a careful look at the following picture. Denso features a beautifully shaped very thin center electrode that better focuses the energy. the rotary being of smallish displacement yet capable of making big power needs all the help it can get to fire the highly compressed mixture. the NGK has a significantly larger center electrode. it is Denso for me in the leads going forward.

https://imagizer.imageshack.com/v2/1...923/q8ZiCM.jpg
from the "Tuning Ignition Section" of my site here are plug P/Ns:

Denso Iridium

5720 IRE01-31 10 heat range

5721 IRE01-32 10.5

5722 IRE01-34 11

5741 IRE01-35 11.5

NGK Iridium

5501 R 7420 10 heat range

4857 R 7420 10.5

7756 R 7756 11



NGK Surface Gap TRAIL POSITION

4017 R 6601 10 heat range

4586 R6601 11

Going to bring a set of 6601's to swap out the Trailings 7420's on the next dyno. I'll update on my build and here.

Admittedly thread tangent, so feel free to respond off-thread if you care to:
Would love to hear your initial impressions on the G40... maybe in the Single Turbo section.
My front is the higher EGT and knock. What fuel trim % increase are you starting with to try and balance out the front and back rotors? I'm thinking 5% more fuel on the front as an initial trim.

"front higher EGT and knock"

if you have a math channel on your ECU i suggest you set up an equation front minus rear so you have a line graph of the differential. EGT diff is often dynamic. zero in on where and you will better be able to fix it.

currently i have around a 30-60 F diff between my egts driving around in vacuum. under boost the egt diff is between 20 and zero.

here's a boost segment from yesterday, just 10 psi at 30 TPS and 5122 RPM. if you look at the bottom where my math channel is you will see the F diff is less than 1 degree. this data point is only on primaries, no secondaries. from previous logs w my 9180 around 26 to 30 psi boost close to 600 i am around 20 F diff.. i do run 10% more fuel in my rear rotor under significant boost and RPM. same timing F & R.

https://imagizer.imageshack.com/v2/1...924/sqKcJc.png
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Why not surface gap all around?

Looking forward to R6601 v R6725 v R7420...

"Why not surface gap all around?"

i do not have that answer.

i am running them in (only) the trail based on advice... i am quite sure that if the person giving me the advice was also running them in the lead he would have so advised me.

the other reason came from another person i respect. he has delivered all his motors w the OE 9s in the trail. they of course also do not have a ground strap that can become a glow plug.. he was not aware of the
6601s which offer a far better option because they come in 10 and 11 heat range. he considers the trail to be more dangerous than the lead as it is first exposed to the compressing charge. the charge is significantly less compressed and therefore is more easily ignited than the later exposed lead. a reasonable concept from an accomplished builder. no guarantees here of course.

i am out this morning with Denso 11s in the bottom and the 11 surface gaps up top.

update on 11 heat range

after a few miles and some 17 psi pulls it was time to take a look:

https://imagizer.imageshack.com/v2/1...924/nO6x2n.jpg

the ground strap on the Denso tells the story. not too cold. an ideally chosen heat range results in a ground strap that is annealed half its length. if a plug is too cold the annealed portion will be less than half. too hot more than half. mine are more than half so they are not too cold. i found that they seemed to hot start and cold start no differently than my 10s. this is with IGN-1A coils and Magnecor wires.

the colder the plug, the less height for spark plug mountain and exhaust close ridge.

the less height of SPM and ECR, the less wear on the apex seal.

Seven Eleven

received a lengthy email from someone with lots of experience w the surface gap plugs. he runs them in all four holes and prefers them to the traditional plugs that we run. crisper idle, throttle response, more power.
i am ordering more 11s and will give them a try in the leads.

I have a friend that's been using these in all 4 spots for years as well around 500whp with the 10's. Says he found them in a Mazda Race catalogue years ago and decided to try them and has told me the same thing, doesn't notice any drawbacks under throttle and gets a smoother idle. I know that's not very empirical but lines up with what you're hearing at least :icon_tup:. He's also telling me he finds they don't foul as fast. He runs them without any washers.

"He runs them without any washers."

your friend might be the guy that emailed me. he mentioned he ditches the crush washers. sounds like a plan and i will do the same. i will be looking at another set of 11s on Tuesday and will give them a spin.

Appreciate you keeping us updated. Curious to see how these go

I found that thin copper crush washers used to index plugs on certain motors can be used in place of the normal washers. It helps the plug reach better since they're 19mm instead of 21.

the Mazdacomp catalog used to list a thinner washer just for this. moving the spark plug closer to the combustion chamber = better combustion. your limit though is when the plug hits the apex seal, if you look its happened here and there with the Autolite plugs

I'm the guy who emailed Howard. Here is the whole run on story for anyone bored enough to want to read it. For the record, I read a lot on the forum and have tuned mycar based on various information I have found here and abroad. I just very seldom post anything;

" I just happened across your spark plug article. I actually stumbled across these plugs in an old Mazdacomp catalog a few years ago. They recommended the 10 or 11 heat range version for road racing FD RX7s in both leading and trailing. I actually use them in the leading and the trailing on my rotary swapped 808 wagon. I can say I feel that they work extremely well in the leading position. Being a surface discharge plug, they never seem to foul. Objectively, they crisped up the throttle response off idle as well as at lower rpm. I am running 20psi with water injection on a S366SXE on a half studded, (street ported), S4 FC block. I have had zero issues even while tuning the car myself and occasionally making silly mistakes. I also noticed a power difference using these plugs. I have no way to quantify it but, the butt dyno says so. I believe this is due to the way the spark projects outward from the surface of the plug and exposes more of the spark surface area to the fuel/air charge with no ground strap on the way. I am actually shocked that my lowly LS2 coils are able to fire these plugs off with (700cc of) water at 20psi with no issue (running 4.9ms dwell). To make up for the fact that the plugs are 2mm shorter, I remove the washer on the leading plugs. I checked this on a junk rotor housing I have and there is still plenty of clearance. I find these plugs to be much superior to the race plugs most people recommend for rotaries; R7420 R6725. I personally found these to not idle as well and foul much more easily."

I researched spark plugs a lot while building my car. I found the BUR9s in all 4 holes worked quite well up to 15psi. I figured if I was going to run more than that, I needed colder plugs and water. I was unimpressed with how the R7420-10 plugs worked. I found they would foul fairly easily if idling for any length of time. I also felt the made less power than the BUR9s at the same boost..... Butt dyno feel anyway. So I tried these R6601s and haven't looked back. They are relatively cheap and Ihave been running the same set for 2 years. My car gets about 3000km per year and most of them are hard, abusive, kilometers.... With a few street legal drags thrown in for good measure.

I was going to try the NGK BUE plugs originally but the fact they have a 13/16" hex, and more importantly have no resistor, I decided against them. They are also a surface discharge plug and were originally used in racing outboards. I read that they didn't have a listed heat range but would have been equivalent to a 12 or 13. Maybe an option for someone running really high boost? I did read of a few guys using them for racing but not a lot of info out there on these.

Appreciate the feedback. It looks like they did make a hotter heat range, for lower HP but have discontinued them.

https://www.ngk.com/ngk-7885-r6601-9-racing-plug

I dont think at my power level(330rwp) I could step up to the 10 heat range even with the Twin Power.

they don’t play well with IGN-1A ignition coils and were working their way to becoming side surface gap plugs :suspect:


https://cimg8.ibsrv.net/gimg/www.rx7...211ae3e1a.jpeg


installed by the previous owner; good enough to still make over 500 whp though, but have to wonder how much more they were holding back, literally zero knock logged on high boost still.
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I think you may need to close that gap justa wee bit there!!! :cool:

You may still be able to find some old stock 9s somewhere. They were available last year still as far as I remember. Considering that fouling with these plugs has been basically non-existent, you might get away with 10s. Not sure.

I would really like someone else to try a set of these in lead and trail and see what you guys think. I was pretty convinced they made more power. Would be interesting to hear if anyone else gets the same impression.

I actually did find a set of 4 9s I could buy. Might scoop them up and throw them in the trailing to see what happens.

Will wait to see Howards feedback for leading.

So is the consensus to remove the crush ring so it extends farther into the motor?

EDIT- Couldn't take it, got excited and found a new set of 9s on eBay for $49 delivered. Purchased and should be here by Saturday.

here is the link to Paul Yaws Article. like Rob Golden, Paul Yaw has a big port engine in a REPU, so no turbo.
https://web.archive.org/web/20150302...w/ignition.htm

again the warning with the Autolite plugs is that they aren't gapped out of the box, you need to set it, and you also need to make sure that the plug come out of the box is correct
i used them to tune in my P Port, they were like $3 a plug...