mellojoe

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.

demon340

ruxvette

To paraphrase Ft Morgan Al...this ain't a '53 Buick.

RicK T

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.

~STOLEN~

im gonna go with it has a 3/4 ghost cam in it

Landru

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

mellojoe

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.

Turbo6TA

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.

.

mellojoe

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.

LMB-Z

The harder you push on the "gas" pedal, the faster it goes.

FatsWaller

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.

HOXXOH

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.

BlindSpot

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.

kevinkar

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.

Sayfoo

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.

VitesseMotorsports

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...

Corvette_Ed

I think we need to talk. I've been putting it off, but I think it's about time.

VitesseMotorsports

It's never too late !

Corvette_Ed

PM sent.