Gearbox talk

[JAMES]

What is the big difference from those who ran them ?? 288vs the 268 and 237 .1 im looking at another 268 but im open motor is 383 with 450 hp dynoed

[SWAMPHUNTER45]

It is a process where you must match three elements.

Engine rpm
Prop speed
Gear Ratio

[JAMES]

well my engine target would be around 5400 my prop would be 3 bld r, or whispertip 79" im putting a new boat togeather and seen alot of 288 for sale reason why i asked

[firefight-n]

if your going with a 78-79 inch prop you'll want to stay around 2.3 gears. With 2.88 gears you'll want somewhere around an 81-83 inch prop. There are some calculation charts floating around here somewhere. Maybe talk to ffjpowell, I know he has that chart.

[SWAMPHUNTER45]

5400rpm mated to a 2.12 ratio would put prop speed at 2547rpm

I would run a 383 at 4800rpm or below but that's just my preference.

Either way a 2.12 or maybe 2.37 will work. There are a lot of 383 builds with similar prop sets to search on here and read about.

Those 2.8 drive ratio's are better served on a race boat or screamer engine not a iron block stroker unless your goal was to spin several huge wide blades at a very low tip speed.

[jeepinocala1111]

What is the big difference from those who ran them ?? 288vs the 268 and 237 .1 im looking at another 268 but im open motor is 383 with 450 hp dynoed

2.38 with a 80" r for your engine. I have the 2.55 just a bit much, power is great but everyday cruise could be better I have a heavier boat though.

[JAMES]

Yea no 2.1 i use to run 2.68 loved it lil higher rpms then i like at crusie but thats fine im going with at least 237.1 and prop would be 79 min. Just getting combo ideas thanks ANYONE GOT A BOX FOR SALE OR PROP PM ME HAVE CASH SERIOUS BUYER

[SWAMPHUNTER45]

A 2.68 at 5400rpm puts your blade speed at 2014rpm if your wanting to spin up the 2.37 is probably the best ratio for you putting blade speed at 2278rpm.

Give darrin and Patti a call they have huge data bases an can offer up a lot of wisdom...may surprise you

[Des Moines Boater]

I have a 383 stroker also. I have 80 inch NGR blades with a 2.7 gearbox. I too think a 2.37 would be a better set up for that engine. I'll probably stay with the 2.7 for awhile. I got beat up pretty bad when I mention going to a lower ratio. Some think the 2.68 is the best for every set up. I run dry without a problem but a 2.37 would spin my prop at my cruise speed but at a lower rpm. I have a ballistic gearbox and love that it is quiet.

[One Eyed Gator]

Do not get hung up on prop RPM, it has to do with tip speed as well.

Motor GB Ratio Prop Dia Prop RPM Tip Speed mph
5400 2.37 79 2278 535
5400 2.37 82 2278 555
5400 2.55 79 2118 497
5400 2.55 82 2118 516
5400 2.68 79 2015 473
5400 2.68 82 2015 491
5400 2.88 79 1875 440
5400 2.88 82 1875 457

To me I would run the 2.55 box with the 79" R setup. or the 2.68 with the 82" R Setup. Cant speak for the whirl wind I have no experience with there products.
Just my 2 cents for what it's worth

[swamper2]

mY 406 WORKS GREAT WITH THE 2.38 AND 3-80IN. R'S

[jeepinocala1111]

mY 406 WORKS GREAT WITH THE 2.38 AND 3-80IN. R'S

You have the correct setup. I have a 2.55 and believe I would benefit from going to a 2.38 just a bit more tip speed making it more efficient.

[One Eyed Gator]

Jeep sent you a PM

As long as you have motor making plenty of torque and a good torque curve I will have less effect than say on my stock 5.3

Kind of like you can run 44" tire on a Toyota with a 22R if you have the right gears. Put a strong v8 in it and the gearing is not as critical.

[nomad41]

I had the 2.38 with an 3 blade 80" R. I swapped with a guy in La. For a 2.68. And changed to an 82". For me I love it. I probably have more hp then you will have. I am pitched pasted the 3 mark and wot is 5400. But I can't remember the last time I hit wot. And I carry a lot of stuff on my boat. Still lighter then last boat.

[JAMES]

Nomad I had to 268 on my last boat this boat will have a whole bunch more motor that's why I want to keep a 268 I did make my decision on how I'm going with for my motor and will be about five weeks before it's done but it will be true horsepower true torque dino tuned ready to sit on my boat it will be 450+ hp in real good torque obviously it's costing me more and I want to spend but I'm getting all forged motor Good quality so i want a good box/prop combo

[Tony480]

2.68 oxbox hands down. Best warranty and customer service in the business. Just look how many used oxdrives you see..that says it all

[Moritz]

I have a 2:68 stinger with 50 hours will sell

[warrior-p]

I have a 2.38 ballistic with 60 hrs for sale if your interested with four whirlwind blades to go with. I am looking for a 2.3 century belt drive

[Prototype]

James,

A few things to consider and most disregard this? The gear is an option and so is the PROP! The magic formula to size or weight of hull or load cannot be defined. Most just estimate from advice and are happy with it? That's Okay but fine tunning a boat could get into serious money for optimal performance. I didn't see anything on your hull or load or rigging to recommend anything? I do own four ox 268's two with clutch's and two without that are not for sale if it matters? 12 foot laser to 17 foot 190 aluminum hull, all propped correctly!

[Moritz]

I have A stinger 2:68 gear Box and A Felber big block 496 600 hp I am wanting to sell 10,900 going to a bigger engine

[GGolden]

If any one is looking to sell a gearbox I would be seriously buyer if the price is right.. 2 to 1 up to 238to 1 it is going on 406 sbc


Sent from my iPhone using Southern Airboat

[BGREEN427]

There is a 1.9 to 1 precision on orlando Craigslist.

[SWAMPHUNTER45]

The selection of a gear or belt drive ratio should be an exact fit which perfectly matches your engines performance output to your propellers targeted rpm range where peak performance will be obtained. It takes some thinking, effort, research and data to hit it right. Most people who just "guess" will get it wrong. No two engines will perform the same unless built identical and even then it is not unheard of to see a 5% variance in output on a blueprinted build.

A dyno sheet can be a valuable data source and utilized to make an informed selection on ratio. If a dyno sheet is not available the engines cam*, displacement, stroke, compression ratio, torque and horsepower need to be known specifications. The differences between a 2:1 or 2.37 ratio can be significant in some engine builds and further magnified if mismatched again at the prop.


*cam data
Advertised duration
Duration intake / exhaust @ 050 degrees
Lobe separation angle
Lift intake / exhaust

[Prototype]

Swamp?
It's about like people searching old posts to look for a deal on a new to them drive?

Golden is posting to a year old post and probably lucky things havn't changed substantially. Other than scotty rolling him to the classifieds for a used something.

[SWAMPHUNTER45]

Exactly why I commented with "research" Proto, and your comments to James back in January ring true. That said a person cannot look at another persons choice without knowing all the specs and base the decision off of their choice. My Cadillac application is a prime example.