Based on TheMAN's discussion of an alternate OEM spark plug type suitable for our engines, I decided to follow his recommendation and change my plugs to the ZFR5F-11 extended nose type. See his thread at:
The tools I used were a 3/8" drive torque wrench and ratchet, a 3" long extension attached to a 10 mm socket to remove and install the coil pack mounting bolts and a 6" extension attached to a 5/8" spark plug socket to remove and install the plugs. I obtained the new plugs from my local Mazda dealer using the part no. provided by TheMAN in his post. Cost was $12.39 including local NJ tax. Before installing, I checked the gap with my wire gauge and found it to be as specified, 1-1.1 mm (.040"-.043").
The old plugs turned out to be Denso K16PR-U 11 which, according to the FSM, are equivalent to NGK BKR5E-11 both of which are OEM specified for our engines. At 15000 miles, the old plugs were in exceptionally good shape with virtually no visible wear and a nice light, chocolate brown color on the ceramic nose. Before installing the new plugs, I coated the threads with Permatex Anti-Seize Lubricant and then tightened them to 13.5 ft/lbs torque (midway between the FSM recommendation of 11-16 ft/lbs [15-22 N/m]). Prior to installing the boots, I coated the inside with Permatex Dielectric Tune-Up Grease which prevents sticking and possible boot damage on subsequent removals. Be careful when reinstalling the coil pack bolts as the FSM recommended torque setting is only 69.5-95.4 in/lbs (7.9-10.7 N/m) which works out to 6-8 ft/lbs. Since this is close to the lower limit of my torque wrench, I opted to just snug up the bolts with my ratchet.
Unlike TheMAN's experience, on startup my engine idle seemed to be somewhat rougher than before. Additionally, my launches from a standstill felt less smooth and slightly jerky. In general, my low speed performance seemed inferior to what it was. At this point, I took the car out on the Interstate to test it at speed. Immediately, I found a noticeable increase in performance and just as TheMAN stated, I found the engine seemed to rev more freely and to reach high RPM's more quickly than with the OEM plugs.
As pointed out in the article, the ZFR5F-11 plugs may advance the timing slightly (good for power) since the extended reach places the electrodes closer to the center of the intake charge than is the case with the OEM plugs. Additionally, it was pointed out that the plug tip may run hotter (possibly promoting detonation) since it protrudes more deeply into the combustion chamber. Given these two factors it was suggested that it might be beneficial and even necessary to switch to a higher octane rated fuel.
With these considerations in mind and as my tank was almost empty after my test run, I decided to fill up at this point with 89 octane fuel. Since I bought the car and up until now I have always used 87 octane as recommended in the manual. With the combination of the higher octane fuel and the change in the plug structure, it then occured to me that it might be beneficial to reset the PCM so that it could "learn" the new operating parameters.
After resetting, I went out for another test run. I don't know if it was the octane increase, the PCM reset or both together but, if anything, the high speed performance was even better than during the first test run with the car definitely feeling, to some degree, even more powerful. The low speed performance was also improved with noticeably less roughness and a smoother launch from a standstill-more like what it was prior to the plug change. Now, one week into the mod I can no longer really tell if the low speed roughness is still there or if I have just learned to compensate for it by adjusting my driving style. The idle still seems a little rough but, hell, I don't really know anymore. This can drive you crazy if you let it.
IMO, this is a very successful and worthwhile mod. It produces a power increase you can feel and is one of the easiest mods available requiring only that you change the plugs. Perhaps the only disadvantage is that you are constrained to use higher octane fuel at a time when fuel prices are extremely high. It's also interesting to note that the ZFR5F-11 is the manufactuers plug of choice in Japan for cars very similar to our own.
The tools I used were a 3/8" drive torque wrench and ratchet, a 3" long extension attached to a 10 mm socket to remove and install the coil pack mounting bolts and a 6" extension attached to a 5/8" spark plug socket to remove and install the plugs. I obtained the new plugs from my local Mazda dealer using the part no. provided by TheMAN in his post. Cost was $12.39 including local NJ tax. Before installing, I checked the gap with my wire gauge and found it to be as specified, 1-1.1 mm (.040"-.043").
The old plugs turned out to be Denso K16PR-U 11 which, according to the FSM, are equivalent to NGK BKR5E-11 both of which are OEM specified for our engines. At 15000 miles, the old plugs were in exceptionally good shape with virtually no visible wear and a nice light, chocolate brown color on the ceramic nose. Before installing the new plugs, I coated the threads with Permatex Anti-Seize Lubricant and then tightened them to 13.5 ft/lbs torque (midway between the FSM recommendation of 11-16 ft/lbs [15-22 N/m]). Prior to installing the boots, I coated the inside with Permatex Dielectric Tune-Up Grease which prevents sticking and possible boot damage on subsequent removals. Be careful when reinstalling the coil pack bolts as the FSM recommended torque setting is only 69.5-95.4 in/lbs (7.9-10.7 N/m) which works out to 6-8 ft/lbs. Since this is close to the lower limit of my torque wrench, I opted to just snug up the bolts with my ratchet.
Unlike TheMAN's experience, on startup my engine idle seemed to be somewhat rougher than before. Additionally, my launches from a standstill felt less smooth and slightly jerky. In general, my low speed performance seemed inferior to what it was. At this point, I took the car out on the Interstate to test it at speed. Immediately, I found a noticeable increase in performance and just as TheMAN stated, I found the engine seemed to rev more freely and to reach high RPM's more quickly than with the OEM plugs.
As pointed out in the article, the ZFR5F-11 plugs may advance the timing slightly (good for power) since the extended reach places the electrodes closer to the center of the intake charge than is the case with the OEM plugs. Additionally, it was pointed out that the plug tip may run hotter (possibly promoting detonation) since it protrudes more deeply into the combustion chamber. Given these two factors it was suggested that it might be beneficial and even necessary to switch to a higher octane rated fuel.
With these considerations in mind and as my tank was almost empty after my test run, I decided to fill up at this point with 89 octane fuel. Since I bought the car and up until now I have always used 87 octane as recommended in the manual. With the combination of the higher octane fuel and the change in the plug structure, it then occured to me that it might be beneficial to reset the PCM so that it could "learn" the new operating parameters.
After resetting, I went out for another test run. I don't know if it was the octane increase, the PCM reset or both together but, if anything, the high speed performance was even better than during the first test run with the car definitely feeling, to some degree, even more powerful. The low speed performance was also improved with noticeably less roughness and a smoother launch from a standstill-more like what it was prior to the plug change. Now, one week into the mod I can no longer really tell if the low speed roughness is still there or if I have just learned to compensate for it by adjusting my driving style. The idle still seems a little rough but, hell, I don't really know anymore. This can drive you crazy if you let it.
IMO, this is a very successful and worthwhile mod. It produces a power increase you can feel and is one of the easiest mods available requiring only that you change the plugs. Perhaps the only disadvantage is that you are constrained to use higher octane fuel at a time when fuel prices are extremely high. It's also interesting to note that the ZFR5F-11 is the manufactuers plug of choice in Japan for cars very similar to our own.
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