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Old 05-11-2016, 04:12 PM   #1
Cali Chase
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Fsae engine thoughts

So my car currently runs a cbr600rr that weighs 125lbs dry, makes 73whp and 42w trq peak.

The engine is great, cheap to pick up used ones, and reliable. But I'd love to drop weight with a smaller engine.

I'm looking for a production engine under 710cc but would prefer a 400-500cc 2 cylinder that is under 65lbs. If I felt that an engine this small doesn't give me enough power, then I could work on a small turbo build to up torque. However with a reduction in weight of 50lbs, I could certainly take a loss in power.



I am not fond of the vibrations from single cylinders, so they are out of the option.

Any ideas?
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Old 05-11-2016, 04:30 PM   #2
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Old 05-11-2016, 04:39 PM   #3
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What are the FSAE rules on forced induction?
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Old 05-11-2016, 04:42 PM   #4
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Old 05-11-2016, 04:49 PM   #5
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Looked them up. So basically no restriction on turbocharging. You just have to run the restrictor before the compressore and throttle body. Are most teams not running a smaller engine with boost? That seems the obvious best choice. You could probably get more power out of less weight easily.
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Old 05-11-2016, 04:59 PM   #6
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don't think you'll find a more competitive engine for fsae than the cbr600 f4i. when i was on the team we turbocharged it. won the acceleration. that thing was a rocket! that was in like 98 lol. i don't think they have turbo charged the recent cars.

lots of time on the dyno!



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Old 05-11-2016, 05:16 PM   #7
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Fsae engine thoughts

So a lot of teams are trying to do single cylinder turbo but can't get them to run reliably, and they shake the cars apart. The key would be a 2 cylinder. There's no need to turbo a 4. We won accel last year with our cbr na. It's a great engine but there are better alternatives now a days!

Only restrictions with fi is that before it has to feed back into the engine, it must pass through the restrictor. Meaning after a certain rpm point, you have already reached supersonic speeds and can't push anymore in.

Problem is that there are no lightweight 2 cylinders with approx 400 cc that can benefit the most from that.
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Old 05-11-2016, 06:06 PM   #8
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Fsae engine thoughts

So I read the FI rules and the restrictor just has to be before the compressor. To get similar power the smaller engine must use a similar amount of air as the bigger engine. I don't see why that would result in a unique super sonic flow just on the FI cars. Either both configurations experience it (by my calculations it's definitely an issue) or neither does.

Does your engine choice have to be 400cc? I wonder how much you could boost a Ninja 300 engine haha.
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Old 05-11-2016, 06:15 PM   #9
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Your car runs a motorcycle engine?
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Old 05-11-2016, 06:38 PM   #10
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So I read the FI rules and the restrictor just has to be before the compressor. To get similar power the smaller engine must use a similar amount of air as the bigger engine. I don't see why that would result in a unique super sonic flow just on the FI cars. Either both configurations experience it (by my calculations it's definitely an issue) or neither does.

Does your engine choice have to be 400cc? I wonder how much you could boost a Ninja 300 engine haha.

Nope doesn't have to be a 400, 300 would be better! But yes you are correct. Supersonic is an effect that occurs on the bigger cc engines too.
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Old 05-11-2016, 06:39 PM   #11
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Your car runs a motorcycle engine?

Yes mainly because of cost. The German teams funded by amg and Audi build there own engines, but spend 25k plus to do so.
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Old 05-11-2016, 07:37 PM   #12
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Well I agree with you on going lighter. Turbo is the way to go since you have a hard limit on flow rate. I'd look at sourcing a 250-300 size street bike engine. Those are usually >2 cylinder. The ninjas may even be 4 which would be ultra smooth.
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Old 05-12-2016, 11:53 AM   #13
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From a cost standpoint you aren't going to beat a 600cc sportbike engine. They are severely lacking in torque though, and are very peaky engines.

You might look at the Kawasaki 636 engine, it's a little bigger. Or a Triumph 675 triple, is going to have a good blend of 2 and 4 cylinder qualities with a much broader torque curve.

Seems to me that FI would really complicate things.
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Old 05-12-2016, 12:21 PM   #14
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From a cost standpoint you aren't going to beat a 600cc sportbike engine. They are severely lacking in torque though, and are very peaky engines.



You might look at the Kawasaki 636 engine, it's a little bigger. Or a Triumph 675 triple, is going to have a good blend of 2 and 4 cylinder qualities with a much broader torque curve.



Seems to me that FI would really complicate things.

It's about power to weight. With the restrictor, all engines make about the same power regardless so FI allows you to get that power with less mass.
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Old 05-12-2016, 01:02 PM   #15
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the hell is going on in here, wat kinda freak show is this
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Old 05-12-2016, 01:27 PM   #16
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It's about power to weight. With the restrictor, all engines make about the same power regardless so FI allows you to get that power with less mass.
wat?

How would a smaller engine with FI and restrictor make the same power as a larger engine with FI and restrictor?
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Old 05-12-2016, 01:35 PM   #17
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Because of the restrictor. They are limited by sonic flow through the restrictor. The max displacement engine while naturally aspirated reaches that flow limit at higher RPM. A restrictor effectively limits the max power by setting a hard wall when the flow is approaching super sonic.

There is probably benefit to getting the restrictor to max air flow earlier in the RPM range though. It'd be an interesting power curve. Torque would drop off at the higher end because of the limited flow rate. Your power would level out. But you're probably better off using a lighter engine and keeping it revved up because either way, you're outputting similar power.
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Old 05-12-2016, 01:50 PM   #18
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I would think an engine with better torque characteristics that develops more power down low is going to be less affected by the restrictor, compared to an engine that needs to rev to 15,000 RPM to make its power.

I recall my school using a 450 dirtbike engine in some vehicle of theirs. That would be pretty wicked.
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Old 05-12-2016, 01:51 PM   #19
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OP can you use a 2-stroke?
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Old 05-12-2016, 02:44 PM   #20
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OP can you use a 2-stroke?

Nope has to be a 4 stoke. Sae just changed the rules for 2017 and the max cc increased from 610 to 710. This allows engines like the sv650 and triumph as stated before. They are both Powerful engines but not light.
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