defrance between 1;61 gear 1;89

[wicked pissah]

i dont know how the gear ratio works i have built a 350 v8 about 280/300 hp im pushing a trophy 1986 2160 dropped in this v8 with 1;89 gears because we boat at 6000 ft i have a 15/19 prop on it now but i have to go up to a 21p my hp is incredible im topping out at 5000 rpm 36mph and i still have throttle left over so should i put a 21p or change back to 1;61 i dont know how it works changing gears weather im turning faster or slower gears

 

[Maclin]

Re: defrance between 1;61 gear 1;89

You need to go back to the lower number gear ratio I think. The ratio number tells you how many revolutions the engine makes for every revolution of the prop.

Typically the more HP the lower the ratio.

I bet you would need to go to a 1.5 and maybe even a ~1.3 if you bring the boat down to lower elevations with that engine.

 

[Maclin]

Re: defrance between 1;61 gear 1;89

More specifically, I would put the 1.6 in with a 21p and see if that keeps your revs at 5000 or below. A 23p may be in your future even then.

 

[tpenfield]

Re: defrance between 1;61 gear 1;89

defrance is not a word . . . maybe it is French

 

[steelespike]

Re: defrance between 1;61 gear 1;89

A 1.89 Is really close to what some 3.0s run at 1.98 Also 1.32 for a 260 hp is reasonable.
Lower numbers are harder to turn but can produce higher speeds and keep a big motor within its rpm rating.
I would think your 1.89 would be very hard to get a big enough prop to get the rpm down to the limit.
I think a 1.61 is typical for a 4.3.
I forgot about the elevation maybe a 1.61 isn't so bad.

 

[CoffeeHound]

Re: defrance between 1;61 gear 1;89

defrance is not a word . . . maybe it is French

I feel sorry for the boaters that can not read the Sea, the winds., the clouds,, or a weather report ,, but can read words that are miss-spelled just to get a click on their ladder of posts !!

 

[theBrownskull]

Re: defrance between 1;61 gear 1;89

I would go with 1.47:1.

 

[jestor68]

Re: defrance between 1;61 gear 1;89

Since props are available in pitches up to 28", there is no problem adding pitch to get your rpm done within the recommended range.

What brand of prop are you running now?

The quick answer to the OP's question is; the 1.89 means more gear reduction to the prop than than the 1.61. Means the prop is turning slower with the 1.89 compared to the 1.61.

The 1.89 gear ratio seems perfectly suitable for his 6000 ft altitude operation.

The statement; "5000 rpm with throttle left" is not very helpful for selecting a prop. You need to open it up momentarily to see where the rpm peaks(not past 5800).

 

[wicked pissah]

Re: defrance between 1;61 gear 1;89

sorry about the miss spell im not very good at spelling but boy can i build a great motor from scratch ok so if i have this right my motor is turning 1;89 rev for 1 turn of the prop i need less revolutions from my motor it will turn the prop faster lowering my overall rpm and putting more burden on my motor so 1:61 will do that

 

[wicked pissah]

Re: defrance between 1;61 gear 1;89

jestor 68 thanks for your post what i ment was i dont want to push my motor over 5000 rpm but there is a lot of throttle left i could go to 6000 rpm but that would blow my nice new motor i need to prop up to get my rpm down to 4800 where i want it

 

[jestor68]

Re: defrance between 1;61 gear 1;89

sorry about the miss spell im not very good at spelling but boy can i build a great motor from scratch ok so if i have this right my motor is turning 1;89 rev for 1 turn of the prop i need less revolutions from my motor it will turn the prop faster lowering my overall rpm and putting more burden on my motor so 1:61 will do that

You are complicating this too much. It's very simple. All you need to do is put on a "bigger" prop with more pitch. I am guessing that a 21" or maybe a 23" would hold your rpm down. I can't be certain until I know how high the rpm will go now.

Since these props are available in 1" increments, it's easier to fine tune the selection(but you need to know where the starting point is).

Jam that throttle wide open for a short burst too see how much rpm it'll get, so we can then say; you need to add this much pitch.

The 5.7 motors of that year group usually ran a range of 4200-4600 rpm.

The higher gear reduction(1.89) is easier on the motor than the lower one.

Is this your boat?

 

[jestor68]

Re: defrance between 1;61 gear 1;89

jestor 68 thanks for your post what i ment was i dont want to push my motor over 5000 rpm but there is a lot of throttle left i could go to 6000 rpm but that would blow my nice new motor i need to prop up to get my rpm down to 4800 where i want it

If you really think it run generate that much rpm, put a Solas Amita(aluminum) 15-3/10 X 23 pitch on it. That should reduce your potential rpm by about 850 rpm.

 

[wicked pissah]

Re: defrance between 1;61 gear 1;89

yes jestor68 that is my boat i have a 280 1;61 in my shop along with the 1;89 that is on the boat now im trying to find the right combo of drive and prop the boat originally had the 4cyl volvo in it and that was clearly not big enough to push that boat so i ripped it out along with the out drive 270 2;15 volvo dropped in a v8 so now im trying to dial it in im going to look in to that prop i know i need a bigger one

 

[Maclin]

Re: defrance between 1;61 gear 1;89

A V8 would have come with a ratio more in the range of 1.5, so the 1.8 is definitely too much gear reduction. The 1.6 you have in house is closer to what you need. And at your elevation it is probably exactly what you need. Again, with the 1.6 I would start with a 21p and see what the WOT numbers are, then see if another pitch change is needed.

 

[Bondo]

Re: defrance between 1;61 gear 1;89

yes jestor68 that is my boat i have a 280 1;61 in my shop along with the 1;89 that is on the boat now im trying to find the right combo of drive and prop the boat originally had the 4cyl volvo in it and that was clearly not big enough to push that boat so i ripped it out along with the out drive 270 2;15 volvo dropped in a v8 so now im trying to dial it in im going to look in to that prop i know i need a bigger one

A V8 would have come with a ratio more in the range of 1.5, so the 1.8 is definitely too much gear reduction. The 1.6 you have in house is closer to what you need. And at your elevation it is probably exactly what you need. Again, with the 1.6 I would start with a 21p and see what the WOT numbers are, then see if another pitch change is needed.

Ayuh,.... I agree,... Donno how the elevation will play out, but the 1.6 is the place to start,...

Sell the 1.8,... it's of no use to ya....

Originally Posted by tpenfield
defrance is not a word . . . maybe it is French

I feel sorry for the boaters that can not read the Sea, the winds., the clouds,, or a weather report ,, but can read words that are miss-spelled just to get a click on their ladder of posts !!

Ayuh,... Works fer Me,....

I call it a sense of Humor,....

guess I shoulda posted Twice, eh,..??

 

[jestor68]

Re: defrance between 1;61 gear 1;89

yes jestor68 that is my boat i have a 280 1;61 in my shop along with the 1;89 that is on the boat now im trying to find the right combo of drive and prop the boat originally had the 4cyl volvo in it and that was clearly not big enough to push that boat so i ripped it out along with the out drive 270 2;15 volvo dropped in a v8 so now im trying to dial it in im going to look in to that prop i know i need a bigger one

I thought we were dealing with a Mercruiser stern drive. Regardless, more gear reduction is what I recommend in order to turn the larger diameter props at your working elevation.

Adjust my prop recommendation accordingly, since the Solas I mentioned was for a Mercruiser.

For your 280, it looks like the Solas Titan SS 15-5/8 X 23 would work well with that gear ratio. Since it's only a few bucks more than the Volvo aluminum prop, I would go with the Solas SS.

 

[dufrain]

Re: defrance between 1;61 gear 1;89

I went through this same deal with a 2.0 gear ratio alpha gen 2 mercruiser when I swapped out the 3.0 for a 350. I tried a 26 it was too much so next I tried a 23 ss michigan rapture. It pulls good planes out easily with 7 people on board and runs around 48gps and 4800rpms. It works fine. My boat is a 99 chaparral 1930 sport Le that originally came with a v8 but someone swapped in a newer 3.0 and 2.0 alpha. But if you have the 1.61 you may as well put it back on there and the 19 prop may be just right. And the motor would probably stand the rpms but I know on the mercruiser alphas your not supposed to spin them much past 5000