Thats what is needed but i'm sure they are more than 7 or 8 K just guessing

You can do it with an old fashioned 406 - but for that money it'll be a carb not efi.

My 406 makes 500 hp and 500 ft lb.

It takes good exhaust and careful selection of head intake manifold and carb to run and idle correctly for a stern drive app but you can build one like it for 8-9K if you go about it correctly and get lucky with a few parts.

With old school SBC's you can find good heads and reasonable priced rotating assemblies cheap, but youll end up paying for the exhaust whereas with the BB you can usually find used exhaust systems for sale. I went wih the classic West Coast choice of high end manifolds the Imco Powerflows.


In the end I spent about just as much as it would have cost to do a regular guy big block and wouldnt do it again, but at the same time must admit its roaring little beast in a 1900lb boat and really fun putting big blocks on the trailer.

Uncle Dave

UD, are you running a cast crank in that thing? I agree it could be done with a little 406, but I would want a steel crank and am not a fan of the Chinese ones. So basically my thinking was for the price of a good 3.75 inch steel crank I could just about get a 3.875 or 4.0 inch stroke crank for the same price and have another 14-28 ci. Also, what kind of compression are you running in that thing and what heads and camshaft are you using? Just curious.

AMT made a twin small block powered 30' cat that ran right around 105mph with twin 390hp SBC. Set up on drivelines. From what i understand they only made one, but also based on the reviews of it, it ran pretty well for that power package. They were from PCM engines, originally the ZR6 package, now they are called the ZR409.

I know that Arnaldo at Predator will build you the same boat, since they have the AMT molds now. That is one of my ideas for a new boat.

:lolhit: ignorant SOB arent you, seams to me I know quite a few 110+mph 30' and 28' cats with twin 300HP egg beaters that will run. I think you need to start reading a little about the subject HP to weight ratio. The Ls engines that the others have mentioned are putting up bigblock power without the weight.

As have already been asked. What brand and model boat are we talking?

Not anymore but I did for 10 years in this very (light) boat. You can get away with it in alight setup as long as you dont spin it too fast and land opened up.

Agreed on the chinkonesian stuff for high HP apps, Its got a scat crank in it now not my fav for sure but plenty good enough for 500 ponies.

The big arm small blocks dont seem to have ideal rod angles for longevity - I did a 430 and it lasted about 5 years whereas I got 10 out of the same combod 406. (use being basically wide open from the time you turn the key to the time you shut it off)

Its got brodix track 1 heads with a decent port job and a custom engle hydraulic roller set with 114 lobe centers instead of the normal 110. Idles at 800 rpm like a kitten.

Id say compression is about 10.5 -1 maybe a bit higher.

built these 400 ci a while back 400 + hp easy. I know Thunder Marine Engines in N.ft.myers is building some sbc's right now that have some hp for a magnum. Maybe you could contact them.

Looks clean. Nice and tidy - simple. RELIABLE.
The nice thing about a SBC is that a regular guy can usually keep it running- very simple.

I also forgot to mention I probably got away with the cast crank as long as I did because I splay capped the block. There is almost certainly some measure of rigidity that mod buys - and of course bumps the price.

The other upside that with twin SB's you can get to the plugs pretty easy.

Uncle Dave

If you bump your budget up to about 12k per side I can hook you up with LS3's 450hp, all aluminum, closed cooled, turn key ready to go..