Correcting gear ratio with prop size

[Tgibson94]

Alright, sorry to jump to another boat and prop size..

I have a 98 regal 2100 lsr.
It has a 5.0L EFI 230hp motor. Currently it has a alpha one gen 2 with 1.62 gear ratio. And a 14-1/2" 19 pitch prop..
It does alright hut I believe it could be better.

I know the correct ratio according to the charts is 1.47
But is there a way to help the motor with switching up the prop?

 

[Scott Danforth]

Alright, sorry to jump to another boat and prop size..

I have a 98 regal 2100 lsr.
It has a 5.0L EFI 230hp motor. Currently it has a alpha one gen 2 with 1.62 gear ratio. And a 14-1/2" 19 pitch prop..
It does alright hut I believe it could be better.

I know the correct ratio according to the charts is 1.47
But is there a way to help the motor with switching up the prop?

Start your own thread. Hijacking isn't cool

 

[QBhoy]

Alright, sorry to jump to another boat and prop size..

I have a 98 regal 2100 lsr.
It has a 5.0L EFI 230hp motor. Currently it has a alpha one gen 2 with 1.62 gear ratio. And a 14-1/2" 19 pitch prop..
It does alright hut I believe it could be better.

I know the correct ratio according to the charts is 1.47
But is there a way to help the motor with switching up the prop?

Maybe should go on your own thing and ask, but no, a 1.47 wouldn’t be close to the norm on your engine. The only 5.0 that rarely has that ratio is an mpi on a performance boat.

 

[Tgibson94]

I have a 98 regal 2100 lsr.
It has a 5.0L EFI 230hp motor. Currently it has a alpha one gen 2 with 1.62 gear ratio. And a 3- blade 14-1/2" x 19 pitch prop..
It does alright but I believe it could be better.

Is there a way to help the motor with switching up the prop? Different pitch?

 

[QBhoy]

I have a 98 regal 2100 lsr.
It has a 5.0L EFI 230hp motor. Currently it has a alpha one gen 2 with 1.62 gear ratio. And a 3- blade 14-1/2" x 19 pitch prop..
It does alright but I believe it could be better.

Is there a way to help the motor with switching up the prop? Different pitch?

Hi. That would be likely the right ratio for that set up. At a guess, you may get away with a little pitch on her. I’d guess the 19” would be a good all rounder for that boat perhaps,
What kind of rpm and gps speed are you getting full throttle and trimmed up well ? Really fundamental to know that at the very least, before anyone could give you an answer. Anyone that does…either has an identical boat and drivetrain…or they are guessing.
Tell me gps and rpm full throttle and what kind of prop you have now…and I could likely give you some decent assumptions and opinions on a fair number of different props and how they tend to generally perform.

 

[airshot]

Help the motor with what ?? What is the wot rpm? What is the motor rated at wot ??

 

[jimmbo]

What is the Engine's WOT Rpm Range, and what is the top Rpm is it getting? Mercruiser or Volvo?

 

[Scott Danforth]

Start with what is the current ROM at WOT

What speed are you getting at WOT

What is the issue you perceive to have

What is the actual scale weight of your boat

Is your compression numbers within spec (135-150 psi)

 

[jimmbo]

I have a 98 regal 2100 lsr.

It does alright but I believe it could be better.

Is there a way to help the motor with switching up the prop? Different pitch?

You are asking a lot of a 5 liter on a 21 ft boat. It is not known for torque, and the Higher HP versions of the 5 Liter are even weaker in the Torque department.
If you think that changing props is going to turn a Tugboat into a Hydroplane... Not gonna happen
There is no such thing as a Speed Prop, that will add an extra 10mph. In most cases, changing Pitch(while remaining within the same Prop Lineage) and remaining within the WOT Rpm Ranges results is almost no difference in Top Speed. You will see a difference in Acceleration.
Now if you have a light Hull, a Prop with different Blade Design, Blade Area, Rake and Cupping, may allow the Motor to be mounted Higher on the Boat(not easy with an I/O), and different Trim Angles. Some props designs can actually lift the entire boat vertically, reducing Wetted Area. In these Scenarios, you might see a few mph faster.

 

[tpenfield]

I have a 98 regal 2100 lsr.
. . . .
It does alright but I believe it could be better.

Is there a way to help the motor with switching up the prop? Different pitch?

Depends on what you mean by 'helping the motor' . . .

Helping it on the lower end . . . (time to plane, water sports, etc). You could go DOWN in pitch (so 14-1/2 x 17 pitch), as long as your top end RPM is currently on the lower end of the rated RPM range for the engine.

If you mean helping on the high end (i.e. top speed), that would be called a 5.7 (or 6.2) engine. (i.e. a fork lift upgrade)

Typically boats come with the correct propeller for all-round performance. Lots of folks try to perform 'propeller magic', but there is only so much that can be done, and usually helping one part of the performance spectrum sacrifices the other end of the spectrum.

 

[Scott06]

I have a 98 regal 2100 lsr.
It has a 5.0L EFI 230hp motor. Currently it has a alpha one gen 2 with 1.62 gear ratio. And a 3- blade 14-1/2" x 19 pitch prop..
It does alright but I believe it could be better.

Is there a way to help the motor with switching up the prop? Different pitch?

As others have mentioned what is your current WOT rpm ? What mph are you getting on GPS and what is the current prop? Is it a basic Aluminum black max or similar ?

Is you engine in a good state of tune - no performance issues?

I have a 21 ft sea ray with a 5.0, I have a 4 bbl carb vs your efi but more or less should be the same.
Swapping props is always a trade off unless you are horribly under or over pitched. If you go down in pitch you will get better hole shot at the expensive of top speed. up in pitch vice versa. If you want better pulling for watersports consider a 4 blade but not sure what you are looking for based off given info.

 

[jimmbo]

I would Not put my faith in GPS speedometers on a boat. They will measure speed across the Bottom of the Lake/River, but not speed across the water, as they fail to take any current into account

 

[Scott06]

I would Not put my faith in GPS speedometers on a boat. They will measure speed across the Bottom of the Lake/River, but not speed across the water, as they fail to take any current into account

Sure but better than the dash dreamometer for prop slip cals

 

[jimmbo]

Only if runs are made in opposite directions over the Exact same Distance, as 5 mph current becomes a 10mph difference between the directions when using GPS

 

[airshot]

GPS uses satellite beams and the time and distance between them, current makes no difference other than your boat will actually be faster going with the current due to less drag !!!

 

[QBhoy]

GPS uses satellite beams and the time and distance between them, current makes no difference other than your boat will actually be faster going with the current due to less drag !!!

Not technically true really. If there is a 5mph current and you are going with it. You’ll be running 5 mph more than you actually are, according to the gps. So for the purposes of propping a boat…not ideal perhaps. If we are being picky about things . But I’d rather that, than go from a dreamometer pitot dash effort

 

[Scott06]

Not technically true really. If there is a 5mph current and you are going with it. You’ll be running 5 mph more than you actually are, according to the gps. So for the purposes of propping a boat…not ideal perhaps. If we are being picky about things . But I’d rather that, than go from a dreamometer pitot dash effort

picky? I think we got a bunch of bored guys waiting for spring , or maybe ran out of beer....

yes correct but we will correct for current in the slip calcs later on....

 

[QBhoy]

picky? I think we got a bunch of bored guys waiting for spring , or maybe ran out of beer....

Haha. No doubting that !

 

[airshot]

Not technically true really. If there is a 5mph current and you are going with it. You’ll be running 5 mph more than you actually are, according to the gps. So for the purposes of propping a boat…not ideal perhaps. If we are being picky about things . But I’d rather that, than go from a dreamometer pitot dash effort

Yes your boat is goung to go faster as it goes with the current and the gps will show that speed, but your boat is not going faster than what the gps shows!

 

[QBhoy]

Yes your boat is goung to go faster as it goes with the current and the gps will show that speed, but your boat is not going faster than what the gps shows!

Very true. But for the reasons of propping…I suppose I can understand some of the thinking above.