4.3L++ Which Gear Ratio to Use?

[imported_TheMan]

Just read a post on the upper gear ratios for someone with a 4.3L engine and saw some posts by assorted people (bondo, wca_tim, etc.).

I would like to order an SEI outdrive but am looking for the best bang for the buck. I've acquired most of the pieces for my engine upgrade (edelbrock 2114 intake (vortec), vortec heads, edelbrock 1409 carb) and figure it will be in the 215-225 HP range as a guess. It is a non-balanced shaft engine.

I'm looking at recommendations from users as to which outdrive ratio I should purchase. I wish there was a way for me to test, but I don't think there is. With the current boat set up I'm turning 4600 RPMS on the 2:1 gear ratio and topping out at ~39 MPH with a fully loaded boat (1000lbs people+gear). Probably some other performance related issues to work out too such as water logged foam, excess equipment, crappy bottom paint... I think the engine at least is tuned pretty well at the moment.

The common sense solution would be the 1.81 ratio used for Merc, and is what I was thinking until I read the last post. Seems Bondo uses the 1.64.. anybody able to comment/offer opinions?

Boat is used primarily for wakeboarding right now with some occasional tubing and general cruising. Thanks in advance!

 

[180shabah]

Re: 4.3L++ Which Gear Ratio to Use?

For your setup I would use the 1.62:1. Merc uses 1.47, 1.62 and 1.81(H) on the 4.3MPI which is rated at 220hp. Your power should be right in that neighborhood.

I have a similar boat(18' Mariah) with a 4.3LX(4bbl, non vortec). It is rated at 175hp, and with a 1.84 ratio I run props that range from 19"-23". If I ever get around to doing the head swap(I've had them for almost a year) that 23"er will probably end up being my primary. A drive ratio change would help keep me in the lower pitch range.

 

[wca_tim]

Re: 4.3L++ Which Gear Ratio to Use?

I was really pleased with the 1.81 in my 18 foot checkmate. and it also ran good behind the 383 I replaced the 4.3 with. I swapped it out to a 1.47 the other day, You'll be fine whichever way you go.

If you're a little more interested in top end, then go 1.81,if you're a little more interested in holeshot, go with the 1.65. theyre probably close enough that you'll be happy with either...

 

[Bondo]

Re: 4.3L++ Which Gear Ratio to Use?

If you're a little more interested in top end, then go 1.81,if you're a little more interested in holeshot, go with the 1.65.

Ayuh,....

I Agree,... But I think you've got That part Backwards....

 

[wca_tim]

Re: 4.3L++ Which Gear Ratio to Use?

Ayuh,....

I Agree,... But I think you've got That part Backwards....

Guess I should have explained what I was thinking there a little better. Hopefully I'm starting to get a handle on this.

Since higher pitch props (of similar design) require a little more torque to accellerate, but turn through the water a little slower per speed, a higher pitch prop turned with a gear ratio that will give about the same wot max rpm will generally give a little better top end (up to say 32" pitch) and a little poorer holeshot. Whereas a lower pitch prop it is the opposite. This is my current understanding based on a of reading, some of my own recent experiences, and observations made by others.

I was thinking that if went with the higher gear, would be running a lower pitch prop to get approximately the same rpm at wot.

my boat was a little faster with the 1.81 gear ratio, then with the current 1.47, but running a solid hub 29" prop on the river (where it is not uncommon to catch a little bottom or hit things once in a while) seemed like a recipe for disaster... I've tried a half a dozen different props on the current set-up and am still a few mph slower than the best with the 1.81 29" combination.

 

[Bondo]

Re: 4.3L++ Which Gear Ratio to Use?

Ayuh,....

But,.....
Most of the posters here are running Standard Props,... Which are Commonly available in pitches from 15" to 23",....

You're talking about Hot-Rod applications....

 

[wca_tim]

Re: 4.3L++ Which Gear Ratio to Use?

Point taken. Sometimes I forget that not everyone thinks in detail about getting the absolute most out of everything... or thinks through the many possible reengineering options for things like this...

especially in the case of two gear ratios, that under the circumstances being considered are probably going to give little or no difference in performance outcome once propped right...

I also forget that where I live there are some really good shops and that I can drive to three shops within 20 minutes that I know of and buy or even borrow used props anywhere from 15" to 30" pitch, with a number of other options if I just call one of the guys who just have a lot of props around from their own playing or side businesses... add another 10 or more shops if you expand the drive to an hour or so...

thanks for the reminder.

Ayuh,....

But,.....
Most of the posters here are running Standard Props,... Which are Commonly available in pitches from 15" to 23",....

You're talking about Hot-Rod applications....