Throttle Body Cam Design

[Pavsta]

Hi all,

I have a mate in my motorsport team that is having to design the throttle cam. He has 22mm of cable travel available and he has also determined a relationship between frontal area of the throttle butterfly compared to its degree of rotation.

Any ideas or suggestions as to what to do interms of designing the cam??

All help is much appreciated.

 

[NormPeterson]

What does the engine's torque curve look like? I suspect that if it's a little lacking in the low revs that you can speed up the initial relation between cable travel and throttle plate movement to your advantage. Note that some slowing down of that relation must occur elsewhere, which may be of separate benefit.

Throttle plate size matters, too. I do know that an overly large throttle combined with a quick early opening linkage makes for some difficulty in modulating the power output, especially while exiting slow/lower gear corners even when the pavement is smooth.


Norm

 

[NormPeterson]

"overly large throttle combined with a quick early opening linkage makes . . ."

should read

"overly large throttle combined with a quick early opening linkage and lots of available torque makes . . ."

 

[GregLocock]

Carb or efi? There are additional problems with carbs.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Pavsta]

Its efi.

Like i said previously, the guy has a curve comparing degree open with frontal area of the space between butterfly and throttle body casing. This rleationship isnt linear but has a slight curve to it.

I was personally thinking that the inverse of the curve could essentially be the shape of the cam which would inevitably linearize the previous relationship.

 

[patprimmer]

Cross sectional are is not directly proportional to power, otherwise power would only be limited by throttle size.

There comes a point when more throttle makes no difference.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Fabrico]

Linear will work, but most throttles are set up to move slower from idle where better control is desirable. You don't need much control at or near full throttle, so most move quicker past about 50-75% open. The ECU may need re-programming for the new TPS readings.

 

[mattsooty]

Ahhhhhhhh the joys of old technology!

It depends on what you want, if you want the car to feel 'sporty' and 'urgent' then a faster ramp rate from closed throttle will give this. If you want it to feel tractable then the opposite is true......Anywhere in between is down to taste!

Try the 3 types, sporty, tractable & linear and then decide.

Dont worry though, the TPS wont need recalibrating.

MS

 

[Pavsta]

I probably should have stated in the first question that we are more stuck with actaully determining the radius of the cam for the desired ramp.

We know we want the cam to have an increasing ramp rate (slow at closed - faster at open) and it is just the mathematical approach to determining the cam radius that is becoming annoying.

 

[SomeYahoo]

Quick noodling puts me out of cartesian coordinates and into polar. Your circumference is 22 mm for the 1/4 turn or so that you need (0->pi/4). Integrate from 0 to pi/4 radians for theta, and create a function for r such that the travel is 22mm. You can play with the variables inbetween to get the ramp you want.

Hope this helps...