Proper plug and gap for a Volvo Penta 5.7GS PEFS

[ramairta1]

Hey guys,

I recently changed my plugs and made the mistake of going with champion plugs. When I pulled the original plugs (AC delco) I noticed and was VERY surprised to see the gaps between .043 to .048.
I called my local boat mechanic and and researched online. All i found and told was .035 gap and went with it.

Although the boat runs OK, I have noticed a decrease in engine performance with the new plugs. It's the only thing I changed. Cap/rotor/ plug wires were all good.
Everyone told me Champion was GARBAGE. I picked up some NGK 3754's to replace the Champions. Now I am trying to figure out why the original plugs appear to have been gapped at .045

The engine is a 2000 VP 5.7L GS (NOT GSi) PEFS engine code. It is a carb motor NOT EFI. I do believe it has the vortec heads as it uses the longer plugs.
The NGK 3754 is the cross for the AC,autolite, and champion plug.

I am considering just gapping them to .045, approx where the AC plugs that were in it were gapped. It was running GREAT before even though the plugs looked liked they needed to be changed.
If it's not broke don't fix it, I know! I was just trying to be pro-active and give her a tune up.
Any have this same motor setup with any thoughs?
thanks for reading...

 

[Gary H NC]

Re: Proper plug and gap for a Volvo Penta 5.7GS PEFS

Is the serial number plate missing? Usually the gap info is on the sticker too.
I would stick with the AC Delco MR43T plugs.
Some motors just run the best with the AC plugs.

 

[ramairta1]

Re: Proper plug and gap for a Volvo Penta 5.7GS PEFS

Hey Gary,

Where did you get the mr43t plug number? That crosses to a 4323 NGK.
Is that the shorter plug for the non-vortec heads??

The Ac plug I show (believe came out of my boat) is a R44LTS, which crosses with the junk champions I put in: RS12YC.. I believe that is a .71 reach.

The owners manual shows for the GS and GSi they both use: VP part number 3854399. That crosses to a rs12yc I belive?


It shows the GSi at .045 gap and the GS at .035
Does not indicate anything about vortec or non vortec heads, but does show a picture of 2 plugs, one short, and one a little longer.

Now I am really confused..

 

[Don S]

Re: Proper plug and gap for a Volvo Penta 5.7GS PEFS

You should be using the AC-MR43LTS according to the OEM service manual. You should also be using the .035 gap due to the GS having a Prestolite BID ignition system. The GSi (fuel injected) uses the Delco EST ignition system and a .045 plug gap.

The AC-MR43LTS converts to an NGK BPR6EFS

 

[nitwhit]

Re: Proper plug and gap for a Volvo Penta 5.7GS PEFS

AC MR43T is for the older, non-Vortec head motors. Yours, being a 2000, should have the Vortec heads and require the longer MR43LTS plugs. Someone may have gapped the old ones off the wrong specs as the .035 should be correct. The NGK's are decent and definitely better than the Champions but I've always had the best luck with AC's in GM motors.

 

[ramairta1]

Re: Proper plug and gap for a Volvo Penta 5.7GS PEFS

Thanks a lot guys--
i should have replaced the AC's with AC the first time.
The Champions are garbage. The rs12yc champion crosses with an NGK 3754, but the ac mr43lts crosses with an NGK 3623 (BPR6EFS).

I am just going back to the AC MR43LTS gapped at .035 Being a GM guy I have no idea why I didn't do this in the first place...
I'll keep you posted as to the performance results.
Thanks again for all the help.