I'm no expert but 1.36 gears would drop the pitch of the prop needed. Some of the 272 owners will chime in as to the props they are running but I would assume something in the 24 range. With 1.36 you would need a 20-22 pitch and those aren't that common nor as effiecient (assuming 30 is the "ideal" prop).

More info will come I'm sure.

 

I had sb 300hp mpi's with Alpha's 1.50 and 23 pitch spinning 4800 to 5000 rpm. My quess is with 960 to 1000hp total, the pitch would be 28 to 29 with the bb's and 1.50.

 

A couple guys on here have 272's with 540's. I'm sure they'll be posting prop info soon.

 

Thanks t500hps

 

Where are you figuring your HP from and is that dressed out marine HP or DYNO bare with headers?

With a 630 DYNO HP I run a Bravo 1 28P. Now what a 1.36 would need I don't know.
On BAM's Prop calculator @ 12% slip it figures you would need about a 25pitch with the same RPM.
So If I were to go 1.36 gears I could theoretically run my original 25P Mirage props.

If you are going from 260HP 5.7 Merc motors then your prop probably is a 23 Mirage.
By my guesstimating with 500HP DYNO, the 23 Mirage will put you in the ballpark and play from there.
I would say maybe a 22Hydromotive would suit you better but that is.....
JMHO.

 

PLUS++++++++++++

WELCOME TO THE BOARD :star: :star:

Looks like the Formula 272's are starting to dominate the boards. :laugher: :laugher: :shocked:

 

My HP figure is just a guess. I have 454 .030 over w/Rec port heads, Merlin intake, SRP 10 to 1 pistons. 850 Holley, MSD ignition and Crane FTH cam 534, 553 (.050 226/236) 112 lobe. Stainless Marine Exhaust. If I can find 1.50 gears cheaply than that is fine. Just trying to save money.

 

454 .030 over is about a 460 cid.
10-1 comp ratio with stock rect heads.
I'm no engine guru but I can't see more than 450 HP.

JMHO

 

Was just told that by a few engine builders in the area. Just a quess on HP. Do you think I can get away with 1.36 and a pair of 22 to 24 Bravo 1 props. The cost saving to me is important.

 

A .30 over 454 is 468 cu in. Mine was originally 454/420, punched to 468, Merlin, Holley, Comp 292H cam, 10:1 compression. I'm guessing 475 to 500 hp per side. As for gearing, I can't help you, I have surface drives. I think the 1:36 gears would be stronger, and you could find props that would work would be my guess. Of course, this advice is worth exactly what I cost.

Best of luck, keep us appraised of your decision.

 

By the prop calculator Spinning the motor @ 5200 it says 70MPH with the 22P and 77 with the 24P
I'm running 81 W/ 540 cid 9-1 comp 635HP dyno with a Bravo-1 28P 1.5 drive.
I can not see a 468CID being only 4 mph slower than me

Recalculating back to 4800 the numbers come to 70 with the 24P. and 5000 RPM @ 74MPH.
I think that may be realistic.

It takes a LOT of HP to make these old 272SR-1 "BIRDS" run fast. The longer "BIRDS" seem to run faster with the same HP.
I was expecting mid-upper 80's and by all calculations it should have done it.
But I have yet to see it, and I'm not alone with this problem. Several others have tried and are not any faster than me. Except 1 that "GUESSED" his HP to be around 700++ with shorty drives, in rough saltwater conditions.

 

I guess to answer your original question....
the 1.36 if available for less $$$ then YES you could run it.
The props are available and with Bravos available down to 22P you should be fine.

Keep us posted on your decision and progress.

 

Thanks to you all for the info. Will keep you posted in my outcome. Probably mid spring.
If anyone is interested in learning more about childhood stroke please visit our web site www.geocities.com/boothbrandi
Please pass on to any one interested
Thanks

 

The boat will perform better with the 1:50 ratio all around with the proper prop selection though.

 

By the prop calculator Spinning the motor @ 5200 it says 70MPH with the 22P and 77 with the 24P
I'm running 81 W/ 540 cid 9-1 comp 635HP dyno with a Bravo-1 28P 1.5 drive.
I can not see a 468CID being only 4 mph slower than me.

It takes a LOT of HP to make these old 272SR-1 "BIRDS" run fast. The longer "BIRDS" seem to run faster with the same HP.
.

78.6 gps with the above mentioned power.
302 SR1.

 

78.6 gps with the above mentioned power.
302 SR1.

I'm calling a "FOUL" on you Cuda . You forgot to mention "surface drives" and the guys a newbie here. No 272 with your engines and Bravos could keep up with you. :laugher: :laugher:
I agree with Obnoxious , 1.5s will probably give you the best overall performance.
1.36s take a lot of power or a light boat or a very high X dimension to turn.
My guess would be about 70 mph with 24" or MAYBE 26" bravos and 1.5 gears

 

Does anyone know where I can get a good price on a pair of 1.50 gear sets to rebuild mine?

 

Does anyone know where I can get a good price on a pair of 1.50 gear sets to rebuild mine?

forcnme, pm me, I have a pair of 1.50 Bravos off my 292 that I can make a deal on.

 

I'm calling a "FOUL" on you Cuda . You forgot to mention "surface drives" and the guys a newbie here.

Upon further review(post 11), the flag was picked up, there was no foul on the play. :laugher:

 

Upon further review(post 11), the flag was picked up, there was no foul on the play. :laugher:

:laugher: :laugher:

 

I say go with the 1:36 gears and you can run small pitch props - and they're a little faster....

spin the drive faster and the engine slower....

I switched my Imco's from 1:50 to 1:34 last year and dumped my 34p 4 blades in favor of 28p 5 blades....

I like this setup a lot!

 

I say go with the 1:36 gears and you can run small pitch props - and they're a little faster....

spin the drive faster and the engine slower....

I switched my Imco's from 1:50 to 1:34 last year and dumped my 34p 4 blades in favor of 28p 5 blades....

I like this setup a lot!

Major difference in technology between these two hulls. Don't know if the results would be the same. Azz heavy , non step , deep X against a staggered engine , stepped hull higher X , probably notched transom and gobs more HP.

 

By the prop calculator Spinning the motor @ 5200 it says 70MPH with the 22P and 77 with the 24P
I'm running 81 W/ 540 cid 9-1 comp 635HP dyno with a Bravo-1 28P 1.5 drive.
I can not see a 468CID being only 4 mph slower than me

Recalculating back to 4800 the numbers come to 70 with the 24P. and 5000 RPM @ 74MPH.
I think that may be realistic.

It takes a LOT of HP to make these old 272SR-1 "BIRDS" run fast. The longer "BIRDS" seem to run faster with the same HP.
I was expecting mid-upper 80's and by all calculations it should have done it.
But I have yet to see it, and I'm not alone with this problem. Several others have tried and are not any faster than me. Except 1 that "GUESSED" his HP to be around 700++ with shorty drives, in rough saltwater conditions.

Hi there Opie272!
What is this prop calculator you speek of and how would I go about using it? I am also looking for the perfect combination, prop - drive - motor. I am considering trying a 26 pitch Bravo 1, I can spin the heck out of a 25 pitch Mirage plus (over 5200 rpms on my 502), with 1.5 bravo gears.

Adam

 

Hi there Opie272!
What is this prop calculator you speak of and how would I go about using it? I am also looking for the perfect combination, prop - drive - motor. I am considering trying a 26 pitch Bravo 1, I can spin the heck out of a 25 pitch Mirage plus (over 5200 rpms on my 502), with 1.5 bravo gears.

Adam

Here ya go.
To calculate you have to put in what you know and go from there.
To change fields you have to clear out the theoretical and actual values then recalculate.

http://www.go-fast.com/Prop_Slip_Calculator.htm

 

It,s been a long time coming but finally got the boat done. I have a pair of 468's w/Rec port heads, Merlin intake, SRP 10 to 1 pistons. 850 Holley, MSD ignition and Crane FTH cam 534, 553 (.050 226/236) 112 lobe. Put new Bravo Transom assemblies and used 2000 1.5 gear ratio Bravo drives w/nose cones and 24 Bravo one Props spinning out. I had put full hydraulic external steering and increased my trim tab length by 4"(Bennet dual ram). Put the boat in this week end it ran 70.2 GPS at 5250 rpm what a disappointment.

I feel that my exhaust and the extra length on my tabs are holding me back. I had ran out of money and had to go with a homemade exhaust setup. They are GLM cast manifolds with Gil small block dry pipes 3.5" OD (now wet pipes) that I modified to fit. Going with that I no was going to hurt my HP but it only cost me a total of $725.00 for both engines compared to $4000.00 for Stainless Marine. I will try my hand an making Headers on day.

The tabs only come up to level with the haul not like K-planes that come up to negative. They seem to drag in the water more than before, hence scrubbing of speed.
I think I will put the tabs back the way they were and tune the carb a bit more and see what this weekend brings. Hopefully 1 to 2 mph more.

All yea thanks for the help with the gear ratio, 1.5 is where I need to be.