Z51 Performance Package
Race Director
Joined: Oct 2004
Posts: 10,089
Likes: 14
One more thing, of all people, I thought you would have known that RPM makes a big difference on mileage. Remember Lindberg and what he did with the P38's in the Pacific during WWII. He taught the pilots to run over-square which was thought to be taboo on an internal combustion engine. He had the pilots running low rpms and high manifold pressures in order to get better mileage. If you turn the engine at lower rpm's the friction losses go down and you run the engine with more throttle angle and thus less pressure drop across the throttle body.
However, my real point, is for the A4 to have as good of acceleration as an A6, you need to put in 3.90 gears and you will NO LONGER be cruising at 2300 rpm at 80, now you'll be cruising at almost 2800 rpm. Now look at the mileage. We are now comparing an engine running at 2800 rpm versus the A6 running at 1700 rpm. That's a big difference.
Why would you look a gift horse in the mouth? It's one of those few instances where you get more performance and better mileage. Sounds like a win/win situation to me!
However, my real point, is for the A4 to have as good of acceleration as an A6, you need to put in 3.90 gears and you will NO LONGER be cruising at 2300 rpm at 80, now you'll be cruising at almost 2800 rpm. Now look at the mileage. We are now comparing an engine running at 2800 rpm versus the A6 running at 1700 rpm. That's a big difference.
Why would you look a gift horse in the mouth? It's one of those few instances where you get more performance and better mileage. Sounds like a win/win situation to me!
GM Powertrain published a set of graphs that showed the expected MPG improvement going from the A4 to the A6 was 3%. But the EPA MPG tests didn't confirm that, so the A6 cars have the same highway MPG rating as the A4 cars did. Even if Powertrain was right, 0.9 MPG is nothing to get excited about.
As for the lower low gear, the Powertrain graphs showed a 15% torque increase for the A6 compared to the A4 with a 2.73 rear ratio. With the optional 3.15 ratio the advantage dropped to only 2.5% (I know that doesn't agree with simple scaling, I can only assume that they took other factors into account, perhaps differences in torque converter multiplication ratios at the different RPMs). Anyway, we know the C6 is traction limited at launch, so more launch torque isn't all that helpful anyhow.
While theoretically the A6 presents some advantages over the A4, in reality those advantages aren't very large, in the single digit range, and may be offset to a significant degree by the greater complexity, size, and weight of the A6. It is true that an A6 Corvette currently holds the showroom stock quarter mile record. But I'm not so sure that means much in the mod happy go faster world of drag racing in general.
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
What Lindberg was telling pilots to do doesn't really apply here. First he was dealing with mechanically supercharged engines. Second, cruise power on a P-38 was between 30% and 40% of peak power. Our C6s aren't pulling anywhere near that at 80 MPH cruise. I've seen a figure showing drag power at 60 MPH for a Corvette is 7 hp. Now drag power goes up with the square of speed, but it should still be in the 15-20 hp range at 80 MPH. That's 5% of peak power, the accessories are typically pulling more power. Very different operating condition from a P-38 at cruise.
GM Powertrain published a set of graphs that showed the expected MPG improvement going from the A4 to the A6 was 3%. But the EPA MPG tests didn't confirm that, so the A6 cars have the same highway MPG rating as the A4 cars did. Even if Powertrain was right, 0.9 MPG is nothing to get excited about.
As for the lower low gear, the Powertrain graphs showed a 15% torque increase for the A6 compared to the A4 with a 2.73 rear ratio. With the optional 3.15 ratio the advantage dropped to only 2.5% (I know that doesn't agree with simple scaling, I can only assume that they took other factors into account, perhaps differences in torque converter multiplication ratios at the different RPMs). Anyway, we know the C6 is traction limited at launch, so more launch torque isn't all that helpful anyhow.
While theoretically the A6 presents some advantages over the A4, in reality those advantages aren't very large, in the single digit range, and may be offset to a significant degree by the greater complexity, size, and weight of the A6. It is true that an A6 Corvette currently holds the showroom stock quarter mile record. But I'm not so sure that means much in the mod happy go faster world of drag racing in general.
GM Powertrain published a set of graphs that showed the expected MPG improvement going from the A4 to the A6 was 3%. But the EPA MPG tests didn't confirm that, so the A6 cars have the same highway MPG rating as the A4 cars did. Even if Powertrain was right, 0.9 MPG is nothing to get excited about.
As for the lower low gear, the Powertrain graphs showed a 15% torque increase for the A6 compared to the A4 with a 2.73 rear ratio. With the optional 3.15 ratio the advantage dropped to only 2.5% (I know that doesn't agree with simple scaling, I can only assume that they took other factors into account, perhaps differences in torque converter multiplication ratios at the different RPMs). Anyway, we know the C6 is traction limited at launch, so more launch torque isn't all that helpful anyhow.
While theoretically the A6 presents some advantages over the A4, in reality those advantages aren't very large, in the single digit range, and may be offset to a significant degree by the greater complexity, size, and weight of the A6. It is true that an A6 Corvette currently holds the showroom stock quarter mile record. But I'm not so sure that means much in the mod happy go faster world of drag racing in general.
Racer
Joined: Mar 2007
Posts: 338
Likes: 0
From: KC KS
That's the way I understand it. I have a 2007 F55 with stock sways and run mine in "Tour" mode most of the time. On rough roads in "Sport" mode it feels pretty stiff, enough to make my back uncomfortable. I switch to "Sport" mode when I want to play. It's really pretty cool to change your suspension with a flip of a switch.
Banned Scam/Spammer
Joined: Aug 2005
Posts: 15,607
Likes: 3
From: 41-33 Cry it out Koko!!!
St. Jude Donor '08-'09-'10-'11
I'll take the A6. You just can't argue that it's not quicker, as you said, the quickest stock car is an A6. And once you make the A4 equivalent in gear ratio by putting in 3.90 gears, you and I both know the mileage at 1700 rpm at 80 versus 2800 rpm at 80 will be enough to hurt your wallet. Plus, the engine will wear greater while always running at 2800 rpm versus 1700 rpm. Again, it's just a win-win situation. But it sounds like you are admitting to that.
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
Sorry to beat a dead horse, I just get frustrated with people that keep saying that 4 gears are enough in a Vette. GM obviously thought there was an advantage and so do a lot of other faster A6 Vette owners. It may be only a slight advantage, but at the drag strip .2 of a second is significant (I could have said it was .35 seconds looking at the 1/4 mile list, but I think that is a bit much). And to get this .2 second advantage with a car that actually gets slightly better fuel mileage is amazing.
Sorry,
Glenn
Sorry,
Glenn
Advanced
Joined: Dec 2006
Posts: 59
Likes: 0
Aaaagh!
The tell-tale 2005 Rotor Inner Ring of Rust. (Post #35)
Buff the rust down and get some heat resistant black or aluminum paint on there quick! No need to be an artist, just paint slightly beyond the line and the brakes will give you a neat line within miles.
The tell-tale 2005 Rotor Inner Ring of Rust. (Post #35)
Buff the rust down and get some heat resistant black or aluminum paint on there quick! No need to be an artist, just paint slightly beyond the line and the brakes will give you a neat line within miles.
Last edited by geoffliz; Jun 10, 2007 at 09:12 PM.
