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Discussion Starter · #1 ·
I was thinking of lowering the gearing on my 670ho. I was thinking of two teeth on the small cog. Any experiences would be helpful. Is there enough adjustment in the TRA clutch to compensate for changes in gearing?

Thanks for any comments!

C
 

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Dropping 2 teeth will get that thing high in the air. Go one tooth, 2 will loose you alot of topend but give you massive takeoff.
 

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Discussion Starter · #3 ·
A friend of mine tells me that you have to change both the top and bottom gears, is he right?
 

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The chain can be used if only a tooth or two difference. Meaning if top is 25 and bottom 40 = 65 teeth. Going 24 top and 41 bottom still 65. More than 2 maybe 3 teeth difference might need a different chain. Thats kinda an experimental field when it comes to extreme gear changes and your local parts store can get you a smaller or larger chain if you do go radical.
 

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I don't really agree with gearing down twins, to figure your chain links just add your gears 24+39=63 divide by 2=31.5+40= 71.5 so you need a 72 link chain. So to figure if a certain gear set will work just add both sprockets teeth together then divide by 2 add 40. Just remember that chains are in 2 link seperations (68/70/72) so just get your numbers as close as you can.
 

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Discussion Starter · #8 ·
My reasons for a gearing change are:

1) There is a drastic power band hit right at the speed that I like to drive at on the trails (25-30 mph) and I would like to change that spot. I don't need any more top end.

2) I pull a sleigh and haul all the fire wood to heat my house so lower gearing wouldn't hurt!

Thanks for the posts.

C
 

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the stock gears are just about the best you are going to get, I tried different combinations and they are no better than stock.
 

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what is your gearing now?......My mach z stock was 26/44.I can change anywhere from a 24 to a 27 on top.Don't be afraid to try changing..............Dynamo Joe has done hours of testing on this and will tell you by dropping several teeth on top DOES NOT MEAN you'll lose top end.alot of it is based on clutching as well.Don't believe all that you'll lose top end stuff.try it.you should gain acceleration.
 

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machz830 said:
what is your gearing now?......My mach z stock was 26/44.I can change anywhere from a 24 to a 27 on top.Don't be afraid to try changing..............Dynamo Joe has done hours of testing on this and will tell you by dropping several teeth on top DOES NOT MEAN you'll lose top end.alot of it is based on clutching as well.Don't believe all that you'll lose top end stuff.try it.you should gain acceleration.

Yup, right on. I've seen ppl dropping 4 teeth smaller on the top gear and still hitting there same top end speed. I've droped 2 teeth and i'm still getting the same top end i've always gotten. I just get there faster.
 

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Discussion Starter · #12 ·
I got stock gears. 25/43 with a 9 tooth driver. The Summit X 670 has 21/43 with a 9 tooth driver. That's why I figured just a top gear change should work. Makes sense, I just don't know what, if any, clutching changes need to be made.

I think I am going to go with 2 teeth and see how it works. My dealer says if I go smaller than 23 teeth, the price goes up considerably because they manufacture the gears with a different material (can't remember what).
 

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A 21 tooth gear in HPE is $22.95, a 25 tooth gear is $26.95. Maybe he ment that because you would need a new chain it was going to be costly. You should have a 74 link chain now and you would need a 72 link chain for the other gears which that chain is like $45-$50.
 

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JoeyO said:
Yup, right on. I've seen ppl dropping 4 teeth smaller on the top gear and still hitting there same top end speed. I've droped 2 teeth and i'm still getting the same top end i've always gotten. I just get there faster.
So your sayin when you ice drag and drop your gears 4 teeth from stock, you take off like a bat out of hell and still get your same top end? So a 20/44 tooth configuration that hits 108 on the 1000ft and 110mph max, will be just as fast as the stock 23/44 config that hits 121mph on same lake 1/2hour after gear change? Your out of your mind. Once you hit your maximum rpm range the rotating assembly cannot go as fast as higher gears than lower gears that slow down the secondary, or lower gear. So when your top gear rotates 1.91 times to make 1 revolution of the bottom gear it will be faster than 2.2 times per 1 revolution? Come on now, think about it. When your sittin at 8900 rpms and your sled goes 108 then you bump up gearing back to stock and your hittin 121 at 8700rpms, thats basic arithmatic my friend, not a few hours of testing. I went through 2 gallons of gearlube changin gears and trying different ratios, and it took way more than hours more like weeks and lots of moola.
 

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when drag racing or running speedruns its very hard to get full shiftout. usually does'nt happen in such a short distance. think the dropping 3-4 teeth is pushing it a bit. i have dropped 1 tooth in gearing running speedruns and gained mph. think what he is looking for is low end power, as was stated, to pull a sled for hauling firewood. does'nt sound like this sled is going to be used for hole shots. so dropping 1-2 teeth on the gears i don't think is going to hurt anything other than a little more low end power. could always call the manufacturer and ask them there thoughts.
 

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cgies said:
My reasons for a gearing change are:

1) There is a drastic power band hit right at the speed that I like to drive at on the trails (25-30 mph) and I would like to change that spot. I don't need any more top end.

2) I pull a sleigh and haul all the fire wood to heat my house so lower gearing wouldn't hurt!

Thanks for the posts.

C
What you need to do is trade that 670HO for a Skandik.
I'm having a hard time envisioning your sled hauling firewood and sleighs, not to mention a favorite speed of 25-30mph.
 

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Yeah if your just haulin wood and sleds then id go down a few, but man, use a 2up sled for that...lol
 

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Where in Ont. are you? I'll trade you strait up for my SLE. Just what you need. Long track, two up seat, reverse, ele. start, ~80 short studs for them icey spots, lighted compass, and a nice warm breeze exiting the left side of the hood to warm your hands or defrost your glasses if needed. Heck I'll even throw in the saddle bags.

That'll fix that "drastic power hit".
 

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Discussion Starter · #19 ·
I'm up in Kenora. When I get time, I love to get out on the endless lakes where WOT is quite common. There can be only one (sled in my garage)...so I chose a performance sled. If it were possible, I would love to have a Skandic or a Bravo for hauling wood. Anyone want to convince my wife of that? :eek: I'll probably hang on to the Z for a long time 'cause the way the used market is, she is worth more to me than what I would get for her. And you know she has never blown a belt on me! Even pulling a bull elk out of the bush!:D
 
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