Dart Big M Block Questions
 

Ladies, Gentlemen and others....

Quick question, that may lead to others....

I'm entertaining a fantasy of building a 632 monster, starting from a Dart Big M block. Can this engine be built and shoehorned into the same space as the 496HO that's currently under the sundeck of my PowerQuest 280 Silencer, and keep it under the hood? Looking for any contingencies/concessions that would be involved in making it work, not so much reasons why it won't. Obviously, if it just can't, it just can't, but I figure since I'm starting from scratch......

Thought I'd get this question outta the way first, then we can move onto more in-depth material.

Thanks. Brad.
(937)-545-8991

You made me laugh with the “and others”. So sad but true. Just hope it hasn’t hit the offshore world quite yet anyway!!! 😂.

Geterdunn,

Strangely enough, I got it from a HS biology teacher during my sophomore year, something like ‘86. She was a hoot.

Thanks. Brad.
(937)545-8991

She probably read 1984 also. I was just a few years ahead of you graduating in 85 but wasn’t paying Attention to anything. She was obviously in the know how!

All depends on your intake and exhaust systems. But the 496 has a 10.2” deck height like the 632 would, so theoretically it’s possible.

Hogie,

What about block length? I just trying to imagine cramming four cylinders per bank at 4.6”+ diameter into a block the same length as one with a bore of 4.3”. Something’s gotta give. I don’t know how much extra length in the block I can accommodate. Just curious where the extra space is taken up. Cylinder wall? Block length? I’m new to this, as is obvious.

Thanks. Brad.
(932)545-8991

block stays the same it the bore size that changes, even a sbc and a bbc are the same length from the motor mount back

Mark IV 454's and your latest Gen 496 are 4.250" bore standard.
The ability to go the 4.625" max bore most aftermarket blocks suggest is the fact the Mark IV big block was designed with 4.840" bore centers and carried onto the later generations.
So, couple that with the thicker and "siamesed" cylinders on the aftermarket blocks are cast with, they can go the 4.625" and there's no need for the block to be longer.

https://cimg1.ibsrv.net/gimg/www.off...f7470f9e50.jpg

Cheech,

Thanks for the info.

Just to be clear, speaking specifically to length, I can expect a fully dressed Dart Big M engine to fit in the same space as the Merc 496 I have now….? Technically, it should be shorter, given there is a ProCharger pulley that would not be in the mix. Or this space could be repurposed for a dry sump oil pump pulley. Is this correct?

If you're starting from scratch, a 632 benefits from a "raised cam" block to give better clearance for the big stroke you'll be running. You can do it with a standard cam location, but it's easier and less hassle when you use a raised cam block.
Be aware that your head choices include options that have raised or angled exhaust flanges, which will have some effect on the overall width/height of your exhausts as installed in the boat.

Otherwise, it's pretty much dimensionally identical to any other talladetalldeck big block chevy.

McCollumsTN,

Cool. Thanks. This is exactly why I at as Ted th is quest here. So, on to the next….

I’m also going to be height constrained. I will not be able to move forward if I cannot stuff this thing under the sundeck. As far as I can see, the big obstacle here is the intake manifold. As with the existing 496, I would plan for EFI, and would like to use a front throttle body intake. All the top TB options see seem to appear to be way too tall. I’ve found several options I like, but, so far, short of a handful of custom shop offerings ($$$$), all I can find are for small block builds. Any suggestions?

We’ll most likely get to a full parts list before this is done, but let’s get this one cleared away for now.

Thanks. Brad.
(937)545-8991

No perfect solutions for what you want to do.

This is closest and it’s only for a 9.8” deck height block I’m pretty sure. A 632 needs a 10.2 or 10.4” tall deck block ideally. You’d need spacers.


https://cimg6.ibsrv.net/gimg/www.off...31417f5de.jpeg


The next easiest solution would be to find a tall deck tunnel ram that fits under your height requirement and have a custom lid made and hole cut in the front for a throttle body.

The nicest and most expensive solution is custom fabricated manifold like Kwrights.

If you don’t have to have the tall deck, you can fit 565-582in^3 in a 9.8” deck height block.

Hogie,

The block I’m looking at is a 10.2” deck with .400” high cam position. Perfect for a 632ci.

Kinda thinking about fabing a manifold together myself. I do have the capacity and the resources to do it. I like challenges like that, and it would give me the opportunity to make it more my own. Any idea what all the “extra” holes are in that intake are? The injector ports I get. The rest, not so much… Extra injector ports? MAF sensor? ???

Thanks. Brad.
(937)545-8991

I would think the biggest problem would be that no bravo based outdrive is going to last with the torque that a motor that big would make.

Compedgemarine,

I spoke with George at AADS a while back, and he seemed pretty confident. But I get it. Something else to consider. I will, for sure, readdress that conversation with him before moving by forward.

Thanks. Brad.
(937)545-8991

If you dont want to run a trans, then the Imco SCX is probably the strongest bravo style drive, projects are like the bunny it keeps going, why are you stuck on a 632 ? whats your HP goal

F2,

850 or so, I guess. More if I can get it (duh). I’m not stuck on anything, I just figured the 632 was about as big as one could stuff in the space I have, and I could probably build it for less than I could a smaller Whipple engine, assuming I could get it under the sundeck. I know I can’t do much with the 496 without addressing at least the pistons (Merc tells me the S#s indicate forged rotating ass’y except the pistons).

This whole fantasy started when we bought the PowerQuest. I love the boat, and have no intention of letting it go. But, I was all excited about owning a boat with a blower motor, as that’s what a grew up skiing behind. I figured the 496HO/ProCharger combo, supposedly rated at 615HP, would work well enough as a muscle boat and a pleasure/family/ski boat. It has come to my realization that the ProCharger is not really all that it’s cracked up to be, and the boat really struggles to pull a slalom out. I’ve since propped down (from 28 to 26”), and it’s a much more manageably planing boat, but I lost 2-3MPH in the swap, and that pissed me off.

Since I’ve always been a GoBigOrGoHome kinda guy, the NA 632 seemed the perfect solution. 🤷‍♀️

Thanks. Brad.
(947)545-8991

First that`s going to destroy your outdrive, I don`t care what George says, bravo gears are small and you can`t change that fact.
Secondly, rod angles and whatnot , all that is $hit in stuff over 600ci.
I don`t like this plan at all.
Sorry, not sorry.

Ded,

Don’t be sorry. That’s what I’m here for. If a 572 or whatever is the ticket, that’s what I’d build. God knows I’m the student here.

The ONE thing I don’t want is a scatterbox looking for an excuse. The plan would be to do the build, do the swap and sell an extremely low hour 496HO/ProCharger combo to recoup most of the cost. If the damned thing blows up, just on principle, I just might get buried in the boat. Same with the outdrive. What I want most of all is an ultra reliable boat that runs strong. I know it can be done. It’s just a matter of forming a plan and working the wrinkles.

George doesn’t use Bravo gears (at least, that’s what he tells me). He machines the casings to accommodate larger gears, shafts and U-joints. His “Stage 1” is supposedly good for 700HP for 200 hrs, with a two year warranty. I do get it, though, and, if another $15K is in the cards to make this all fly, the wife is gonna put her red headed clamps on it pretty quick. It’s already going to be hard enough to convince her we “need” the boat to go any faster than it does now. She didn’t grow up on an 85MPH, 21’ semi-flat bottom day cruiser, like I did. 67 already kinda has her white-knuckling it.

Thanks. Brad.
(937)545-8991

Dan hit the nail right on the head. Personally I wouldn't go any bigger than 565. You can stay with standard deck, rod angles are good and no goofy geometry on parts. I have 565's 9.3 compression efi's that make just a few hp shy of 800 hp. with a real good torque band. And on drives I wouldn't consider anything less than the scx. Already been down that rabbit hole. Any ways that's my 2 cents worth.

KWright,

Noted. Soaking it all in.

Thanks. Brad.
(937)545-8991

Kwright,

Are those 10.2” decks or 9.8”?

Curious….

Thanks. Brad.
(937)545-8991

9.8

If I`m spending your money
 

Big M block.
565ci
Machine for 55mm cam and .904 lifters.I believe you can buy them from Dart with those options.(so over kill lol)
Solid roller.
Tunnel ram
JE pistons
Molnar crank and rods.
Belt drive
Pro 1 heads.
Shaft rockers

probably run forever :drink:

or buy it already built from Shafiroff
 

Dan,

The breakdown on the short block is as follows.

Stage II

Rated For Up To 1250 HP

• 4.500 Bore x 4.250 Stroke
• 8.5-1 CR
• Dart Big "M" Block w/Splayed Nodular Caps
• Manley Fully Counterweighted 4340 Crank
• Double Keyed Crank Snout
• Callies Ultra-H Rods w/L19 Bolts
• JE Pro Series Blower Style Pistons
• 5115 Low Carbon Case Hardened Steel Pins
• Hell Fire® 1/16 • 1/16 • 3/16 Rings
• Clevite 77 "H" Series Main & Rod Bearings
• Internally Balanced

$ 7,495.00

I personally would not put that much power in that hull. I don't know how much power someone has put in that hull, but I would not want to be the guinea pig.

This is about 90% of what you’re trying to do.


https://cimg6.ibsrv.net/gimg/www.off...ed1c84342.jpeg
What you want is very custom, better find a reputable builder.

Watching his daughter racing right now. Of course I am.

I like the color of that motor,,looks sinister

Im infatuated with these intakes, having made good hp now with two of them on motors I built and dynoed I plan on doing some testing soon with the rectangle port version. The last one I built and dynoed IS going in a 280 powerquest like the OP's hull. A few things on THAT hull is there is very little room in front of intake on a front mounted throttle body, we determined there is only enough room in front of TB for about a 7, 7.5" ' long cone filter. Tested multiple cone filters and adapters on flow bench AND dyno on this last one. A 90 degree bend feeding the TB on the proflow IS the end of the world as far as hp so its very important what goes on front. Id be interested in whats done to that TB on the Pat mussi engine as the box stock edelbrock needs work to make real power from its stock form.
I DO know the 280 hull is VERY touchy, I bought one this summer as a short term investment and I have quite a few customers with THIS hull.
Jason scott's 280 ran 85 radar at shootout this year, on my dyno his motor made about 630 hp and foot lbs of tq in dyno trim during a glory pull, as installed in boat was probably more like 580, 590 ish. It had a extremely modified 502 mpi intake and a great tq band. While tuning on the water, we saw high 70s in his boat. I will tell you though, with ANY weights in that hull, especially in cabin or a full tank of gas, its GLUED to the water and feels like a slow , ass, turd. I drove his boat loaded down weeks after the shootout at hotboat and it felt like it really needed a supercharger, it went from being sort of zippy to struggling to get on plan from adding extra fuel and passengers with a 28 labbed on it
Jeff H had the same hull, 280 PQ, ran 82 If I remember right at shootout with another 502 I modified the intake on and dynoed here then tuned on the water, his made about 610 hp in dyno trim on my dyno, made about 580 with water EMI jacketed manifolds . His boat ran mid 70s in normal operation but again, very sensitive to load.\
The stock 280 I bought has a 340 hr 502 mpi in it, boat wouldn't break 60 mph with a std 24 pitch although its been claimed and accepted that different versions have ran mid to upper 60s bone stock under perfect conditions. I did a injector change on this one after I flowed and cleaned the stock ones, determined there were several over achievers (running rich), I then reflashed ecm and added a 02 bung to one stock manifold to actually dial in the tune properly. That got the boat into the 62/63 range, having hull bottom cleaned and a labbed 26 over trimmed on fumes, by myself got boat into the 66 or so range BUT throw 2 passengers in and boat wouldnt barely go past 60. IF you really wanted one of those to go fast, Id gut the cabin out, alot of weight in front of the step which is very far forward.

Arcticfriends - how about something like this and run two fa’s/air cleaners ? I’ve never tested one. But…..:)


https://cimg9.ibsrv.net/gimg/www.off...5208d15444.png

Id like to see what it did on the flow bench and on the dyno. The condensed version ive experienced was THIS :
"1150" cfm edelbrock 90 mm tb flowed sub 1000 out of the box,the 92 mm holley was very similar.
With my dyno partner norms grinding, massaging, etc, we got from sub 1000 to 1200, 1220
bolting a fairly long radius 90 on took us back below 1000, a short radius 90 was worse
clamping on most 4.5"id cone filters that will fit in a boat and not hit back seat in a single took us back to that 1000ish mark or less
putting a 18$ siectre 4.5 x 6" volute on tb took us from that 1200 mark to around 1400, it took a 102 mm tb that barely flowed 1200 to over 1700). With most 6" id clamp on cones, on volute, we went back to 1150 to 1280 depending on size, length, media density
so on the dyno,this 9.4-1, oval port 502 was in the 650/660 hp range. With.most the 4 5" id clamp ons we went to the 620 to 630 range (i spent over 500$in cone filters, pieces out of my own pocket to try)
i stretched the 4.5 x 6 volute over the tb by slicing the area it clamped on, stretching it with heat gun grinding lip off od of tb , etc
very next pull we made over 680 hp. With tuning was mid 680s. Then we tried every 6" id clamp on i bought. Turns out a USED 6" id KN chevy truck filter i borrowed worked the very best and there was virtually no hp penalty.
the first boat i put one of these proflow intake motors in was slow AF but, boat was water logged, ( this was 3 years ago,boatshowed up for motor install with bilge plug in, green slime growing in boat, 2 feet of water in it) single vee , scaled 9200 lbs on a aluminum trailer (29 ft envision single).with a 90 degree elbow on in that boat (this was before this last dyno ,flow bench experiment), boat lpst 300-400 rpms and 3,4 mph.
So im learning these moniblade tb's can make ppwer but smallest thing can KILL power, Smitty

Arctic,

Just my Frankenstein mind wandering here....

I know this sort of thing happens all the time in the model boating world, because I've made "long" rods for many engines within our realm. It's pretty easy to do, with only a shim under the cylinder sleeve equal in thickness to the difference is rod length from stock. While I'm sure there are a number of "lack of" success stories that didn't bother reporting back, I got many calls from very satisfied customers. Being two strokes, with piston/sleeve transfer ports for valves, there are other factors coming into play when doing these sorts of things in our model boating world that are not in play with cam valved four strokes in our monster motor world, but reducing rod angle was one of the benefits being chased after.

Since rod angle seems to be the primary concern for the 632, If one were to go with, say, a 565 build, would it serve to start with a 10.2 deck block and use longer rods? Just doing the basic math, using 6.7" rods instead of 6.385 rods takes up all but the last .085" of the difference between the 10.2" and the 9.8" decks, assuming the difference would be exactly .400" between the two deck heights. An automotive machine shop could easily take that off and one would be back to nominal deck height and an even milder yet rod angle. Would there be any benefit in this? Any harm? I know other alternative parts would come into necessity, like pushrods, but that shouldn't be an hill for a climber, I wouldn't think.

After some rudimentary AutoCad work, some numbers, if applicable, based on 4.25" stroke:

6.385" rods reaches max rod angle of approx.18.4 degrees of rod angle, at 71.6 degrees ATDC and 1.7805" below TDC.
6.700" rods reaches max rod angle of approx.17.6 degrees of rod angle, at 72.4 degrees ATDC and 1.7960" below TDC.

Don't ever let a self employed toolmaker get bored......:popcorn: Crap like this happens: (I did that, BTW.)

Thanks. Brad.
(937)545-8991

Dan,

Dart Blem 31273655 Big M Sportsman Block, 4 Bolt Caps, 4.600 Bore, 10.200 Dk | eBay

BBC CHEVY 496-572 BRAVO 335cc REC. PT ALUM. HEADS FOR SOLID ROLLER CAM BRAVO-919 | Skip White Performance - We have the best prices you will ever find for aluminum heads, rotating assemblies and strokers

Rotating Assemblies - Ohio Crankshaft
I would use the 540-555-565 Super kit, and substitute the rods for 6.7" rods, assuming no condemnation from the previous post.

Thanks. Brad.
(937)545-8991

After reading through your post, I see you talk about being able to pull a water skier. If that is your goal you need to have an engine that will pull right off idle. Torque in the 800 to 400 rpm range. That's going to take a whole different set up. The cu in is not going to carry you down that low with performance style heads. I think you are at a fork in the road, stump pulling low end power for sking or high end power for speed. Jmo

Gen 6 502 to a 540 would be a nice combo and pretty easy on the wallet...........4.25 x 6.385 x 4.50

imho - building more torque just for water skiing is crazy thinking to me. It’s so damn easy to change a prop, unless you are surrounded by great white sharks or alligators, oh well no skiing then snyway…..lololol

More torque for using thr bigger prop to water ski. Nuts.

I don’t think the op has broken enough outdrives yet and thus this line of thinking…..,,,,,;

KWright,

I hear ya. And I know there is very often a choice and a tradeoff that needs to be made. I've been boatin well long enough to know that everything is a sacrifice of some sort or another in a boat. But, here's my crux....

Back in the day, my dad had a SeaRay 260cc (built on the Pachanga hull, as I understand it), with the bone stock 315HP 454. It weighed 5500lbs. We all skied behind it. We all called it "Great White". It was, by no means, a performance boat. Granted, having grown up skiing behind a 21' semi-flat bottom with a blown 482 V-drive, it was a bit underwhelming for me, as a ski boat, but my wife and several friends learned to ski behind it, and it would pull several of my dad's fat azz friends out on slaloms. This boat would also ran 55MPH or so.

The PQ we've got now weighs almost a 1000lbs less. I'm looking for neither Wakesetter ski boat performance nor race boat performance. I'm looking for something right down the middle, but performing better at both than I'm currently getting. That tells me more everything: HP, torque, ci, etc.... I have to think this is not unattainable, and I'm not looking for the ultimate in anything, other than as much the best of both worlds as I can find.

Thanks. Brad.
(937)545-8991

SB,

I haven't broken a single outdrive yet, eleven years into owning my own boat (after four decades of boating with by dad prior), and I intend to keep it that way. Obviously, the outdrive would be addressed and upgraded as part of this project.

Truthfully, my days of skiing much are likely behind me, but my son likes to ski. Although the kids don't spend much time with us on the boat anymore, we do still boat as a family enough to want to be able to jerk a skier from time to time. I think we dropped the ski rope out maybe twice this last year.

As I stated just prior, I have to think a middle ground is feasible. Besides.... More HP is never going to go to waste, right? Always a good thing, right?

Thanks. Brad.
(937)545-8991