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Iridium plug heat range thresholds

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Old 12-08-18, 07:55 AM
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Iridium plug heat range thresholds

Hi guys I've done a lot of searching but trying to find some definitive advice on this topic

At what boost/power thresholds would we want to choose NGK 7420 10s, 10.5s, and 11s?
Let's assume powered by IGN-1a coils.

I currently have the 10s with the IGNs, but hoping to find out if it might be wise to move a bit colder.

Thank you
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Old 12-08-18, 09:06 AM
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10-10.5 ~400HP
10.5-11~500HP
11+ ~600HP+

Going through this recently myself the advice that stuck with me was “run the coldest plug you can without trouble”. There’s some trial and error there but the colder plugs handle boost conditions better.

I bought Denso Racing 31’s which are similar to NGK Racing 10’s. The NGK Rancing 10.5’s were the favorite among those I spoke with.
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Old 12-08-18, 10:41 AM
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VA

Personally I use HIMNI racing's recommendations on their site. Which for reference is line with Molotovman's advise. If you're in the 400-450HP range I'd stick with the 10's unless you actually suspect an issue.


The below excerpts are from Himni Racing's website concerning they're plug recommendations:

<QUOTE>
HR recommends NGK Spark Plugs for Street, High Performance and Race rotary engine applications. There are a few different options regarding spark plugs for the rotary engine. Let our decade + of hands on experience, testing, retesting & high HP yields do the work for you. We have broken proper plug selection down into an easy to understand, 4 basic categories. Standard, Platinum, Iridium & Competition. (see below)

This NGK BUR7EQP spark plug is the Platinum Mazda factory (Stock/OEM) LEADING spark plug for all 1986-1995 (FC & FD) RX-7s. This resistor/platinum spark plug is recommended for city and highway driving & is used in all the 86-91 N/A, Turbo II & the 93-95 13B-REW twin turbo engine.
This NGK BR7EIX spark plug is the IRIDIUM XI. For Mainly City Driving, N/A only, No porting but high performance, 7 Heat.
This NGK BR8EIX spark plug is the IRIDIUM XI. For mostly Highway Driving, N/A only, No porting but high performance, 8 Heat.
This NGK BR9EIX spark plug is the IRIDIUM XI. For mostly City/Highway Driving, Street ported N/A, Non-ported Turbo with slightly increased boost & bolt-ons , 9 Heat.
This NGK BR10EIX spark plug is the IRIDIUM XI. For mostly City/Highway/Race, BridgePorted N/A, high boost turbo, 470 HP, pump gas, 10 heat.Specification part number breakdown: NGK BR10EIX
This NGK R6725-105 spark plug is the COMPETITION. For the most extreme performance, race only, max porting, highest boost, outright race. Short run times, zero street use, hard cold starting. 10.5 heat. Requires a thin wall socket to install/remove.
This NGK R6725-115 spark plug is the COMPETITION. For the most extreme performance, race only, max porting, highest boost, outright race. Short run times, zero street use, hard cold starting. 11.5 heat. Requires a thin wall socket to install/remove.

For N/A & STOCK Turbo 13B engines that want a pure OEM plug for original reasons, zero performance or reliability gains, the rawest form of OEM plug available, one ideal configuration, installs with normal spark plug socket.
- Configuration: Use Two (2) Standard TRAILING (BUR9EQ) & Two (2) Standard LEADING (BUR7EQ) spark plugs per 13B engine... a total of 4 plugs.PLATINUM:::
For Stock or slightly Modified N/A or Turbo 13B engines. Same as the Standard plugs with slightly increased performance, a few cents more expansive, a little more spark intensity, longer electrode life, a more complete burn, Two ideal configurations, installs with normal spark plug socket.
- Configuration #1 (N/A & Stock Turbo engine w/ a few bolt-ons, stock boost level producing UP TO 220 HP) Use Two (2) Platinum TRAILING (BUR9EQP) & Two (2) Platinum LEADING (BUR7EQP) spark plugs per 13B engine... a total of 4 plugs.
- Configuration #2 (Modified Turbo engine w/ bolt-ons, slightly increased boost levels producing UP TO 260 HP) Use Four (4) Platinum TRAILING (BUR9EQP) & spark plugs per 13B engine... a total of 4 plugs.The colder Trailing plug (heat range 9) provides substantial detention resistance needed to keep the engine "safe" when boost has been increased above stock levels vs's that of the leading plug. (heat range 7) This WILL NOT make extra power however, it will help to protect the engine at higher boost settings.IRIDIUM XI:::
For N/A & Turbo engines ranging from bone stock to hard-core race. The ultimate in plug performance, max yield, all (4) plugs will use a matching heat rang, the most potent spark, high output, long electrode life, complete burn, about the cost of platinum, superior, requires a thin wall socket to install/remove.

#1 BR7EIX (x4) Mainly City Driving, N/A only, No porting but high performance, 7 Heat.
#2 BR8EIX (x4) Mainly Highway Driving, N/A only, No porting but high performance, 8 Heat.
#3 BR9EIX (x4) City/Highway Driving, Street ported N/A, Non-ported Turbo with slightly increased boost & bolt-ons , 9 Heat.
#4 BR10EIX (x4) City/Highway/Race, BridgePorted N/A, high boost turbo, 470 HP, pump gas, 10 heatCOMPETITION:::
For the most extreme performance, race only, max porting, highest boost, outright race. Short run times, zero street use, hard cold starting.
#1 R6725-10.5 (x4) 10.5 heat
#2 R6725-11.5 (x4) 11.5 heat
</QUOTE>

Last edited by jjandros; 12-08-18 at 10:52 AM. Reason: More info. Better organization.
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Old 12-08-18, 10:41 AM
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it depends somewhat on how you drive the car.

when they ran daytona, which is full throttle for 24 hours they went to 11's or even 13's at 265hp.

the JC Cosmo on the other hand had hotter plugs, 6's and 8's, because its a low revving luxury car.

if you look in the JDM world, they switch to 10's pretty much all around much sooner than we do in the US, pretty much at 300-320hp.

IMO it is also perfectly valid to go from 7's and 9's to 9's and 11's...
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Old 12-09-18, 05:11 AM
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Originally Posted by Molotovman View Post
10-10.5 ~400HP
10.5-11~500HP
11+ ~600HP+
Do you mean either 10s or 10.5s for 400hp, or 10s leading and 10.5 trailing for 400hp,? And is this HP at the wheels?
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Old 12-09-18, 06:44 AM
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Originally Posted by mikey13b View Post
Do you mean either 10s or 10.5s for 400hp, or 10s leading and 10.5 trailing for 400hp,? And is this HP at the wheels?
All 4 of each type.
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