New Dyno Run! (Awesome/Weird)

[No_Dominion_2]

I recently got another set of dyno runs done after doing some modifications. Same shop, same dyno, same tire pressure, but different tires (Previous: PSS, New: PS AS/3+). Previous run (305 RWHP) was with Eventuri intake, headers, and tune. Current run (346 RWHP) was Evolve CSL airbox, headers, DKF resonated S1 pipe, RPI mufflers, underdrive pulleys, and Alpha-N tune.

Overall I'm very, very pleased with the increases in performance, especially the big bump in torque (which I can definitely notice). But the strange dip after 6K has me curious. I definitely don't feel that dip at all when I'm driving, and the fact that it recovers quickly to jump back up to where I expected it would end up makes me wonder if there was an error in the dyno process. We did two pulls, with nearly identical results, and max RWHP only varying by .6 HP. Though I'm now making significantly more HP/TQ compared to my previous session, the overall slope of the graph is remarkably similar between both runs, up until the point of the new "dip".



So, my thoughts about possible causes:

1. Tire slippage at high roller speeds caused faulty readings until proper traction was regained. I haven't put on summer/extreme performance tires yet, since it only recently started getting warm. I had a nearly new set of Pilot Sport AS/3+ on during the current run, whereas I was running Micheling PSS during the previous session.

2. For some reason my engine is truly losing that much power, but then able to regain it, and add more, all within a short RPM span. Doesn't seem likely, but I have to consider it.

3. Other/unknown

I'm leaning towards the tire-slippage possibility, not just because my butt-dyno doesn't register that loss-then-gain of power that the graph represents, but also because of math. Stay with me, if you will:

My previous dyno run, (slope was consistent with essentially all other dyno run plots I've seen) at 6K RPM my HP was 273, at which point it continued to climb in an overall linear fashion (typical of the S54) until it essentially leveled out at 7K RPM at 302HP (within 3 HP of my max for that session); an increase from 6K-7K of 10.62%

Applying this set of principles to my new dyno run, which at 6K RPM displayed 314 HP, the same slope on the graph would result in 347 HP at 7K, stunningly close to my new max (346 HP) for this new session. The low point after the dip was 288 HP at 7200 RPM; I just don't believe it is logical that the engine would be able to lose 26 HP between 6K and 7,200 RPM, and then be able to increase from from that point back up to a max of 346 HP. I have a feeling that the tires started to slip for a bit, and when they regained proper traction, the numbers were able to return where they should have been.

Anyone with more practical experience/thoughts, please feel free to chime in. I'm by no means a chassis dyno expert, just trying to evaluate based on what I know.

Cheers!

[pokeybritches]

Google "virtual dyno", download and install it, then do a few runs on your own to see if that dip is present.

Slip is plausible if a dip is not present with Virtual Dyno. Do you recall the diameter and number of the roller drum(s)? A 20" roller or greater is ideal. A single 8.5" or smaller roller, condition of the anti-slip grooves, and friction material can all affect traction on the dyno. What type of dyno was used?

Tuning is also a possibility, assuming the dip is still present with Virtual Dyno. There are certain limiters in the ECU that must be removed, and failure to do so will result in the ECU trying to limit torque via throttle body closure. Alpha-n tunes are highly sensitive to hardware changes. If the ECU detects the onset of knock, it will cut timing and reduce power depending on the knock severity. If your tune does not take into account your exact mods, more than likely fueling needs to be adjusted. You use BMWLogger to monitor lambda, fuel trims, and timing.

Separately, hard tires tend to read higher on certain types of dynos. Strap tension affects readings too. That's one of the challenges of roller dynos- a change in the condition of the run, even with a variable that seems unrelated, can affect the final numbers. I don't doubt you have a power gain with your improved hardware, but I wouldn't get too wrapped up in the actual numbers. The dip is certainly cause for concern.

[Michael9218]

Was your DSC turned on?

I had a similar issue with a power dip at 7,000 rpm that turned out to be speed related and was caused by a DSC glitch. Back to back tests on track confirmed that with DSC on the motor power dipped at a given spot on track. Turned off the DSC and all was good. My car is track only, so I just don’t use DSC.

[F360C]

Not the first person I have heard having a werid dip at 6k ish. I wonder if its the DSC like Michael pointed out.

Who did the tune? Evolve? Good peak power numbers!

[No_Dominion_2]

Originally Posted by pokeybritches

Google "virtual dyno", download and install it, then do a few runs on your own to see if that dip is present.

Slip is plausible if a dip is not present with Virtual Dyno. Do you recall the diameter and number of the roller drum(s)? A 20" roller or greater is ideal. A single 8.5" or smaller roller, condition of the anti-slip grooves, and friction material can all affect traction on the dyno. What type of dyno was used?

Tuning is also a possibility, assuming the dip is still present with Virtual Dyno. There are certain limiters in the ECU that must be removed, and failure to do so will result in the ECU trying to limit torque via throttle body closure. Alpha-n tunes are highly sensitive to hardware changes. If the ECU detects the onset of knock, it will cut timing and reduce power depending on the knock severity. If your tune does not take into account your exact mods, more than likely fueling needs to be adjusted. You use BMWLogger to monitor lambda, fuel trims, and timing.

After speaking with Abdul with Evolve, it now seems most likely that the AFR is off a bit for my mods at those higher RPMs. I ordered a Veepeak OBDII dongle yesterday, and will use an app to pull AFR readouts so they can fine tune, well, tune.

Originally Posted by Michael9218

Was your DSC turned on?

I had a similar issue with a power dip at 7,000 rpm that turned out to be speed related and was caused by a DSC glitch. Back to back tests on track confirmed that with DSC on the motor power dipped at a given spot on track. Turned off the DSC and all was good. My car is track only, so I just don’t use DSC.

DSC was engaged, I should have thought to turn it track mode or off completely. I'll definitely keep that in my for my next session.

Originally Posted by F360C

Not the first person I have heard having a werid dip at 6k ish. I wonder if its the DSC like Michael pointed out.

Who did the tune? Evolve? Good peak power numbers!

Yeah, Evolve gave me an amazing deal on the airbox and upgraded my previous MAF tune. Total cost for the complete airbox kit with install components and tune was like $2,900. Hard to say no to that.

When I make the move to upgrade cams, I'll probably switch to TTFS, though. Remote dyno based tuning on the fly has definite advantages.

Thanks for all the responses, everyone!

[Vanne]

id suggest to swap to Pokey, lost of guys are saying he does great work, AND he contributes to these forums. He's doing my tune.

[Steeler]

Originally Posted by Vanne

id suggest to swap to Pokey, lost of guys are saying he does great work, AND he contributes to these forums. He's doing my tune.

Beat me to it Vanne.

Plus 1,000 on recommending Josh.
Zero concerns with his knowledge and attention to details, ever.

[No_Dominion_2]

Originally Posted by Vanne

id suggest to swap to Pokey, lost of guys are saying he does great work, AND he contributes to these forums. He's doing my tune.

Originally Posted by dbarton62

Beat me to it Vanne.

Plus 1,000 on recommending Josh.
Zero concerns with his knowledge and attention to details, ever.

Damn, I didn't even realize he did tuning... pokeybritches I'll get ahold of you through PM.