Corey S

Well, unfortunately I cannot say exactly for sure, since we changed more than one thing between these dyno runs. But, the only other thing we changed was exhaust related, too.

First, let me list the powertrain mods on THWAP that stayed the same between these two dyno runs:

--RS4 K04's (from Achtuning)
--RS4 IC's (from Achtuning)
--Full Samco hose kit
--Bailey DV's
--AWE lightweight flywheel
--RS4 pressure plate
--AWE RSK04 fueling kit
--A/C removed
--100 octane fuel
--AWE/GIAC K04 street chip (A-box) (tuned for 91 octane)
--ECU adaptation time less than 3 miles for each run.

Ok, the two things that changed:

1. Replaced stock exhaust manifolds with the AWE/McNeil RSK04 Headers.

2. On the previous run, we had APR downpipes, no cats, and UUC VM2 exhaust. Now we have AWE downpipes, with a merge collector right after the flex joints into a single mandrel bent 3.5" straight pipe, no cats and no mufflers.

Using just the at-the-wheel data, I simply subtracted our previous run from our most current run.

<img src="http://www.imolaracing.com/images/turbo/headerdiff.jpg">

We were very surprised to see as much gain as we did. As I had expected, the HP gain was greatest above 6000rpm. But, to our surprise were the gains as low rpm. That big spike of 70ft-lb gain at 2750 is real, and it's because the turbos now reach full boost earlier. The following dip is because just as the new setup is coming off of overboost, the old setup is hitting overboost. Previously, with stock headers, we saw full boost at ~3200rpm, now with the AWE/McNeil headers we're seeing full boost at ~2850. That's definitely a noticeable improvement on the autocross course!!

Throttle off/on transitions within the boost curve happen faster, too, indicating that lag is noticeably reduced.

<a href="http://www.awe-tuning.com/pages/gallery/awe_rsk04/awe_rsk04_manifolds.jpg">Link to pic of headers</a>

Enjoy!

bitjockey (bum)

Impressive. Do they sound any different?

PhoenixGTS

What is up with the big dip at 3,200 rpm?

SlvrBullet Unloaded

Kenny is the man! That is all...

Funkweasel

Pat about this idea in this <a href="https://forums.audiworld.com/s4/msgs/1006997.phtml">link</a>. At higher rpms I'm guessing the small K04s themselves play a large part of the restriction versus the manifolds, but aren't a large part of the restriction at low rpms. Hence the big gains down low (boost sooner, less restriction, etc).

Corey S

Almost every boost controller will exhibit a little boost overshoot when the boost first comes on (especially on quick spooling turbos), then it settles back down in a few hundred rpms.

With the new headers and exhaust, the boost hits max overshoot sooner, then settles back down almost exactly at the point where the boost hits max overshoot with stock exhaust manifolds. Makes the difference plot look kinda crazy at low rpm, but once boost settles out in either configuration, the added power from the new headers holds up pretty solid.

Corey S

The K04's sound a little different from the K03's, but I'm not sure the headers made much of the difference.

Our latest exhaust configuration does sound better than any other we've had, tho, but both of the recent setups were loud, too!

PhoenixGTS

increase and opens the wastegate a bit so it does not open all of a sudden to control a spike. I know the stand-alone boost controllers like the HKS unit can do that (or something that works like that). Can you feel that dip when you are driving, in other words does it show up on a regular dyno graph? Or is it only in the "increase" graph?

Funkweasel

Maybe twiddling the N75 a bit clockwise would lessen it?

Corey S

The regular dyno curves do not have a dip. There is a "hump", if you will, at the point where the boost overshoot happens, but it settles back down to a steady torque curve with almost no dip.

You can feel the "hump" a little, but not any dip right after.