Which Belt Drive Ratio ?????? Help!!

[ffjpowell]

I have researched all the previous posts and am a little confused....

I am currently having a boat built and am ready to order the Belt drive and prop... I am going with the 81.5 R's for blades.. Motor is a 383 stroker, DYNOED @ 440 Torque (5000rpm), 425 HP (5400rpm), going on a 14x8 with poly, 2 fat mans up and triple below, walkboards, etcccc... It is a ride boat (90%) and occasionally a work boat (10%) with heavy loads. Don't care about top end and more concerned about running dry ground and cruising RPM and carrying the heavy loads.

I have spoke to several people (manufactures and others) and have got responses from 2.3 - 2.68 ratios. I guess I am not understanding the differences in how they would work for my application.. so....

My question is which Belt ratio to go with for my application???

Please help!!!

[odcjohn]

go with a 2.68 with a 2 blade s or 3 blade r

i have one guy running a 2 blade s with a 2.38 on a 383 with little more power and it pushes like a freight train not a speed demon but great ride/hunt/work boat

good bless

[jeepinocala1111]

You better make sure this is correct because if you get the ratio wrong you will be cruising at a high rpm. And you do not want to spin that prop to slow. Find someone with that setup and find out the true cruise rpm. Your boat builder should know what you need. You may want to consider a gear box and no belt. I have a 2.55 stinger with a 3 blade ngr and like it may lean towards a 2.38 in the future.

[CarMotorBarge]

What engine RPMs do you want at WOT? Also are you planning to use a 3 blade?

[ffjpowell]

Tnk u so far.

5400 max and yes a 3 blade?

[ffjpowell]

Why a gearbox? Whats the benefit?

I am not a huge fan of the sounds a gearbox makes, the rock crushing freaks me out. I like to be able to hear any possible issues...

[CarMotorBarge]

The gear box is lighter. That is the primary advantage. So the 3 blade likes to be in the 2000 to 2200 RPM range at the prop. You are getting the short hub so you need a little more tip speed so you need to be closer to 2200. 5400 / 2.52 = 2143. The 2.52 is a good choice.

[barhopper]

I run a 16 x 7.5 heavy boat. Same motor with a little more hp and a 2.3 belt. I turn it 5100 at about 2.5 on a three blade r. If I was doing it over I think I'd go to a 2.5, more pitch, more blade length. Better low end. I don't care about fast but I need all the getter done I can get.

[ffjpowell]

Thanks for the responses. I appreciate it.

[ffjpowell]

Do yall think i would benefit going to a longer blade? Short hub to med hub??? To increase tip speed or would i be going backwards.
How does the length of the blade equat to the numbers 5400/2.5=2143
I am leaning towards the 2.5... based on the numbers thus far.

[BenBad]

Here is what I have been using to come up with prop speeds and gear ratios.
http://www.hoverhawk.com/propspd.html

[SWAMPHUNTER45]

No disrespect to the good folks in Pennsylvania who produce an excellent belt driven product and have been pioneers in the industry.

I laugh at the rock crusher comment for a gear drive as I run a "ROTATOR" aka rock-crush-tor.

Having resisted a gear drive, I can tell you that my Rotator with 4 S blades hooked up to one of the stronger big inch engines in the swamp is taking the torque and not crying about it. Not bad at all really, some will produce a growl or lash noise at idle or deceleration but mine is quiet as a drive costing $2,000 more and we are very happy.


ScottyRoll, DoDoBird and Cocoa18 ran similar 383 set ups back a year or two ago maybe reach out.

I'm thinking 2.37 for R and 2.68 for S, but that's just an opinion from someone who is not a sbc expert so take it for what that's worth.

[Des Moines Boater]

My boat is a 13.5 x 7 with no poly and I have the same engine as yours. I sold a rock crusher sounding gear box and went with a 2.7 Ballistic. I don't know about the R or S blades. Mine has the NGR blades pitched past the 3 mark. The Ballistic is quiet and only weighs 70 pounds. I hear the Ox Box is also quiet. The 2.7 pushes my boat anywhere I want to go. It runs dry with no problem. Don't forget the gear box is right handed and the belt drive is left.

[CarMotorBarge]

Do yall think i would benefit going to a longer blade? Short hub to med hub??? To increase tip speed or would i be going backwards.
How does the length of the blade equat to the numbers 5400/2.5=2143
I am leaning towards the 2.5... based on the numbers thus far.

If you want push on the hill, I would get the medium 3 blade hub. The increased diameter will give you more push on the hill. You will lose some top end speed (MPH), but you are probably OK with that.

Also with the longer hub, I would recommend the 2.67 instead of the 2.52. The additional gear will help you get more pitch in the prop and you will still have adequate tip speed.

So for comparisons, here is what I am currently running on my LS3. I have a 4 blade R with the short hub (prop is 83.5" in diameter). I am pitched at 13 to 13.5 degrees and my WOT RPM is 5300 on the water. I am using a 2.68 Rotator. The boat runs really good on the hill. You can plug these numbers into the calculator above.

I am going to put a 3 blade R with the short hub on the boat this week. I will lose push on the hill, but I am doing this because I plan to do a little racing Labor day weekend. The shorter prop snaps faster and has more top end. Need to see how many A/C boats I can outrun with my 5 seater barge.

[Deano]

No matter the percentage capable, I reckon that number would be entirely
contingent on how many are willing to line up and risk the embarrassment.

[scottyroll]

Jason,

If you are only going to spin your engine up to 5400 then I would recommend the 2.37. The 3blade that you mentioned is a good fit regardless of the ratio. I am not a fan of the 2 blade S especially after switching over to a 3blade profile.

I was running a 355 SBC governed @ 5k the last time you saw me. I am now running a junk yard LS set to the same limit for longevity if we can call it that since it already had 130k+ miles when it showed up to the shop. It's a very light setup all things considered and I am content with its performance...until I find a well priced turbo/blower package of course! lol

[StingerDrives]

Why a gearbox? Whats the benefit?

I am not a huge fan of the sounds a gearbox makes, the rock crushing freaks me out. I like to be able to hear any possible issues...

The "rock crusher" sound comes from a loose a gearbox. New gearboxes are built tight and over time as the gears lap into each other they naturally wear and become looser. Properly maintaining the gearbox with good oil goes a long way and reduces wear on the gears. Another reason for the "rock crusher" noise is bad bearings. The bearings themselves can make an awful lot of noise when they're bad.


Any new gearbox that leaves Stinger (for an airboat) cannot be turned by hand. We build them tight to make them quiet. Customers typically report that the only things they hear are the blades and engine.

[jeepinocala1111]

Why a gearbox? Whats the benefit?

I am not a huge fan of the sounds a gearbox makes, the rock crushing freaks me out. I like to be able to hear any possible issues...

The "rock crusher" sound comes from a loose a gearbox. New gearboxes are built tight and over time as the gears lap into each other they naturally wear and become looser. Properly maintaining the gearbox with good oil goes a long way and reduces wear on the gears. Another reason for the "rock crusher" noise is bad bearings. The bearings themselves can make an awful lot of noise when they're bad.


Any new gearbox that leaves Stinger (for an airboat) cannot be turned by hand. We build them tight to make them quiet. Customers typically report that the only things they hear are the blades and engine.

My stinger gearbox has zero 'rockcrusher' noises. I would only think that after they wear in some you maybe get noises from not taking care of them or prolonged sitting the bearings may start to rust at the top that will also make noise but mine has been on the boat for many years and I hear zero noises from the box. But for a suggestion to stinger 'if they do get loud' use a different gear profile it will work the same except never give noises. I have never heard a 'rockcrusher' sounding gearbox myself.

[nomad41]

Welcome aboard Sharon. I run a stinger and its an older one and there is no rock crusher noise from it. Its as quiet as the new ones.

[Deano]

AFAIK, that 'rock crushing racket' being referenced typically comes from a different box that uses spur cut gears rather than the helical cut gears Stinger uses. I've never heard a Stinger make a racket that could remotely rival one of those (particularly an older one).

Sharon, it's good to see you here and especially, making yourself available.

[warrior-p]

I have tried all the gearboxes and the best isnthe ballistic. However, I do have a ballistic 2.38 for sell with approx 60 hrs and four whirlwind blades.

[Rick McC.]

I have a 2/1 belt drive turning a three bladed whirlwind prop.

It rumbles a bit at idle, but is pretty quiet otherwise.

Edited to add:

425 HP 454 Edelbrock crate engine with a dual feed 750 Holley.

The hull is an 18X8 (plus two foot grass catcher) aluminum with no poly. We run over rock and oyster bars from time to time (saltwater boat), and didn't want a shitload of screw holes and poly shreds to deal with. Rigging is all stainless.

The belt drive is rated for 500 HP, but we've had two belts break in 10 years, so far. Because of that; I don't stand on the throttle from an idle. Hopefully, that makes it easier on the belt.

I should have provided more info yesterday, sorry about that.

[br,lc,LA]

Are you 100% sure if Peak TQ was at 5000 and that your HP peak is at 5400? If that is the case the your TQ curve drops quick...

I am always in the favor of aiming for my HP peak to be at WOT with the prop toward the upper end of its efficiency range (about a 500rpm range) and in your case with 81" that range is 1700-2200(+50) depending on prop manufactuer (Whirlwind provides a lot more data online than Sensenich so that where I get my #s.). Thrust is function of utilized shaft HP and RPM and that is where you get your ground power from...

Spinning 2140 at peak shaft HP would be a very sweet spot so I agree a 2.52 belt would be nice. You also have to look at the whole picture also. What size boat, how heavy, how big a loads you plan to run, so gearbox weight shaving is helpful also. And there are a couple gearbox manufacturers that have the art and backlash issues well worked out so the noise of the past you refer to is becoming well a thing of the past. (marvel of modern day engineering and quality CNC tools)