Different Drive Modes

[SatinBlueG3]

Sorry for the noob question but is the power limited when your not in track/ sport mode?

[Jack B]

Sorry for the noob question but is the power limited when your not in track/ sport mode?

Even with ESC off there is still some PCM intervention.. I believe the modes you are referring to are primarily shock settings on the non-SRT cars and do not impact the PCM control over power.

[CNU_Physics]

with ESC off is it intervention with Traction Control or Stability Control or Both?

[Whiskey]

With a Viper you get full power all the time. It's not like the Euro trash that limits power.

[Jack B]

With a Viper you get full power all the time. It's not like the Euro trash that limits power.

That is not quite true, if you log, throttle, rpm and mph you can see the pcm still has control, it is not all about pedal position. Pedal position and throttle position can be quite diff.

[Whiskey]

That is not quite true, if you log, throttle, rpm and mph you can see the pcm still has control, it is not all about pedal position. Pedal position and throttle position can be quite diff.

I agree with you but I don't think that was the OP's question. There is no setting that can be turned on to intentionally limit power output.

Examples:

"Street mode" that limits vehicle to 500hp.
Eco Mode. Limits power for best mpg.


What you are talking about is different because there is no mode to cause it to intentionally limit power on the Viper. What you are talking about is petal position vs TB position and that's just to aid the user in traction...at redline you still get the full 645hp. It's well known the car will pull timing for "high" intake temps thus limiting power. But again, it's not a user configured setting.

We do have "Limp Mode" but that's not user configured but is a power limited mode. It's not user triggered unless we consider bending a pushrod or spinning bearings user configured lol.

[Old School]

What you are talking about is petal position vs TB position and that's just to aid the user in traction...at redline you still get the full 645hp.

I thought this was emissions related.

[StrokerAce]

I was under the impression that 30% pedal does not equal 30% throttle opening. I do not believe it to be linear as I have never seen another drive by wire car that is but I might be speaking out of turn. Either way that doesn't limit the power either. WOT is WOT but 50% pedal usually doesn't mean 50% throttle.

[Lawineer]

It's also "drivability related." You don't really want 20% pedal to = 20% throttle opening. Power output isn't linear with % throttle position.

Unless "pedal to the floor" =/= WOT, it's not holding back power.

Now, it certainly pulls power by way of the tune based on intake temps, coolant temps, blah blah blah, but that's another story and unrelated to drive mode or stability control.

[Jack B]

Pedal to the floor does not guarantee wot, the stock pcm brings in the throttle according to programming and sensor input. Even at max rpm power may be limited, especially in first and second gear where traction can be compromused. I will have to look back, however, t believe WOT is 81% when logging, in other words, in 3rd gear and beyond, WOT is denoted as 81%, even though fully open.

[usmcfieldmp]

That sounds similar to my recollection of logging my Cobalt. I seem to recall that idle is around 20% throttle; WOT is around 89%. I haven't tried logging my GTS.

[SatinBlueG3]

I agree with you but I don't think that was the OP's question. There is no setting that can be turned on to intentionally limit power output.

Examples:

"Street mode" that limits vehicle to 500hp.
Eco Mode. Limits power for best mpg.


What you are talking about is different because there is no mode to cause it to intentionally limit power on the Viper. What you are talking about is petal position vs TB position and that's just to aid the user in traction...at redline you still get the full 645hp. It's well known the car will pull timing for "high" intake temps thus limiting power. But again, it's not a user configured setting.

We do have "Limp Mode" but that's not user configured but is a power limited mode. It's not user triggered unless we consider bending a pushrod or spinning bearings user configured lol.

Yes, this was my exact question. Thank you for everyone's feedback.

[Lawineer]

Pedal to the floor does not guarantee wot, the stock pcm brings in the throttle according to programming and sensor input. Even at max rpm power may be limited, especially in first and second gear where traction can be compromused. I will have to look back, however, t believe WOT is 81% when logging, in other words, in 3rd gear and beyond, WOT is denoted as 81%, even though fully open.

Wonder why they would do that, especially in third.

[Jack B]

Wonder why they would do that, especially in third.

I think most cars are the same. I believe they define it as relative throttle position. That % is the same for all gears. My point was you typically do see true WOT until 3rd gear. That is not all bad, WOT does not produce max power at all rpm/load points.

[Steve M]

When logging pedal position (driver demand) vs. throttle blade position (airflow delivered) vs. RPM, I've noted the same as what Jack has noted in his logs, provided I'm understanding him correctly. Basically, when you mash the gas pedal to the floor, the throttle blades don't open fully until pretty high up in the RPMs. Even then, they never truly open 90°. There are a couple of reasons for that:

1. The twin 74mm plastic (2008-2010, 2013-2014) or twin 76mm metal (2015-2017) Viper throttle bodies found on the Gen 4 and 5 cars flow massive amounts of air...way more than what's needed to feed these engines. Ever notice how even guys that run big honking 9L displacement variants don't touch the throttle bodies? They don't have to open up all the way for a good portion of the RPM range to feed the amount of air required to meet the driver demand, even with a larger than OEM displacement.

2. The reason they don't open fully is best illustrated by some cheesy graphics, so please bear with me.

At idle, the blades on a drive by wire car are always cracked...that's why there's no need for the typical idle air control valve like you'd see on a cable driven throttle body.

https://i.ibb.co/vHcmDRD/Throttle-Body-Diagram-at-Idle.png

At part throttle, the driver presses down the gas pedal; the PCM sees that demand and determines the amount of torque required to deliver it, along with all of the other demands (A/C, alternator, water pump, etc.); for a given amount of torque, the PCM knows how much airflow (and fuel + timing) needs to be delivered, and opens the throttle blades a set amount to achieve the desired airflow:

https://i.ibb.co/Y3sTs7x/Throttle-Body-Diagram-at-Part-Throttle.png

The relationship between the % the throttle blade is open vs. the cross-sectional area of the opening is most definitely not linear.

At wide open throttle, the blades eventually open all the way, but not to 90° as seen here (not drawn to scale to illustrate the point):

https://i.ibb.co/vwRMtsS/Throttle-Body-Diagram-at-WOT-1.png

The reason why should hopefully be obvious in this next diagram:

https://i.ibb.co/bWZ2q4R/Throttle-Body-Diagram-at-WOT-2.png

The shafts upon which the throttle blades rotate are significantly thicker than the blades themselves. I've not measured them, but it isn't trivial. You can see them here:

https://i.ibb.co/728pnRG/Throttle-Blade-Shafts.png

That's why you'll only see WOT values of around 86-87% on these cars. Opening them more than that would be a waste. It would also take extra time to shut the blades like when you let off the throttle, or heaven forbid, during a runaway throttle situation where the PCM has to step in and shut everything down as quickly as possible. Every millisecond counts when it comes to safety, so the throttle blades essentially always have a head start on the way to closing.

Not sure that helps anyone, but I've had the idea for these diagrams floating around in my head for the past few months, and haven't had time until today to get it down in a reasonable format that will let me get it out of my brain so I can move on with more important things. Like taking out the trash.

[former345bhpLS1]

Awesome post Steve! Thank you for the education. :)

-Nick

[Jack B]

More food for thought. On my car, the max % of throttle position did not change from stock, to HC, to 9L I believe that max % that is logged is actually plate full open. I will look tonight at some logs for the actual number.. For now let's say it is 89%, that number remained the same for all phases of my build. As I said I never see full throttle in 1st and 2nd, however, I see 89% in 3rd., 4th.and beyond.

[StrokerAce]

I figured the two TB's at 100% flowed more than could be used. Glad to know my brain, though limited, was partially correct. Haha Maybe I'm operating on 89%?

[Old School]

I am by no means an expert at drive-by-wire throttle bodies, but does the 89% actually refer to the mechanical rotation of the throttle blades or is it the percentage of the actuators rotation range? Which could be 100% blade opening. I always assume the throttle body relearn procedure was to find the mechanical "ends" of throttle rotation.

[Arizona Vipers]

Scot Rickord from Prefix was telling me at full throttle the throttle bodies themselves only open up 97%, they leave it this way even on their high horsepower builds.
He was concerned that I could be losing some velocity when I switched to Motec which might be opening up the throttle bodies 100%

[Jack B]

Scot Rickord from Prefix was telling me at full throttle the throttle bodies themselves only open up 97%, they leave it this way even on their high horsepower builds.
He was concerned that I could be losing some velocity when I switched to Motec which might be opening up the throttle bodies 100%

My guess is the you are correct and the relative 89% we see is actually 97% of the mechanical opening.

[Lawineer]

I figured the two TB's at 100% flowed more than could be used. Glad to know my brain, though limited, was partially correct. Haha Maybe I'm operating on 89%?

Twin 74mm or 76 throttle bodies are definitely no a restriction on this car unless you really start cranking out power- probably getting to 1000hp or so.

[Arizona Vipers]

Funny side note, these throttle bodies are actually old school Jeep 4.0 throttle bodies lol

[Lawineer]

Funny side note, these throttle bodies are actually old school Jeep 4.0 throttle bodies lol

Well, I can assure you those things weren't restricted at the throttle body either! 190 hp, lol.

[Jack B]

Here is a partial log. This area of the log is immediately after a pedal to the floor shift (1st to 2nd) at 6,300 rpm. here is some detail:

1. The straight red line at the top shows the pedal is at 91% or on the floor. The pedal percentage never goes beyond 91%

2. The brown/gray line is rpm, it drops to approx 5,100 after the 6,300 shift point.

3. The throttle (green) drops to 57% after the shift to 2nd, even though the pedal is on the floor. Note, the throttle eventually goes horizontal, that is WOT or 81%.

4. In addition, the timing (black) drops just like the throttle, it goes down to 9 degrees. The throttle and timing curves are almost identical, just offset by a little.

Ignore the higher/second rpm line, that is related to drive shaft speed


48358

[Jack B]

I figured out why we do not see 100% of throttle or pedal. These sensors are 0-5 volt devices. As an example,when the pedal (above post) sensor indicates 91%, while it is 100% depressed, the reason is, at that point the voltage sensor is reading 4.5 volts which is 0.91 X 5.0 volts. The same would apply to the throttle sensor, that is why they are called relative values.