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Hey all, it has been a while since I have posted. So I'd figured I'd catch you guys up on what I have been doing.
I am an active member of the University of New Haven's (UNH) ASME (American Society of Mechanical Engineers). This year the UNH chapter has decided to enter the 2009 SAE (Society of Automotive Engineers) Supermileage Competition. The task at hand is to make a lightweight vehicle achieve the highest mileage possible. The engine required for use is a Briggs and Stratton 475 Series Engine. The rules are far and extensive but frame and body design is widely variable. The vehicle must do 6 laps around an oval track using a predetermined amount of fuel. (In this case the fuel is Iso-Octane, expensive stuff)
This year UNH got last place unfortunately because we failed to complete the required 6 laps. But our estimated fuel mileage was 240 mpg. We unofficially beat two teams out of 25 giving us 23rd place. Now I know you are going to say how many flaws we have in our design but let it be known we had $1000 and a month to complete it. There is a lot of detail about the vehicle so I'll answer as the questions are asked.
This Years Car
Carbon Steel Frame
Three lightweight aluminum byclicle wheels
Push Rod Steering
Engine to Jack Shaft to Wheel Transmission (6:1)
All Stock Briggs and Stratton 475 Series motor (except parts listed)
Handle Based Throttle and Braking
Straight Pipe Exaust
Three Point Harness
Next Year's Car
Carbon Fiber Frame
Carbon Fiber Body (possibly unibody)
Carbon Fiber Based Wheels
Direct Power Chain Transmission (12:1)
Heat Sinked Carburetor Spacer
Dual Spark Plugs
Extended/Cold Air Intake Manifold
K&N high flow air filter
Handle Based Throttle/Braking
Climbing Harness Based Restraints
Straight pipe Exhaust
And of course ideas are always welcome.
Last edited by rcman50166 on Mon Jun 08, 2009 11:51 pm, edited 10 times in total.
Your missing some numbers. Whats the full model, type and code numbers? I wanna know exactly what engine you guys/gals are using.
When life gives you lemons...throw them back they suck!
Ask and you shall receive.
http://www.briggsandstratton.com/engine ... spx?pid=92
Good thing this wasnt a speed race
I gotta say though, 240 MPG isnt bad. Now why cant Chevy come out with something that awsome?
"I'm spending time without a gender for tax reasons. It's great if I get hit in the groin, but a total nightmare in the bathroom."
Obsequium parit amicos; veritas parit odium.
You are correct. The average speed could not exceed 25 mph. And 240 mpg is relatively bad. The first placer this year obtained 1820 mpg and the record is 3000 mpg.
My thoughts exactly. Especially when I saw the first place car. And the even more surprising thing was the all time record was set by a high school, not college.
Anyways does anyone have ideas that could help our team out? Next year we will have a near unlimited budget as everything will be sponsored.
on the chaindrive, POLISH the SPROCKETS!!! Mainly the teeth where the chain rides, for chain lube use "hot sauce" reel lube(find it in fishing tackle), if you use bicycle wheels, make sure they are perpendicular to the ground(not cambered like last years, roller ball bearings friction goes way up when side loads are applied).... Also, think about restricter plates, I noticed you're using k&n air filter, but remember that more air=more fuel to maintain stoich.... also on tires, depending on track surface, sometimes less pressure is faster, you don't want super hard tires on a rough(most racetracks have more texture than a lot of roads) surface because vertical deflection removes some of your forward energy, you want the tires soft enough to roll smoothly without transmiting track texture into a verticle plain of movement....
since you can modify crank bearings, find out what size bearings they are and get some micropolished bearing... plays a huge factor, also polish the crank and make sure and run a light synthetic oil....
some of this you may know, some you may not...
All very good information! We were think hard rubber tires but i guess I'll have to see what the track was like (I wasn't the driver)
But excellent information, who else knows stuff to share?
Last edited by rcman50166 on Tue Jun 09, 2009 11:28 am, edited 1 time in total.
Another item would be to see if you can modify the cam to make it an Atkinson-cycle instead of an Otto-cycle. To do that with a single cylinder engine, the intake will need an accumulator and reed check valve. This change on multi cylinder engines greatly reduces the high vacuum when pulling an intake stroke against a closed throttle. The accumulator can be a replacement for the intake heat sink you proposed.
If you can't modify the cam for an Atkinson-cycle, then the displacement may need to be reduced so the engine only runs at efficient throttle settings and shuts down at all other times.
Info on the cycle is here; http://en.wikipedia.org/wiki/Atkinson_cycle
Some teams in the past have sleeved the cylinder to make it a much smaller displacement. I'll have to check the current rules to see what is permitted. If you are allowed to install a second cam on the cam shaft, the engine can be throttled by the cam angle of the additional cam that delays the intake closing. This permits the throttle to remain mostly open for low intake vacuum. As mentioned earlier, an accumulator is needed to do this on a single cylinder engine.
EDIT.. I just looked at the rules. You can sleeve the cylinder and replace the piston. You can change the bearings but they must be retained by the original block. Nothing prohibiting custom camshaft push rods, valves, cylinder heads, fuel system, etc is mentioned. Direct cylinder unit injection is not prohibited as far as I can tell on page 10 of the rules. It looks like you must retain the original block and any bearings and cylinder sleeve must be retained by the block. Another engine inside the block is not permitted.
If you want ideas on modifying for the Atkinson-Cycle, PM me. Note, this applies only to the team. I won't go into high efficiency engine design with the general spudfiles by PM. I learned much of the theory by studying the Prius engine.
Last edited by Technician1002 on Tue Jun 09, 2009 11:43 am, edited 2 times in total.
Wow, I'm glad I asked for advice now. You guys are mentioning things I have not thought or known about. As for the sleeve, it is done every year in one team or another. But the trouble is, it greatly reduces the engines reliability. A team managed to seize theirs this year. I have heard that a pressurized oil system is required to detune the displacement. And what about engine balance?
Don't use GREASE on the chain, you want a LIGHT oil, the hot sauce I told you about is what they use on HIGH END fishing reels, you'll be amazed at how well it works on chains... And seriously, throw the sprockets in a tumbler to polish them... any bearings in the driveline or chassis, make sure you get the highest quality, off the shelf bearings are CRAPPY compared to whats actually available... the balance of the motor is very important... also is the main drive sprocket from the motor a direct drive??? or is it a oneway clutch setup??? is it going to be 4 wheeled, 3 wheeled.... Another thing is depending on # of piston rings, you may be able to lose one, you only need the top ring and the oil ring(most racing pistons are single ring design), also you can groove the piston (like you would a pellet) to reduce surface friction... And I prolly don't have to tell you this, but you want the motor LOOSE... Check the clearance service limits of all the rotating and moving parts and whatever is in spec to the tightside, polish it until it's at the very loosest end of the specs....
DON"T FORGET THE MATH... Calculate amount of power required to do the amount of work that needs done, and then detune the motor so that it only uses as much fuel/air as required to do the job at hand, anything more is waste and waste=ineffeciency....
Once again you continue to impress. The clutch on the drive train was centrifugal. However we plan to use a cable engaged clutch, much like that of a ride on mower. The vehicle will be three wheel based of course to remove the need of a differential and the friction of another wheel. I have heard that the ideal detune displacement is right around 50cc.
Also who knows anything about aerodynamics? Our team is crossed between two common body style shapes. One is the teardrop, which is cut in half so the body hugs the ground. The other is the bullet shaped body. Like the 1st placers body. It is elevated and does not hug the ground.
With 3 wheels youcan weightbias towards the single rear tire so that there is less weight/friction on the front 2,... Engine design I would stroke the crank, reduce the bore and run a relatively low compression ratio, once you calculate the amount of power you're going to be making, then you can go about lightening rods, installing weaker valve springs.... on the chaindrive/sprockets, use the largest sprockets you can and keep the correct gear ratio, smaller sprockets eat up power by causing the chain to have to flex more to achieve the smaller radius...
The more you tell me about what you guys have planned, the more info I can give...
Finally, my powersports racing/building/tuning background is being usefull on SF....
Aerodynamically, close to the ground=friction, unless you are going after downforce, you want some space between the chassis and ground....
VERY GOOD! However we run 100 octane "Iso-Octane" as our fuel. It requires quite a high compression no? What is your take on belt drives vs chain drives?
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