some drive ratio explaining
 

hi all, whats the diff between a 1.50 and 1.36 and which application are they best suited for......can you have 1.50 lower and 1.36 upper(guessing not:party-smiley-004:) want change from b1 to an xr and want to no which setup is better...its 26' pq with about 540hp n 580lb tq thanks

.14, I couldn't resist. The ratio is the number of turns of the input shaft in comparison to the output shaft of the drive. 1.50 turns to 1 turn verses 1.36 turns to 1 turn.

Unless you want to buy new props, keep the same ratio you have now. Not sure, but I would think the 1.5 would have more torque on a prop verses a 1.36. But when you change props to get the same speed result, I would think they would cancel each other out. I would think a 1.5 would have less stress, making the life of the drive last longer. I'm no expert.

There's no reason to use anything other than 1.5:1 on a V-bottom unless you have enough power to run out of prop selection, and by that time, you are going to be blowing bravo drives. Cats are a different story.

ok cool, i was looking to buy an xr lower with 1.36 gear ratio from the classified sec here(real good deal) and then try and find an upper but will keep looking for 1.5 thanks

On most drives, part of the reduction happens in the upper, and part happens in the lower unit. Multiplying the two ratios together gives the overall ratio. For instance, a typical SSM IIIA or V has a 1.31:1 upper and a 1.125:1 lower for a 1.48:1 overall. Typical Bravo has 19/16 = 1.1875:1 upper and 19/15 =1.266:1 lower for an overall 1.50:1

Fixx
 

A 1.50 drive ratio will make the boat accelerate quicker to its speed,a 1.36 ratio,,wont be as quick to jump on plane as the 1.50 but the 1.36 would be a stronger as to the 1.50 ratio..

would the transom assembly needto be changed as well

No.

You would also need to drop about 3" in prop pitch going from a 1.5 to a 1.36.
Like was said, no reason to switch to a 1.36 unless you are running out of prop sizes, which you shouldn't be with your combo.

The XR uppers are all the same gear count / ratio. The XR final ratio is all determined by the lower gear count. The standard Bravo and the XZ have different gear counts / ratio in the upper, but the lower is all the same. Hope this helps.

I disagree with the statement regarding V-bottom boats. On my single engined v-hull (which does over 100 mph), I picked up over 3 mph going from a 1.5 gear ratio to a 1.35. The props around 28 are the most efficient(lower slip %) as to slip when comparing them to their larger pitched bretheren. Also, as a prop increases in pitch, the blade is more parralel to the water, causing more transom lift. (ie the smaller pitched props tend to carry the bow easier with less trim.)

Just my documented observations on a couple of near and over 100 mph v-bottom boats.

Chris

Agreed. I had more typical rigs in mind. Over 100 mph, you are in a different league and are playing with a lot more power. What are you running?

Whipple stage X upgrade on a 600sci motor.

540 cu/inch (Callies crank)
Heads ported by Chapman racing
Whipple proprietary cam
4.0 Whipple Supercharger with MOAC innercooler

1067 hp at 6200 rpm

A far cry from my 600sci...which made 589 hp stock.

Chris

That's a pretty trick rig. Did you buy it down here in Portland? I was guessing you had to be over 1000 hp to get that kind of speed.

What are you doing for a drive?

Never mind- you can't see avatars and descriptions when you are replying...

:eek: I didn't know you could get 1000+ HP out of a 540? That's amazing! I have Dart Block 502's (509). Are your engines reliable? What Gas?

I guess it is all a matter of perspective...Teague gets 1200 hp out of a 565 spinning 6000 rpm...1335 hp out of a 565 spinning 7200 rpm...both on pump gas... my motor producing 1067 hp at 6200 rpm...doesn't seem all that remarkable.

I believe that Mercury's 1200 hp motor is 557 cu/inches...which is the same bore as mine...but with a 1/8 inch longer stroke.

Dustin has pulled over 1800 horsepower from a 582 on race gas.

My motor was rated at 1067 horsepower on 91 octane on Dustin's Dyno, and I get 92 octane fuel here in Washington.

The motor was built by Dustin Whipple...he is a friend of mine.

Chris

holllly crap thats is NICE :ernaehrung004: sure beats chit outta my 535 hp......frig me n i upgraged from 400 hp

I originally bought my boat from Tim of OCM with a Merc 600sci in it...It has since gone thru a few motor modifications :D

Chris

Cool,

I live about five blocks from Tim. If you ever bring your boat down to the Columbia and go roaring past St. Helens, let me know, and I'll listen for it. Maybe that will help motivate me to finish my rig instead of working all the time.

P.S. Sorry Paintman, this has degenerated way off topic...

bottom line...

1.5 gear ratio seems works great for most boats...but there are always boat/speed exceptions.

Chris