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Not sure about forced induction engines, but with NA engines, especially with healthy camshafts, it is often beneficial to reduce the actual throttle opening at '100%' pedal position to improve torque. It seems to come down to resonance charactristics in the inlet tract and can make a noticeable difference in driveability and response below where the cam's''come on song'.
May be worth trying on your vehicles.
Got any more detail for this claim?
Not off hand - forgot something important , though, this was with IR four cylinder engines - so quite likely to be limited to that type intake. Also, IIRC, there was also speculation it was down to the butterfly affecting reversion. I would not be surprised if forced induction or plenum intakes showed no difference.
I was putting it out as something that those with electronic throttles might find of interest.
I've heard this claim before (touted as a benefit to DBW) from a reputable source but I think the reason given was to do with velocity (or static vs dynamic pressure).
Looking at it the other way, I can imagine that if the manifold was already "saturated" (for want of a better description) at any given throttle position then opening the throttle further may not increase power but I struggle to see how it would reduce it.
It's possible on very specifically tuned runner lengths and valves timings that having more manifold vacuum (from a partially closed throttle) increases pulsation effect during overlap.
That is what I would expect, some engines may have characteristics where a partial throttle at low rpm improved cylinder filling over a fully open throttle - I mentioned it as I knew of two instances where it applied - unfortunately too far back in the memory banks to recall the full details, 'cept I'm sure they were 4 cylinders and running ITBs - maybe Fords? As I said, I would expect it to be limited to these types of engines or, at least, NA.
I can think of instances where, on a race car (and certainly on a 'road' car), it would be worth checking and modifying the actually opening, if required - where the track has tight corner(s) where the engine drops under it's optimum rpm in 1st gear and you need to maximise the torque, leaving a speed-restricted pit area, maybe on a rolling restart and maybe on a stationary race start. Going to depend on the vehicle characteristics and circumstances, of course.
I wouldn't say I see this often, but it is a situation I've personally struck and it's quite common if you look at the mapping of the DBW throttle in high revving sport bike engines. A few years back I mapped a Synergy V8 which is a custom 3.0 litre V8 that uses a billet CNC machined block, custom flat plane crank, and a pair of Kawasaki ZX12R cylinder heads with individual throttles. It revved to 11,500 rpm and we found that for maximum torque the engine didn't want to see full throttle until 6000 rpm. In fact at 2000-4000 rpm we saw maximum torque with only 40% throttle opening.
I don't personally have any solid answers for why this is the case, I just gave the engine what it wanted for best performance. My first thought was that with a set of pretty large throttle bodies, full throttle may have resulted in a reduction in airspeed, or perhaps it negatively affects mixture formation due to a lack of air turbulence. I really couldn't say with any certainty.