mx5cartalk.com

Pretty handy page
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

NKG say the same plugs for the 93-98 as for the 98-05 MX-5
Recommended Plug - BKR5E-11
Iridium Option - BKR5EIX-11

And I think the iridium “max” is listed as a BKR5EIX-11P
Looks like they might make an IRI Series to suit too.

Now looking at the Bosch website and this pdf
http://apps.bosch.com.au/products/saa/sparkplugs_passenger.pdf

They recommend DIFFERENT plugs for the 93-98 and the 98-05.

BUT they also call the 93-98 engine the B8.

(I cant stick in tables so i hope this makes sense)

Year-Capacity-Engine-Code-Resistor
89-93 - 1.6L - B6 - FR7DCX
93-98 - 1.8L - B8 - FR8DCX
98-05 - 1.8L - BPD - FR7DCX

Performance (Super 4)
89-93 - 1.6L - B6 - FR78X-4pack
93-98 - 1.8L - B8 - FR78X-4pack
98-05 - 1.8L - BPD - FR78X-4pack

Performance (Platinum)
89-93 - 1.6L - B6 - FR7DPX
93-98 - 1.8L - B8 - FR8DPX
98-05 - 1.8L - BPD - FR8DCX

Denso's website says

for a 95 you should use :
Standard Plug K20PR-U11
Premium Plug PK20PR11
Iridium Plug IK20
(gap 0.044)

for a 99 you should use:
Standard Plug K16PR-U11
Premium Plug PK16PR11
Iridium Plug IK16
(gap 0.044)

The Champion website
SAME - 93-05 Double Platinum Stock # 7071 Part # RC12PYP
93-98 Iridium Plug Stock #9201 Part # 9201
98-05 Iridium Plug Stock #9202 Part # 9202
SAME - 93-05 Premium Gold Plug Stock #2071 Part # 2071
SAME - 93-05 Single Platinum Stock #3071 Part # 3071
93-98 Traditional Spark Plug Stock # 71 Part # RC12YC
98-05 Traditional Spark Plug Stock # 318 Part # RC12MC-4

Autolite
93-05 Autolite Double Platinum APP3924 APP3924
93-05 Autolite Single Platinum AP3924 AP3924
93-05 Autolite Traditional spark plug 3924 3924

98-05 Autolite XP Iridium XP3924 XP3924 (not listed for the 93-98)

Splitfire
93-05 Splitfire Triple Platinum spark plug TP392D TP392D .044
93-05 Splitfire Spark plug SF392D SF392D

For the NGK's, BKR6E-11 is the 'colder' running heat range plug.

'colder' plugs are usually recommended for forced induction, but I also stumbled across this earlier. I'm not too sure how applicable it is, but it is based on someone's experience between the two NGK alternatives.

From miata.net

My Mazda handbook lists 2 NGK plugs as OK to use in the Miata. One is the BKR5E-11, and the other is the BKR6E-11. Let me explain the difference.

The BKR5E-11 is the hotter running of the 2 plugs. Now do not confuse the "heat range" of a plug by thinking this is telling you how hot the Spark is. The spark will be the same from all plugs regardless of heat range.

The spark plug heat range basically is to tell you how well they keep themselves clean, specifically the white insulator around the center electrode.

The BKR5E-11 is the hotter running plug for people who do not push their car very hard. The tip of the plug stays hotter for easy city type driving, so the tip of the plug stays clean enough to fire reliably.

The BKR6E-11 is a "colder" running heat range, for people who regularly rev the motor high, OR who do a lot of highway driving. The consistant high speed highway driving keeps the top hot and clean. This "cooler" plug transfers more combustion heat to the head of the motor so the coolant can take it away. The NGK web page also suggests this cooler plug to sustained highway driving.

I drive about 50 miles a day commuting for work on 4-lane highways. I had been using the hotter "5" heat range spark plug, but when I had my oil analyzed I showed a problem of high Nitration. This can be caused by excessive heat in the combustion chamber. So I recently switched to the cooler operating BKR6E-11 spark plugs, and my engine is really running super. It seems to be even running better than before, but maybe it is just my imagination.

But I am anxious to see if it helped the Nitration situation I am concerned with. It should help.

And anything that helps a high performance engine run cooler is a PLUS in my book.

If you do a lot of city driving, and rarely rev it to the limit, the BKR5E-11 is probably best for you. But if you do a lot of 4 lane commuting, I suggest you try the NGK, BKR6E-11. My friend and I are both running the "6" right now and are very happy with them.

http://forum.miata.net/vb/printthread.php?t=275245

Yeah, my ADM NA8 Owner's Manual spark plug recommedation is also NGK BKR5E11 or BKR6E11.

Useul info, Dave. Thanks for posting it. How about moving it over to the Technical Guides?

Probably also with mentioning that one your plug gets a rusty stain at the bottom of the ceramic is prone to arcing and should be replaced.

If you don't drive your car much and particularly if you live in humid areas this can happen well before the plug gets to end of life based on km or electrode wear.

In this case there is no point buying iridium / platinum etc is not worth it.

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