Z4M - SuperSprint X-pipe, Powerloops and Eventuri (dynos and data logging)

[///MBan]

Hi all,

After living with the car for a while with Supersprint V1 stepped headers, S-pipe with HJS cats and a Severn tune, I started considering trying to deepen the exhaust note and enhance the intake sound.

I liked the sound clips I had heard of the Supersprint Powerloops and I figured I may as well get the X-pipe at the same time. I honestly wasn’t expecting to keep the X-pipe on because I had heard it increases rasp, which I’m not a fan of, but I wanted to have the option to ‘tune’ the exhaust sound through combining different sections. Supersprint sells two variations of the X-pipe: one with a slip joint for joining straight to the Powerloop mufflers (which also have a slip joint) and one with a flange for joining to the standard rear mufflers. So, I ordered the X-pipe with flanges at both ends, the Powerloop mufflers and the adaptor that adds a flange to the mufflers. I also replaced all the exhaust hangers and hardware.

X-pipe with flanges at both ends – P/N 789833
Powerloop mufflers – P/N 789836 (L), 789806 (R)
Flange adaptor for rear mufflers – P/N 044933

I also ordered an Eventuri intake. The Gruppe M was an option too, but I had seen some dynos online that appeared to indicate that the Eventuri may add a few hp. I wasn’t keen on the red scoop for the Eventuri, so I painted it black (not shown in the picture below).

Eventuri, X-pipe and Powerloops_SML.jpg (97.78 KiB) Viewed 507 times

Even I could have installed the Eventuri, but to satisfy my curiosity regarding it adding power, I asked my workshop to fit it and the exhaust and run it up on the dyno after fitting the intake and then again after fitting the exhaust. Unfortunately, they did baseline runs and then a set of runs with everything installed, so I will never know how much each part contributed to the gains.

2021 Jun - Header tune 6 vs full exhaust intake and T6_SML.jpg (86.87 KiB) Viewed 507 times

There looks to be a gain from one or more of these parts (approximately 3%). The shop didn’t add my stock run from a while ago to the printout but below are Excel charts I’ve been using to compare various dyno runs. All up, the car is now making about 12% more peak power than stock. Peak torque (vs stock) is only about 3% up, but the gains at rpm below where the peak occurs are between 6 and 10% and the gains from just over 5,000 rpm to red line are between 10 and 20%.

HP vs speed - stock and FBO.jpg (44.34 KiB) Viewed 507 times

TQ vs speed - stock and FBO.jpg (44.03 KiB) Viewed 507 times

Driving the car back home I had some reservations about the exhaust. It was a bit boomy, droned and rasped. At idle it sounded good and above 5,000rpm it sounded great but in between not so much. However, over a few heat cycles and couple of hundred km, the boominess toned down and the rasp decreased a lot. The drone was still substantial from 1,800 to 2,200 rpm, so I started driving around that rpm range. A few months later I had the stock X-pipe swapped back in and on balance this is the best setup for me. I do miss the complex sound the SS X-pipe added. It was a metallic, guttural ‘zing’, overlaid by the Eventuri. When the exhaust shop was re-fitting the stock X-pipe they noticed that the fastener for one of the slip joints between the header and section 1 had snapped off. They commented that the weld for the fastener looks pretty weak. They fitted a regular exhaust clamp (which looks average) as there wasn’t a good way to fix the existing fitting. A bit disappointing all ‘round. This wasn’t the shop that installed the headers by the way.

While I had all the SS exhaust parts fitted, I logged some third gear runs. The gains were more significant than the 6hp gain on the dyno would indicate (**based on what may be a totally flawed method of calculating distance traveled from rpm change over time**). After 10 second full throttle acceleration in third gear from 2,000 rpm, the car traveled 3m further in comparison to before fitting the Eventuri and SS X-pipe and Powerloop mufflers. For reference, headers, cat’d section 1 and a tune resulted in the car traveling 7m further than stock under the same conditions.

Next up for the car is a full suspension refresh and (probably) KW V3s.