I've build a bunch of motors for cars, but none for marine use. I've got a 21' 1985 Scarab with a stock 350 in it now. It will run 59 on the GPS. I've got a 400 chevy block and crank laying in the garage that I'd like to build for this boat. I know that with a marine motor you want to make the power down low and peak out around 5000rpms. Can someone give me some info on the type of cam, heads, and compression that I should run. I think CompCams makes a 264 X-treme marine cam that might work OK. What do you think? How much power should it make? Will it tear up my Aplha drive? I know that a 400 small block (if built right) can be a real torque monster.

I just built 2 409's for my Nova winter before last. I have the XM262H cam in my engines. I like it although I could use more lift but my blocks have been decked a few times, and the heads were shaved.

For starters I would buy the book from Dennis Moore on how to build a small block marine engine. There is a ton of good info in there.

But for starters, the 400 block is a siameese bore. Meaning there is no water jacket around the bores. Instead there are steam holes. It is important these steam holes get drilled into the heads also. Felpro makes a Marine Performance head gasket for 400's with the hole already in them. I would recommend them. I think the number is 17031, but don't hold me to that.

For the heads I would go with the stock GM Vortec heads. They flow well out of the box and they are cheap. But you can look around to see what fits your needs. I have World Products Torquer II heads. With 2.02/1.60 valves, 76cc combustion chamber, and 170cc intake runners. According to desk top dyno, I get around 410 HP. And 485 Ft/lbs. of torque. But I have also ported and polished the heads, and have roller rockers so I guess I'm around 425 HP. If you go with the Vortec heads you will need a intake that will fit on vortec heads. I have a Edelbrock Performer RPM intake. It does well and is designed for the rpm ranges that boats operate in.

If you have the money ditch the cast crank and get a forged 400 crank. If not the cast will survive if you dont beat it to hard. I had 2 cast cranks in mine. 1 was cracked and the other was okay and was reused. If you buy a new crank besure to check the radius on the rod journal. After market cranks sometimes have larger rads, such as Eagle and Scat. The rads can interfer with the bearings. In my case the stock GM crank was okay but I had to put Clevite racing bearings that had a champher on it to clear the radius.

As for compression keep it 9.5 or below. If you go with higher compression, you will shell out for the premium gas like I have too, or risk having detonation and breaking parts. I'm running 10.1:1 compression but I have to use 93 octane, and I have my timing retarded alittle. I still use my stock Thunderbolt IV ignition.

With the engines I have, they idle well, which is important for close quarters, And they have a butt load of power. So much so as I have to by new props and go up 3 inches of pitch to start so I can start to get them tuned right.

One word of caution. I would assume by having a 1985 21' Scarab you have an Alpha 1 outdrive. Be nice to it. Use Mercruiser Hi Performance Lube and add a drive shower. Alpha 1's are made for 300 HP max. You will be throwing down close to 400 or more. An upgrade to a Bravo may be in your plans too. Good luck and keep everyone posted. There is one thing cooler than building an engine, and thats listening to it fire up the first time.

Jeff

Not meaning any offense but you could by my Scarab!

No seriously to make the power you need it will take a hot small block or a big block. Either option is going to be hard on your drive. If you need to change the engine and drive you might as well start with something else.

I have already done it to this boat.

1995 22 Scarab with a new 502/502 from GM performance. Bravo One drive, 27" Mirage Plus prop. Plus all electronics, stereo, covers, etc.

Runs upper 70's GPS depending on load and temp. Will run 72 with 5 people, full tank, and an icechest.

Its in the classified section also.

Didnt' you have the Jasper engine in your boat? If so why are you switching? Did you have problems with the engine?
Just wondering. My new SBC has a custom roller shortblock I ordered from Jasper from their Performance dept.....Just wondering.....

"Bad-Habit"

Yep, It's got the Jasper in it right now. It runs like a top, haven't had a single problem with it. I love to build motors, that's why I'm asking about building the 400 that I've got. I'm stioll trying to decide if I should build the 400, or do some mods to the Jasper 350 that I've got now. The Jasper runs great, I hope you like yours.

i would not put any lightweight head"vortec"on a 400 sbc. the head gasket thing is crazy close.after market thick deck heads are worth the extra$

Get a good Exhaust system,save yourself some grief

If you are runing in salt water and using a seawater cooling system then I suggest you choose a 383 or go big-block.

Roby

Help

Where Do You Get A Dennis Moore Book

I've Been Checking Every Where

Thanks

you an put alot through a alpha don't worry. I run abut 570 hp through one. Just be nice