I am fairly new to this site, so thanks in advance for any help you guys can offer.

This is a two part question, but first some background info. I have a 509 making 630 dyno proven hp. I bought the motor from the classfied section on this site, but it was not really used as it was shipped strait from the builder. It had been sitting at the builder for some time as the guy I purchased it from was a good friend of his and had built it as a "backup" motor for his boat, but it was not used and was finally sold to me. Point is he did not remember every last detail about the motor, but did pull the dyno data and fax it to me and did remember some of the hard parts, including that the heads had 250cc intake runners,he called them GM performance heads, with iconel valves. I assume the heads are decent considering the hp the motor is making. I cannot get the casting number as it is too damn cold to mess with boat.
The motor runs great, I have only been able to put about 3 hrs on it as all this took place in Oct.
Now for the questions.
part 1. I have a set of nice 345cc merlin heads. Will I see any gain or loss putting these on my 509? It is a full roller N/A motor with 950 proform carb, and Stainless marine dry exhaust. The heads are comparable with iconel valves and the like. The merlin heads are mark 4 where my 509 is a gen 5???(no fuel pump boss) will they work with the right gaskets?

Part 2. My brother has a stock injected 7.4 mag motor(385hp) in a 97 Baja. Will my 250cc heads which are I assume are way more "built" then his factory mag heads work on the injected motor with out a lot else other then maybe a different exhaust? Will he see any gains and are they compatible with the efi system? My brother does not want to lose the EFI, and swithching to carb is not realistic for him.

Sorry for the long post!! I know that some of you can awnser my questions with even having to think hard.

Thanks
Stuart

even with a 509(which I run as well) the 345 heads will be to big, you will loose power in the rpm range you run the boat in, ports just to be and the boat will be lazy, I would say no bigger that 310's I'm sure you will get other opinions as they are like ......... but going large on heads, intake runners, or cams just kills boats, as most never see over 5600 or so...Rob

Thanks fror the reply Rob, That is what I was afraid of. The heads came off a merlin 540 that was in the boat that had great midrange, but I was not sure about on the 509. The two motors where actually comparable on all out hP, but I am afraid that displacement diff would kill the deal.

Unlike what the wife thinks bigger is not always better. Save the big heads for when you add the blower and or a 100 cu in.

What he said.

Those big Merlins are awesome on a blower engine though.

I got buy them from you though ??????? If the price is right.

Or i trade u my 320 cc heads + cash !!! They are from my old 509 and made around 720 HP with a 1050.

Daredevil email me and we can most likely work out a trade.
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