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what type of engine would you choose!

  • motocross 450cc single n/a

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  • enduro ~500cc single n/a

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  • enduro ~500cc single turbo/super

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Discussion Starter #1
I joined my universities formula SAE team and figured id turn to the great people on here to hear some suggestions on engine choice.

it will basically be a modified version of some motorcycle/ dirtbike engine.

Key point here is the engine has to breath through a 20mm restrictor. for context these restrictors can flow a max of roughly 80 hp of air.

max displacement is 610cc on pump gas. it can be super or turbo charged but throttle and restrictor must be before the compressor.

weight and reliability are big factors in this.


currently we are looking at a supercharged single motocross bike. as far as what brand or specific engine we are up in the air. so if you know some good engines mention them!
 

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Discussion Starter #3
My vote would be for a CBR600 motor and to turbo it
this would definitely make the most power if unrestricted. we are definelty considering this as an option.
problem with this is the weight and how restricted it would be. we would hit peak power at like 6000 rpm and it would be heavy. although it would be absolutely nuts coming out of corners.
 

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The only single cylinder motorcycle engines i would think of would be the newer (2007 and up) motocross bikes. The switch to fuel injection from carbs on the 450s, let them make more power down low with some sacrifice up top.

Only thing that would sway me from the single cylinder motors are the reliability of the trans. Because i (ASSume) that you would bore/stoke out the motor to get to the 600cc limit.
 

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the artist formerly known as drexelstudent11
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FSAE cars struggle so hard for grip as it is, you don't need the full bore power of a 600cc race rep motor- destroke an SV650 vtwin maybe? the less cylinders, the better the traction, but a motocross 450 single is just too high strung as it is to really work well in fsae
 

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^ Normally they are high strung. But with the recent introduction of fuel injection. The bikes have been "toned down". 2013 Suzuki RM-Z 450 makes peak power ~52hp @ 8,900 and peak torque @ 7,600.

Bike makers are realizing that smooth and controlled power make for a faster bike on the dirt.
 

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They call me Awesome!
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My vote would be for a CBR600 motor and to turbo it
this would definitely make the most power if unrestricted. we are definelty considering this as an option.
problem with this is the weight and how restricted it would be. we would hit peak power at like 6000 rpm and it would be heavy. although it would be absolutely nuts coming out of corners.
IIRC the restirctor is about the size of a quarter (TINY!). At that point the only thing a turbo will do is flatten out the torque curve, most teams opt out of a turbo simply because it's easier to tune without it.

FSAE cars struggle so hard for grip as it is, you don't need the full bore power of a 600cc race rep motor- destroke an SV650 vtwin maybe? the less cylinders, the better the traction, but a motocross 450 single is just too high strung as it is to really work well in fsae
You'd lose a lot of compression and I just don't see this as being a performer. Plus you'd have to prove that it's no more than 600cc.

Snowmobile motor + CVT.
IIRC it has to be a 4 stroke (I'm sure there are Snowmobile motors out there that are).


My team went through this decision making scenario when we started in on our last car and we came up with a WEIRD solution. We were actually going to run a single cylinder Harley Davidson. We contacted Harley and got them to send us a fresh off the line 1200cc V-Twin with an altered / balanced crank that only had a single piston. We removed the front jug and were planning on throwing a custom fuel injection system and turbo on it in order to flatten out the torque curve. We figured this would offer us the a unique design, enough HP, and lots of torque. Obviously this never got finished and to the best of my knowledge it's still sitting in a box at UAH.

If I had the chance to do it over again I'd have done a Husqvarna single with a turbo. It's already setup for EFI, weighs less, require a smaller area as far as engine compartment (less weight), offers good low end torque, spins up quick (less rotating mass), etc... Yes, they're less common but I personally liked the idea a lot.

That being said, if this is a new program without an established car; get a sportbike I4. They're drop in and go ready! Focus on one system per year, that's where we over stepped our bounds. In on year we tried to redesign the chassis, suspension, and drivetrain...

Best luck to you man!
 

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I guess with that restrictor you need something optimized for low end, maybe like a big thumper.
I would still go turbo though, even if you end up with a rally car torque curve

 

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A couple things about the SIR that will need to be considered:

Is there a stall test? What RPM and how long to stall? With or without sensors connected? This will serves as a guide as to how large a plenum you want to design.

Multi-cylinder motors vs. single-cylinder motors of the same displacement pull less air per stroke...that means an SIR will spend less time in the stalled region and recover faster, allowing the plenum pressure to recover faster.
 

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Sounds like most people are going along the thought lines I am. Since you seem to be restricted on top end power, take whatever you get your hands on and try to optimize the torque curve. No matter which way you go your top end will be your choke point. So focus on everything up to there (all you need is 300 spartans if you do it right). Just from the sounds of what I'm reading here I would opt for high(er) comp, long(er) stroke motor, with a turbo charger. The CR and stroke will help immensely with the bottom end of your curve, and spool the turbo faster which wil get you that airflow you are looking for sooner to pull hard through to your power threshold nicely.

Might be a bitch to tune but I think something along these lines would be an optimal setup. Should give you all the torque you could ever want when ever you want it.

I'm not terribly familiar with FSAE cars, or motorcycles. But this theory seemed to work really well for me in my car as far as torque generation and spool characteristics are concerned.
 

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They call me Awesome!
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A couple things about the SIR that will need to be considered:

Is there a stall test? What RPM and how long to stall? With or without sensors connected? This will serves as a guide as to how large a plenum you want to design.

Multi-cylinder motors vs. single-cylinder motors of the same displacement pull less air per stroke...that means an SIR will spend less time in the stalled region and recover faster, allowing the plenum pressure to recover faster.
I don't recall there being a stall test, granted I haven't been since like 02-03.




OP, lemme ask this; are you a fresh startup team? Do you already have a chassis / suspension design in place?

If you're already established, do a single; if you're not, stick to a 600cc 4 cylinder. The abundance of support for the I4 in FSAE is GREAT and quite frankly you'll have your hands tied up with the frame / suspension design for the first few years.

Keep in mind, if you're a new team, the goal is to take a car to competition and finish competition. Winning or even finishing in the top third is completely out of the range of expectations for a young team. Get a base design and refine it a little each year.
 

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Speaking of Rally cars... how about a 'cheater' restrictor plate like Toyota pulled on the WRC Celicas :)

In 1995 TTE was banned for 12 months[1] from the World Rally Championship (WRC) for cheating by designing an illegal air restrictor[2] on the ST205 that included both a bypass mechanism and spring-loaded devices to conceal it from scrutineers.[3] In the 1996 and 1997, despite lack of works team appearance in 1996 due to the ban, TTE supported the Celica ST205 rallied by Italian HF Grifone Team, Toyota Team Sweden, Marlboro Toyota Team Belgium, and Tein Sport in the selected WRC events, before introduced the Corolla WRC in the 1997 Rally of Finland. When they returned to the WRC for 1998, they did so with a Corolla WRC driven by the crews of Carlos Sainz/Luis Moya and Didier Auriol/Denis Giraudet. They finished the season in second overall in both the Drivers' and Constructors' Championships.
 

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Discussion Starter #15
Wow thabks for all the comments guys. Lots of good info ill have to read through tonight. The team is new but not brand new. We have a car right now that meets requirement for everything but engine.

It has a 510cc inline twin snowmobile engine with cvt and everyone hated the cvt. We also neved had it running with a restrictor.

We are toning it down to just a straight up design year and hope to have an entire car in solidworks and lots of time to test various components on the old car.
 

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Stick with the CVT. Then you can tune whatever motor you use for peak power and not have to worry about what the engine makes down low.
 

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the artist formerly known as drexelstudent11
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You'd lose a lot of compression and I just don't see this as being a performer. Plus you'd have to prove that it's no more than 600cc.
how would you lose compression? you'd increase the rod length to offset the destroke?


and by 450ccs being high strung, I'm not just talking about RPMs- I'm talking about needing lots of maintenance (like checking the valves every 10 hours), probably easier on an FSAE car vs a bike, but still no fun
 

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Discussion Starter #18
Stick with the CVT. Then you can tune whatever motor you use for peak power and not have to worry about what the engine makes down low.
thats not exacty how it works and getting the transmission to work can be a huge pain in the ass. especially to make it reliable
 

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thats not exacty how it works and getting the transmission to work can be a huge pain in the ass. especially to make it reliable
If you tune the CVT right it damn near is. Yes making it reliable and working the way you want it can be a PITA. But the F500 guys seem to have it figured out pretty well and tuning the CVT right would make all the difference for them.
 
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