Alpha one gears, power upgrade

[Shabah180]

Someone has told my buddy, who currently has an alpha one, 4.3l with a 1:47 that if he where to upgrade to a 5.7l (carbbed) he would have to change the gears because the current gears are set up for a 4.3l arnt as strong as they would be if it came with a 5.7l.
Never geard it before is that true?
Thanks for the professional info!

 

[Bt Doctur]

1.47/ 1.50 is for a V8 1.84 is the V6 ratio

 

[Shabah180]

1.47/ 1.50 is for a V8 1.84 is the V6 ratio

My first boat years ago had a 3.0 with a 1.47 alpha. In theory, if he has a 4.3l with a 1.50 he will he okay? Theres no such thing as a 1.50 with "beefier" gears is what im asking i guess.

Thanks for the reply.

 

[Bt Doctur]

Didnt think you could get a prop with that low of a pitch for a 3.0 ,that should have been the 1.98 .If he keeps the V8 under 300 Hp a 5.7 will be fine.

 

[Shabah180]

Didnt think you could get a prop with that low of a pitch for a 3.0 ,that should have been the 1.98 .If he keeps the V8 under 300 Hp a 5.7 will be fine.

Honestly sir, it was was from a dealer and not a very straight one, i got the run around.. bad experience for a first purchase years ago.

Again thank you.

 

[Scott06]

The ratio between the various engines is just to keep WOT rpms in range given available prop pitches typically 17"-21". An alpha one is the same strength regardless of gear ratio. I swapped a 4.3 to a 5.0 kept the same 1.81 drive, just had to go from 19" pitch to 21" to keep rpms in line. I have about 60 hrs on it, beat on it pretty good with a loaded boat and water sports with absolutely no issues. As BT stated stay under 300 hp change gear lube regularly it will be fine.

 

[Shabah180]

The ratio between the various engines is just to keep WOT rpms in range given available prop pitches typically 17"-21". An alpha one is the same strength regardless of gear ratio. I swapped a 4.3 to a 5.0 kept the same 1.81 drive, just had to go from 19" pitch to 21" to keep rpms in line. I have about 60 hrs on it, beat on it pretty good with a loaded boat and water sports with absolutely no issues. As BT stated stay under 300 hp change gear lube regularly it will be fine.

Thanks, thats what i had thought originally but someones pulling the bigger horsepower proper gear ratio card. So it is possible to keep the 1:81 and prop to compensate. Best suited would be a 1:50 but it wont kill the boat.
Thank you sir for the info.

 

[Scott06]

Yes you can compensate within reason, as you can run out of prop selection. With a 5.7 and a1.81, unless the boat was real heavy you'd probably need a 23" pitch. You can always buy an drive upper if you can't prop around it.

 

[Shabah180]

Yes you can compensate within reason, as you can run out of prop selection. With a 5.7 and a1.81, unless the boat was real heavy you'd probably need a 23" pitch. You can always buy an drive upper if you can't prop around it.

Yes within reason, maybe my ratio is wrong too it may be a 1.65, but with the 70 hp or so jump can the gears that came factory withstand the torque of that tall of prop?
I know they roll off the factory floor with the best ratio, and if he needs to change it he will just to save grace its more to get the absolute regarding ratio's vs power. I know they change ratios in different elevations i have no idea if certain boats are designated off the line with the proper ratio for those elevations.
People are saying if they stay with the same gear ratio as the 4.3 the 5.7 will burn the gears out prematurily.
But all the searches with guys who have done this, have not changed it (within reason) from a power upgrade.

 

[Scott06]

Gear ratio has nothing to do with the gear strength only the reduction required for a given engine and hull combination to keep the engine in the correct WOT range. It's a matter of being able to prop it properly. If it were my project I'd swap the 5.7, try to demo props from a prop shop and see if you can keep WOT below 5000. If you can't you can always swap the upper later.

 

[Shabah180]

Gear ratio has nothing to do with the gear strength only the reduction required for a given engine and hull combination to keep the engine in the correct WOT range. It's a matter of being able to prop it properly. If it were my project I'd swap the 5.7, try to demo props from a prop shop and see if you can keep WOT below 5000. If you can't you can always swap the upper later.

Thanks scott inagree with you. This guys trying to tell me the friction and this and that will blow up the alpha drive and adament about it. Cause the 4.3l gear ratio cant handle the power of the 5.7. Hes just set in his ways i guess so i try not to absorb "wrong information" and get second opinions.
Thanks for explaining it!

 

[Rick Stephens]

Be nice to know what pitch he is running with the 4.3L. I'm running a 4 blade 21, I bet I wouldn't be able to prop up high enough for the added torque of a 5.7L. Pretty big jump in ponies too.

He probably missed the point the dealer was trying to make. Or maybe the dealer just bolluxed up the technical. If you start pushing the ponies you need a Bravo drive. If you up the torque you may need a lower ratio drive just so it can be propped properly and efficiently.

 

[Shabah180]

Be nice to know what pitch he is running with the 4.3L. I'm running a 4 blade 21, I bet I wouldn't be able to prop up high enough for the added torque of a 5.7L. Pretty big jump in ponies too.

He probably missed the point the dealer was trying to make. Or maybe the dealer just bolluxed up the technical. If you start pushing the ponies you need a Bravo drive. If you up the torque you may need a lower ratio drive just so it can be propped properly and efficiently.

Yes rick thats right. Like the guys stated above, that would be a main concern is running out of prop room. Hes a heavy duty diesel mechanic and tries to aplly his training onto marine applications and fires off advice and calls people morons if they dont share the same view.
There's formula's as well you can use to see in theory where you will be at. With ratio/rpm/prop pitch.

But scott is right i believe, it will not cause the drive to "blow up" the gears wont overheat, after all whatever prop your spinning, will be at the same wot rpm so your gears wont be moving any faster. Causing no i'll affect to the drive.

 

[Scott Danforth]

if you have the 1.62:1 drive, you can swap in the 5.7, however you will be at the limit of what you can get for props.

if you have the 1.84:1 drive, you will be outside the window of what you can get for props

 

[Shabah180]

if you have the 1.62:1 drive, you can swap in the 5.7, however you will be at the limit of what you can get for props.

if you have the 1.84:1 drive, you will be outside the window of what you can get for props

Good info man, it triggered a massive argument in a different forum. Seemed people where just pulling "facts" out of thin air and not backing any info up. I cant remember what ratio ive read i think its the 1:62 for the 5.7 needs to be converted to a 1:81 over 5000' elev.
im beginning to understand (finally) the basics of how the gears work. The input shaft would turn 1.81 times per 1 rotation of the prop. So its reduced gear ratio from what would typically be the ideal ratio. He would have to run a taller prop.

I dont have the calculation reference for the ratio/ prop/rpm all dodge gave me in front of me but when i get it i'll do the math and see where it would end up with a 23p prop. I have a bravo 3 so im not 100 on the avail prop sizes for this drive.

 

[Scott Danforth]

The 5.7 comes with a 1.47.

 

[Shabah180]

The 5.7 comes with a 1.47.

Ok thank you scott. You guys know a lot more than i do thats why i ask here. Always get good information thanks again for taking the time to chime in!!

 

[Rick Stephens]

This should help