throttle body camber

[B]

Does any one know of any equations or angles/curves etc for throttle cam... i.e. what curve do i give it and/or the accelerator pedal so that I get a linear acceleration... or at least the relationship between air flow intake to accelerator angle/travel remains linear.

and on that note... is a linear relationship ideal? I have heard word that an inverse exponential type relationship may be more appropriate as it would give better throttle control closer to full throttle...

or is it better to keep a the pedal torque constant? i.e. have a both curves (curve on throttle body and curve on accelerator pedal) constant and of equal radius.

any comments?

[B]

Does any one know of any equations or angles/curves etc for throttle cam... i.e. what curve do i give it and/or the accelerator pedal so that I get a linear acceleration... or at least the relationship between air flow intake to accelerator angle/travel remains linear.

and on that note... is a linear relationship ideal? I have heard word that an inverse exponential type relationship may be more appropriate as it would give better throttle control closer to full throttle...

or is it better to keep a the pedal torque constant? i.e. have a both curves (curve on throttle body and curve on accelerator pedal) constant and of equal radius.

any comments?

[Storbeck]

I would say your dyno could give you a pretty good idea what the "throttle position vs. percent of maximum power" curve would look like.

If you don't have a motor on the dyno to do this with, I am no help. I also have no idea about the second question.

edit- I suppose what I meant to say was "throttle position vs. maximum available torque" though at the given rpm that would be proportrional to power, and airflow, so It's kind of all the same.

[murpia]

Drive-by-wire maps are often linear pedal to torque demand (with dead bands either end). Torque is what the driver demands, not power.

Depending if your throttle is a butterfly, barrel, slide or spike the throttle position to air mass flow relationship (and hence torque) will be different. It will also be different at different rpms. The dyno is probably a good bet for tuning, maybe design something with interchangable cams or linkages to speed development. Then track test.

Ian

[SnailRacer]

Don't know if this is exactly addresses what you're looking for, but I will share our experience in the matter. We ran a rather large (48 mm ?) butterfly throttlebody, under the argument that the bigger the throttle body, the better (considering the obstruction of the blade at 90 degrees). We quickly found out that a near-linear pedal angle to butterfly angle linkage didn't work so well -- the response was very binary from the driver's point of view. We changed our linkage to be more nonlinear so that the early degrees of pedal travel only open the butterfly a little, while the later degrees of pedal travel open the butterfly alot, and much improved our driver happiness.

[B]

cheers SnailRacer.. thats exactly what i was looking for, thankyou for the confirmation... although I was hopeing for a bit more detail regarding the no-linear relationship... I'll just take a stab in the dark.. quadratic sounds good to me...

[BeaverGuy]

Be careful what you are making non-linear. Airflow vs. Throttle Angle is allready non-linear for most throttles though some have a larger region that approximates linearity than others.

This is a plot of airflow for our 35mm Barrel throttle. The CFD Results were choked while the tested results weren't. That is the reason for the use of a Normalized flowrate.
http://web.engr.oregonstate.edu/~gilletjo/throttleFlow.JPG

From this you can see that if a linear airflow to pedal travel is desired, ie. power to pedal travel, or torque to pedal travel for a fixed RPM, then a linear pedal angle to throttle angle may be fine. However, this is a case of this specific throttle size and type a butterfly or slide would have a noticeably different angle/airflow relationship. And either a power vs. throttle angle or airflow vs. throttle angle graph is neccesary to get the relationship that you want.

[B]

Thanks Beaverguy

I spoke to a mechanic today who builds drag cars and mods high performance turbocharged cars. He said that the first ½ of the pedal travel should open the butterfly valve 1/3 of full open (i.e. 30deg) and the 2nd half of the pedal travel should open the other 2/3 (60deg).

any comments?

and can anyone recommend a desired amount of pedal travel (for the accelerator)...