Re: 1979 merc 7.5 into a 9.8
Hi Locknut,<br /> It's possible, but not easy. The biggest difference between the two blocks is the porting - 9.8hp block has bigger ports. You can't simply hog out the ports, as there are port timing issues that may be slightly different, too. You'd need the specs from a 9.8 to machine your 7.5. You'd also need the 9.8hp carb.<br /> Easiest way would be to find a 9.8hp powerhead. Lots of these motors out there with blown out lower units, so finding one shouldn't be a problem. Try your local marinas, eBay, etc. Make sure you match the years fairly closely, as there are lots of little, annoying differences between model years - different bosses, etc. for mounting electronics, fuel pump, etc. Next easiest would be to find a good 9.8hp block and swap your motor's innards into it. Hardest way would be to find the specs, disassemble your powerhead, and have a machine shop machine it to 9.8 specs. A 9.8hp block won't have the "Comet" sticker on the block - but stickers can be removed so don't use that as a 100% assurance. Both blocks have the "Lightning" designation cast into the block.<br /> So basically, it's carb and porting to gain the extra ponies... You won't gain anything by simply adding the 9.8hp carb.... what goes in must come out.<br />- Scott
