My TDC resetting topic has me thinking about throttle behaviour, or rather engine response to how far the pedal is pushed. My engine seems to stop responding once the pedal is about 2/3rds depressed. That is, the last third or so doesn't seem to make any more power.
Judging by feedback from the arseometer, it feels as if the butterfly is already fully open by the time the pedal is 2/3rds to the floor? Or, as if perhaps throttle body might be bigger than it actually needs to be? If so (?), then perhaps opening the butterfly past X° doesn't really do anything much because the constriction isn't the throttle body ID, but is instead say intake valve or port size, or something, maybe?
I don't know, but I do subjectively feel that the last 1/3rd or so of throttle pedal travel is rather pointless, at least with my engine. Anyone else?
Regards,
John.
Have you carried out a "Throttle Reset" ?
Quote from: bazzbazz on February 11, 2018, 04:30:30 PM
Have you carried out a "Throttle Reset" ?
Yes, but not for a long time, maybe about a year or so ago. Afterward there didn't seem to be any noticeable change in the way the engine felt or worked. I'll have another calibration session, but I don't expect any improvement.
I'm finding that this characteristic affects how the engine feels to drive. It contributes to a subjective feeling of the engine being underpowered in some circumstances, whereby you make a big input with the right foot and so 'expect' a big output. Instead, the engine only responds up to X pedal movement, then from there on is unresponsive to further opening, so feels 'wrong' and 'soft'.
I don't think there is an actual performance problem here, the engine is running sweetly and objectively accelerates well, feeling responsive up to about 2/3rds pedal movement. After this (with further movement) the performance feels as if it goes 'flat' because further pedal input does not generate an increase in power output. It is only a psychological issue to do with linearity of control and 'feel', not a real problem re power output.
I'd much rather a short pedal travel where all the travel feels to have some affect, than a long travel where much of the travel feels to do nothing. I do prefer a short pedal travel rather than a long one (I always have a very short travel adjusted into my kart pedal), but I'd be OK with a long pedal if it was reasonably linear in its' affect from closed to fully open. My throttle pedal lacks linearity, i.e. response to pedal movement seems so 'digressive' that it (response) becomes zero well before the pedal hits the floor.
It works the other way round too. As it is, when the pedal is already open a long way (floored or near to it) and I want to modulate acceleration or actually reduce speed somewhat, lifting off a bit doesn't do anything. I have to back off quite a lot to get a power reduction, because it takes a big lift to get any reduction in acceleration rate or actual speed, which is actually quite annoying.
This tends to suggest that the throttle body ID is not a constriction to airflow until the butterfly has been closed quite substantially, which tends to imply that the TB is too large in ID. If this is actually what is going on, then one 'fix' might be to place a block under the throttle pedal to eliminate the 'useless' pedal travel...
I'm fairly sure this isn't all just in my head, just wondering if anyone else has felt the same thing...
Regards,
John.
If you have diagnostics you can actually graph the pedal movement, & throttle body movement together & compare.
Alfa's electronic accelerator is tuned down with respect to pedal position so as not to allow the end user to be too abusive on the go.
See Novitec GP1.
http://shop.alfisti.net/Tuning-Styling/Alfa-147/Motor-Sports-Airfilters/Novitec-GP1::6627.html (http://shop.alfisti.net/Tuning-Styling/Alfa-147/Motor-Sports-Airfilters/Novitec-GP1::6627.html)
"If you have diagnostics you can actually graph the pedal movement, & throttle body movement together & compare."
I haven't desperately needed "diagnostics" as yet, so don't have it. I should get something...
"Alfa's electronic accelerator is tuned down with respect to pedal position so as not to allow the end user to be too abusive on the go.
See Novitec GP1."
I do think car manufacturers may well play games with what the throttle actually does, made possible by the electronic nature of FBW. Personally I wish it was just a cable connecting the pedal to the butterfly, without a computer making decisions on my behalf.
It occurs to me that there could be a reason a car manufacturer might be tempted to fit a TB that is somewhat larger than actually needed. A 'too big' TB will flow more air at smaller throttle openings, so will tend to make the engine feel more powerful / responsive at lower rpm / lighter throttle opening (i.e. feel more 'sporty' for a given max power). This would make a car feel 'zippier' in say an urban environment, where it is constantly accelerating from rest / low speed to moderate speed.
The downside is that this would adversely affect linearity of engine response as the throttle is opened further and further. The overly bored TB may well be capable of flowing significantly more air than the engine is capable of ingesting, because the 'bottleneck' is not the TB bore but something like valve or port size etc etc. This may make the last part of the throttle opening more or less redundant.
Of course, this being an electronically controlled FBW throttle, it should be possible to create any pedal to butterfly motion relationship the engineers may want. Of course for this to be useful the TB bore would need to be at least X size, or more. Keeping in mind that a TB that is too large won't restrict flow and thus won't reduce power, there might be some incentive to specify a TB that is just a bit too large just to ensure it doesn't ever choke the engine?
A clue might be found in how modified an engine needs to be (i.e. how much of an increase in air flow due to cams, porting etc.) before the stock TB starts to become the limiting factor. If the stock TB is fine with modifications that modestly increase airflow and thus power output, then this may imply that it could be a bit oversize for an unmodified engine?
Anyway, you can try this at home; accelerate hard in say third gear (or whatever works for you and whatever speed and safety restrictions apply on your test road) until rpm climb reasonably high, then back off just a bit. Does the rate of acceleration diminish? Or, do you have to lift off quite significantly before it does? If your engine is like mine, then the latter is the case.
I sometimes find that when I lightly back off from WOT there is a sensation that the rate of acceleration increases slightly, when it should be decreasing. I don't think the acceleration rate actually does increase, but I think that it doesn't decrease until the pedal has been backed off to a significant degree.
Subconsciously you (I) expect an instant drop in acceleration / speed the moment the pedal is lifted, but because this doesn't happen there is a feeling that acceleration increased. A bit like when you lock up the brakes on a slippery surface, the car feels like it starts to go faster, even though physics dictates that it can't.
Regards,
John.
I run my diagnostic software on an old IBM ThinkPad with dock. They're cheap and tough. Mine uses XP Pro but you could probably also install an OS like Mint. There are many times it's handy, you can use it to test presumptions, identify certain referenced components in generic fault codes, check for swapped modules and confirm firmware version.
There's stuff MultiECUscan doesn't do, like show individual coil or injection data, but it's still a worthwhile product in the paid format.
Quote from: bazzbazz on February 12, 2018, 05:28:54 PM
If you have diagnostics you can actually graph the pedal movement, & throttle body movement together & compare.
So if a substantial mismatch were seen then this could be a cause of the characteristic I'm seeing, maybe.
'Normal' would be to see pedal and butterfly movement 'graphs' match each other from idle to WOT? Lets assume that the 'throttle system' does this, but a significantly non linear relationship between pedal position / butterfly angle and power output still exists.
This would at least hint that the throttle body is capable of flowing significantly more air at WOT throttle than the engine can actually ingest (full flow into the engine being achieved before the butterfly is fully open), which would cause the last X° of throttle opening to be ineffective with respect to increasing power (wasted pedal motion, adding to the FBW sensation that the pedal isn't really quite connected to the engine (though of course the same issue could exist with a cable TB)).
The effect of an overly bored TB would be to increase initial throttle response, but diminish response the closer to WOT the butterfly moves. The full flow that the engine can actually use would occur at less than fully open butterfly. So, the driver sensation is that the engine seems to become less responsive to pedal motion the closer to the floor the pedal is pushed (this sensation may exist to some degree anyway, but I think the 'dead' pedal motion makes it feel significantly worse). Also, backing off from WOT won't result in the engine backing off from the power it's making, unless the pedal back off is significantly great enough (which adversely affects throttle control and sensitivity).
If this anaylsis (i.e. series of guesses and speculations) is correct, then ideally a slightly smaller TB could be installed. Failing that, a reprogramming of the ECU throttle maps might work, limiting butterfly opening to only that needed to provide the maximum air the engine itself can actually use (if one knew what the hell they were doing). Failing either of these things, a block of wood under the accelerator pedal...
Regards,
John.
Quote from: Cool Jesus on February 13, 2018, 07:50:26 AM
See Novitec GP1.
According to some graphs I've seen, I think that this and similar devices have a similar affect as the 'sport' button in our Saab 9-5.
My understanding of such devices (FWIW) is that they act as a digressive multiplier of pedal input. The signal sent to the ECU (and hence to the TB) with pedal motion is modified by the device, i.e. initial pedal motion is multiplied by X at the TB, but as the pedal motion increases the degree of multiplication increasingly decreases (can that be said this way?), creating a (more?) digressive relationship between the pedal position and the butterfly angle.
With the device, the butterfly initially moves more per unit of pedal motion, but it still takes the same amount of pedal motion for the butterfly to reach WOT. At first the butterfly moves more, then it moves in a manner increasingly closer to the original stock motion, reaching WOT at the same pedal position as would occur without the added device.
The device will make the engine feel more responsive / powerful with smaller pedal movements, but will be less effective at larger throttle openings since the modified and standard pedal / butterfly response curves will converge as pedal position moves closer to the floor. The tendency will be to make the engine feel more responsive with small pedal movement, but less responsive with very large pedal movement.
Don't get me wrong, I quite like our Saabs' 'sport' button, it's my preferred mode. However I tend to doubt that fitting a device such as the GP1 will have much affect on the issue I'm discussing, i.e. possible oversize of the TB and the driveability issues this may cause.
Regards,
John.
Can't comment much on the technical side of the Novitec GP1 module other than their literature makes comment on the ECU making changes to variables it can control (such as fuel delivery) in order to haven't he vehicle meet emission standards. So it may not be just a direct input correlation between pedal and throttle plate.
What I can say is, I installed the module on my 159 yesterday and acceleration response to pedal input is now day compared to the OEM night. Huge difference to now be able to take advantage of the engine's power output. Highly recommend the gadget. There are other brands also, not just Novitec. I think I went with Alfisti.net because of price and an offer of returning it within a month if you're not happy with results.
Hi John,
The missus had a 147, however I don't recall what type of throttle it used. If its just the plain old butterfly type then that type of response is typical of the design. All things being equal, the larger the throttle body / throttle plate the more likely the non-linear response.
Using a karting analogy, we went to great lengths to ensure the butterfly on the Walbro carby was exactly in-line with the air flow through the venturi. Not so much to do with air flow but more to ensure correct mixture creation at high airflow / high rpm. Could be worth 400rpm if not correct. On a flow bench it was proven to me the airflow through the Walbro and other similar pumper type carbies like the Ibea or Tillotson, the butterfly could be only 70% open and potential airflow would be at around 97%. The disturbance of the fluid through the carby caused by a not fully open butterfly had a significant impact on emulsion creation and flow, not so much on total air flow. Not so much of a problem on the slide type throttle of the Dellorto fitted to a Rotax.
Maybe car manufacturers compensate for the logarithmic type response of the simple butterfly valve with a bit of electronic wizardry in the servo system between pedal and valve. It would make sense. The "throttle" on a fuel injected car is only responsible for fluid control rather than mixture creation so would make sense to let the inlet valve events control ultimate airflow.
Its a bit like a steam locomotive. The most efficient mode of operation is to run with a wide open throttle and modulate power / speed via the infinitely variable valve events / travel provided by this very elegant design. Funnily enough Alfa Romeo copied the steam locomotive with the multiair engine!!!
Hi Colin,
I thought your name was familiar, and it has occurred to me that you could possibly be the kart racing Colin Edwards. We may have previously talked on Kartbook...?
I can't see the precise butterfly plate position being an issue with this (but I've been wrong before, maybe a couple of times...). And of course a fuel injection TB has no direct bearing on emulsification / dropletisation (I made that word up) since the fuel is entering the airstream nowhere near the TB.
It wouldn't surprise me if the Walbro et al were at max airflow before WOT, especially if fitted to something like a J engine. It also wouldn't surprise me if at least slightly 'oversize' TBs are quite common in road cars...
Of course running a constant WOT is how diesels operate, and is known to be more efficient than choking the throttle to control power output. It's my vague understanding that a significant amount of research has been / is being done into trying to run petrol engines with a constant WOT, controlling engine speed / power output with extremely variable valve timing and / or lift. But it tends to be very complicated to achieve, and complication = cost and reliability issues...
Regards,
John.
The Fiat / Alfa Romeo MultiAir engines fitted to the Giulietta, the Mito, the 124 and I believe Giulia Veloce do not feature a "traditional" throttle. The throttle-like device associated with the Multiair appears to be only required for low < medium rpm. Valve timing, lift, travel and duration etc provide the control of airflow and ultimate power output. Innovative use of high speed servos and hydraulics. Very clever!
I know of the MultiAir engine, but don't know much about it. I've been meaning to check out how it works, but for some reason just haven't gotten around to it yet. It does sound very clever as you say.
Regards,
John.
So I used a lump of wood attached to the underside of the pedal, blocking approximately the last 25mm or so of pedal travel. The result is interesting.
The size of the wood block (a bit of dowel) is fairly arbitrary. I just attached the block and tried it out (engine not running), then cut some off, then cut a bit more off until the pedal travel felt (underfoot) about an inch or so less than stock, roughly equating to how much of the last % of pedal travel felt (to me) to be more or less superfluous (i.e. no significant engine response to using the last 25mm or so of travel, as very roughly estimated by my ankleometer).
The stock pedal travel was about 70mm or so. It's now about 45mm, so throttle pedal travel has been quite significantly reduced. Does this cause the engine to make less power at pedal WOT? Does this mean that full butterfly WOT is not actually reached? Does butterfly WOT actually make more power than some lesser butterfly opening? I don't have any hard data, can't say.
I can say; quite subjectively, that the engine feels somewhat more responsive and powerful than with the stock pedal travel (which is a bit weird). The butterfly obviously cannot be opening further, so airflow cannot have been increased, at most the flow is relatively unchanged, or at worst is less, than before.
I think it's partly psychological, i.e. a placebo of sorts, related to the perceived reduction in pedal travel. The mind is tricked into feeling a more enthusiastic engine response simply because a smaller action (foot movement) was needed to achieve it. However, I really don't think there has been any significant actual loss of power (the sensation that power is increased is fairly compelling, so I tend to think there is no actual reduction).
With the stock pedal travel there came a point where further movement really didn't feel like it was doing anything more, just wasted woolly pedal motion. Even if the mind is not conscious of this, I suspect it is still registered subconsciously and contributes to 'feel'. With the shortened travel the pedal now does not reach a point where it ceases to feel that it is having some effect on power output. The engine response feels less 'doughy' (especially) near 'full' throttle, and in general feels more responsive.
Lifting off the throttle, the rpms feel to drop more immediately. Full throttle acceleration in first and second gear (using higher rpm) now feels at least as 'energetic' as before, but with better controlled and faster shifts. I think this is because the pedal now no longer needs to be 'lifted' that 25mm before any actual power reduction starts to occur. In stock form this 25mm of 'lift' takes some amount of time, not a lot but enough to be felt as a lessening of responsiveness to the lift, and contributing to less precise timing of all the actions the driver does when changing gear (all I really know here is that the shift feels better...).
Whatever, some may scoff but I really like the affects of this unlikely pedal modification, in whatever %s they might be real and / or imagined...
It does seem to me at least not unlikely, given this subjective 'evidence', that the TS TB is at least a bit oversized relative to the maximum airflow that the engine can actually achieve, and / or, the the butterfly reaches WOT significantly before the pedal contacts the pedal stop on the floor...
Regards,
John.
I would simply put it in 3rd or 4th gear, floor it till it started to run out of steam then slowly reduce throttle to see if there was a corresponding reduction in engi e speed/power.
Or is that over simplifying things?
Baz,
I've played this way already, though in 2nd and 3rd gears. Flooring it in 4th until it "runs out of steam" gets a bit faster than is wise on the public thoroughfare...
What I have found is; with my car (pre pedal mod), with the pedal flat to the floor and rpm climbing into the higher reaches (but not nearing redline), that the pedal can then be lifted about an inch or so before there starts being any obvious reduction in acceleration, then deceleration.
This moment is accompanied by a subjective sensation of the car very briefly accelerating even more than with the pedal fully on the floor, from the instant the pedal starts being lifted to the instant the deceleration starts being obvious. This is obviously not a real thing, the car is not actually accelerating harder for this brief moment, it is a false perception related to the conscious and subconscious expectation that the car should begin to decelerate at the very moment the pedal is lifted, but it doesn't. It's like when you brake on a very slippery surface and the brakes lock up, the car feels as if it acelerates, even though this is an impossibility (physics don't you know...).
Keep in mind the subjective nature of this 'test', and that attention is split between 'observing the test' and not crashing the car.
Regards,
John.
For anyone intrigued enough by my experience with this, it would be very easy to repeat the experiment. All you'd need is a small block of wood and some duct tape.
I'd be interested if anyone had a seemingly similar result, or if I'm just going a bit gaga in my old age...
Regards,
John.
Quote from: johnl on February 21, 2018, 05:03:04 PM
All you'd need is a small block of wood and some duct tape.
Images from
Indiana Jones & the Temple of Doom come flooding back with
Short Round driving like a maniac through Shanghai. ;D
I've been wondering whether this phenomena (seemingly more power at partial pedal throttle than pedal WOT) might be less to do with absolute butterfly opening, and more to do with the ECU defaulting to a very rich AFR in WOT open loop mode (as it is my understanding is a common practice, because the rich AFR is very 'safe'), and the rich mix resulting in some power loss.
So, I went looking on the web and found nothing definitive to support the idea, but a few things suggesting it might not be a crazy notion.
I've stolen the following explanation from some Mazda enthusiasts forum. I'm not saying this is unarguably a correct diagnosis of the issue, but it does pretty much mirror what I have been suspecting. It is a succint explanation, so rather than rewriting it I'm just cutting and pasting, with attributuion to 'Josh'.
"The reason there is more power at partial throttle than full throttle is because of the ECU's fuel delivery system. At WOT, the ECU basically dumps the maximum amount of fuel it can for that particular engine speed. This is called "open loop" operation because it ignores feedback from the O2 sensor. At partial throttle, the ECU is still operating in "closed loop" mode, where it injects the appropriate amount of fuel based on engine speed and O2 sensor readings. So at partial throttle, there is a more stoichiometric mix in the combustion chamber, providing a quicker, more complete burn, which ultimately results in more power.
This practice is the same for just about every car I've heard of, turbo or not. The intention is to avoid detonation at WOT by making the fuel mixture as rich as possible. This is not a problem or anything the dealer can address. It is a common design for fuel injection. It merely requires a little more attention to detail when learning how to drive your car fast.
-Josh"
I somewhat disagree with some of the last paragraph, I think it is a problem. Still happy with my lump of wood...
Regards,
John.
It seems nobody is attempting to replicate my experience with this...
With more familiarity all I can say is that my engine is now much more 'fun', feels significantly more 'lively' than before, and even the gear shifts feel better (maybe rpm drop starts to occur slightly more quickly in response to pedal lift, because the pedal doesn't have to come back / up through that part of the pedal travel that increases power above what WOT seems to produce?).
My speculation is that maybe the TB is at least a bit bigger than it really should be, or, that WOT causes the ECU to default to a 'safe' open loop map wherein the AFR is so rich that it is affecting power, or, that with WOT something (i.e. detonation, mapping?) is causing the ignition timing to become somewhat retarded, or some combination of the above.
If the TB butterfly is not reaching fully open (with reduced pedal travel), and it isn't too big, then this might suggest that more improvement could potentially be possible (if full pedal travel were reinstated) if the ECU could be 'persuaded' to remain in closed loop when the butterfly approaches / reaches fully open...
It's all a bit weird, but I'm pretty sure I'm not imagining this.
Regards,
John.
I've been reading with some interest, you really need a second car of identical spec (without modifications) to validate the postulations though. ;)
CB,
Of course you are completely correct to imply that what I am describing is an utterly subjective experience. This is a data free zone so far, and the engineers' credo should be kept in mind; "in God we trust, all others must provide data". For my own purposes with this I am happy to accept the feedback from my arseometer...
However I don't think that a second car is needed to validate / quantify this. One car and a rolling road would do it.
For experimental purposes the mod itself is dead easy, a block of wood and some tape to hold it in place. So it costs almost nothing to try it (unless you just have to have data, and so were to be paying for dyno time). But before that, I'd try the 'hold it flat to the floor and then back off a bit' experiment first.
If the car seems to accelerate a tad harder at some degree of partial throttle than it does actually at full throttle, or ever seems to not start slowing as soon as the pedal is backed off from the floor, then I think there is an issue worth exploring...
Regards,
John.
I'm just trying to convince you to acquire a second 147. Purely for experimental purposes, of course. ;)
Have pondered the behaviour you describe on and off. A question came to mind; the interplay of intake tract and variator solenoids against the ECU map.
The other more general comment is, driving a car in the city you want pretty instantaneous acceleration from a dead or near stop, but not to insane speeds. Possibly the car is programmed with this in mind?
Don't forget kids, the Variator cuts in at 3000 rpm.
Irrespective of load and throttle position? I'd have credited it with more sophistimacation.
Quote from: Citroënbender on February 27, 2018, 10:32:35 PM
I'm just trying to convince you to acquire a second 147. Purely for experimental purposes, of course. ;)
Last thing I want / need / have time / funds for is another car...
Quote from: Citroënbender on February 27, 2018, 10:32:35 PMHave pondered the behaviour you describe on and off. A question came to mind; the interplay of intake tract and variator solenoids against the ECU map.
It is a question, and I have no idea how to investigate or answer it. However I have no reason to think the variable intake tract and / or valve 'variator' are not working as they are supposed to, and don't suspect these things to be a problem or player here with this issue, but I can't say either one couldn't be...
Quote from: Citroënbender on February 27, 2018, 10:32:35 PMThe other more general comment is, driving a car in the city you want pretty instantaneous acceleration from a dead or near stop, but not to insane speeds. Possibly the car is programmed with this in mind?
I suspect this to be a potential motivation for why a manufacturer might fit a slightly oversized TB (or at least to err on the oversized side), i.e. for a given engine size and all else being equal it would tend to create a 'zippy' feeling when accelerating from rest to moderate speeds, or from low to moderate speeds, i.e. typical urban operation. Of course if the TB were excessively oversized then the car might become somewhat more difficult to drive, with too much response for a small throttle opening.
And another of course, a similar 'zippy' characteristic could be achieved electronically (I presume), i.e. just how the TB butterfly responds to pedal input, one not necessarily equalling the other. It could likely be done either way, i.e. mechanically or electronically, or maybe both ways at once...
With my car, limiting the throttle pedal travel has not resulted in a discernible reduction in higher speed acceleration. If anything it is better the higher the speed. It is also much better for pedal modulation when backing off / on / off etc. at higher speeds / rpms / larger throttle openings. Now, a small lift has a significant affect, rather than a large lift being needed for a significant reduction / increase in power.
Previously, once past X pedal position, the response to the pedal became 'doughy', whether hammering down or lifting off. Lifting off was weird, because lifting the pedal from the floor would initially cause no reduction in power, or even a slight increase (at least it sometimes felt like a slight increase). This meant that (from pedal on floor) quite a big lift was needed to make a modest reduction in power.
I will say that I rarely rev this engine over 5,500rpm. There is just no point as there is little power increase above this, and the gear ratios are close enough that shifting at 5,000 to 5,500rpm doesn't drop the engine out of the power band (i.e. below 3,500rpm or so). This is the same now as it was prior to limiting the pedal travel.
Regards,
John.
Quote from: bazzbazz on February 28, 2018, 12:39:57 AM
Don't forget kids, the Variator cuts in at 3000 rpm.
CB responded: "Irrespective of load and throttle position? I'd have credited it with more sophistimacation."
"sophistimacation"...?
I thought it was 3,500 rpm, but I really don't know. Would it not be possible to rig up a dash light that illuminated whenever the variator was activated? This would give some idea of just how strictly the variator was locked to rpm, or how much the point at which it activates 'floats' depending on other inputs...
Regards,
John.
From memory you can see its status on the ECU parameters listing with MultiECUscan. It's a two person job, though - one to drive and the other to observe.
Ok, I'll bite.... what's a variator?
Cylindrical device attached to the front of the intake Camshaft used to alter the timing. Electrically controlled, hydraulically operated.