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View Full Version : Another Spark Plug Question ('04 MCX 5.7)


deminimis
07-07-2012, 12:14 AM
I read the other threads regarding spark plugs and the MCX. This engine is basically an old Vortec engine (for example, basically what came in a 1995 Chev/GMC C1500, with, perhaps, some marine-specific mods?). So, why all the hubbub about spark plugs? Seems to me a plug designed for that engine/ignition combination ought to be the correct plug or at least not detrimental? For example, NGK Iridium 7177. Engine Freak or others, please feel free to enlighten me as I really want the 411 here (also, I have 8 fresh 7177 at the ready, but I'll wait for your words of wisdom). Thanks.

Engine Nut
07-07-2012, 08:15 AM
I read the other threads regarding spark plugs and the MCX. This engine is basically an old Vortec engine (for example, basically what came in a 1995 Chev/GMC C1500, with, perhaps, some marine-specific mods?). So, why all the hubbub about spark plugs? Seems to me a plug designed for that engine/ignition combination ought to be the correct plug or at least not detrimental? For example, NGK Iridium 7177. Engine Freak or others, please feel free to enlighten me as I really want the 411 here (also, I have 8 fresh 7177 at the ready, but I'll wait for your words of wisdom). Thanks.

My plug recommendation for 5.7L engines is to use the standard (MR43LTS) in Vortec engines that do not have catalytic converters and Iridium or Platinum plugs (41-932, 41-993 or 41-101) in engines with catalytic converter exhaust.

Platinum and Iridium plugs like to run hot and lean. The non-catalyst engines run relatively cold and rich. The standard plugs tolerate those conditions better. The catalyst engines run a little warmer and much leaner and do better on the Platnium and Iridium plugs.

deminimis
07-07-2012, 10:24 AM
Thanks Nut!

deminimis
07-07-2012, 11:50 AM
Std. Plug, 045-.050"?

j.mccreight@hotmail.com
07-07-2012, 12:11 PM
0.045" is specification.

deminimis
07-07-2012, 12:17 PM
Thanks!!

deminimis
07-08-2012, 01:09 PM
Orig plugs (a little black overspray on the two front ones) were AC 41-932 with gap burned back to or set at. 055" Fresh TR5's in there now.

Shooter McKevin
07-09-2012, 12:17 PM
Any change in performance with the new plugs / proper gap?

deminimis
07-09-2012, 12:29 PM
Admittedly, the boat purred before and it still purrs. No noticeable seat-of-the-pants difference in performance (power-wise). However, it appears (that is a big "appears") that I'm not burning as much fuel, yet no real way to show that as I've never figured out the gals/hr consumption. Since first day in the water this year was July 4, I could be harboring some false memories of last year's fuel consumption too. Regardless, plugs, cap and rotor were all way, way overdue for a change. All done now.