Reply to "Engeneering challange ... Progressive Throttle Linkage"

Well as far as I know it’s just as shown but you have to attach a cable to the drive arm somehow and the initial angle which you pull on the arm can also affect the rate of opening throughout the motion. Most of the over/under geometry linkage schemes that achieves similar results to what I describe for slower initial opening can actually gain the opening rate per inch of pedal/cable travel as you approach WOT which may aggravate Dago’s situation.

I liked the cable driven wheel because angular displacement of the wheel was proportional to pedal/cable travel regardless of what direction you pulled from and it kept the cable tangent to the wheel at all times preventing deflecting and binding on the cable sheath. I positioned the wheel at about the average height of the lever arms driving the throttle shafts so the change in rate through that part of the linkage motion was pretty much negligible. Most OE accelerator pedals produce about 2 ½” more or less of cable travel. You can size the wheel diameter and rest of the linkage from that. When combined with the 50-55mm throttle bore range it just seemed to work well providing a good compromise between top end power levels and resolution…..may be some serendipity too.

This whole affect is similar to sizing throttle plate area on TB of a common plenum intake. Same thing happens when you go to large on the single TB there, just not as extreme. It's more exaggerated in IR because you typically have so much more throttle plate area for a given displacement. It may seem like a lot of theoretical BS but it’s a case of where matching the kinematics of the linkage to the throttle plate open area really does translate to predictable throttle response and better drivability……trying to reduce theory to practice doesn’t always turn out that way but it's sort of satisfying when it's so.

Best,
K