Mercruiser 350 into 383 engine build

[105mich]

As a winter project I am going to build a en engine using mercruiser 350 block. Initial Questions...

Can I just use a 350 GM truck block instead if I am starting from scratch like this?

Does it have to be 4 bolt main or will 2 bolt main suffice?

Does mercruiser even do 4 bolt main engines? All the blocks Ive seen are 2 bolt.

I already have a machinist/engine builder who can handle the boring/stroking as well.

Thanks!

 

[jimmbo]

"Does it have to be 4 bolt main or will 2 bolt main suffice?"

You answered your question, in the next line

"Does mercruiser even do 4 bolt main engines? All the blocks Ive seen are 2 bolt."

 

[matt167]

Buy a late model truck engine. Tear it down have machine shop mag the block and heads. Get a 383 kit. Have it bored and piston fit. Rebuild the cylinder heads. Add a marine cam and all marine parts. You'll need a 4bbl vortech intake. Rock solid horsepower

 

[105mich]

Ok cause I did find a late 80s mercruiser block that is in good shape, but it is 2 bolt main, but I know those can only take so much hp vs the 4 bolt

 

[105mich]

And what do you mean by late model?

 

[alldodge]

Ok cause I did find a late 80s mercruiser block that is in good shape, but it is 2 bolt main, but I know those can only take so much hp vs the 4 bolt

:nono:

You want a truck or marine motor after 1996

 

[matt167]

1996 or newer vortech block gets a roller cam and vortech heads. You will blow up an alpha one well before you get enough horsepower to puke a 2 bolt crank out the bottom. And 2 bolts are actually stronger in some cases.

 

[105mich]

Well since I am going to be building the engine from scratch just the block and having machined/performance components etc can I use a block from pre-1996 and just make sure it matches with a bravo drive? I know the alpha doesnt like above 300 hp. The block I have found is between 87-95 year range

 

[Scott Danforth]

talk to your local machine shop.

if the cost of the core block, then cleaning the block, line-honing, decking, boring and honing is more than $1100. buy a brand new block from GM.

stick with post 1996 blocks on builds below 450 hp. you need a baby M motor on any serious HP small blocks.

2 bolt vs 4 bolt comes down to what is your intention with the boat and motor, and what drive you have behind it.

also, the block coming from the Tonawanda engine plant doesnt know if its in a truck, a boat, a generator, a fork lift or a trash pump. its all the same block and heads.

rough guide below

• just a mild build of about 320hp at prop - a 2-bolt motor would be fine. so would cast crank and cast pistons
• slightly above mild build of about 350hp at the prop, a 2-bolt motor, cast crank, forged rods and hypereutectic pistons
• wild build about 400hp or more at the prop and spinning at 5500 RPM or more.... a 4-bolt motor, forged crank, forged rods, forged pistons
• a 434 cubic inch 700hp blown tall-deck small block - a Dart Baby M motor.

 

[alldodge]

Depends on the boat and how its driven. Buddy has 383, with roller, 4 bolt in his 21 foot Checkmate and has a 8 inch extension box holding the drive. Been 12 to 15 years and has never touched the drive other then regular maintenance

 

[105mich]

I am looking at something between slightly above mild build and wild build. Thanks for the info, I will check with my engine builder what that machining cost will be

 

[Bondo]

I am looking at something between slightly above mild build and wild build. Thanks for the info, I will check with my engine builder what that machining cost will be

Ayuh,..... The '86 to '95 block can work, just don't use those heads,......

Ya most definitely want Vortec heads,....
Deck the block to 0", hyper D-dish pistons, .040ish" head gaskets, for a compression ratio right at 10:1,.....
Plenty of horsepower, gobs of torque, 'n still runs on regular gas, though non-ethanol is best(for all boat motors),.....

 

[Scott Danforth]

here it the GMPP block pre-clearanced https://www.gmperformancemotor.com/parts/88962516.html

here is the new GMPP block (needs clearancing) https://www.gmperformancemotor.com/parts/10105123.html

here is the baby M https://thmotorsports.com/400444-dart-31132211-short-blocks (only available as a 2-piece RMS) here is Dart's web page. http://dartheads.com/product-category/small-block-chevy/blocks-small-block-chevy/

google around for prices in your location. talk to your machinist

may also want to check out racingjunk and the classifieds on OSO

 

[105mich]

Ok I appreciate the help guys! All in all, if I am doing the slightly above mild-wild build, what is total cost to build the engine about?

 

[105mich]

Cost of build

Approximately what would it cost to build a marine engine from start to finish? I am looking at 350 to 383 boring/stroke or starting with new 383 block purchased. Not a crazy wild build but moderately wild to get between 350-400 hp

 

[AShipShow]

between a case of beer and a new car... Thats a very hard question to answer... but maybe someone whos done it will chime in with what they paid... My closest experience is marinizing a 4.3 from a Chevy truck.

One thing worth considering is what outdrive do you have? Alpha drives are typically said to be okay to about 300 horsepower... Anything over that and you are probably into a Bravo drive which will run you probably at least $800 used... plus you'll need the whole transom assembly which means you might be buying a used boat for the drive.

 

[alldodge]

Doubt starting another thread with one specific question which for the most part was answered in the first one. Need to give the guys time to see it and respond

 

[GA_Boater]

Doubt starting another thread with one specific question which for the most part was answered in the first one. Need to give the guys time to see it and respond

Exactly.

 

[105mich]

Well so far Ive gotten bits and pieces and want to put the whole thing together here

 

[105mich]

My initial guestimate is around 5k