Supermileage Vehicle
 

I am part of a team creating a supermileage vehicle for a collegiate competition. For the competition we are given a Model 9 Briggs and Stratton engine. This is an L Head or Flat Head engine. We would like to convert this to a overhead valve and possibly an overhead cam engine. I was wondering if anyone has seen this done or has done this? Or if anyone had tips on how to do this? We would like to know if we need to make a custom head or if there is an existing head that we could adapt for this use. I would also like to hear tips and suggestions on other things we can do to improve our mileage. We have the carbon fiber aerodynamic body under control, but would like to hear other ways of improving efficiency.

Back when they still used the 2 hp Briggs, the folks at The University of Akron just built a custom head. I think it was OHV w/ pushrods & rocker arms.

Most teams would sleeve the cylinder to reduce displacement. Use/make a real low Rpm cam that's good for a lot of torue.

Weight, Weight, Weight. Pulse & Glide has always been a big part of that competition. Just make sure you gan get the engine to start when you need it to. Make sure your alignment is spot on.

Ceremic bearings in the wheels. Make sure when gliding that the only part of the drivetrain spinning is the rear wheel.

Don

Thanks for the input, we are working on sleeving the cylinder and currently have a chain drive with a sprocket from a bike so the only thing spinning is the tire when we are coasting. We are looking into possibly using a cvt, is this a bad or good idea in your opinion?

Thanks Again

cvt usually has a lot of loss. A centrifugal clutch and chain with sprockets is the way to go. If you need gearing, consider an internal hub bicycle gear on the rear wheel. However your power output may be too much for bicycle equipment.

Are there any rules limiting what you can do?

HIGH COMPRESSION. Especially with those sleeves you will be able to raise compression greatly. Just make sure you have adequate tuning. The only problem I see with high compression is if you employ P&G is the amount of energy you will lose turning the engine over (IF you bump start it)

For the transmission we are currently using a centrifugal clutch with a chain and sprocket...

There are rules limiting what we can do, although there are really not that many, if you would like to look at them in detail you can view them on SAE's Supermileage site...i cannot however post the link as i am a new member here...

For the engine we many not modify the block but we are free to modify the head and any internal components. For the transmission, steering, body, chassis, ect. we are able to do whatever we like, as long as it passes safety inspection.

so, no sleeving?

For our SuperHighMileage Car we basically grafted Honda 50 OHC bits on top, as well as sleeving it down. We erred in making the sleeve's interference fit way too aggressive and the cylinder cracked in competition. It was working fabulously up until that point.

Here are the official rules for modifying the engine:

B2.3 Engine Modifications
The base Briggs & Stratton engine may be modified in any manner that otherwise complies with these rules with the following exceptions.

B2.3.1 Cylinder & Crankcase
The cylinder and crankcase must be identifiable as components of the base engine supplied by Briggs & Stratton to the entrant.

B2.3.2 Crankshaft Support Bearings
The crankshaft support bearings (journals) may be altered or replaced but must be retained solely by the Briggs & Stratton crankcase.

B2.3.3 Piston Friction Surface
The piston friction surface may be altered or replaced but must be retained solely by the Briggs & Stratton crankcase.

NOTE: Encapsulating another manufacturer's engine within the Briggs & Stratton cylinder/crankcase assembly is in violation of these rules.

B2.3.4 Crankcase Ventilation
Crankcase cannot be ventilated to engine intake air.