A3 vs S4, First 1000 miles
01-11-2008, 10:18 AM
#12
Forced induction helps compensate for altitude to some degree. Much depends on how high,
design of the forced induction system (capacity), intake, and fueling among many things.
The ideal air/fuel ratio is about 14 to 1. At sea level air has a certain density (temps play a part too, but we'll ignore that). As you go higher, the air is less dense, and a normally aspirated engine can't get enough oxygen molecules for the available fuel molecules, and so the mixture is adjusted for this less dense charge. A less dense charge means less power.
When you use a compressor (turbo or supercharger), in addition to the usual function, the compressor can compensate for the loss of ambient air density by pumping extra air into the engine. Eventually you reach the pumping capacity limits of the compressor and the engine will begin to lose some power due to a less dense charge, but this is usually at a far higher altitude than you would first notice losses in a normally aspirated car.
This is why fast piston powered aircraft use some form of forced induction. WW II is a prime example.
Obviously I am glossing over a lot of technical details, so you might want to do some research into the various factors that determine output under certain conditions.
The ideal air/fuel ratio is about 14 to 1. At sea level air has a certain density (temps play a part too, but we'll ignore that). As you go higher, the air is less dense, and a normally aspirated engine can't get enough oxygen molecules for the available fuel molecules, and so the mixture is adjusted for this less dense charge. A less dense charge means less power.
When you use a compressor (turbo or supercharger), in addition to the usual function, the compressor can compensate for the loss of ambient air density by pumping extra air into the engine. Eventually you reach the pumping capacity limits of the compressor and the engine will begin to lose some power due to a less dense charge, but this is usually at a far higher altitude than you would first notice losses in a normally aspirated car.
This is why fast piston powered aircraft use some form of forced induction. WW II is a prime example.
Obviously I am glossing over a lot of technical details, so you might want to do some research into the various factors that determine output under certain conditions.
01-11-2008, 10:26 AM
#14
AudiWorld Super User
Join Date: Aug 2003
Posts: 2,677
Likes: 0
Received 0 Likes
on
0 Posts
2nd
I have an S4 and had A3 Sline for about 1200 mi. while the S was in the shop, I posted before and i still miss that DSG, best evar.
Agreed with your review, the A3 = Lots of fun, and while feels a bit floater on the road, it's quite peppy, and handles good.. did I mention how freaking fun is the DSG?.
I'm also tired of the oil stuff and will be returning my lease ONLY because I think that a carmaker that states oil burning/consumption every 600mi is normal, basically, to me is on crack. (I bought an Aveo as a commuter and I've been driving the hell out of that little car and not a single drop of oil has been consumed)
Agreed with your review, the A3 = Lots of fun, and while feels a bit floater on the road, it's quite peppy, and handles good.. did I mention how freaking fun is the DSG?.
I'm also tired of the oil stuff and will be returning my lease ONLY because I think that a carmaker that states oil burning/consumption every 600mi is normal, basically, to me is on crack. (I bought an Aveo as a commuter and I've been driving the hell out of that little car and not a single drop of oil has been consumed)
01-11-2008, 10:57 AM
#15
AudiWorld Senior Member
Join Date: Aug 2006
Location: Near Manhattan
Posts: 1,093
Likes: 0
Received 0 Likes
on
0 Posts
With your spirited driving (as you've described), I'm surprised you're hitting 30mpg
I'm now at 10k and my MPG has slipped a little. I'm now clearing about 28.5mpg highway with maybe 3-4 "full pedal thrusts" for the tank full. That's not a lot of spirited driving.
Quite frankly, if the 2.0 TDI gets 32+mpg highway and is just a little bit slower than the 2.0T, I'm switching. My 1.8T 225hp Audi TT with Quattro (Haldex) would get 30mpg highway without having to be overtly light footed. :-/
Quite frankly, if the 2.0 TDI gets 32+mpg highway and is just a little bit slower than the 2.0T, I'm switching. My 1.8T 225hp Audi TT with Quattro (Haldex) would get 30mpg highway without having to be overtly light footed. :-/
01-11-2008, 11:11 AM
#18
Audiworld Junior Member
Thread Starter
Join Date: Dec 2007
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
Re: With your spirited driving (as you've described), I'm surprised you're hitting 30mpg
Me too! my driving is mostly highway or country back roads. drove 250 miles last week. Hit 90 to 100 for some good stretches of open country road. Stayed pretty legal the last 50 miles or so on a major well patrolled highway. The computer said 30mpg. I didn't double check it. Driving the same routes the same way in the S4 was getting 19-20
01-11-2008, 12:09 PM
#19
Audiworld Junior Member
Thread Starter
Join Date: Dec 2007
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
one more thing, build quality
One thing I forgot,,the S4 felt like it was chiseled out of a block of titanium. When you shut the door it felt like closing a vault. When i close the A3 doors, it feels, well like my buddy's lexus rx330. That's not a bad thing, and there are those 700 pounds. Probably some deadening material. Nothing I can't live with for the weight and cost reduction
01-11-2008, 01:09 PM
#20
AudiWorld Senior Member
Join Date: Mar 2005
Posts: 894
Likes: 0
Received 0 Likes
on
0 Posts
2.0 TDI ?!?!?! Do you know something I don't know?
From all I've read, AoA only plans to bring the 3.0TDI over and then only in the Q7. I'd be first in line at the Audi dealer if a diesel A3 or A4 was available in the states.
Currently, Mercedes is the only company I know of offering a diesel passenger car in the states in the form of the E320($53,000+). And no, I don't consider an SUV or pick-up truck to be a passenger car.
Currently, Mercedes is the only company I know of offering a diesel passenger car in the states in the form of the E320($53,000+). And no, I don't consider an SUV or pick-up truck to be a passenger car.