eng./outdrives/ratios/?

[starsnstripers]

OK bare with me here i'm a little confused and in need of some assistence. Going from a 250ci L6 165hp to a 292ci L6 200hp mercruiser outdrive-prealpha 1.65 i believe. I was told the 292 was sluggish and a low rpm motor. I think the 250 must be the same in rpms. So if i use the 292 with the hp it has can I change the drive ratio to get more prop rpms? Wouldn't i want to go to a 1.50 OR ? comments/recomendations? (without recomending V engine)

 

[FreeBeeTony]

Re: eng./outdrives/ratios/?

Think I would leave it at 1.65:1......

 

[Don S]

Re: eng./outdrives/ratios/?

Use the present gear ratio, and find what prop it takes for the bigger engine. If you have to go over, say a 21 pitch, then to keep the effenciency up you may want to go to a ratio change. But I really think you are over estimating what is going to happen at the prop, and it's not going to be 200 hp.

 

[Bondo]

Re: eng./outdrives/ratios/?

But I really think you are over estimating what is going to happen

Ayuh,..........
She'd need to be 1 snotting little 292 to worry about the outdrive Ratio.......

 

[starsnstripers]

Re: eng./outdrives/ratios/?

Yes Don, i understand there wont be 200hp at the prop but in reference to the higher hp than the 250ci. The 250ci the boat had was running a 19P prop. So your saying with the extra hp it may run over the recomended 3900-4300 rpms so i might just change to a 21P prop to get it to the recomended wot and gain the efficiency I'm looking for?

 

[Don S]

Re: eng./outdrives/ratios/?

Run it with the 19 and see what you get. Adjust from there.

 

[starsnstripers]

Re: eng./outdrives/ratios/?

OK, I'll do that and if it over revs then try a 21P right? Oh speaking of props, I have two 19P props that came with the boat but i'm not sure what the Dia. is. There are #s 4873146A40 do you just measure it or whats the formula? Whats the largest diameter you can have on a prealpha ? Thanks

 

[Don S]

Re: eng./outdrives/ratios/?

OK, I'll do that and if it over revs then try a 21P right? Oh speaking of props, I have two 19P props that came with the boat but i'm not sure what the Dia. is. There are #s 4873146A40 do you just measure it or whats the formula? Whats the largest diameter you can have on a prealpha ? Thanks

Post that over in the prop forum, bet you get the answer.
Link to Prop Forum

 

[starsnstripers]

Re: eng./outdrives/ratios/?

Ok thanks for the advice on the hp/ratios

 

[starsnstripers]

Re: eng./outdrives/ratios/?

Geesh Don, Sending me over there with 90% outboard guys. I might get an answer in about 6 days! ha ha Btw glad to see you faired the storm out there.

 

[achris]

Re: eng./outdrives/ratios/?

Geesh Don, Sending me over there with 90% outboard guys. I might get an answer in about 6 days! ...

I resemble that comment!!!

If it eases your mind. My unit is running 1.65:1 and I have 220hp at the prop.

See you over there. (prop forum)

Chris.......

 

[180shabah]

Re: eng./outdrives/ratios/?

Stick with the 1.65, you'll be fine.

I am running 175hp through 1.81 gears turning a 21" prop. Hoping to be about 220 by spring though

 

[starsnstripers]

Re: eng./outdrives/ratios/?

Yeah, i'm going to see what happens. Seems thats the way to go from everyone. Thats a good thing i didn't want to have to invest in another drive or new gear change. My drive may even be a 1.68 I think thats the other ratio from this era. Not much difference but i'd like to know what i have. Anyone know the difference?

 

[MikDee]

Re: eng./outdrives/ratios/?

Wait a second here, couldn't you just pull off the top cover on the outdrive, and count the gears to find out the drive ratio? I know I replaced the gears on my 78' 305/228hp Mercruiser Type 1, yrs ago when water got in there, & cooked them. I believe they were 1.5X1 reduction.

 

[Don S]

Re: eng./outdrives/ratios/?

He already knows what gear ratio he has, it's a 1.65, just like every other 160/165 Mercruiser had. He's just thinking he needs a different gear ratio because the 292 is rated (NEW) at 200 crank shaft HP.
The thing that everyone keeps saying is run what you have and check it with your 19" pitch prop. Don't just go off and start replacing gears for no reason.

PS: The 1.68:1 ratio is in an Alpha I Gen II outdrive, not an old 1 drive.

 

[starsnstripers]

Re: eng./outdrives/ratios/?

Yeah, 1.65 i spun the drive and it's not 1.5. I'm taking the avise and running it. Seems at most a prop change. Thankyou, See following forum on this outdrive something i noticed might change ordering parts

 

[achris]

Re: eng./outdrives/ratios/?

PS: The 1.68:1 ratio is in an Alpha I Gen II outdrive, not an old 1 drive.

Sorry Don, it's one of those rare times again ....

The 1.68:1 was run on a few early 160s. The ratio in the Alpha I Gen II drives is 1.62:1. I know 'cause I got one.

Chris.................

 

[Don S]

Re: eng./outdrives/ratios/?

Sorry Don, it's one of those rare times again

It ain't that rare! :redface:

I was talking with a customer about his 1.68 VOLVO drive earlier that day. Guess where the number came from...... Oops.

 

[MikDee]

Re: eng./outdrives/ratios/?

He already knows what gear ratio he has, it's a 1.65, just like every other 160/165 Mercruiser had. He's just thinking he needs a different gear ratio because the 292 is rated (NEW) at 200 crank shaft HP.
The thing that everyone keeps saying is run what you have and check it with your 19" pitch prop. Don't just go off and start replacing gears for no reason.

PS: The 1.68:1 ratio is in an Alpha I Gen II outdrive, not an old 1 drive.

"Sorry about that", As Maxwell Smart used to say
But yes, I would run what is there "run what I brung", the 19P, and check the rpm, then prop to suit, simple as that.