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Lower unit gear ratio Question??

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Old 09-09-2009, 09:46 AM
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Default Lower unit gear ratio Question??

SO,

I need to buy a new lower for my outboard, I have a choice of 1.62:1, or 1.75:1 ratio. My 225 had a 1.62, and jumped on plane, since I have had the 250 with the 1.75, it was having trouble getting the boat up, but ran great up top, once it hits 2000 rpm it takes right off, just having trouble reaching that. I also know I am propped correctly, because once planed and running WOT and trimmed, I get the 5800 the motor is rated for. I know I may have some other ignition, or injector related issues, but need the lower before I can diagnose them, just want to make the right choice. Which lower will allow the motor to spin up faster?? I know I should know this, but having trouble relating it to my car days, its been a while, and just dont want to go the wrong way. Also, I am going to try the SEI lower, cant beat the price, I'll let you all know how it works out.
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Old 09-09-2009, 10:35 AM
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The 1.75 is the engine turning 1.75 times to one rotation of the prop. So going to a 1.62 will be worse on your engine. Every engine is different depending on two stroke or four stroke. Sometimes the two strokes get more power with porting that changes the torque curve and can make the more powerful engine sluggish at slow speeds. Most of my outboard race engines were 1.87.
I would stick with the 1.75.
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Old 09-09-2009, 11:24 AM
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Correct. 1.75 is the lower gear ratio of the two. Try different props.
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Old 09-09-2009, 12:46 PM
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Originally Posted by Brad Zastrow View Post
The 1.75 is the engine turning 1.75 times to one rotation of the prop. So going to a 1.62 will be worse on your engine. Every engine is different depending on two stroke or four stroke. Sometimes the two strokes get more power with porting that changes the torque curve and can make the more powerful engine sluggish at slow speeds. Most of my outboard race engines were 1.87.
I would stick with the 1.75.

Appreciate the info, I just couldnt think straight
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Old 09-09-2009, 12:49 PM
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Correct. 1.75 is the lower gear ratio of the two. Try different props.
I dont think its the props, turns the correct RPM on the high end, and as far as prop design, these are the same 2 props I used with the 225. Obviously the 250 has an ignition, or injection related problem on the bottom end, just want to get the best ratio for the boat once its figured out, also to rule that out in the troubleshooting/testing.
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Old 09-09-2009, 06:04 PM
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Rick,

Lee Austin is kinda up the road from you and can give you any insight you might need to get in the direction you want to go.

TC
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Old 09-09-2009, 09:43 PM
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Rick,

Lee Austin is kinda up the road from you and can give you any insight you might need to get in the direction you want to go.

TC

Hey Trent,

I'll give ya a call soon, just been crazy busy. Are ya gonna make it to clearwater??

Rick
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Old 09-09-2009, 10:29 PM
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I do not know what engine you have but the only difference between the 225 and the 250 is the 250 may be allowed to rev higher and that is how it gets the 25 more horsepower. If this is true, it may not have any more torque on the low end and this might be the reason it is sluggish on the bottom end. In other words the 250 has to pull a higher gear than the 225 and does not have anymore torque or horsepower on the low end. If the 250 does not have anymore torque at 1000 to 1500 rpm than the 225, I would go with the gear ratio you had on the 225.
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Old 09-10-2009, 11:38 AM
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I do not know what engine you have but the only difference between the 225 and the 250 is the 250 may be allowed to rev higher and that is how it gets the 25 more horsepower. If this is true, it may not have any more torque on the low end and this might be the reason it is sluggish on the bottom end. In other words the 250 has to pull a higher gear than the 225 and does not have anymore torque or horsepower on the low end. If the 250 does not have anymore torque at 1000 to 1500 rpm than the 225, I would go with the gear ratio you had on the 225.
I run a 250 EFI now. That was kinda my thought, but 25HP shouldnt make that much of a difference getting the boat on plane, obviously I have another problem. I ordered the lower in the stock 250 ratio, 1.75. I also have a lead on a MAD EFI System, once I get the lower installed, gonna swap to that along with a hopped up ECU
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Old 09-10-2009, 05:50 PM
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What pitch prop are you running now? 3 or 4 blade?
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