I keep forgetting all the spark plug options and the heat ranges so I decided to assemble some of the data, mainly for Force Induction folks, and racing folks
note that the trailing plug hole in the rx8 housing is shallow, so if you plan to use an rx7 plug think about spacers.

one of the common turbo setups is to install BUR9EQ (rx7 trailing) in the rx8 leading position for a 9L, 9T heat range, it is now believed that going colder on the trailing side is crucial.
for low boost we can keep the stock plugs and gap them, Greddy recommends 0.30

RX8 OEM Plug NGK
RE7CL Heat Range 7, and in 2006 release a heat range of 6 (iridium) (21mm)
RE9BT Heat Range 9 (iridium) (19mm)

RX7 OEM Plug NGK
BUR7EQ is leading Heat range 7 (21.5mm) (Platinum)
BUR9EQ is trailing Heat Range 9 (21.5mm) (Platinum)

Denso Selection
RX8 Racing Specific
IRL01-27 heat range 9
IRT01-31 heat range 10

NGK Selection

RX8 Racing Specific
R7440A- L Heat Range 9,10 (21mm) (iridium)
R7440B- T Heat Range 10,11 (19mm) (iridium)


RX-7 Racing Specific
R6725- Heat Range 9,10,10.5,11,11.5 (21.5mm) (Platinum) T&L

R7420- Heat Range 9,10,10.5,11 (21.5mm) (iridium) T&L

AUTOLITE Crazyness

Autolite Racing Spark Plugs AR3932 Heat Range 10 (19.05mm)(copper)
AR39 (31=11-35=7)

according to the thread it was gapped at .2 and he had no issues running 500hp on a REW, before he had misfires or pre-ignition

FD Spark Plug Tech 2013 - Page 2 - RX7Club.com

Resorces
Verrill: Plug Color Chart
NGK Spark Plugs USA


Pre-ignition

Pre-ignition occurs when the air-fuel mixture is ignited by a hot object / area in the combustion chamber before the timed spark event occurs.
When the spark plug firing end (tip) temperature exceeds 800°C, pre-ignition originating from the overheated insulator ceramic can occur.
Is most often caused by the wrong (too hot) heat range spark plug, and/or over-advanced ignition timing. An improperly installed (insufficient torque) spark plug can also result in pre-ignition due to inadequate heat transfer.
Pre-ignition will dramatically raise the cylinder temperature and pressure and can melt and hole pistons, burn valves, etc.
Knock

Occurs when part of the air-fuel mixture in the combustion chamber away from the spark plug is spontaneously ignited by the pressure from a flame front originating from the spark plug. The two colliding flame fronts contribute to the “knocking” sound.
Knock occurs more frequently when using low octane fuel. Low octane fuel has a low resistance to knock (low resistance to ignition)
Knock is related to ignition timing. (Knock is sometimes referred to as “Spark-knock”.) Retarding the ignition timing will reduce knock.
Heavy knock often leads to pre-ignition.
Heavy knock can cause breakage and/or erosion of combustion chamber components.
Knock is sometimes referred to as “ping” or “detonation”.
Misfires

A misfire occurs when the spark travels the path of least resistance instead of jumping across the gap. Misfires can be caused by the following:

Carbon fouling
Worn or deteriorated ignition system components
Too large of gap size
Spark timing excessively advanced or retarded
Damaged spark plugs (cracked insulator, melted electrodes, etc)
Mismatched ignition system components (plug resistance / wire resistance, ignition coils / igniter modules, etc.)
Insufficient coil primary and/or secondary voltage – voltage required to jump the spark plug gap higher than coil output

found this in a thread too, thought it would be useful


Did a search and was surprised at the different plugs offered.
I did have my car set to the 06 RX-8

NGK Iridium IX Spark Plug Part No. 2669 $7.09
Autolite Double Platinum Spark Plug Part No. 458DP $2.09
NGK Racing Spark Plug Part No. 4554 $3.59
Autolite Racing Copper Core Non-Resistor Spark Plug Part No. AR3932 $4.09
NGK Racing Spark Plug Part No. 4091 $3.09
Autolite Double Platinum Spark Plug Part No. 295DP $2.09

I thought we only used on type. and leading /trailing at that
NGK Laser Iridium Spark Plug (RE7C-L) Part No. 6700 $20.09
NGK Laser Iridium Spark Plug (RE9B-T) Part No. 6701 $20.09

 

Wow ....good work man !

FWIW

I was using BUR9EQPs all round till a recent dyno identified some pings that didn't go away with less timing and more fuel + W/M (@16psi)

Switched to R6725 10.5 and 11.5 (extra washer on the trailings) and will be testing that combo soon.

 

I think the NGK BUE plugs are probably the best for trailing. They are as cold as physically possible and the are hard to foul. Only problem is you need a very thin wall socket to use them.

Disclaimer: I haven't found a need to try them yet, but I do have some sitting in my desk for if I need to go that cold.

NGK Spark Plug BUE

 

do you have a more specific part number?

 

Probably out of my league here... but has anyone tried cross referenceing an e3 replacement? They are pretty much unfoul-able(?) and never need gapped. Just a thought, i have run them in my Suburban and my Cherokee.

 

R6725 can be RX8 specific despite having only one length, many road racers run them, they don't use an extra washer that I know of

 

Good to know Teamrx8!!

 

I tried screwing one into an old housing I have and they dislodged carbon at the bottom of the hole . Not a full on interferance but close enough to want some extra clearance .

 

let me know what you decide Brett, I am looking at purchasing some.

 

I found the BUE plugs in this thread:
What Plugs? - Page 3 - RX7Club.com
they are PN 2322

 

Using Autolites here, going on 10 months on this set.
At about $4 each I'm very pleased with them.

.

 

What did you gap them at?
what kind of pony's are you running?

 

This is a widely held misconception.

Detonation is not auto ignition. Auto ignition can happen, but as far as the engine is concerned the event is similar to a regular spark plug firing and does not cause knock by itself. Diesels do not regularly knock, but they do have auto ignition.

Also it's not the two flame fronts colliding. That happens normally in our engines (and any other 2 plug per cylinder engine) and is does not cause detonation by itself.

Think about a firecracker. If you take the gunpowder out of it and lay it on the ground it will burn quickly without exploding, but if you wrap it tightly in a paper wadding and light it the pressure can build up enough to cause everything to detonate at once.

Detonation in an engine is caused when the unburnt fuel air mix is exposed to too high a pressure for too long with just enough heat to light it off. It's a supersonic explosion, instead of a slow burn, and the knocking/pinging sound is caused as this explosion reverberates through the housing.

It's a chemical reaction and as such it can be influenced by lead salts, lead powder, MTBE, water, or even steam.

Because detonation causes this extreme pressure wave it brakes down the boundary layer of air that normally insulates the housing, rotor, and the spark plugs. This causes them to be exposed to the hot combustion gas directly, which in turn puts more heat into the coolant and oil causing power to be lost, as well as putting extra heat into the spark plug.

The increase in spark plug temperature can lead to preignition, preignition causes higher peak pressures (and temperatures) earlier in the rotation, which then causes more knock.

If you run too hot a plug, and stay in detonation long enough, preignition will take over and that's when things start to break. You can either run a colder plug, use a higher octane, run less timing, or inject water but you must stop preignition from taking over.

 

Thank you for clarifying!

 

Thanks for the info Farzda this looks like it wil be a good thread.

 

My bad just seen this, gap is .2 same as HC
Car made 423

.

 

Been using BR10EIX in the REW....they need a specially modified socket to get them in and out...but they work great at 500+

They are running them in a 1000HP Methanol drag car and having no issues either

 

I was told to avoid those . Due to instances of the electrode falling off and destroying the engine .

 

Been using then for years in big HP engines and never had one fail. But we chuck then out often though. They don't foul as easy as the NG reading plugs that were costing me $35 each

 

My engine builder went nuts when I said i was buying the EIX

Assume you mean 'NGK racing' ?

 

LOL autowreck to the rescue.....yes NGK Racing plugs

 

NGK Spark Plug for BR10EIX Racing - Racing Beat

 

That's nice . Well done

 

well I don't see how the electrode can fall off that anymore than any other plug, certainly more robust than the rotary race plug electrode you just installed, which I remember someone (was it you?) fretting about this previously. The R6725 is pretty much the racing rotary standard the world over as long as you can afford them.

any way, this jumped out at me;

not sure why they imply it's not for turbo rotary engines

 

I'm running these in the Leading position haven't had any problems yet....

R7440A- L Heat Range 9