Do Gen 6 heads fit gen 4 and 5 engines?
I want to bring an old 1988 454 Merc 330hp engine up to 450hp and was wondering which heads I could use?
1. Did Merc ever use Chevy large oval port 049 heads?
2. What years did Merc use the 990 rectangular heads and in which hp engines? 3. Did Mag 425hp, and 500hp EFI both use 990 rectangular port heads with same size valves?
Thanks
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You know, I was going to give you an answer. About half way through the post, I wanted to double check so I did some digging. It's so confusing as to what will fit what and what won't and which gaskets need to be used with which heads vs the block, that you'd be better off just sticking with Mk4 heads on a Mk4 block. Then you are sure that things will work.

I do know that my '88 mag motor came with 990's and that 330's did not. I have heard of 049's being used on engines, but I don't know if they came from the factory.

All told, I know that Bruce is selling a freshened 454 mag for a ludicrously low price. Frankly, it's shamefull what he's asking. Rather than trying to work with your 330, I'd highly recommend you buy the mag from Bruce.

Cord,
My 88 330hp came with 061 medium oval ports.

Chuck

OBS. JimV (Valeko race heads) would surely have the answer for you. porting marine heads is his business " heads I win" is on the side of his boat. drop him an email.

my $.02

I have had good success using 781 large oval port heads on early bbc. You will need to increase valve size to 2.19 and 1.88. They flow fine stock up to 5000 rpm. 049's are very similar to the 781's.

I have a set of 049 heads that were done by Valako, they have the 2.19/1.88 valves, Iconnel on the intake and stainless Manley on the exhaust, pocket ported, good springs and retainers, gasket matched and ready to bolt on never ran on my motors (selling my boat)had 2 sets, one set left= $750.00 Days 517-267-1171 or e-mail me [email protected]