Rev-hang revisited - fix may be available soon

[theholycow]

If the rev hang was that bad wouldn't it have been apparent on the initial test drive?

He mentioned that the short test-drive never got it warmed up enough for rev hang to kick in. That is consistent with my experience with rev hang in the 2008 VW...it drove perfectly when it was cold, but after the engine was sufficiently warmed up rev hang reared its ugly head.

[ClutchDisc]

If the rev hang was that bad wouldn't it have been apparent on the initial test drive?

He mentioned that the short test-drive never got it warmed up enough for rev hang to kick in. That is consistent with my experience with rev hang in the 2008 VW...it drove perfectly when it was cold, but after the engine was sufficiently warmed up rev hang reared its ugly head.

Oh okay. So does rev hang generally not show up until the car is warmed up? Wouldn't you notice it at a lesser degree when cold?

I've never driven a car with rev hang, so I don't know much about it.

[stevenj]

Yes, I should have noticed it, I am still kicking myself about it, but the car was cold and the test drive was short.

[tankinbeans]

sorry i had to

[theholycow]

If the rev hang was that bad wouldn't it have been apparent on the initial test drive?

He mentioned that the short test-drive never got it warmed up enough for rev hang to kick in. That is consistent with my experience with rev hang in the 2008 VW...it drove perfectly when it was cold, but after the engine was sufficiently warmed up rev hang reared its ugly head.

Oh okay. So does rev hang generally not show up until the car is warmed up? Wouldn't you notice it at a lesser degree when cold?

I've never driven a car with rev hang, so I don't know much about it.

That's a good question. So far we have two data points (Suzuki and VW) but I don't think that's enough to declare a trend. However, I do know that NOx emissions are worse with hotter combustion temperatures. If we take it as gospel that the real and only reason for rev hang is NOx emissions, then somebody who is writing the program for rev hang might include an exception when combustion temperature is expected to be lower.

[stevenj]

Abruptly closing throttle makes the mixture too lean resulting in higher combustion temperatures and higher NOx. It all gels.

[daleadbull]

Personally, I'd have no worries because a flashed tune is reversible. And as far as modifying cars in this day and age, it's the same old thing I've been doing my entire life. I've yet to find a car that I found 100% perfect, so I always make some changes to my cars to make them perfect for me.

I'm curious as to what mods you've done to your car so far. I know you've said that you have no rev hang on your Audi but are there times when the rate at which your revs drop vary? Like when the engine is cold or when the AC is cranked up etc.?

But back on topic, the easiest way to get rid of or minimize rev hang is to get a ecu flash. You often get improved throttle response, eliminate rev hang, more power, and also just as good or better fuel economy. Win all the way around imo, and I doubt any dealer will void your warranty because of a simple flash.

[Shadow]

Personally, I'd have no worries because a flashed tune is reversible. And as far as modifying cars in this day and age, it's the same old thing I've been doing my entire life. I've yet to find a car that I found 100% perfect, so I always make some changes to my cars to make them perfect for me.

I'm curious as to what mods you've done to your car so far. I know you've said that you have no rev hang on your Audi but are there times when the rate at which your revs drop vary? Like when the engine is cold or when the AC is cranked up etc.?

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Honestly, my Audi has been as close to perfect as any car I've ever owned. There's very little I'd change. But one thing that I didn't like after driving the car for a few months was the stock exhaust system. It was simply far too quiet. I wanted to hear my exhaust just a little without it being too obnoxious. I spent a while looking at the different options out there and after meeting up with a few local Audi guys, I finally found the solution. I purchased an AWE 3" dual exhaust system and bolted it on in my garage the same day. I can't say enough good things about it. Looks great, sounds great, adds 9 or 10 "free" HP, has no drone whatsoever, and makes a nice deep tone, especially as the revs drop while coasting/braking. But when you go full throttle, it really wails. I was shocked that an exhaust system could be so mellow under normal driving and then sound so great under hard acceleration. It really made all the difference when it comes to driving the car....especially with a stick.

Here's a before (not the best angle, but that's all I could find on my Photobucket) & after:





And I like that I can see the tips poking out on both sides of the car now too. Before installing the exhaust, the right side of the car had no exhaust tips at all.

[Shadow]

I know you've said that you have no rev hang on your Audi but are there times when the rate at which your revs drop vary? Like when the engine is cold or when the AC is cranked up etc.?

Forgot to answer your question....

Anyway, I'd have to say no. I find no difference at all with the way the revs drop if the engine is ice cold, full temp, or anywhere in-between. I've been driving a lot with the AC on lately and I have to say that any difference is barely noticeable. The revs don't seem to drop any differently, but like all cars, the idle RPM is a bit higher with the AC on, so I can't say that there's no difference at all. But it is so minimal that it's almost unnoticeable.

[daleadbull]

^ Car looks great, I love the wheels and the stance. I'm assuming both are stock since you didn't mention anything...

Yea, AWE makes great exhausts but pretty $$$. Did you get the switchpath one where you can open and close the flapper?

[tankinbeans]

^ Car looks great, I love the wheels and the stance. I'm assuming both are stock since you didn't mention anything...

Yea, AWE makes great exhausts but pretty $$$. Did you get the switchpath one where you can open and close the flapper?

I'm seeing a very heavy influence from Lamborghini in the design, especially the boot area.

[Shadow]

^ Car looks great, I love the wheels and the stance. I'm assuming both are stock since you didn't mention anything...

Yea, AWE makes great exhausts but pretty $$$. Did you get the switchpath one where you can open and close the flapper?

Yup, stock 19" wheels/tires and stock suspension, but it does have the Sport Pkg, so the bigger wheels and tires and a lower ride height come as part of that package.

The AWE exhaust was like $1600 if I remember correctly. Definitely pricey, but so is everything for these cars. The exhaust has no flapper/alternate paths. It's basically a 3" system from the downpipe to the tips. AWE also sells a replacement downpipe, but I decided that I didn't want it. I've been in an A5 that did have it and it definitely increases the volume of the exhaust system, so I'll probably never get it because I'm really happy with the way it sounds now.

[stevenj]

After several months I am back with update on my efforts to cure the rev hang. I believe I succeeded and details are here: http://www.revhang.altervista.org. You are invited to read it.

[Shadow]

After several months I am back with update on my efforts to cure the rev hang. I believe I succeeded and details are here: http://www.revhang.altervista.org. You are invited to read it.

I admire your effort, but I'll continue to be skeptical of your decision to "build a box" that cures rev hang when it is already completely curable via a simple canned tune that also offers many other benefits as well.

Tell me this: Why would anyone want to install hardware (the box) to "fool" the ECU rather than just modifying the software via a simple tune instead? What is your advantage?

[watkins]

Or just deal with it.