Righthand drive Z4M – SuperSprint V1 stepped headers and Severn tune (dynos and data

[MBan]

Hi all,

**sorry for cross-posting: this is also on Z4forum**

So, the issues I had installing the SuperSprint headers are not going to be that relevant to all the North American members but hopefully you will still be interested in the dyno results and tuning from Josh at Severn Tuning (Pokeybritches on the forums).

This post got a bit longer than I intended, so here’s an executive summary:

• The SuperSprint V1 stepped headers marketed as being for righthand drive cars do not fit without modification
• Despite the modifications need to get the headers to fit, they still made more top end power before tuning
• Josh from Severn Tuning provided excellent support and customisation for my tune, resulting in gains in the order of 10% power and torque over large sections of the rev range
• The gains on the dyno seem to be reflected during data logging in real-world conditions
• The tone of the exhaust has changed a bit, with more ‘fizz’ evident but not what I would call unpleasant rasp.

For reference, I have a ‘Euro spec’ Z4M, with the better (cat-less) headers and S-pipe. I bought the V1 stepped headers and S-pipe with HJS catalytic converters a while ago but only just got around to having them installed… unfortunately, the installation didn’t go to plan as the rear bank did not clear the steering shaft. I had the option at that stage to send them back to SuperSprint in Italy but since I had already paid to have the stock headers taken off and to have the SuperSprint headers ceramic coated, I thought I would have the workshop modify them and see what happens. Pictures below of the clearance issue and the workshops modification.

[MBan]

Josh from Severn Tuning supplied three tunes to test with the headers: one ‘best’ guess (Tune 1) and then two with Vanos changes to see where some more gains could be found.

The workshop ran the car on the dyno with stock everything (my car has no other modifications besides a set of lightweight wheels) but due to the modifications to the headers and the workshop’s other jobs, as well as sending the headers back for re-ceramic coating, it was then about three weeks before the post-header installation runs. As a result, I’m not sure how comparable the results are.

All runs except for the stock one were done on the same day with the car left strapped to the dyno.

The first chart below shows all runs at the same time, which is pretty messy.

Below that is a dyno chart of stock versus Tune 1. Tune 1 was best overall but Tune 2 and 3 were better at high revs. With the stock tune, the headers made more power than stock in the high end and a bit more down low but were worse through the mid-range. So, the headers definitely need a tune to get the most gains.

[MBan]

I then took the car home and did some data logging for all three Severn tunes at an off-street location that allows a full third gear run. I sent the dyno charts and data logs to Josh, who then developed a couple of fine-tuned maps, resulting in Tune 6. I took the car back to the dyno and ran Tune 6 against the stock tune. In hindsight, it would have been good to also run Tune 1 on the same day but given it takes 50 minutes to load each tune, it just wasn’t feasible. The first dyno chart below is completely stock vs Tune 6 (done nearly a month apart) and the second is comparing stock tune (with headers installed, obviously) and Tune 6 (done on the same day with car kept strapped to the dyno). I was expecting Tune 6 to perform a bit better but when I compared the two stock tune with headers runs (one week apart) as a rough internal control, the readings were down on the second day, perhaps indicating that Tune 6 would have put up better numbers if it was run on the same day as Tunes 1-3. I’m not really sure why that would be but if nothing else it shows that comparing dyno runs from different days is pretty tricky. I didn’t get a dyno print out comparing the SS headers with stock tune over the two different days, but I did enter the data in MS Excel to create a chart (Tune 6 also included for reference). See below.

[MBan]

Finally, some third-gear data logging. The first chart below shows the MAF signal for the car when it was completely stock (on a slightly hotter day), compared to Tune 6. It looks like these data reflect the dyno results, with Tune 6 pulling in quite a bit more air than the stock run in the low and high rev ranges with the advantage being a little less clear around 4,500 – 5,500 rpm. Josh stated that MAF signals are not reliable enough for tuning, so they also may not be reliable enough to draw many conclusions. The second chart below shows the difference between the stock car and Tune 6 for distance covered over time. Again, not sure how reliable it is to take this information from the data logs but the stock runs were all pretty similar and the runs for Tune 6 all covered more distance than stock in the same time. The result is that over a third-gear run (approximately 10 seconds) the car with headers and S-pipe with a Severn tune covered 5.5m more than the stock car.

[MBan]

Subjectively, the car feels really strong, particularly from 5,000 rpm but the low rev range also feels super sharp now. Sound-wise, the volume hasn’t changed much but it does ‘fizz’ a bit more. I think the ‘fizz’ is rasp that is damped by the stock X-pipe and rear mufflers but I actually quite like it and I’m not a fan of rasp. The intake sound is now less audible from inside, which is a downside in my opinion.

I’m super happy with the Severn tune and Josh’s support. I would recommend him in a heartbeat. The headers were a pain and I wonder how much (if any) power and torque was lost through adding the notches to the two primary pipes. Obviously, the whole thing cost more as well. SuperSprint, to their credit, took the product off their website as soon as I let them know. Still, I’d prefer that the headers fitted.

[maupineda]

Thanks for sharing

[Vanne]

Again, thx for sharing

[MBan]

No problem, I enjoyed writing it up.

The number of people modifying Z4Ms must be pretty low these days, particularly in RHD, but hopefully this will help when someone searches for information.