Rotary Spark Plugs

[Mike Spencer]

OK; Blatant newbee question, but I'm qualified! :D

I run IT7 and have only had my car for a little over a year. It's a 12A (presumably the 13Bs behave similarly). I run the car every 2 or 3 weeks just to keep the internals properly lubricated. Today something kind of wierd happened.

(Background; The car was last raced at VIR in May) The car started briefly, then stalled 3 or 4 times. I finally got it running, but it sounded strange. To make a long story short, I was only running on 1 rotor. When I pulled the spark plugs from the non-firing rotor they were severely carboned. After a quick cleaning, it now runs alright. I am planning to replace all 4 plugs before my next race (last weekend in Oct). Just wondering if rotories foul plugs or if I have a "deeper" problem.

I currently use NGK R(ace) plugs. Also, I premix my fuel with synthetic H1R (motorcycle racing) 2-cycle oil; 1 oz. per gallon.

Thanks, in advance.

[C. Ludwig]

Originally posted by Mike Spencer@Oct 1 2005, 05:39 PM
OK; Blatant newbee question, but I'm qualified! :D

I run IT7 and have only had my car for a little over a year. It's a 12A (presumably the 13Bs behave similarly). I run the car every 2 or 3 weeks just to keep the internals properly lubricated. Today something kind of wierd happened.

(Background; The car was last raced at VIR in May) The car started briefly, then stalled 3 or 4 times. I finally got it running, but it sounded strange. To make a long story short, I was only running on 1 rotor. When I pulled the spark plugs from the non-firing rotor they were severely carboned. After a quick cleaning, it now runs alright. I am planning to replace all 4 plugs before my next race (last weekend in Oct). Just wondering if rotories foul plugs or if I have a "deeper" problem.

I currently use NGK R(ace) plugs. Also, I premix my fuel with synthetic H1R (motorcycle racing) 2-cycle oil; 1 oz. per gallon.

Thanks, in advance.

61622


We run the stock NGK 8 heat range plugs in both leading and trailing. The R in NGK nomenclature stands for Resistor and not Race FWIW. Some claim a slight HP bump from the high dollar fine wire NGK plugs. We've never tried them and never really felt the need. I really don't have a problem with foulding plugs. have fouled a couple sets due to the senario I'l describe below.

In my experience part of your fouling problem is probably starting the car and letting it idle as you described. Plugs foul due to a rich mixture and not being given a chance to heat up to their working temp in order to burn off the accumulated carbon. Idle mixtures are rich by neccesity so there's not alot you can do about that. In engines that require a very cold plug under high load working conditions it's common practice to start them and warm them up on a cheap, hot plug to avoid fouling the good plugs. I'm guessing you're using a stock heat range plug. You really don't want to go any hotter than that. You really just need to run the engine a little harder when you start it to get the plugs up to temp or keep an old set for your occasional firings and a good set for racing.

Are you premixing that oil on top of the stock injection oil?

[lateapex911]

Good advice from Chris-

A bit more on the "race" plugs. Just in case you do have them, you can ID them by their unique thin wire design. Mazdaspeed recommends that if you will be using them, that you start the engine and let it warm completely before installing them, and they will foul and decay in performace if run cold.

They are very expensive.... multiple times the cost of even the better plugs, and the hassle is significant for the average Joe racer with no crew. I was told the HP was around 1 or maybe 2.

To me, that's the kind of plug you put in when you know you are getting every fraction of a second out of your driving, you are on spiffy new tires, and the q-session or the race is important.

I think Mazdaspeed recommended the turbo plugs as good alternatives.

In answer to your question, no, I don't think there is anything fundementally wrong with your engine.

[Mike Spencer]

Originally posted by C. Ludwig@Oct 1 2005, 11:47 PM
...Are you premixing that oil on top of the stock injection oil?

61625


Chris/Jake -

First of all, thanks!!! You two and a few others always seem to be the ones responding to all the newbie questions. I know all of us appreciate it. We just forget to tell you once in a while. :023:

Regarding the stock oil injection, yes I believe so. I am following the recommendations of the previous owner who had good success with the car and so far I&#39;ve had a *LOT* more car than driver! <_< It&#39;s possible the oil injection has been disabled, but I really haven&#39;t checked.

The plugs that came in the car are NGK "R" (which I now know means "resistor"). They are definitely not "thin wire". The guy at Auto Zone said they have been replaced by a newer number. I plan to replace them with the same/updated part number for the race, and probably get a "stock" set (assuming they are a different number) to keep in the car between races.

I&#39;m probably being overcautious running the car so often, but I&#39;ve heard of rotaries getting dried-out apex seals and requiring a rebuild. Besides, it&#39;s fun! :P

Anyway, thanks again!

[C. Ludwig]

No problem. Love to help if I can. :023:

I mis-spoke in my first post. We run the 7 heat range plug. The way the NGK numbering system works that is one step hotter than what you&#39;re running. The complete number is BUR7EQ. I&#39;ve never seen an NGK with the ground straps that look like the ones in your picture so maybe they are just pretty old? You can try to go to the #7 plugs. The hotter plug should help your fouling situation slightly and won&#39;t be any danger to the engine. A good place to compare plugs and maybe learn a little bit about them is Spark Plugs.com (http://www.sparkplugs.com/) . They&#39;ll have about any kind of plug you ever dreamed of wanting.

Also, in a pinch I&#39;ve used the Autolites. They&#39;re the cheapest surface gap plug you&#39;re going to find. They&#39;re half the price of the NGKs. Not sure of their relative heat range but we&#39;ve ran them here and there without a noticeable difference. For a cheap plug to use for your occasional engine running this might be your best choice?

And for some reason this website won&#39;t let me post the pics from the links below. So you get just the links instead.

Standard NGK BUR*EQ $6.40 @ sparkplugs.com
Standard NGK Pic (http://www.sparkplugs.com/productImages/1/NGK3559%2D2%2Ejpg)

Fine Wire Denso (looks the same as the NGK) $35.30 @ sparkplugs.com
Fine Wire Denso Pic (http://www.sparkplugs.com/productImages/3/5719%2Ejpg)

Standard Autolite 2626 $3.21 @ sparkplugs.com
Autolite Pic (http://www.sparkplugs.com/productImages/5/2626%2Ejpg)

[lateapex911]

No problem Mike!

I have used the Autolites too...and I was actually told by a local rotary &#39;guru&#39; that they actually had more &#39;juice&#39;, LOL..

I never would have thought so, (Autolite?!?) but they seemed just fine. No seat of the pants issues, and my lap times we as always.

I think the thin wire racing plugs ran me $25 from Mazdaspeed the last time I ordered, but that was years ago, when I thought a HP might help at the end of the straight! Dollar for dollar the Autolites look like the deal. ;)

Your plugs look a bit rich and I&#39;m sure it&#39;s nothing to worry about.

[C. Ludwig]

Seems the high dollar, fine wire plug from Mazdaspeed is a R6725-11 or R6725-105. These are 11 and 10.5 heat range plugs respectively. Pretty cold. They&#39;re $29.50 from Mazdaspeed and $31.61 from Sparkplugs.com. The hottest one that Sparkplugs.com lists is a 9. FYI anyway. :)

[tdw6974]

Autolite Race Plug AR3934 Heat range 8, AR3933 heat 9, and AR3932 Heat range 10. Seem to work fine Car starts better with these than the NGK Plus can get then overnight from most auto parts stores including the chain stores. T weaver

[Marcus Miller]

Same as Tom; if I remember correctly. :blink:

I run my plugs 4 double regionals (or equivalent)


Marcus, who thinks they are probably overdue for changing.

[Chris Taylor]

I can&#39;t remember part numbers, but I run two you have pictured and two surface-fire looking plugs. Everybody likes to throw around HP numbers, but I&#39;ll tell you what makes a bigger difference than the type of plug -- the location of the electrode in the housing. New spark plugs were a 2-3HP increase, situating them properly were another 5. :119:

Every time we find 20 horsepower on a stock 12A I rejoice that I&#39;ve got a friend with a dyno. :023:

Chris&#39; 2nd HP tip of the day: run the thinnest $2 paper filter you can find. K&N likes to brag, but the Purolator I had on the car for the first run put up 5 more HP than a brand new K&N for the 2nd, and a ~12 hour paper was equivalent to the K&N. PS - the hotter the engine is (to an extent) the better your power output. I suggest finding a 190 degree thermostat.

Oops, I&#39;ve said too much. :D

[ddewhurst]

***New spark plugs were a 2-3HP increase, situating them properly were another 5.***

Chris, do you also index your trailing plug ?

[Chris Taylor]

Haven&#39;t had time to do that yet... but it is on the list for the next dyno session.