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

How much power is he telling you it will make, and how much are you looking for? And, how long are you wanting the engine to last between rebuilds?

i would think you'd have 3k plus into the block and machinig and another 3,500 min into the heads. That's 6,500 just between those two. With the kind of power your your planning to build I wouldn't scrimp at all on the rotating assm. Some have great luck with scat cranks but I honestly would be scepticle in anything over 454/496. I know there's a ton of them out there running flawlessly but i would really consider rethinking the internals. It's kinda like purchasing one of those White engines you See on eBay for peanuts. Nothing against them or any other company selling cheap engines and may be perfectly fine for street with short spurtts but not balls out for several minutes at a time.

I recently got some numbers together for a couple 565/572's

Block and machinig/prep 3k
Rotating assm 5k
Heads complete. 4k
Intake, cam, carb, lifters 3k
Gaskets, pushrods, accs 1k
Oil pan-pump, valve covers. 2k

18k Each apprx.

Corners can be cut here and there so say nock off 2k but then add the other little things that add up. Some of the above numbers are rounded off but the general cost are there.

I will say I admire you wanting to build reliable NA power regardless how you get there.

What kind of power and what RPM? I don't know if I would go that big with the heads and camshaft with out headers on a NA engine. As far as 4-3/4 crank if you don't rev the nuts off of it might work ok. That's my 2cents.

And I don't think you will have a good ring pack with that stroke and a 6.7 rod.

He is claiming 1000hp. I'm looking for a minimal 850hp. My opinion there is no need to spin over 5800 RPM. By comments in this post, his numbers seem to be on the extreme end of the spectrum. Im tired of buying other people's boats with a motor on the way out. Im looking to build a reliable motor that will last in a boat I plan on keeping for a long time. I want to be on the conservative end and have parts that will live. I have a huge oil cooler, 2 oil filters, canton 14qt pan and accusump system. We plan on traveling the U.S. and do several poker runs this year. I have the components to support a motor for long run durations, now I need a motor that can do it.

My opinion, if you are wanting a "Reliable" fairly long lasting engine, would be build yourself a 540-565 engine with the 9.8 block(4.25x4.xxx bore), and put a roots/screw blower on it(8-71,10-71, sounds like budget minded so prob roots/carb?), with a mild hydraulic roller camshaft. Keyword, "mild'. Enjoy a valvetrain thats easy on parts, and go boating. With that combo, 850hp can be done with 5-6lbs of boost, idle well, and live a long life. You'd be good with a sportsman priced crank/rods, off the shelf stuff, and a basic set of aftermarket heads, standard wet sump oiling, basic valvetrain components, nothing exotic. Focus on good machine work, good assembly, and a good tune, and you'll be good to go. The GEN 3 stainless marine exhaust works best with forced induction. Just my opinion.

Im of the same mindset, keep stroke (piston speed) reasonable by keeping stroke in that 4.250/ 4.375 range, keep bore at 4.500 ( stiff cylinders that wont deform), and low boost it if needed to reach your hp goal

1000hp forget about that the 850hp can be done but I would still be worried being a NA motor and manifolds. What outdrives do you have?

For the OP, follow Eddie Youngs advice and stay at/under 4.5 stroke.

My suggestion is to look at the Chevy 572 - 620 HP and use them as a base engine. You can buy the long block for 12,500 and finish for not a lot of $.