Anyone try a Parallel-Twin engine in FSAE?

[B. Dondlinger]

All,

With a recent batch of middleweight parallel-twin motorcycle engines, has anyone tried to use one in an FSAE car?

Given that a 20mm restricted engine generally chokes around 10,500 RPM, and the peak power speed of most 600cc I-4 motorcycle engines is in the range of 12,500-14,000 RPM, the valve timing, valve size, and mean piston speed are not well matched to the restrictor.

Would an engine that was designed to operate below this choked flow RPM require less work to achieve the best balance of maximum power, minimum investment, minimum fuel consumption, and minimum weight?

While most of these engines are in the 650-700cc range, they are not far from the 610cc regulation. An engine could be modified by sleeving down the cylinder to reduce bore or welding the crankshaft to reduce the stroke.

[Jay Lawrence]

There are several teams who have used parallel twin engines, but mostly from snow mobiles. Obviously the disadvantage here is the lack of gearbox etc., but some teams are likely to see that as an advantage (though I'm not aware of any particularly successful implementations).
As for the new range of bike engines: hopefully by the time they become more prevalent in the 2nd hand market the rules committee will have realised how outdated the engine choice limitations are and people will be able to consider a wider range of options. Until then I'd say it's a case of too much effort for too little (or at least unknown) reward.

[MCoach]

Credit to mbirt for this one, but we've worked extensively with the Rotax ACE600 which would make an amazing efficiency focused engine.
It comes naturally aspirated with a belt type CVT (standard snowmobile stuff) and we've run them on various blends of ethanol, gasoline and isobutanol for the clean snowmobile competition. We've turbocharged them to make 95hp on E85 and achieved 250ish g/kW*hr BSFC at its best as seen on our dyno in its most recent configuration. These numbers are unrestricted for the CSC competition, mileage may vary. Stock internals.

They aren't as light as a single, only rev to 8k-ish, only make 60hp stock, BUT, they get 30mpg in a 500lb (quoted without rider) snowmobile. With that, they don't really need to be modified to get the required power and efficiency for the competition.
He's muttered for years over retrofitting one to our cars.

Anyone have BSFC numbers of their engines to compare for fun?

[Swiftus]

You could always count the KIT custom parallel twin. Turbo-ed for ~70kW with a super flat torque curve.

[tromoly]

We ran a Yamaha Genesis 80FI (500cc parallel twin with PTO for CVT), I believe the engine itself weighs within a couple pounds of a Yamaha YFZ450 single, add in pulleys and secondary and whatnot and the total weight is I'm guessing only 20-ish pounds lighter than running an I-4. I want to say the most power we got out of it was 60hp, and I think there is some valve overlap that causes the plenum to be scavenged and causing the second piston to be starved of air, it's been a couple years so I may be remembering that part wrong though.

[Z]

Brian,

Other than the Rotax-ACE and Yamaha-Genesis mentioned above, I think the most common twin in FS/FSAE is the Aprilia (but a Vee-2). I call it "the hand-grenade".

For a good example of a, ahem..., "decision matrix" approach to choosing the configuration of engine, see this "AMG-595-Engine" thread. Ahh, yes...., start with the decision clearly made, then do NOT let any facts get in the way!

For better reasoned discussions on choosing engine, and assuming you have the spare time, you can look through these two quite long threads (~20 pages each, by now).

"Any way to objectively choose engine?"

"Fantasy engine."

Z

[B. Dondlinger]

Fortunately the FSAE duty cycle is much less than a typical engine duty cycle and expected life. So might be worth the risk welding/ grinding/heat-treating the crankshaft. Alternately, if the block is sleeved down and custom pistons are made, there are opportunities to raise the compression ratio.

Benefits of the parallel-twin approach are:
- more steady state flow through the restrictor than a single cylinder,
- less weight than an I-4,
- improved fuel consumption,
- simple packaging (over v-twin or I-4).

Some likely motorcycle engines:

• Yamaha FZ07,---689cc, 80mmx69.0mm, 70hp@8,800 rpm, 48ft-lbf@6,600 rpm, (Bore changed to 75mm, or Stroke to 60mm to equal 610cc)
• BMW F800,------798cc, 82mmx75.6mm, 85hp@7,500 rpm, 61ft-lbf@5,750 rpm, (Bore to 71mm, or Stroke to 57mm)
• Kawasaki 650,--649cc, 83mmx60.0mm, 71hp@8,500 rpm, 47ft-lb@7,000 rpm, (Bore to 80mm, Stroke to 56)

What would be the ideal engine bore x stroke ratio for this application?

[craigorydean]

Well Seeing how Honda Just decided to remake a 471cc (500cc label) Street motor cycle I think that if they produce that line for long enough for them to be wrecked it will hit the FSAE market. They Have the displacement space to mod the engine in bore and stroke and still stay well away from the rules limit of 610cc. As well as it has an integrated 6 speed gear box that could be modded to only 3 needed gears (2-4).

We as a team bought a brand new engine back in 2012 (KFX450r).Our budget was 5k USD. We made that choice cause we didn't have enough money to buy a new dirt bike and part it out and that was the only crate engine the stealership said they could get us. If this Motorcycle was available then it probably would have been the one we would have purchased due to the many of things that have been said on this thread previously.

I hope a team wanting to switch engines really takes a look at this cause i feel it could be a pretty good set up if done right.

Brian,

Other than the Rotax-ACE and Yamaha-Genesis mentioned above, I think the most common twin in FS/FSAE is the Aprilia (but a Vee-2). I call it "the hand-grenade".

For a good example of a, ahem..., "decision matrix" approach to choosing the configuration of engine, see this "AMG-595-Engine" thread. Ahh, yes...., start with the decision clearly made, then do NOT let any facts get in the way!

For better reasoned discussions on choosing engine, and assuming you have the spare time, you can look through these two quite long threads (~20 pages each, by now).

"Any way to objectively choose engine?"

"Fantasy engine."

Z

If you take the approach that Z and a lot of people on the "Any way to objectively choose engine?" have gone though Neither of these were good choices for us. We should have looked to see what engine could have purchased 3 of for 5k USD. which most likely had been a 03-06 R6 or GXR. But we thought the best way for us to be successful (this is still the thought that is around UT-San Antonio) is to have a "light" (Sub 375 lbs) single car. But we have never reached that goal so I don't know how viable that plan was for us.

[Z]

Brian,

I guess you haven't had time to read the AMG thread I linked to above. The "decision matrix" approach does NOT add up for the parallel twins.

Benefits of the parallel-twin approach are:
- more steady state flow through the restrictor than a single cylinder,
- less weight than an I-4,
- improved fuel consumption,
- simple packaging (over v-twin or I-4).

Taking these one at a time.

1. A N-A single with a ~4 litre plenum can comfortably flow 60 hp. Fit a turbo or SC and it will flow the full 120 hp available through the 20 mm restrictor.

2. A single has even less weight than either the I-2 or I-4.

3. A single has the potential for the best fuel consumption of all configurations (mainly due to smallest combustion chamber surface, and least frictional losses).

4. This is the BIG ONE, and also the one most ignored by FSAE Teams. In short, ALL motorcycle engines package badly in an FSAE car!

I quickly looked at the three engines you suggested above, and all three are the typically too tall and too long (when final drive included) motorcycle configuration, so give very bad overall mass distribution in an FS/FSAE car. The reasons for this are covered extensively elsewhere.

And FSAE most certainly does NOT need a 6-speed gearbox, so why buy one?

Z

[MCoach]

We ran a Yamaha Genesis 80FI (500cc parallel twin with PTO for CVT), I believe the engine itself weighs within a couple pounds of a Yamaha YFZ450 single, add in pulleys and secondary and whatnot and the total weight is I'm guessing only 20-ish pounds lighter than running an I-4. I want to say the most power we got out of it was 60hp, and I think there is some valve overlap that causes the plenum to be scavenged and causing the second piston to be starved of air, it's been a couple years so I may be remembering that part wrong though.

We were definitely having a scavenging problem with the ACE as well. I'm unsure about the Genesis, but the ACE600 is an odd fire engine. Combined plenums will pump down for a 1st cylinder while the trailing cylinder will always be starved for air. We were running into lean limit problems about 1.3-1.4 Lambda because cylinder one was lean misfiring while cylinder two was starved for air, therefore having enough fuel in the chamber to be knocking. Took us a few hours to figure out what was going on there. We wrote some cylinder balancing software to compensate for the starvation rather than tackling it head on. An awesome intake manifold like Wisconsin-Madison came up with is another way to go about it.

What would be the ideal engine bore x stroke ratio for this application?

[/quote]

Considering your signature at the bottom, you might be one of the better people here to answer such a question. Considering traditional theory, increasing revs while maintaining torque from a power cell is just free power. So , big bore (3.7 - 4"-ish), accompanying stroke to meet displacement limits. Rev to the moon --> max power. However, efficiency targets dictate the opposite end of the spectrum. Long, long stroke, small bore = max combustion efficiency. Something about 100(ish)mm x 58(ish)mm is probably a solid combination that'll work for a single. 110mm x 64mm if you like displacement.

3. A single has the potential for the best fuel consumption of all configurations (mainly due to smallest combustion chamber surface, and least frictional losses).


Z

Agreed. They also are jam packed with high performance materials, geometry and weight savings choices due to them common ones being paired with dirt bikes that are meant to jump around a lot. They also tend to be really robust for FSAE because we don't bounce them off the rev limiter every 5 seconds like the motocross guys do. However, some of the range extender engines made by Mahle, Rotax and the like may also be favorable choices (hypothetically) due to their advanced focus on efficiency, friction loss reduction, and combustion efficiency. Less loss = more free power!