OD Units

[greg]

Anyone aware of an OD Unit more compact than a generic Laycock British OD Unit? Gear Vendors and USA gear are both physically larger though similar. Thanks. If this is "Top Secret/Sigma Classified" just ignore.

[Sumner]

Anyone aware of an OD Unit more compact than a generic Laycock British OD Unit? Gear Vendors and USA gear are both physically larger though similar. Thanks. If this is "Top Secret/Sigma Classified" just ignore.

I see you are posting Motorcyle questions.  Does this pertain to a bike or car??  If a car the following are my thoughts.

You can also get 4 and 5 speed transmission where one or more gears can be set up as overdrive.  We are doing that this year and others have done it. 

Personally I think this is a better route than say the Gear Vendors (or other transmissions with a fixed OD ratio) as you have many more choices as to what the OD ratio will be now and in the future.  I feel that for most cases if you are really trying for that last little bit of speed that the Gear Vendors 18% overdrive is too much of a spread and will result in too much rpm drop going into overdrive in a lot of cases.  People have set records with them though.

And of course a quick change can get you there in all kinds of steps also.  For a car over 250 mph I think the best tuning tool would be the 4 or 5 speed with the quick change, but that can be a lot of bucks in one step.

The importance of gearing to maximize your top speed at your peak hp rpm can not be overstressed.  If you read the links below you can see why even though our HP peak was at 7400 all that we could pull was 7000.

You can read more of my thoughts on the subject if you want here:

http://purplesagetradingpost.com/sumner/bvillecar/bville%20-%20LSR%20Thoughts-5.html

and here along with some thoughts from Tom Burkland:

http://purplesagetradingpost.com/sumner/bvillecar/bville%20-%20LSR%20Thoughts-6.html

c ya,

Sum

[greg]

No, actually for a shaft drive bike. Cannot go third member route due to unavailability seals and bearings, cannot go primary route due to design issues and that leaves deep gears or OD unit. Carefully installed 1.28 OD box weighing 50 lbs sounds better than cutting new gear shaft and respective gear.

[Sumner]

No, actually for a shaft drive bike. Cannot go third member route due to unavailability seals and bearings, cannot go primary route due to design issues and that leaves deep gears or OD unit. Carefully installed 1.28 OD box weighing 50 lbs sounds better than cutting new gear shaft and respective gear.

Make the shaft shorter and drive a jack-shaft with it that then has the ability to run different sprockets on the one end with chain drive to a sprocket on the rear wheel.  You are running Modified aren't you??

c ya,

Sum

[greg]

At this point it will be butchered, more than modified. With the engine configuration the 90 degree boxes I've found (to go with sprockets) offer as much or more difficulty with my fab work than sticking with the inline parallel shaft gearhead concept.

[greg]

Lenco and Laycock: most compact.