Repowering with a 1994 Gen 5 7.4
 

Hi guys, I need some suggestions on repowering a gen 5 7.4 motor. My old motor was a stock 83 Mer 330 with 73 Chevelle heads (oversized valves) and adjustable valvetrain with roller rockers. It had the crane version of the mer 420 cam with holley 750 and torker intake. It would push my 25' checkmate 53mph at 4600rpm with a 21" Q4 prop. So after all that I had an exhaust manifold crack and drop water in the bottom end and screw up #6/#8 the motor is done!!!!

I got a deal on a 1994 gen 5 short block with stock crank, fresh .30 over bore 8.5 to 1 hyper with peanut port heads, and a mer 365 cam with behive valve springs. I would like to make this motor at least push my checkmate the same speed if not a little faster. How do I do it? I've heard the peanut ports are not great, the gen 5 have weak rods, small rod bolts, and a non adjustable valve train. I was thinking alum heads, alum exhaust, arp rod bolts, switch over my intake system / cam with valvetrain and see what happens

Ideas?.

I'd buy a takeout 502MPI, 496HO, 500efi, or 525efi drop it in and go boating.

Wish I could but I have a daughter in college. That's why " I REALLY got a deal on a 1994 gen 5 short block " :boat:

Since I'm sure better minds than mine will ask..what's your goals and most importantly budget? Trust me when I tell you that you can get so deep into a rebuild that Dave's suggestion could actually be the "cheaper" route.

Also what are you doing for exhaust? That can play a roll in the grand scheme as well for cam selection and so on

My setup was a 330/ TRS with the below the waterline thru hull 3" exhaust ports. I had the cast iron center riser standard with iron 3' 15 down angle risers. I'm going with the alum version from Moore Performance with the 4" risers (if I can make them work). My goal is to either maintain my speed or get to 55mph. Having said that this is a long heavy boat [ 25' day cruiser ] and speed cost money which I don't have a lot of for the next 3 years. If I can reuse what I have that would be great. I just don't want to go thru the hassle of the swap and I my top speed is 45mph with the gen 5. Budget $2000.

I'm no expert but I think a good set of iron heads like dart or something and a healthy roller cam/rockers should get you a serious power upgrade...if you can find used on here that would be a good thing for your wallet of course...I'm thinking the TRS will be your weak point as I'm sure you already know...as far as specifics on cams/heads I'll let the more knowledgeable fellas step in! lol good luck!!

Sorry could not get it to drop the font size. I was thinking these with my Mer 420 cam and arp rod bolts. CHEVY300cc OVAL PORT ALUMINUM HEADS BY PROCOMP

FULLY ASSEMBLED, SETUP FOR USE WITH HYDRAULIC FLAT TAPPET CAMS UP TO 560 LIFT.

119cc COMBUSTION CHAMBERS

You need to find out what pistons you have. You say they 8.5 cr but with what chamber volume??

You are correct 8.5 - 1 speed pro hypernumatic (sp)