spark plugs discussion 5.0 mpi

aerobat77

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Aug 12, 2014
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germany
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hey gents ! after service for a new season - pulling the drive , cheking allignment, gimbal and bellows , engine and drive oil and plugs change ... i made yesterday my first ride and the boat runs great . ( 2006 sundancer 240 5.0 mpi b3 )

i take good care of the boat but do not "overbaby" ist so i change plugs only every other year and i struggle to believe in the mighty and expensive iridium plugs mercruiser calls for . ( tr55 ix )

i had ngk tr55 installed and i replaced with ngk tr55 ( non iridium) - the iridium would be tr55ix

last year the engine had with one year old plugs a very slight vibration at trolling speeds about 1600 rpm which i disregarded as "nature of the beast" , to my surprise with brand new plugs it runs now noticeable smoother . further , even when its very subjective and depends on load and conditions , i could swear it has a little better hole shot and with full water tank but little fuel and two person aboard i squeezed 64.3 kmh ( +40 mph ) at 4850 rpm out of her .

i never saw this numbers last year with very similar load ( it was more 62 kmh , 39 mph at 4700 ) - all gps speeds.

due to my understanding the best plug in this world at WOT cannot do more than ignite the mixture . how hard it bangs inside the cylinder is not plug dependant but my boat seems to very appreciate brand new plugs .

are the us v8 blocks indeed such plug sensitive and would be it worth buy the in europe very expensive iridium plugs for maybe even more better engine run ?

what is your experience in iridium / non iridium plugs , and do the v8 eat plugs ? ( my old ones were only about 90 hours / two years but there is like said some difference with brand new plugs )

thanks for sharing your experience with this !
 
I believe the short answer is; Yes you should use the premium plug. My rationale is that unlike automotive applications, marine engines run at full bore, full time. Cruise for our 496 is in the 3800 to 4000 rpm range. In contrast the 5.3 GM LM7 in my pickup truck rarely runs above 2500 rpm for long periods. The Mercruiser 5.7 is a variant of the same engine.

You also don't have to buy the plugs from Mercruiser. Once you have the plug manufacturers part number, they can be sourced online much more economically.

Henry


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Iridiums are worth the extra $.



on small blocks, could very well be the last set of plugs you need to buy.
 
IMO these motors are not necessarily plug sensitive but certainly spark sensitive.

Case in point - I changed the exxy TR55IX's and also changed my leads after I dropped a cylinder during a trip and later discovered a lead was arcing to the ex manifold under load a while ago. In good conditions I was then able to bang on the overspeed alarms at 4950rpms at over 31 knots whereas the best I got out of it before in similar conditions but lighter load was 29 knots. The TR55IX's plugs are approaching 2 years old now and I recently was able to repeat the 4950rpms and excite the overspeed alarms.

It's nice to know the TR55's also work equally as well.
 
hey gents ! after service for a new season - pulling the drive , cheking allignment, gimbal and bellows , engine and drive oil and plugs change ... i made yesterday my first ride and the boat runs great . ( 2006 sundancer 240 5.0 mpi b3 )

i take good care of the boat but do not "overbaby" ist so i change plugs only every other year and i struggle to believe in the mighty and expensive iridium plugs mercruiser calls for . ( tr55 ix )

i had ngk tr55 installed and i replaced with ngk tr55 ( non iridium) - the iridium would be tr55ix

last year the engine had with one year old plugs a very slight vibration at trolling speeds about 1600 rpm which i disregarded as "nature of the beast" , to my surprise with brand new plugs it runs now noticeable smoother . further , even when its very subjective and depends on load and conditions , i could swear it has a little better hole shot and with full water tank but little fuel and two person aboard i squeezed 64.3 kmh ( +40 mph ) at 4850 rpm out of her .

i never saw this numbers last year with very similar load ( it was more 62 kmh , 39 mph at 4700 ) - all gps speeds.

due to my understanding the best plug in this world at WOT cannot do more than ignite the mixture . how hard it bangs inside the cylinder is not plug dependant but my boat seems to very appreciate brand new plugs .

are the us v8 blocks indeed such plug sensitive and would be it worth buy the in europe very expensive iridium plugs for maybe even more better engine run ?

what is your experience in iridium / non iridium plugs , and do the v8 eat plugs ? ( my old ones were only about 90 hours / two years but there is like said some difference with brand new plugs )

thanks for sharing your experience with this !

I buy mine a O'Rileys auto parts for $8.00 each, Marine Max charges $19.00 each


Sent from my iPad using Tapatalk
 
yes the ngk tr55ix are the iridium ones . at 45 $ for 8 i would not care and install them . our local auto store asks 20 $ for ONE .
 
Rough idling can also be caused by the cap and rotor vs the plugs. When was the last time you replaced those? About $50, four screws and done. I just did mine and the rotor and cap where heavily corroded.
 

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