Spark plug type 454 Gen VI
 

I have a L-29 Gen VI 454. The block casting # 10237297 comes up to be a Vortec 7400 motor. The head casting # 12562934 comes up a 502 rectangular port marine head. I have used the Delco MR 43 TS for years. The motor runs ok, but does not burn the plugs as well as it should. The boat it is in is a 87 Baja 240 sport. I was wondering if i was to switch to Delco MR 43 LTS would this work and burn better.The serial number of the motor is 12568777. This is my confusion, and would take any help on what plugs to use and the gap. Thanks, Dan

that engine runs fat to begin with..if your using premium fuel thats why they look sooty,,the 93 fuel burns slower which keeps the engine from detonation..try running 87 or 89..

Dude you have a bastard engine. Quoting the block casting or serial numbers is not that helpful. In fact it can lead to a disaster.
I don't know why anyone would put rectangular port heads on a stock 7.4L(L29) bottom end without other modifications. If you
have domed pistons and put the LTS plugs in the engine you may crash your pistons into the plugs.

MR43T - standard length
MR43TS - projected nose - slightly longer than above
MR43LTS - very long - stock plugs in the 7.4L MPI engines NOT FOR GEN 6 454/502 MAG heads

I use NGK BPR6FS spark plugs gapped at .040" in my stock 502 MPI. I get a slightly cleaner burn over the stock plugs but
no real performance gain. I burn only 87 octane fuel.

Find out what your engine's internal components are before you put longer plugs in your heads. Your compression ratio will
determine what octane fuel you should be running.

Ask an engine builder if he has a tool you can screw into a spark plug hole and measure the clearance of your piston to the
combustion chamber wall. Not the proper way to determine if a long spark plug will safely fit in your engine but it beats the
alternative.

I forgot to add that the NGK BPR6FS plug that I use is the direct cross to the AC MR43TS.

Thanks, i have always run premium in this motor so hopefully that's it. I will try the lower octane and see how that works. Then proceed with what kind of make of plugs and gap, but i will stay away from the MR43LTS. Thanks for the info

bpr6fs ngk plug is what you should be useing.those cyl heads are 2000 and up gen6 rectangle port heads from a 502.if the l29 is basically stock there is no need to use fuel with an octain rating above 87i really doubt someone has raised the compression ratio on that engine but to be sure i recomend doing a compression test.il bet compression is around 135 lbs..

Thanks for your time and info. So the NGK plugs should be gaped at 40? Once the snow finally goes away in Chicagoland. Boating time.

I also have a gen VI 454 its borded 20 over and has 9.5 to 1 compression I dont know what heads are on it other then they are stock iron heads. Any thoughts on what spark plugs and gap i should run and which fuel i should use 87, 89, 93