Motor/gearbox/prop help

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chasebryant88
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Motor/gearbox/prop help

Post by chasebryant88 » Tue Apr 12, 2016 8:20 pm

I'm needing some advice I'm building a 14"x8" marsh master classic with stainless rigging 5 seater and planned to use a sbc with a 2.5:1 gearbox now I have a 496 BBC supposed to be dynoed around 520hp 600ft/lbs tq I already have the gearbox and it is brand new so would hate to have to lose money and buy a different gear ratio and would like to keep my motor below 5000rpm can anyone recommend a prop setup or should I just bit the bullet and get a different box any help would be greatly appreciated

SWAMPHUNTER45
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Re: Motor/gearbox/prop help

Post by SWAMPHUNTER45 » Tue Apr 12, 2016 9:13 pm

Your gear ratio seems sort of tall and your HP and torque seem a bit short?

Do you have any engine specs ?

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Re: Motor/gearbox/prop help

Post by chasebryant88 » Tue Apr 12, 2016 9:37 pm

Yes the gearbox was purchased with the intention of running a 408 SBC I had but I just recently got the 496 and it will be a lot stronger motor so I've decided to run it but I already have the gearbox so was just trying to see if anybody had a suggestion on a prop that might work with the setup as for the motor it is basically just a blueprint cast iron headed 496 stroker with a few little changes to squeeze out a little more power as the cast headed blueprint 496 is only rated at around 480hp and 550tq

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Re: Motor/gearbox/prop help

Post by SWAMPHUNTER45 » Wed Apr 13, 2016 7:00 am

My opinion is the ratio is to high for that engine unless your going to use Superwide slow spinning blades for push.
Most of the blades that provide snap, speed and push work in the 2200 to 2500 blade rpm zone and that stroker would not live long spinning up.

I suggest a 2.12 ratio @ 5000 your prop speed would be 2358
Probably be a good 3 blade set up with Sensenich R blades or Whirlwind EX

chasebryant88
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Re: Motor/gearbox/prop help

Post by chasebryant88 » Wed Apr 13, 2016 7:57 am

Thanks for the info I'm not all that worried about speed more interested in pushing like a freight train but I also don't want it to by a turd in the water. The guy I bought the 496 from had it mated to a 2.38 with a 3 blade maximus and he said it pushed good but he went with a bigger motor so I'm not sure if I should just get a set of maximus blades and add pitch to make up for my gear or try to trade for a different gear

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Deano
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Re: Motor/gearbox/prop help

Post by Deano » Wed Apr 13, 2016 9:21 am

I agree with Swamphunter's premise that a different gear would afford you more prop options, but . . .

A three blade Sensenich Super Wide would fit those parameters and would work well.
Given your intent to not spin over 5k, you're limited to about 2000 prop rpms.

They push real good at 1800-1900 rpms with pitch in them and are, IMO
likely your best bet to get max push without winding up your big block.

That is a lot of gear for a big block, but with BB torque you ought not need high RPMs.

I am very pro Maximus blades, but for the prop rpm range you are looking
at, the Superwides would in fact be a better fit with that gear.

I bet you would be very pleasantly surprised at just how well such a combination would run.
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but it is not the path to knowledge; it has no place in the endeavor of science."
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mcm4
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Re: Motor/gearbox/prop help

Post by mcm4 » Wed Apr 13, 2016 10:19 am

I have a 565 cu inch bbc with the 2.5 reduction, I run a 86" S 4 blade on 1 with 700 hp and 690 torque at 5200 rpm.... if you put a 3 blade S on yours you will be able to add more pitch and it should run fine.....

I tested my boat with the four blade R 86", four blade R 82", four blade S 82" and four blade S 86"..... I feel that the S gave me better performance in all areas, and chose the longest prop.

My boat used to have about 500 hp, I ran a 2.3 with a three blade S and it worked fine.

To me, on the BBC, the 2.68 made the engine turn to fast to get the blade in the right range. I think a 2.68 is better suited for engines that like higher rpm

I do think that a 2.3 would work well for you to, but I like the 2.5 better as it does not push as fast at idle.

I know guys in Texas with big heavy boats that have 600 plus hp that run the 2.3 and three blade S 86"

might all be wrong but it is my experience

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Re: Motor/gearbox/prop help

Post by chasebryant88 » Wed Apr 13, 2016 10:39 am

First thing thanks for all the info guys and second thing so what I'm getting out of this is if I'm set on using the gear I have I would be best with a 3 blade s but if I'm wanting to change gear that would give me more blade options so my question is what would there be to gain by changing gear ratio? In your opinion what would you consider would give me the best push running swamp/sticky mud/dry ground fully loaded but still do good cruising in water will I gain enough by switching gear and prop compared to my gear and superwides to offset the cost

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nebraskaairboater
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Re: Motor/gearbox/prop help

Post by nebraskaairboater » Wed Apr 13, 2016 11:05 am

At 5200 engine rpm you are looking at 180 prop rpm difference between 2.3 and 2.5. The R's seem to work good at slower rpm when they have a lot of pitch in them I believe is what Waterthunder had posted. If you already had the box and they won't exchange it at no cost to you I'd stick with it and maybe try the old R and S blades and use the one you like most. My dad runs the old style 3 blade R on his Olds 455 with 2 to 1 and is only getting 2000 rpm at the prop at 1.5 and it pushes like a beast on his old heavy flat bottom like mine. Its not speed demon but he doesn't worry about getting stuck here in Nebraska anymore. Just my experience here.

Dan
Dan Porter, Jr.
Fremont, NE
16 x 8 1971 Flat Bottom Fiberglass Hull / 454 Chevy/ 2.38:1 OX Drive / 80" 3-Blade Sensenich S

Joe
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Re: Motor/gearbox/prop help

Post by Joe » Wed Apr 13, 2016 11:43 am

I have a stout 454 and a 2.68 gear box. I run a 3 blade S and it does great. Runs dry no problem,not the fastest but it ain't no slouch either. I had a 2.3 gear and it turned less rpm at cruise, I turn a lil more pitch with the 2.68 but didn't notice any gains from it. A 2.3 would be a better gear but a 3 blade S or a 4 blade R will fit your needs just fine. I plan to go to a 4 blade R in the future.
Compromise is for those that cant get it done!!

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chasebryant88
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Re: Motor/gearbox/prop help

Post by chasebryant88 » Wed Apr 13, 2016 11:47 am

I'm not worried about fast if I wanted fast I would build a 10' step with my small block and gearbox I am more concerned with being able to go wherever I want than how fast I get there

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Re: Motor/gearbox/prop help

Post by SWAMPHUNTER45 » Wed Apr 13, 2016 8:28 pm

If you want push then the 3x "S" blades are the way to go just know you ain't gonna have a snappy or peppy response at the pedal.

A solid cruiser that can push and is efficient in it's range... yes!


Deano the 542 is coming off the run stand

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Re: Motor/gearbox/prop help

Post by bonecollector » Wed Apr 13, 2016 9:22 pm

I used that same engine on a 18x8 with a 82 inch R series set on the 2 mark it turned 5000 rpm with a 2.3 Ox drive I think with a longer R series you could put a little more pitch in it to slow the engine down and it still perform well. IMO
Sensenich, Ox Drive gear box dealer 386-279-3712

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Re: Motor/gearbox/prop help

Post by stpeteairboater » Thu Apr 14, 2016 7:02 pm

I have a 496 bb and just went from a 2.68 to a 2.38. What a difference in performance. Cruising rpms went from 3200 to 2700. Shallow water as low as 2100. I have 3 blade waterwalker stump pullers blades on a 16 foot combee hull.

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akblackdawg
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Re: Motor/gearbox/prop help

Post by akblackdawg » Fri Apr 15, 2016 1:45 pm

stpeteairboater wrote:I have a 496 bb and just went from a 2.68 to a 2.38. What a difference in performance. Cruising rpms went from 3200 to 2700. Shallow water as low as 2100. I have 3 blade waterwalker stump pullers blades on a 16 foot combee hull.
stump puller prop are old school whirlwind, not water waler, and most likely the major problem in your set up. with right prop that engine should be great with 2.68 box, try a set of superwides.
:alaska: If you ain't living on the edge, you're taking up to much space.

15x8 Alumatech hull, with enclosed cab, aluminum cage, LS 3, 6.2 aluminum block ffi, 2.7 Balistic Box, sensinich superwide 3 blade. Built for year around riding in Alaska

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Re: Motor/gearbox/prop help

Post by stpeteairboater » Fri Apr 15, 2016 4:07 pm

Props are waterwalker. The prop max rpm is 2200 per waterwalker and efficiency and safety drop off over that. My prop rpms range from 1,100 to 2,200 for normal riding. With the 2.68 that would put the motor rpms from 2,900 to 6,000 and averaged 3,200 cruising. With the 2.38 they dropped to 2,600 to 5,200 with 2,800 being the cruising rpm. I am happier with the 2.38 vs the 2.68 by far.

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Re: Motor/gearbox/prop help

Post by zz 502 » Fri Apr 15, 2016 4:36 pm

I say 3 blade Superwide from Sensenich and pitch it to your RPM pleasures. With that boat an set up it will go where you want it to go LOADED Down and still have fuel left.
Mine is a 15' Hamant zz502, 2.3 ox, 3blade Superwide Sensenich an its a tractor.
Jmo :old_glory:

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Re: Motor/gearbox/prop help

Post by junglecat » Fri Apr 15, 2016 5:07 pm

One of the club members had 632 with 2.55 box swinging 3 blade 84" R . He changed to 2.3 box and boat performs better and burns a lot less fuel.
Jungle Cat2 2012 Panther Thunder 14'x7'9"/ LiL John Rigging
Larry Smith built 427 SBC
2.68 Ox Box
82" 3 blade R
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