engineermike

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I'm really just trying to get a better handle on this for myself. It did sound like something unusual was involved.


Norm
No problem. Spark source went to “torque control” as well. Top blue line is throttle plate angle. Middle yellow is accelerator pedal. Bottom green is spark timing.

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Norm Peterson

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So I assume that the PCM decides whether to follow driver demand or trip its tip-in limit is based on how fast the driver physically moves the pedal. Any idea how abrupt this might be - IOW, is it like an either-or switch that always happens at X%/second pedal input, or is there any sort of ramping between the two conditions over some range of pedal input speeds? Is there any vague-ish range over which the tip-in limitations are not as severe?

I can see where having to wait a half second for engine response to catch up to what you requested could be annoying at times. Where I'm heading with this is that I suspect that inserting half a second's worth of nonlinearity in the car's handling response would be even more annoying/frustrating for a driver who doesn't care to play co-pilot to somebody else's programming. Wouldn't that be likely to happen with electric drive at one end of the car and ICE drive at the other?


Norm
 

shogun32

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but seriously Norm, back in the old S197 days or back when carbs were a thing, you'd get an easy 1/2 second of delay from intake stall or knock retard or any number of confounding conditions, no? If you mash the pedal at say 4000+ RPM the half second ramp may have been much shorter or non-existent. 3000 RPM is too low to command "instant" full power.

And unless you've fixed the legion of chassis problems with the car, who cares about the engine output, the chassis/tire will give up the half-second easy.
 

Norm Peterson

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but seriously Norm, back in the old S197 days or back when carbs were a thing, you'd get an easy 1/2 second of delay from intake stall or knock retard or any number of confounding conditions, no? If you mash the pedal at say 4000+ RPM the half second ramp may have been much shorter or non-existent. 3000 RPM is too low to command "instant" full power.
Of course. In carburetor days, that was usually on the DIY owner for poor parts combinations (like too much carb or cam) and poor or nonexistent tuning afterward. I'm not sure what's going on with the 4.6 3-valve, though I know it has charge motion plates in the intake tract that claim to help at lower rpms, likely at some cost up top. But they don't seem to be a hindrance in my street driving or while cornering up to and including road course time. I've never had to get into the throttle in my '08 in advance of when I wanted the response to start coming in.


And unless you've fixed the legion of chassis problems with the car, who cares about the engine output, the chassis/tire will give up the half-second easy.
It's not about giving up the half second. It is about having uncertainty during that half second about what the car is really doing/going to do. Subjective feel and driver confidence depend on what you notice on a near-subliminal level.

What the engine is doing (or engine + motors) can make a noticeable difference in the handling. Cars are easier to drive hard when you trust them, and it's a lot easier to trust them when you're not having to predict what "corrections" the electronics are going to insert when you make a control input.


Norm
 

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Who would want this big ass engine at the front of a modern day sports car? The 5.2L is already showing the limits of a front engine RWD car. Putting more weight over the front axle is a recipe for disappointment. The current GT500 is already completely traction-limited as shown by the consistent 11s 1/4 mile times vs 10s on a prepped surface with appropriate tires.

This is literally the reason the Corvette went mid-engine. There's a reason the Porsche 911 Turbo S is a 10.1 second car from factory with a 3.6L engine... You guys can't complain about engineering, then advocate for bad engineering choices.
 

shogun32

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it's a lot easier to trust them when you're not having to predict what "corrections" the electronics are going to insert when you make a control input.
I think we need a 'Norm' driver feedback mode. The electronics won't intervene at all but if the electronics would have, it shocks the driver. 'tingle' mode for small values of out-of-range, big-ass jolt (think cattle fence) for larger. Resistance is not only futile, it's good for you. You WILL be assimilated.
 

shogun32

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You guys can't complain about engineering, then advocate for bad engineering choices.
have you MET the over-60yr old Mustang drvier? :)

edit: I was gonna say '50' but then I realized I R one.
 

Rinzler

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have you MET the over-60yr old Mustang drvier? :)
I was gonna say '50' but then I realized I R one.
LOL! I don't think it's an age thing, people are just obsessed with large displacement engines as if they are the solution to everything.

56% of the GT500's weight is over the front axle; That is bad. The GT500 weighs 4200 lbs; That is also bad. That is where you are going to find more performance out of the current platform. Not with more horsepower.

Here's an applicable excerpt from a C&D article:
1602689568320.png


There is a reason that the guys who race as ALL about weight reduction in these cars. It's not because they don't know what they're talking about.
 
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engineermike

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Well I got that one worked out. I disabled the “anti-jerk tipin switch” and now it blows the tires away instantly when I zombie-stomp it.

I tested it 4 times and it stayed in “driver demand” torque source and “tipin detonation ctrl” spark source. From wot pedal to wot blade 20 - 100 ms delay, which probably had more to do with polling rates than actual delay. Spark timing stayed in the mid teens rather than dropping below 0. Mission accomplished.

I just caution you that there are probably 20+ torque sources, plus air sources, spark sources, fuel sources, and many more, so don’t get hung up on this one.

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shogun32

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I disabled the “anti-jerk tipin switch” and now it blows the tires away instantly when I zombie-stomp it.
And Norm reaches the 4th ring of Heaven! What is the coordinate and revised value?
 

Norm Peterson

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And Norm reaches the 4th ring of Heaven!
Even though I doubt I'd ever run afoul of this tip-in limit, I'm happy for those who might that it can be circumvented.

At the same time, I hope that it encourages anybody who might also do this tweak to improve their own throttle modulation skill. I'm guessing that with a 6.8L engine under the hood that this would be even more important.


Norm
 
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Norm Peterson

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LOL! I don't think it's an age thing, people are just obsessed with large displacement engines as if they are the solution to everything.
It's always been that way, and not just where engines and their displacements are concerned. Thinking that runs something like "mine's bigger than yours" creeps into many of the choices that people make.


Norm
 

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Who would want this big ass engine at the front of a modern day sports car? The 5.2L is already showing the limits of a front engine RWD car. Putting more weight over the front axle is a recipe for disappointment. The current GT500 is already completely traction-limited as shown by the consistent 11s 1/4 mile times vs 10s on a prepped surface with appropriate tires.
There's no reason that a derivative of this 6.8 couldn't be a decent powerplant for a Mustang. No reason it'd have to have a cast iron block, for starters. Or the full 6.8L, for that matter (390 does have a nice ring to it if you're a Ford, Mustang, or Bullitt fan).


Norm
 

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This is literally the reason the Corvette went mid-engine. There's a reason the Porsche 911 Turbo S is a 10.1 second car from factory with a 3.6L engine... You guys can't complain about engineering, then advocate for bad engineering choices.
Engineering is frequently forced to work within constraints that aren't of engineering's own choosing. IOW, do the best you can with what you're given, as long as you stay inside the big box.

Perhaps the poster-boy example of that within the automotive world is one of the cars you just mentioned. I'm talking about the 911 Porsche and its rear engine. If it hadn't been for continuing engineering development over the past 55 years, it would have long ago been consigned to the dustbins of automotive history under 'things that might have had promise but didn't work out'.

Closer to home and as good as they are, both the Coyote and the Voodoo have also had to develop under constraints that you wouldn't choose if your primary focus was on power and performance.


Norm
 

engineermike

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Correct Norm. My favorite example of this is “the factory engineers recommend xyz motor oil so it just be good.” Ok, but if the engineer had his own performance car, would he personally use what is printed in the manual?
 

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