350 to 400 gm motor ??

[seadog2be]

I have tore down my 350 gm marine Motor. It has steel crank, 4 bolt main and cast flat top pistons with valve rele. # 7 cyl must have sat with water in it. it is badly rusted. was going to bore .60 over. however; looked though my junk. found a 400 sb gm motor. has steel crank 4 bolt main. and 10.5 to 1 domed forged and coated pistions. Is there any resone why i could not use this block insted of 350. other than steam holes in head. I seen where felpro makes a marine gasket set for the 400. thanks

 

[Bondo]

Re: 350 to 400 gm motor ??

The Block will run Just Fine..........<br /><br />Those 10.5/1 Pistons will have to be Changed..... Unless you want to Go Broke buying drums of Race Gas..............<br /><br />Why would you go .060 Over..??? Usually you Only go far enough to Clean it up..... .030......

 

[rodbolt]

Re: 350 to 400 gm motor ??

the sb 400 does not work well in most marine applications that are raw water cooled. you can use the 350 crank in the 400 block and reuse your existing flywheel and harmonic balancer. if you use it as a 400 you will need the 400 balancer and a manual shift 400 flywheel. the 10.5 will require at least 93 octane and proped to the high side of 4800-5K. the motor wont like mid range speeds with a large prop. there are several ways to help prevent load induced detonation. one of the most common is add fuel. fatten up the main jets. my advice is to go back with the stock parts in a stock configuration and it will work as designed for years. but you also have to find out where and why the water came from in #7 or it WILL do it again.

 

[seadog2be]

Re: 350 to 400 gm motor ??

I have not heard back from machine shop yet. .60 over was rough guess. The # 7 cly. is pitted badly. My have to sleve. just was looking for cheaper choices. LOL its a boat.. nothing cheap a.