Power losses with a restrictor

[nvpF1crazy]

I was going through some dyno data of teams at an FSG event and found that the peak power of 600cc engines (approx 100 bhp) dropped down to a range of 55 to 70 bhp. This I assume is mainly because of the restrictor.
For single or twin cylinder engines, will the peak power loss be proportionate? I'm looking for a fairly accurate way of identifying the peak power of a Honda CBR250R, Ninja 250 and Yamaha WR450.

[nvpF1crazy]

Throttle body dimensions I could find:
CBR600RR3 - 37mm
Yamaha R6 - 38mm
CBR250R - 38mm

[Bemo]

The power output in the FSG dyno data is given in kW. So peak power of the 600cc engines is in the range of 85-95 bhp.

[TMichaels]

Bemo is right. We are using the derived SI unit for power, since horsepower was originally defined to compare the output of steam engines with the power of draft horses..

BTW: The peak power of a horse over a few seconds has been measured to be as high as 14.9 hp

Regards,

Tobias

[Rex Chan]

I would say the peak power from any engine system on a FSAE car has a lot more to do with what the team was designing for, what the actual made part's theoretical peak power is, and how well the engine ECU/carby was tuned to achieve motion at the wheels.

And since these figured were measured on a chassis dyno, they also depend on the driveline + tyres used. A student made driveline may have a lot of friction. I don't know how many teams measure the friction in their driveline.

[mech5496]

About the proportionate losses...Back in 2007 we made more than 55hp form out restricted Yamaha XT600 while the OEM carbed engine made barely 45...

[Mbirt]

Originally posted by nvpF1crazy:
For single or twin cylinder engines, will the peak power loss be proportionate? I'm looking for a fairly accurate way of identifying the peak power of a Honda CBR250R, Ninja 250 and Yamaha WR450. No. Horsepower is proportionate to airflow. The rules set a theoretical crank horsepower of about 100 through the use of the restrictor. With sufficient intake plenum volume to time-average your intake pulses, engines with max intake air flow well below restrictor choke should behave as unrestricted. In practice, teams do not typically chose plenums this large and sometimes have custom camshaft profiles made to reduce the EGR effect during overlap when intake pressures are low.

Check this thread out too: http://fsae.com/eve/forums/a/t...7348/m/302103904/p/1 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/302103904/p/1)

[DanCiobanu]

Excluding the top and bottom 10 teams, usually 'average' teams see roughly 68% (at the wheels) of the engine's OEM bhp rating. This seemed fairly uniform across the band (1,2,4-cyl engines) that have had 'adequate' intake and exhaust systems.

These numbers I've gleaned (rather unscientifically, at that) from past event programs and contain team-provided numbers - they may contain sand-bagging or inflation, but roughly 68-70% has been the magic number from a population of about two dozen.

For example, an F4i makes roughly 105 bhp on the bike, and will generally make in the vicinity of 70-75hp on a decently well designed intake/exhaust setup (stock cams/internals).

Now you can certainly make more than that, and it would take some serious ineptitude (or a sick engine) to make considerably less, but 68-80hp is generally healthy as a peak # on a stock motor.

[nowhere fast]

Originally posted by nvpF1crazy:
Throttle body dimensions I could find:
CBR600RR3 - 37mm x4
Yamaha R6 - 38mm x4
CBR250R - 38mm x1

4 cylinder 600cc engines tend to gulp quite a bit more air than 250cc singles.

[Spetsnazos]

Originally posted by nvpF1crazy:
I was going through some dyno data of teams at an FSG event and found that the peak power of 600cc engines (approx 100 bhp) dropped down to a range of 55 to 70 bhp. This I assume is mainly because of the restrictor.
For single or twin cylinder engines, will the peak power loss be proportionate? I'm looking for a fairly accurate way of identifying the peak power of a Honda CBR250R, Ninja 250 and Yamaha WR450.

I got the full torque curves for those schools and alot of them are pushing 85-95 hp. Where did you get 50hp from...

[nvpF1crazy]

Originally posted by Spetsnazos:
Where did you get 50hp from...

My mistake! The data was in kW. Comes out in the range you said.

[Spetsnazos]

Originally posted by nvpF1crazy:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Spetsnazos:
Where did you get 50hp from...

My mistake! The data was in kW. Comes out in the range you said. </div></BLOCKQUOTE>

Let me know if you want the torque/hp curves for the top ~20 schools. I also have the engines they used.

PM/email me and I'll send you the excel file.

[Wesley]

Originally posted by nvpF1crazy:
I was going through some dyno data of teams at an FSG event and found that the peak power of 600cc engines (approx 100 bhp) dropped down to a range of 55 to 70 bhp. This I assume is mainly because of the restrictor.
For single or twin cylinder engines, will the peak power loss be proportionate? I'm looking for a fairly accurate way of identifying the peak power of a Honda CBR250R, Ninja 250 and Yamaha WR450.

There are pages and pages of threads and volumes of papers written on the effect the restrictor has on power levels. Looking at the power graphs shows you what you need to be competitive, but tells you nothing about how to get there. That is up to you, as the engineer. Restrictor, runner, plenum, injector geometry as well as plenum volume among many other things all impact volumetric efficiency. There's no single coefficient to scale power output to the diameter of the restrictor.