632ci Build Specs
 

I hired a guy as a fabricator at my shop. This guy can do about anything. He has been going on and on about letting him build me a motor. He put together a list of these parts for $8500 and he will build no charge. I figure if your trying to build your boss a motor you better be confident in your ability.

10.2 Dart Big M Sportsman Block
4.6 Bore
4.75 Stroke
Scat 4340 Forged Crank
7.5cc Dish .2618 JE Pistons
6.700 Carrillo Rods
385cc AFR Aluminum CNC Heads
2.350 Intake
1.880 Exhaust

2pc rear main seal, splayed end caps, decked, boared, complete blueprint, coated cam bearings, fully balanced rotating assembly. I may be off a little on specs or terminology, I was taking notes as he was listing parts.

Do you think this list of parts will work together? Is there anything you would change? I'm not expecting someone to give me there secret build specs. But my goal is to have a large cubic inch n/a reliable motor and I want to make sure the specs look good before i throw away $8500 . He did not specify cam and I am running Stainless Marine Gen III Dry Exhaust. Any information would be greatly appreciated and hopefully end my bad luck with boat motors.

I think you're going to have a really short piston, maybe an American made crank with the Carillo rods.

Callie's or howards promax crank. You'll end up with over 12 - 15k by the time your done.

I'd also make sure your "employee" has built big cubic inch engines. Lots of things to spec and look out for plus machinig etc.

If you're starting from scratch, I would strongly recommend going with a 4.5 stroke max.

Jeff wagoner (wags 382) built 4 5/8 stroke tall deck blower motors last year w 6.535 rods, valve relief was into ring lands and pistons were half way out of bores on bottom of stroke, had it apart before 100 hours for ring seal /ring land problems, went to 4 3/8 stroke, upped the boost and made 1298 hp vs 1100 something, a mile of stroke is not a great idea in something turning 6000 rpms for 20 minutes at a time

Use a 10.6 dart race block. They are more money but you don't have to clearance the block for a 4.75 crank so you save some money there. The cam tunnel is raised .600 so you don't have any chance of rods hitting the cam and don't have to clearance the rods. And the Race blocks are much nicer than the Big M's. I wouldn't use an offshore crank in a 4.75 stroke there isn't much material between the throws like there is with shorter stroke cranks. Oliver makes a nice 7.100 max rod for $1200/set with L-19 bolts. The parts bill for this sort of motor is $12-15,000 unless you want to go exotic on everything then it turns into $25-30,000

Not to throw water on this but I'd sure be checking this guy and his previous engine builds out.
if it sounds too good to be true ......

I agree with this. Stuffing a 4.75 crank in a Big M Block is very labor intensive. The motor gets put together and taken apart so many times you could probably build 10 motors that just go together. From notching the pan rails notching the bottom of the bores (which needs to be done the right way so you don't lose ring seal when then piston is at the bottom of the stroke). Then cam clearancing the rods which is a put together use a big zip tie for a feeler gauge take apart. Torque the rods in a vice and clearance while torqued because you will get into the rod bolt. Then it's things you really don't even think about like pan gaskets. They can't be bought so you have to take the time to trim up a set of gaskets. It's just on and on.

Personally, I will not put anything larger than a 4.5" stroke in a 10.2 block. It's just not worth the extra 34 ci. If you insist on building a 632, go to a taller deck block as mentioned above.
Eddie