Power loss

[Sam Zimmerman]

Last year we measured only 40 hp on the chassis dyno at competition. Our engine dyno said we had 52 hp. We are sure that we lost a bunch because our rear suspension had a lot of toe when we got on the dyno, but 12 hp seems like quite a bit. I also understand that every dyno is different and the numbers won't match up, but...

What kind of differences in numbers have other teams seen between their engine dynos and the chassis dyno at competition?

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[Sam Zimmerman]

Last year we measured only 40 hp on the chassis dyno at competition. Our engine dyno said we had 52 hp. We are sure that we lost a bunch because our rear suspension had a lot of toe when we got on the dyno, but 12 hp seems like quite a bit. I also understand that every dyno is different and the numbers won't match up, but...

What kind of differences in numbers have other teams seen between their engine dynos and the chassis dyno at competition?

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[Mechanicaldan]

What you are seeing is frictional losses through the drivetrain. Seems the numbers indicate a little more than a 20% loss. I'd say that seems right. There probably is some dyno error involved also, and different horsepowers readings for different elevations and temperatures.

Automobiles will loose 25% or more with a manual transmission, and 35% or more with an automatic. That torque convertor robs a lot of power.

On the motorcycle engine, are you connecting to the dyno with the output shaft of the transmission on the motorcycle engine? If so, some of the losses are already accounted for coming through the transmission, and thus, it seems like the motorcycles take a smaller loss, but they just have the 10% of the transmission losses figured in already.

Just curious about what motor you are running and only getting 40 HP?

Cyclone Racing
www.cyclone-racing.com/fhome.htm (http://www.cyclone-racing.com/fhome.htm)
Iowa State University
Project Director

[Sam Zimmerman]

I understand there are frictional losses, but as you said our engine dyno connected to the output shaft of the transmission so 20% seemed high to me. I am curious what others have reached.

btw, we are running a F3 and 40 hp is a bit low, even at the wheels. http://fsae.com/groupee_common/emoticons/icon_frown.gif Our engine had some troubles. We hope to have rectified the problems and last week produced about 20% higher power on the engine dyno than last year even while using a prototype intake made of PVC and wood. (Thanks Charlie) http://fsae.com/groupee_common/emoticons/icon_wink.gif

Anyways, if anybody has some numbers to share, I would be interested in seeing them.

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[Daygo Nighthawk]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Daniniowa:
What you are seeing is frictional losses through the drivetrain. Seems the numbers indicate a little more than a 20% loss. I'd say that seems right. There probably is some dyno error involved also, and different horsepowers readings for different elevations and temperatures.

Automobiles will loose 25% or more with a manual transmission, and 35% or more with an automatic. That torque convertor robs a lot of power.
<HR></BLOCKQUOTE>

25% and 35%?? Man, you guys need some more powertrain engineers.. http://fsae.com/groupee_common/emoticons/icon_wink.gif

But really, with a fairly good powertrain you should get only about 18% loss, 25% with an automatic (varies). The misaligned toe may have lost you that last bit. Also, (in general) the dyno losses become more pronounced at lower power levels (closer to 20%). Larger, high power engines drop the loss to 15%, or less....

___________________________________
College is a fountain of knowledge . . .
and the students are there to drink.

[Charlie]

We saw a 13-15% power loss from our water brake to the chassis dyno. Our water brake is a little on the 'student built' side, but we think it is calibrated fairly well.

Excessive toe & tire pressure can have a big effect on chassis dyno readings, make sure you have a consistancy in those areas.

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Charlie:
Our water brake is a little on the 'student built' side, but we think it is calibrated fairly well.<HR></BLOCKQUOTE>

Our dyno is a lot on the 'student built' side, it was a senior design project a few years ago. http://fsae.com/groupee_common/emoticons/icon_wink.gif

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Excessive toe & tire pressure can have a big effect on chassis dyno readings...<HR></BLOCKQUOTE>
We did have a bit of toe (or maybe it was a bunch of toe http://fsae.com/groupee_common/emoticons/icon_razz.gif) in the rear because we had the car set for the skid pad. We will set everything right before we get on the chassis dyno this year, if we get on the chassis dyno this year. After hearing about the team that broke a chain on the dyno which lead to a broken transmission case before the dynamic events even began, I am not sure it is worth it to take the chance and put our car up there.

Sam Zimmerman
Vandals Racing (http://www.uidaho.edu/~racing)

[Charlie]

We have not ran on the chassis dyno since 2000. It's nice but unless you are sure you can top the highest HP cars (80 hp, we are not there yet http://fsae.com/groupee_common/emoticons/icon_wink.gif ) I don't see much point. The only time we'd do it is after the endurance event.

-Charlie Ping
Auburn University FSAE (http://eng.auburn.edu/organizations/SAE/AUFSAE)
5th Overall Detroit 2003
? Overall Aussie 2003. http://fsae.com/groupee_common/emoticons/icon_smile.gif