Let's talk about Thrust Curves

B6/7 S4/RS4
#1

Sounds like a cheesy pickup line.

I’ll start off by saying that I don’t have have much knowledge of this, and I’m just going off my basic physics knowledge and what seems to make sense. Hopefully it gets some discussion going.

So the general consensus for our cars seems to be to shift around 7800 rpm since that’s when the hp curve starts to drop off (and torque is already dropping). However, the thrust curves of the car seem to paint a different picture since thrust is not only about the torque curve but the gearing as well.

Here are thrust curves for a couple bikes:

http://www.team-integra.net/images/BAEC1978-D3A7-4405-AB2D-2761DC15A96D/articles/tuan/1LBikesThrustCurves02.jpg

So, it seems to make sense to try and shift at the point of the curve for the particular gear that would allow you to end up in an rpm range that would give you better thrust than if you had stayed in the previous gear. In the above examples, it would make sense to get out of the gear at bare minimum before the lines intersect at the right side.

So I took the dyno chart I had and decided to plot the thrust curves assuming 255/35/19 wheels. The dots are each 500 rpm from 2.5k-8k.

http://i.imgur.com/ECBSHlJ.png

Way different. If you take a horizontal ruler and slide it upwards, there’s no overlap at all for the first 3 gears at least.

Now, based on my basic understanding of this, wouldn’t it make the most sense to go all the way to the redline for us to get the best thrust/acceleration in the first 2 gears at least? (I know it’s picking hairs since it’s just 200 rpm different, but bear with me).

In fact, if in some imaginary world our engines could go up to say 10k rpm,the torque would indeed keep dropping, but up to a certain point, it would still be producing more thrust than the next gear up (for gears 1/2)

So what’s the deal here? Am I interpreting these graphs wrong or does it make more sense to wind it out as much as possible in those gears to get better acceleration?

So something like:
1-2: redline
2-3: redline
3-4: 7800?

#2

Here’s a guy with an S4 who was swapping in RS4 gears in order to optimize his thrust curves:
http://www.team-integra.net/forum/15-advanced-tech-corner/199978-interpreting-thrust-curves-2.html#post2404280

and some more discussion/info on thrust curves:
http://www.team-integra.net/forum/15-advanced-tech-corner/194855-gear-ratios-torque-thrust.html

#3

Problem with redline is hitting the fuel cut means slow

I shift just before redline in 1-2 and 2-3 and then a bit sooner in 3-4

Basically what you posted however I don’t rev 1-2 and 2-3 out to 8200. Maybe 7900 on tach (who knows how accurate the tach is…does it lag? Is it early?)

#4

Makes sense.

A lot of people preach about staying in the powerband, but that doesn’t take into account the advantage of the gearing. Our naturally aspirated cars have an advantage of a very broad/flat torque curve that rewards revving our the first few gears.

#5

probably a dumb question but is there a graph image of a b6/b7 S4 thrust curve that someone could link me to?

#6

Google search

Audizine s4 b6/7 thrust curve. I’m sure we did this five years ago.

#7

thanks, found it.

#8

The problem with thrust curves is that

  1. People only plot stock curves, which go out the Window as soon as you tune your car or get exhaust mods

  2. They really only prove that ink sticks to paper

They’re a good guide but you need to try a few things rather than relying on the math. Math doesn’t sit behind the wheel and check his timeslips to see what actually works. He stays in his bedroom playing with his computer which tells him what ‘should’ work.

On a jhm tuned b6/7 s4 you make a lot more torque than a stock car. Stock cars make about 25-30 less torque at the wheels than they make whp. That changes with tune and cat back where wtq nearly matches whp. That’s a huge surge in early torque, so shifting earlier than our friend math says for a stock car starts to maybe make sense. Seat time will answer that.

I found revving the gears to the following rpms worked well when trying to go fast in my B7 with jhm tune and fast intentions cutback and both piggies and cat less 2.5 downpipes.

1st - 7000 but be careful not to hit the limiter
2nd - 6800
3rd - 6500-6600
4th - 6500-6600

#9

I thought the graph seemed odd until I read “stock” and went “oooooh”.

I wanted to do a little reading and work on things before I take the Avant to the track for the first time with JimmyBones sometime in August. I’m pretty sure it’ll be a poor showing for the Avant but I’ll have a good laugh later.

#10

Gp in August but don’t tell anyone. Only announce your trip if you have your shit nailed down… And conditions are good.

Then make a thread about your best result. Starting ‘going to the strip this week!’ threads always leads to disappointment, especially when it’s 90 degrees out.

Go for practice in august, and then go and kick ads in November.