educate me on throttle / engine behavior - CorvetteForum - Chevrolet Corvette Forum Discussion


C6 Corvette General Discussion General C6 Corvette Discussion not covered in Tech
Sponsored by:
Sponsored by:

educate me on throttle / engine behavior

Reply
 
 
 
Thread Tools Search this Thread
Old 05-16-2018, 12:44 PM   #1  
mellojoe
CF Member
Thread Starter
 
mellojoe's Avatar
 
Member Since: Feb 2018
Location: Arizona
Posts: 90
Thanked 15 Times in 11 Posts
Default educate me on throttle / engine behavior

non-NPP / non-dual-mode exhaust, LS2 C6
  • Driving the Corvette around town at one-quarter throttle, the car is quiet, almost lazy. The engine barely gets above 1700 rpm, if that.
  • Driving at half throttle, getting on it a bit, she gets louder, and the speeds go tremendously up. This is your goosing-it on the highway noise.
  • Driving at full throttle, the exhaust noise is brilliantly loud with a huge boost in bass note.

What's the deal? The LS2 does not have variable cam timing. Mine doesn't have adjustable exhaust baffles. What is going on with the fuel / throttle / engine / airflow that gives the LS motor such separate personalities? Help me understand my car better.
mellojoe is online now   Reply With Quote
Old 05-16-2018, 12:50 PM   #2  
demon340
CF Senior Member
 
Member Since: Nov 2016
Location: Aurora IL
Posts: 372
Thanks: 0
Thanked 37 Times in 35 Posts
Default

You probably have a aftermarket exhaust or mufflers, maybe glass packs.
demon340 is offline   Reply With Quote
Old 05-16-2018, 01:26 PM   #3  
ruxvette
CF Senior Member
Support Corvetteforum!
 
ruxvette's Avatar
 
Member Since: Mar 2010
Location: T-Town WA
Posts: 8,387
Thanked 569 Times in 486 Posts
C6 of Month Finalist 2016
Default

To paraphrase Ft Morgan Al...this ain't a '53 Buick.
ruxvette is offline   Reply With Quote
The Following 2 Users Say Thank You to ruxvette For This Useful Post:
Bruze (05-16-2018), Landru (05-16-2018)
Old 05-16-2018, 01:42 PM   #4  
RicK T
CF Senior Member
 
RicK T's Avatar
 
Member Since: Sep 2005
Location: Las Vegas, Nevada
Posts: 20,051
Thanked 426 Times in 350 Posts
Default

I'm guessing you are reacting to the way the "drive by wire" throttle works on these cars.

Realize there is no physical connection between the accelerator pedal and the throttle blade, it is controlled by the computer. The accelerator pedal is just a rheostat that sends an electrical signal to the computer and the computer interprets what you want and opens the throttle the appropriate amount. Being overly simplistic, when you step on the accelerator pedal, say 25% or 1/4, the computer returns only about 3% - 4% throttle blade opening. If you step down 50% or 1/2 throttle, the computer returns about 15% throttle blade opening. From that point on, the more you step down on the pedal, the computer returns MUCH more throttle blade opening relative to pedal movement until they achieve a 1:1 at WOT.
RicK T is offline   Reply With Quote
The Following 2 Users Say Thank You to RicK T For This Useful Post:
BlackMamba89 (05-17-2018), mellojoe (05-16-2018)
Old 05-16-2018, 01:54 PM   #5  
~STOLEN~
CF Senior Member
 
~STOLEN~'s Avatar
 
Member Since: Oct 2010
Location: Greenwood Indiana
Posts: 1,690
Thanked 54 Times in 45 Posts
Default

im gonna go with it has a 3/4 ghost cam in it
~STOLEN~ is online now   Reply With Quote
Old 05-16-2018, 02:59 PM   #6  
Landru
CF Senior Member
 
Landru's Avatar
 
Member Since: Dec 2002
Location: Wayne Township WI
Posts: 8,005
Thanked 304 Times in 265 Posts
Default

A6. Stock exhaust. n-NPP. Quasi-quiet operation at various parameters. loud at WOT.
No pun, it sounds normal to me.

Consider target demo of C6, disposable income types want to drive their C6 to where ever, didn't want bleeding eardrums or drawing all the wrong attention.

2 sides.
One says note's OK, as-is.
Two says far too quiet.
Outliers just right.

#2 type upgrade from a dozen C6 aftermarket can makers.
Great attribute of larger car exhibitions like Mecum/BJ, can makers on site demoing their product. Hearing up close & personal makes for a true informed decision.
Internet, OTOH, absolute worst source for making a choice while usually OK to buy once you know what you want.

But, be careful what you wish for going aftermarket exh.
Drone gets on the nerves, fast.
Have heard same story here many times since '05, members upgrade to something they thought they could live with only to realize it was annoying & impossible to ignore.

Not happy laying out $ to go back stock or something much quieter. YMMV
Landru is online now   Reply With Quote
Old 05-16-2018, 04:08 PM   #7  
mellojoe
CF Member
Thread Starter
 
mellojoe's Avatar
 
Member Since: Feb 2018
Location: Arizona
Posts: 90
Thanked 15 Times in 11 Posts
Default

Perhaps I'm not making myself clear. I apologize for the confusion. I am not upset at the loud car. There is no aftermarket exhaust on the car. I am knowledgeable about cars, turning wrenches, getting my hands dirty, etc.

What I am trying to understand is how GM is able to achieve a 2-step feel to a non-variable-cam engine. Is the ECU adjusting timing significantly to mimic a variable cam? Is the direct injection mapped to specific throttle inputs? Rick_T, thank you for your input. Does the electronic throttle have a variable mapping paired up with engine load? My previous vehicles were much more linear in response. The LS2 feels, as I've mentioned, almost stepped in 3 phases. Low load, medium load, and high load. The characteristics of the engine are so different across its different operational modes. Which is why I mentioned that this isn't a mechanical mode switch (ie: no variable cam, no exhaust diverter, no secondary throttle butterfly at WOT).

I was hoping some more details of how the engine management works in the LS2.
mellojoe is online now   Reply With Quote
The Following User Says Thank You to mellojoe For This Useful Post:
Landru (05-17-2018)
Old 05-16-2018, 05:00 PM   #8  
Turbo6TA
CF Senior Member
 
Turbo6TA's Avatar
 
Member Since: Mar 2011
Location: Florida
Posts: 6,309
Thanked 376 Times in 293 Posts
Default

As far as the big change in sound from your exhaust pipes, are you sure you don't have the NPP option?

Post a photo of the exhaust tips on your C6 ... Take the photo from down low like this photo:



Do you see that valve actuator just above the tail pipe tip? ..... Do you have it too?

In fact, you can see the butterfly of the valve (now open) if you look down the pipe.

.
Turbo6TA is online now   Reply With Quote
Old 05-16-2018, 05:29 PM   #9  
mellojoe
CF Member
Thread Starter
 
mellojoe's Avatar
 
Member Since: Feb 2018
Location: Arizona
Posts: 90
Thanked 15 Times in 11 Posts
Default

No. I am certain there is no NPP exhaust on this vehicle. There is also no cutouts. It is not an exhaust noise I'm specifically curious about but overall engine noise, and behavior.
mellojoe is online now   Reply With Quote
Old 05-16-2018, 05:47 PM   #10  
LMB-Z
CF Senior Member
 
LMB-Z's Avatar
 
Member Since: Jan 2006
Location: Texarkana Texas
Posts: 6,320
Thanked 374 Times in 339 Posts
Default

The harder you push on the "gas" pedal, the faster it goes.
LMB-Z is offline   Reply With Quote
The Following User Says Thank You to LMB-Z For This Useful Post:
mellojoe (05-16-2018)
Old 05-16-2018, 07:11 PM   #11  
FatsWaller
CF Senior Member
 
FatsWaller's Avatar
 
Member Since: Aug 2017
Location: Etobicoke Ontario
Posts: 261
Thanked 45 Times in 37 Posts
Default

Quote:
Originally Posted by mellojoe View Post
Perhaps I'm not making myself clear. I apologize for the confusion. I am not upset at the loud car. There is no aftermarket exhaust on the car. I am knowledgeable about cars, turning wrenches, getting my hands dirty, etc.

What I am trying to understand is how GM is able to achieve a 2-step feel to a non-variable-cam engine. Is the ECU adjusting timing significantly to mimic a variable cam? Is the direct injection mapped to specific throttle inputs? Rick_T, thank you for your input. Does the electronic throttle have a variable mapping paired up with engine load? My previous vehicles were much more linear in response. The LS2 feels, as I've mentioned, almost stepped in 3 phases. Low load, medium load, and high load. The characteristics of the engine are so different across its different operational modes. Which is why I mentioned that this isn't a mechanical mode switch (ie: no variable cam, no exhaust diverter, no secondary throttle butterfly at WOT).

I was hoping some more details of how the engine management works in the LS2.
AFAIK, no direct injection. Otherwise, we could be running 87 octane with no problems. The tune parameters programmed in the ECU are responsible for what you are experiencing.
FatsWaller is offline   Reply With Quote
The Following User Says Thank You to FatsWaller For This Useful Post:
mellojoe (05-17-2018)
Old 05-16-2018, 08:13 PM   #12  
HOXXOH
CF Senior Member
 
HOXXOH's Avatar
 
Member Since: Sep 2007
Location: Peoria/Phoenix AZ
Posts: 13,224
Thanked 667 Times in 557 Posts
Default

The throttle mapping pretty much follows the same sequence that existed on higher performance carburetor cars. Light throttle pressure only opens the primaries, then the secondaries slowly kick in, and finally they become wide open. The cars with 2-barrel carbs generally didn't have enough power to notice a big difference. It's why progressive linkage was created, especially for multi-carb engines.

Without a graduated power increase on a single blade throttle, driving on snow/ice would be a really big challenge for nearly all drivers. The electronic throttle modifiers only are concerned with the relationship of how quickly your butt feels movement in relationship to your foot movement. The exception is the Vitesse, that also can retard the relationship when that becomes a preference for greater control.
HOXXOH is offline   Reply With Quote
The Following User Says Thank You to HOXXOH For This Useful Post:
mellojoe (05-17-2018)
Old 05-16-2018, 08:24 PM   #13  
BlindSpot
CF Senior Member
 
BlindSpot's Avatar
 
Member Since: May 2016
Location: Encanterra Arizona
Posts: 2,461
Thanked 330 Times in 296 Posts
Default

Quote:
Originally Posted by mellojoe View Post
No. I am certain there is no NPP exhaust on this vehicle. There is also no cutouts. It is not an exhaust noise I'm specifically curious about but overall engine noise, and behavior.

OK, so here's a SHORT explanation of the engine management system EMS.



When you are in lower RPM to moderate RPM cruising, the system operates in closed loop. In CL, the ECU is using FB from the O2 sensors and it maintains a stoich Air Fuel Ratio (14.7:1), and working with a relative frequency range (or volume) from the MAF input.



When you're commanding full throttle or approximately anywhere in the range of the last 2000 RPMs before redline, the EMS switches out of CL and enters Power Enrichment. During PE the AFR will run in a range of about 12:1 to about 12.5:1 and the ECM will choose fueling from a hard table, no longer relying on the front O2 sensors. That is a distinctive change that, if you're really good, you might be noticing and might be what you're asking. If you were boosted, it would be quite noticeable.



In addition/conjunction, during these various RPMs and throttle commands, the ECU is also choosing the timing based on a table (matrix). Timing will vary with a few inputs. RPM is one and Spark Air Mass is another. Spark Air Mass has a "rough" relationship to relative throttle position and actual throttle position and NOT commanded throttle position which some here have tried to describe.



This is about all I can give you without going to a much higher level.
BlindSpot is offline   Reply With Quote
The Following User Says Thank You to BlindSpot For This Useful Post:
mellojoe (05-17-2018)
Old 05-17-2018, 12:02 AM   #14  
kevinkar
CF Senior Member
 
kevinkar's Avatar
 
Member Since: Oct 2013
Location: California
Posts: 290
Thanked 25 Times in 24 Posts
Default

Quote:
Originally Posted by RicK T View Post
I'm guessing you are reacting to the way the "drive by wire" throttle works on these cars.

Realize there is no physical connection between the accelerator pedal and the throttle blade, it is controlled by the computer. The accelerator pedal is just a rheostat that sends an electrical signal to the computer and the computer interprets what you want and opens the throttle the appropriate amount. Being overly simplistic, when you step on the accelerator pedal, say 25% or 1/4, the computer returns only about 3% - 4% throttle blade opening. If you step down 50% or 1/2 throttle, the computer returns about 15% throttle blade opening. From that point on, the more you step down on the pedal, the computer returns MUCH more throttle blade opening relative to pedal movement until they achieve a 1:1 at WOT.
This is, in my opinion, the definitive answer to the OP's question.

I had my '05 for 4 years and actually hated the fly-by-wire pedal. It's not linear like a cable linkage to a butterfly valve such as in my '95 Camaro's LT1. That was instant response. The Corvette relies on the position sensor and there's a perceptible lag between pushing with your foot and the results in RPM and sound and the variable percentages Rick T spells out above are not equal and there's a big step past that 1/4 point.

This is why there are modules you can buy to revise that throttle response but sadly they did not apply to my '05 and I never upgraded it. You should try that if you want better 0-25% position response.
kevinkar is offline   Reply With Quote
The Following User Says Thank You to kevinkar For This Useful Post:
mellojoe (05-17-2018)
Old 05-17-2018, 03:40 PM   #15  
Sayfoo
CF Senior Member
 
Sayfoo's Avatar
 
Member Since: Sep 2005
Location: Orange County Ca
Posts: 1,468
Thanked 18 Times in 16 Posts
Default

With a standard exhaust, you are mostly hearing engine/intake noise. It sounds pretty good from inside the car.
But, have you ever heard it from outside the car? Totally different. Wot from outside sounds more like a "woosh", not any kind of thundering/rumbling/hipo sound. This is why they have the dual mode/npp or people go aftermarket.
Interestingly, noise can make a big difference in how you perceive performance. Like with npp, it's just a few hp difference, but many people believe they are going a lot faster when the valves are open.
Sayfoo is offline   Reply With Quote
Old 05-17-2018, 08:58 PM   #16  
VitesseMotorsports
Supporting Vendor
 
VitesseMotorsports's Avatar
 
Member Since: Aug 2015
Location: Rutherford NJ
Posts: 188
Thanked 39 Times in 29 Posts
Default

You definitely need a Throttle Controller ! It will make your Throttle more linear: 5% Gas pedal travel will give you 5% Throttle Body Blade opening, 10% is 10%, 50% is 50% and so on....

The car will feel more responsive and more predictably.

The Controller will also get rid of the built-in lag...
VitesseMotorsports is offline   Reply With Quote
Old 05-17-2018, 09:04 PM   #17  
Corvette_Ed
CF Senior Member
 
Corvette_Ed's Avatar
 
Member Since: May 2012
Location: Dallas/Ft. Worth
Posts: 11,105
Thanked 774 Times in 623 Posts
Default

Quote:
Originally Posted by VitesseMotorsports View Post
You definitely need a Throttle Controller ! It will make your Throttle more linear: 5% Gas pedal travel will give you 5% Throttle Body Blade opening, 10% is 10%, 50% is 50% and so on....

The car will feel more responsive and more predictably.

The Controller will also get rid of the built-in lag...
I think we need to talk. I've been putting it off, but I think it's about time.
Corvette_Ed is offline   Reply With Quote
Old 05-18-2018, 08:22 PM   #18  
VitesseMotorsports
Supporting Vendor
 
VitesseMotorsports's Avatar
 
Member Since: Aug 2015
Location: Rutherford NJ
Posts: 188
Thanked 39 Times in 29 Posts
Default

It's never too late !
VitesseMotorsports is offline   Reply With Quote
Old 05-18-2018, 08:48 PM   #19  
Corvette_Ed
CF Senior Member
 
Corvette_Ed's Avatar
 
Member Since: May 2012
Location: Dallas/Ft. Worth
Posts: 11,105
Thanked 774 Times in 623 Posts
Default

Quote:
Originally Posted by VitesseMotorsports View Post
It's never too late !
PM sent.
Corvette_Ed is offline   Reply With Quote
Go Back   CorvetteForum - Chevrolet Corvette Forum Discussion >
Reload this Page
  • educate me on throttle / engine behavior
  •  
     
    Reply


    Thread Tools Search this Thread
    Search this Thread:

    Click for Advanced Search

    Posting Rules
    You may not post new threads
    You may not post replies
    You may not post attachments
    You may not edit your posts

    BB code is On
    Smilies are On
    [IMG] code is On
    HTML code is Off
    Trackbacks are Off
    Pingbacks are Off
    Refbacks are Off

    Forum Jump

    Sponsored Ads
    Vendor Directory

    All times are GMT -4. The time now is 09:12 AM.


    We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
     
    • Ask a Question
      Get answers from community experts
    Question Title:
    Description:
    Your question will be posted in: