I am going out this weekend to tune my new/used boat, 24 Elim Daytona. It has a 96 454 magnum mpi converted to carb.

The engine is running 9.8 to 1 compresion (forged Pistons), full roller valve train, GM square port heads, stock exhaust manifolds, holley marine elec fuel pump and Mercruiser 500-hp, 800 holley carb.

The advance is currently set at 32 degrees. I am thinking of going to 34 degrees.

The primaries are 90's all around, and the secondaries are 93's.

I can turn 5200 rpm with a 24" Bravo 1 at 68mph.

From other post it seems that the primaries may be set to rich. I have 88's, 86's and 84's I can try. Any thoughts?

What plugs work good for plug tests and how long should I run at 3600 rpm to check the primaries?

It looks like people are using AC MR43T, Autolite #154, Chamo=pion V63C and NGK R5673-7. Do any of these show color better than the others?

Anyone running Bosch Platimum?

As always, Thanks for the forums input. This place has been great in getting me up to speed with performance boating.

Does that motor have vortec heads?

I do not believe that they are the vortex heads but I am not really sure. The base block was a 96 454 magnum. I don't know if this year came with vortex heads or if they were switched when the motor was rebuilt. If you can give me some kind of ID info that would be obvious by looking at the heads I could check. If not I can contact the seller if this is important, which I am starting to think it might be.

Thanks

I went ahead and contacted the seller and confirmed that the motor has a Gen V block and std. GM square port heads/Non-vortex.

Let me know what you think on the tuning questions.

Thanks

What elevation do you run at?

I would jet it like a stock 500hp which stagger the jets and go from there. I use MR43 plugs to read.

What intake do you have? The 500's came with a Dart type single plane and each barrel of the carb had a diff jet. I think sec were 89/93(starboard/port) and prim something like 78/82. Can't remember but that's close. I'm sure they had not been changed both bowls were sealed to the max and blue paint never broken. I went about 73/78 and 88/90 on my 9:1 roller motors with aprox 450HP(I'm still tuning). You are prob. going to need closer to the fac setup but make sure you still have the power valve working. Some people plug them and go richer all the time,may be why yours are so big. There is a post about tuning a 500hp/454 that goes into detail more and also has some input on the orig. jet sizes. Try searching this forum for "500hp/454" "tuning".

the post is called"getting the jetting right" and is currently a few below this thread.

Good questions,

The intake is a Hardin Marine Dart single plane copy. Very similiar to stock 500 set-up.

I run at ~1200'elev, Lake Mead with a few trips to the ocean.

I believe the power valve is in but I will confirm this. Lets assume it is in for the moment.

I have read the post you suggest and it has a great deal of good information. Very helpful overall in undersatanding the process and what to look for.

Any thought on the timing? Does it matter that I am at 9.8 to 1 compression. I was going to try running at 34 degrees total advance but don't want to make a serious mistake on this.

Thanks

That's a lot of compression for iron heads. I run 9.7 with aluminum heads and I have detonation with 89 octane gas. Use good gas. The carb seems to be jetted fairly fat so the 32 degree ignition seems like a safe setting. If you want to make changes there might be some horsepower there but keep a eye on your plugs and temp gages Listen for any misfire up around 4800. Could be detonation.