Supermileage Vehicle

[cmj]

Ohhhh guys.. Sleeves aren't modifying the stock block (unless you're sleeving for a => diameter, then machinework is needed).. it's just dropping in some extra parts. Internals are no limit!

[supermileage]

It has also been suggested that we use a NiCom or Nikasil coating on the cylinder. Does anyone know more about this and the possible benifits?

[cmj]

Anything that reduces piston to cylinder friction is going to reduce mechanical resistance. It just depends on how much the coating is going to cost vs how much it effects your goal. Ceramic coating piston's is another option.

[some_other_dave]

If I recall correctly, Nikasil is a part of aluminum cylinders which are then etched to bring the silicon nodules to the surface. (I think; I could be confusing this with Alusil!) This provides a hard surface for the rings to move on, but you need to use different rings than with cast-iron liners.

I don't know if cast-iron (i.e., cheap!) liners can be Nikasil treated or not.

There's an outfit called LN Engineering that makes Nikasil cylinders for air-cooled engines like old VWs and Porsches. Google will tell you their website, and you can ask them about costs and materials and such. My guess is that if there is any benefit it will not be worth the expense, but that is just a guess.

-soD

[TenEightySalomon]

Weight is truly the biggest factor in these style of competitions. Whatever you are doing you want to make sure the weight of the car is kept at an absolute minimum.

Since I assume you are going to be doing coast-burn style technique, you also need to make sure your engine is tuned to the optimal speeds you will be traveling at the actual competition. Ultimately the teams that win these competitions are those who have best tuned their specific vehicles to the rules/conditions of the sanctioning body (is this one Shell or SAE?) and to the actual track?

Ultimately sleeving the cylinder from the obnoxiously oversized/overpowered 150cc to something smaller is necessary but you also need to ensure you have some efficient means of transferring this power to the wheel (aka drivetrain and minimizing losses here is a big thing as well).

Are you doing this at a university level? How much access do you have to engine diagnostic equipment such as a dyno, wideband 02 metering, dataaq, etc?

Some more info on the project would be helpful in order to answer some more questions - I've got a good amount of experience and had some success with SuperMileage in the past let's say...

[Patrick]

1. Change the bearings to ball or roller type.
2. Machine all the excess mass off the crankshaft.
3. Machine the cooling fins off the flywheel and use ram air cooling (or no cooling at all if the engine will only run for short periods).
4. Change the ignition to an external battery-powered type and remove the magnets from the flywheel.
5. Change to dry-sump lubrication.
6. Machine away most of the piston skirt so that only a small sliver is left to guide the piston down the cylinder.
7. Use only one piston ring.
8. Use a chrome-plated piston ring.
9. Coat the piston with teflon.
10. Use the lightest weight oil you can find.
11. Change the intake valve timing to close when the piston is only 1/2 way down the cylinder (for a modified Atkinson cycle).
12. If you do #11, increase the mechanical compression ratio up to about 15:1 (or more) since the effective compression ratio will be less.
13. Use an axle clutch to reduce rotating mass if the bicycle freewheel doesn't work.

[ConnClark]

I assume your going to be using bike tires so its best to pick the ones with the lowest rolling resistance. Tires with a harder rubber compound will have less rolling resistance. I doubt that cornering and braking will be an issue so get a set of time trial tires with a very hard compound .

There are a few other things that effect rolling resistance too. see this link
Bike Tire Reviews- 4 Things To Know About Rolling Resistance | Cycling-Review.com

Other than that tune the engine lean, route the air intake under the seat and eat at taco bell before the race.

[Frank Lee]

You may learn the most by researching what past winning teams have done.

[TenEightySalomon]

Originally Posted by supermileage

It has also been suggested that we use a NiCom or Nikasil coating on the cylinder. Does anyone know more about this and the possible benifits?

Sounds like you guys are off to the right track, the engine is truly where you are going to make or break your mileage. Our biggest focus points were the weight and efficiency of our engine. Both of these we did a ton of SimuLink and Matlab calculations and really found out aerodynamics play little role in the equation. I'm not sure if the rules have changed at all but when I was a part there were speed requirements (or should I say speed limits) in place and we discovered at the speeds we were traveling it played a very small role in the efficiency or performance of the car.

I would immediately suggest sleeving the engine but paying alot of attention to the thermal properties of the engine as believe it or not, the motor can obviously run "too cold". In most applications heat is of major concern (when it comes to robbing power) but since the motor runs so little I can suggest actually heat wrapping the motor to keep heat in. When we did it we actually machined off all the cooling fins and actually wrapped it in reflective heat (the gold foil type) shields, I know Laval uses simple aluminum foil to effectively do the same thing. There have been many good suggestions on the site but I would be careful when considering options as you want your motor to be reliable and trustworthy because having a motor that only starts 1/10 of the time is not friendly to deal with.

The biggest area's you will gain is by minimizing all losses of efficiency from where the fuel enters the bottle to the contact the drive wheel (and obviously front or "steering" wheels do). CVT's are by nature pretty inefficient and I think you would have better luck running detailed calculations and sticking with a fixed gear ratio than messing around with CVT's. Ultimately you would need such a small CVT and it would have to be fairly well tuned and precisely matched to your vehicles power outputs to the point it would become time-wasting to tune and match. Since you have an idea on the speeds you need to travel in the competition this should serve as a great baseline to begin calculations and simulations for optimum gear selection. Classically, direct drives or chain drives are more efficient than CVT's, of course a transmission could fix this but you have to ask yourself whether the extra weight/complexity of the project is truly worth the effort of investing time into.

Anyways, my 0.02 before heading out of the country for awhile...

Good luck and hopefully some others will put in their thoughts on this as well...

[rfdesigner]

Originally Posted by supermileage

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.

You don't mention how the vehicle is to be driven... EPA course? P&G acceptable?.. etc.

If you're P&Ging then rotational losses on the engine aren't going to be soooo problematic, clearly you want as much preformance as you can get so an atkins cycle is good, you can tune the exhaust and inlet to just one narrow rev range making the engine run easily at that point etc. but if you have to run near tickover then parasitic losses will suddenly dominate, in which case I'd be concidering going electrical on everything and regulating.. i.e. electric oil pump, electric coolant pump etc. then pop in a permanent magnet 'alternator' some DC-DC electrics and then everything can be run as little or much as you need.

just 'brain-dumping'

Derek
(Ususally working on ultra low power radios, i.e. 3mW transcievers.. that's 3mW power consumption, not radiated power, hence my interest in low power vehicle electronics)