Spark plug help please

Liberty44140

I posted a couple of weeks ago about the right plugs for my twin 2006 5.7 mercruiser mag MPI 350's. The book and the engines say AC 41-932 which is now 41-933. These are platinum. I wrote these codes on the work order to the yard to change them and I noted they were platinum. They said they use nkg and I told them that nkg equivalent to what I wrote for Ac is ok. Well they put in nkg BR6FS which look to be copper. I will of course address this with them but my question is are these nkg ok or will they cause a problem with the engines? Thanks 

F1100

They list a different NKG plug for that cross.

http://www.sparkplug-crossreference.com/convert/AC_DELCO/41-933

Liberty44140

Thanks, I'm aware, just trying to figure out if what they put in is ok or not. Looks like maybe these engines require platinum, not copper. 

F1100

I stay away from platinum tipped plugs on our race cars. They are over priced, and do not deliver as good electrical performance. For a boat, if the engines are easy to access I would go standard copper ones.

IF the plugs are a bugger to get at and change... use the platinum ones since they will last longer in place.

Handymans342

What about these F1100?

Liberty44140

Talked to the shop, they are replacing them with the right plugs, Ac 41-933 platinum 

Michael T

.....also be careful which plugs you use IF you have Mercruiser catalytic converters. Mine called for specific plugs. Was that an advertising gimmick? I do not know. But if I was replacing my plugs on a Mercruiser with "cats" that was still under warranty I would confirm - by e.mail - with Mercruiser - before substituting.

F1100

I stay away from all of the fancy plugs TBH, cause you cant set plug gaps easy on those other plugs with multi ground electrodes.

plus if you need to change heat range it costs a fortune with fancy plugs...hence standard plugs are better I looks like that plug would have a huge fuel indexing issue TBH as well.

The only reason they exist is cause some OEM engineers design the engine bays so poorly that in some cases you have to remove the engine to service the plugs. Its a function of design stupidity. And the OEM,s not caring about serviceability of their products over the long term.

As far as plugs effecting the catalytic converters, not sure how they could, unless they are gapped wrong and the fuel is not being lit off.

halifax212

Went through the same with my 2004 5.7 mag. Here is what was cross referenced.

Liberty44140

Thanks Al, Ac 41-933 platinum on the way to the yard now. Thanks!

jme097

I need to check my plugs. Thanks for the reminder lol

Wildboating

@Alswagg

I am being told to switch out my 933's also to these NGK's ITR4a15's  listed above.  Im told they have discovered the 933's are predetonating and could destoy a motor. Is this true, or am i just burning away more cash my tossing my newer 933's?

frenchship

If 933's where causing detonnation don't you think that Mercruiser would have put out a service bulletin to their dealers .......

wm61356

Never heard of a spark plug causing detonation....over advanced ignition timing will.

Cableguy Greg

I put the NGK's that are listed above in my 6.2 about 6 weeks ago. So far, no issues.

F1100

Spark plugs can 100% cause pre ignition, if they are too hot the fuel can ignite off the electrodes or exposed base. Thats why when you go forced induction you usually have to go 1-2 heat ranges cooler.

Liberty44140

I'm on season two with the 933's that merc said to use in their bulletin in place of the 932. No issues. There is nothing online whatsoever about the 933 causing pre detonation or a service bulletin to change that I can fine.Wondering where they got this info. @Alswagg is this just some bad info out there?

Wildboating

This was a Merc tech we are working with that suggested it.   

Wildboating

Of course, im looking for any reason to hold the cash in my pocket versus more parts that will not change any of my current issues.

diggin2day1

2nd season and 150+ hours on my 933 with no issues. 

Liberty44140

May be that those nkg are an upgrade but can't imagine there is a known 933 issue out there. 

Wildboating

Thank you for confirming AL!