Spark Plug Choices for EP 13B
 

I have a street port 13B I run in EP and I was wondering what the up-to-date spark plug recommendations are as I get the car ready for a new season.

I'm not out running the engine to 110% looking for the last few horse power (normally shifting at 7,500 to 8,500), rather, I'm looking for a plug that gives good performance at a reasonable price. I'm always messing with jetting (Weber IDA) for different elevations where we race so a reasonably priced plug is convenient in case I foul a set of plugs during a practice/tuning session.

I started out with a set of super Mazdaspeed/NGK R6725 - 10.5. I hear these are the best of the best but super expensive for my relatively amateur racing efforts where the money is perhaps better saved for more tires.

I have also run NGK BUR9EQP which seem to run well and last for a while.

I see that Racing Beat recommends BR10EIX for my application (a thin walled socket is not a problem). Anyone run these?

I also see that NGK offers a 9 heat range iridium plug for the RX-8, anything good with these?

Thanks!

We always just did the R6725s. We had a couple sets in the toolbox just in case, but in my experience anyway, the only thing that really seemed to go wrong with them is fouling, and that's not a "this plug is dead" thing, but more a "clean this at the shop" thing.

I know, I know, it's $100 in plugs instead of $30-40 or so, but if you talk to the right people you come across so many anecdotes of ignition breakup down straightaways when everything is good and hot that I never wanted to mess with it.

Well, not "never"; I had one motor where I experimented with recessing the spark plugs and running Champion surface gap plugs, but you want to talk about fouling issues...

Cool, I know that the racing community/Mazdaspeed/NGK knows their stuff and that there's a reason they recommend the R6725s.

Do you have any tricks to the 'cleaning in the shop' for them? I've heard about torching them with MAPP torches to clean them up...

Here are a set after having the float level high for a 20min session. To me they look completely fouled and were taken out of service - the engine still ran well, though, at the end of the session.

https://c1.staticflickr.com/1/558/32...5bfd7174_c.jpg

Check out NGK BUE plugs. They work fine in my EP 13B and are relatively inexpensive, like $5 each. I have run these for 2 years with no issues.

We have a harbor freight sandblast cabinet - just made a little sleeve to go over the threads and quick bead blast the carbon off, then blow them with shop air to get any grit out. Only takes a couple seconds.

I have been using this little $10 Harbor Freight spark plug cleaner for 20 years now, and it works great. Don't push the plug all the way in, or else all the threads will get blasted. Like Kenku said, when you are done, "then blow them with shop air to get any grit out. Only takes a couple seconds. "

Pneumatic Spark Plug Cleaner

My PP road racer is a little harder on fouling plugs with a cold start on a cold track day, so I put in a set of 7 or 8 heat range plugs for warming up the engine when cold, and when moving the car from the trailer to the shop. Once I warm it up in the morning at the track, then I leave the R6725-115 plugs in at the track the rest of the day. Once I get a little heat in the motor, it seems to do fine and not foul the plugs anymore. Between the changing out plugs for warmup and the sand blaster, I have only thrown away one set of these expensive plugs in 20 years of racing. Like Kenku said, always keep a spare set in your toolbox, just in case.

Clean up the tune and they'll last longer. The nice thing about the 6725s and 7420s is that they don't wet foul as easily as the surface gap plugs. You got a carb/EFI issue, not a plug issue.

Thanks for the advice!

I picked up one of the 'pneumatic spark plug cleaner' tools, super simple and quick. My battered and charred 6725s look new again. I just have to really look inside them to make sure all the grit is out.

C Ludwig, you're spot on (I read all of your posts over at Improved Touring too). My tune that fouled the 6725s was entirely too rich - I had trouble setting the Weber IDA float levels using the 'tip it upside down and measure with gauge plate' methods (compounded by the usual gauge plate dimensions not taking into account 3.3 berg/grosse glass ball needles). I've had much better luck using an external , screw-in fuel height gauge/tube that the Porsche guys use to directly observe and set float heights on Webers. All should be better now, hence searching out a new set of plugs.

The BUE plugs look interesting too. In the Jim Downing performance book he has a picture of Champion? plugs that look exactly like the BUEs. For now I will carry on with 6725s after trailer trips and morning warm ups using street NGKs.

With a set of 'free' 6725s nicely cleaned up, I sprung for a Magnecor race wire set (I was using the NGK stockers) - I figure they can't hurt.

https://c1.staticflickr.com/6/5811/3...ece41819_c.jpg

I can't remember the alphanumberic jibbajabba that I run, all I can remember is that they are "normal" type NGK racing plugs and not multi prong or surface gap, and they are heat range 10, and they eliminated a misfire I was getting about 30 SECONDS in to a run when I had been running BUR9EQs leading and trailing. I couldn't see doing any kind of road racing on 9 heat range plugs!

Odd that you had problems with Champions, I was having no problems with them. I found a whole bunch of them for sale at Summit for something like 50 cents a plug and bought them all up, and went back to NGKs only after using them all up.

Well, it was one of those things where I was trying to do too many ideas at once and not taking great notes; I'm more competent now but it made an impression. So, story time. I got a couple C53VC and C57VC plugs and then very carefully milled the spark plug recess in the rotor housing so that the spark gap was as close to the combustion chamber as possible. The old saying about if it looks right it is right? Well it looked awesome.

http://lolinter.net/KJ_carstuff/EProd/DSCF0006.jpg

Test housing getting it figured out. Or maybe the final draft, I forget. Whatever, pretty cool right?

So all well and good, except that those housings leaked water. So I tried again, but this time with the plug washer cut off or maybe a bit of the plug shoulder lathed down too, I forget Anyway, broke it in on a friend's engine dyno, and the C57VCs seemed to be too hot to work reliably, so we went with the C53VCs, load it up and go to the track. We get up to the false grid, shut off the car, and then it won't restart. Plugs fouled to hell. Threw in the only set of spare C53VCs, foul those, then realize that of all the plugs in the toolbox... well, because I milled the spark plug recess, I have no confidence on whether or not I can put normal plugs in without the plug hitting the apex of the rotor. You can imagine the expletives.

Nowadays, with better notes, careful tuning with a wideband, and if I get everything else optimized, I might come back to it. At the time, I figured that no incremental power gain from the sexy spark plug setup would be worth a DNS.

*quickedit* Oh yeah, the R6725s are the ones with the kind of recessed spark plug nose and the one fine electrode. Not actually surface gap, but not sticking out very far. Actually, yeah, Andrew-s posted pics of them, duh.

Keep the gap small on the R6725 plugs - .028" is the maximum you want for a high rpm engine. You can run them as tight as .025".

Very late to the party here, but I run an SP 13B with Weber 48IDA as well.. I run the 10.5 plugs in mine and haven't had to touch them in the 3 seasons of so I've been running this car. On cold mornings (40-50 deg F), I usually pump the gas pedal about 4-5 times and hit the starter. it'll usually run for a few seconds and die. depending on how cold it is outside, I'll do that a couple times and then the car is warm enough it will idle on its own about 2500rpm.

note: I'm just about sea level (Houston TX area- elevation about 30 ft!)

In the summer when it's warmer, I'll pump the pedal 3 times to prime it and it fires right up with no fuss.

I have yet to pull plugs hot off the engine and check how they look, but my WB02 shows about 12.7 at WOT and the car never has a problem starting. engine build and tune was done by Louie Rivera, and I trust his setup. don't jack with it, just drive the dang car!