The mysterious bravo III ratio

Stodge

OK I've look in the usual places and have struck out.  I'm trying to find out what the gear ratio of my Bravo IIIs is supposed to be.  Little history:  few years back I hit a submerged object and damaged both drives.  The lowers were replaced with re-man lowers, but the uppers were rebuilt by my mechanic.  I later got "upgraded" from 22p props to 24p props.  The result is that I go 28MPH at 3250RPM and get 1.1MPG doing it. 

But...

At WOT the engines only get to about 3600-3700RPM.  

Clearly there is something wrong somewhere.  My starboard engine was replaced with a long-block, so new block, heads but old fuel injection, computer and exterior items.  I'm not inclined to blame the engines at this point.

Going back to 22p props will help to get more RPM and get on plane better (won't even go there).  But not going to gain 1000 RPM in the process.

So the big question is:  What ratio should my drives be, or what ratio are the Bravo III powered by 5.7L 350 Mags that others have in there 342s??

I read that 2.2:1 is "common".  It is also the highest and would cause the effects I'm seeing if in fact I'm supposed to have 2.0 or 1.81 IMHO.

Anybody know what ratio their drives are?

Willhound

Standard is 2:20.

reneechris14

2.2 on my 05 342
Turn the motor by hand and have a help watch the prop 2.2 for the motor and 1 single rotation for the prop. 2.0 or 1.81 you will need a 15 pitch prop or you will have a 342 tug

Stodge

Thank you for the information.  We'll see if it helps.

Handymans342

So if you have a diesel motor which turns slower than a gasser why not put a 3.1 drive on it??

YYZRC

Alswagg said:

342 with 5.7 came with 2.2 ratio early models came with 24 pitch. Then as the Rpm increases came along 22 pitch is the proper pitch.     

@Alswagg , is it true that Rinker propped boats based on dry weight?

PickleRick

@Alswagg what would you venture to guess my 4.2 220 hp gearing would be?  Max rpm 3600 rpms.  Roughly 9000 lbs boat. Bravo 2

Im currently wot and hitting about 25mph between 3000 3200 rpms

I want to re prop but I'm adding air conditioning as well as verifying my boost this weekend.  I want to rule out performance and i want to include the extra bow weight before i make the prop switch to hit the proper rpm.

I wanted a 4 blade big cow prop but they only make it in a 16p as the lowest i believe.  My current 3 blade is 17p so id think id need to go down to a 13p on a 4 blade or 15 on another 3 blade. I want to use a prop calculator but i don't know my gearing. I have not found a stamped serial number and my data sticker is gone. Id be happy with 3400 rpm full of water and fuel, 3600 ideal with. Half water and sub half tank of fuel

Handymans342

Alswagg said:

Handy , the diesel runs let’s say 3,000 max if you put a 3-1 ratio drive,the prop shaft would only spin 1,000 rpm.  Not enough to hardly move the boat.  A good ratio for diesels are 1.5-1. At least that gets the shaft rpm up to 2,000 rpm.  For instance a gas 5.7 with a 5,000 rpm engine that has a 2.2 ratio has a prop shaft rpm of 2,270 rpm.  Very close to the optimum for a heavy boat. 

Well you just better have something that moves on the lake in a few weeks

Handymans342

PickleRick said:

@Alswagg what would you venture to guess my 4.2 220 hp gearing would be?  Max rpm 3600 rpms.  Roughly 9000 lbs boat. Bravo 2

Im currently wot and hitting about 25mph between 3000 3200 rpms

I want to re prop but I'm adding air conditioning as well as verifying my boost this weekend.  I want to rule out performance and i want to include the extra bow weight before i make the prop switch to hit the proper rpm.

I wanted a 4 blade big cow prop but they only make it in a 16p as the lowest i believe.  My current 3 blade is 17p so id think id need to go down to a 13p on a 4 blade or 15 on another 3 blade. I want to use a prop calculator but i don't know my gearing. I have not found a stamped serial number and my data sticker is gone. Id be happy with 3400 rpm full of water and fuel, 3600 ideal with. Half water and sub half tank of fuel

Rick, get rid of our drive and straight shaft it. 

PickleRick

Id have to re engineer the boat to do an inboard.  Id need a rudder, flip the Motor around to add a tranny and chain drive shaft.  Most likely move the fuel tank forward or dual side tanks.

Id be better off ditching inboards for 2 300hp diesel outboards