Ok, changed out my plugs tonight (29977 mi. already!) to the
NGK ZRF5F11's, recommended by Mr FAQ himself. Bit of a longer reach and used on the J-Spec engines.
Took my car out for a spin and since my tank was nearly empty I threw in 89 octane which was also recommended when using these plugs. The car so far is running very nicely but I am curious if anyone on this forum has used these plugs, and if I should go back to 87 octane for the future and wait and see if there are any signs of pre-ignition. Or am I better off sticking with the 89?
I'm going to keep an eye on my gas mileage for the next few weeks, also.

 

the rule of thumb is that you always want to run as low of an octane as you can get away with. There is no performance gain to be had by running higher octane no matter what plug you're using.

More often than not you'll find worse performance with higher octane unless your car is prone to detonation which ours are not.

I'd be interested to see your gas mileage though. I'm going to be swapping my plugs out next week and going with a slightly different plug made for FI cars.

 

I've got those plugs, I stil use regular gas and have no problems.

 

on the notion of using higher octance gas:
wouldn't 93 generate less carbon at detonation compared to 87 octane, woun'dnt it also give a much smoother drive and acceleration because you are combusting a very good mixture of air/fuel with the 93.
and i totally agree that there is no performance gains using higher octane gas.
the reason i say this, is that this is what i notice each time i fill up with 93, plus, there is a gas station that runs all grade at the same price on sundays.

oh and, i use the Bosch Platinum +4

 

Thanks guys. I didn't do this for any peformance gains. It's more of an experiment. I'm gonna run 89 octane for a few weeks and then go back to the 87 and see if there are any differences in mileage or engine performance and I'll let you know.
My main reason for doing this is I am hoping to finally get my hands on an MP3 ECU next month and I thought these plugs would complement it nicely.

 

Ive gone aprox. 6000 miles with those plugs using 87. Absolutlely no problems at all. Good to go.

 

AS far as i know high octane is only neccesary in high compression ratio engines? This is what i understood becuase i know both my sister's and dad's cars recommend 93. I'm not saying i'm right so please correct me if i'm wrong.

 

higher octan is necessary for higher compression engines, rx-8 is a good example 11.5:1 compression ( i believe thats right?) anythign less than 93 and i hope u like knocking ur engine, and ruining it real fast. Otherwise theres no real need to run higher octane any lower compression engines..one thing i dont get why would different plugs wants higher octane? the spark is what u want to igniter the mixture and its goign to happen regradless of which octane u run with our cars..how does a spark plug change it? just wondering

 

The 'theory' behind these plugs:

The reach is slightly longer, by, oh, 5mm maybe. So the fuel may combust a bit earlier, which, in effect, advances the timing slightly. Probably not enough to make a difference.
So I'm giving it a shot. Can't hurt and I'll post what, if anything, may be gained by it.
Ed Mann's comments also included the opinion that our gas is of lesser quality than Japan's and recommended the 89 for that reason also. I can't say I buy that, but again, what's to lose?