The story on DSR and the Dinan CAI (archive)

My my, but news & rumors travel fast in these parts. There's already a couple threads talking about my dyno results, and I haven't even discussed them yet!

Last Saturday, I swung by Dynospot Racing during the Porsche Boxter dyno day to get an updated dyno run on my M5. My last run was several months and several thousand miles ago (netting 332 RWHP) and I had since added a Dinan CAI and was eager to see whether the expected 5 HP materialized.
Unfortunately, my dyno runs that day showed something seriously awry -- the car was running very rich, especially at high RPMs, and several runs had a huge (40HP) dip in the midrange while others were normal looking but fell well below my previous results.
Naturally, I called Dinan on Monday to chat about the problem. I was very pleased to receive a call back within hours from Steve Dinan himself, and we talked through the results and possible causes. Steve also explained how their ECU modification software works and the design of the CAI. Based on that discussion, I don't see how the CAI or the ECU mods could have caused the performance loss I observed.
The dyno results I obtained are best explained by the ECU observing mild detonation and retarding timing & richening the mixture. There are several potential causes for this: bad gas, bad O2 sensor, bad knock sensor, engine too hot. Of these, my best guess is a tank of bad gas. Prior to the dyno runs, I had refueled at a newly-opened ARCO station instead of my usual local Chevron which I used for my other dyno runs. Bad/low octane gas would certainly explain the behavior I saw on the dyno, especially the inconsistent run-to-run behavior with big dips in the powerband.
I will be revisiting DSR to get another dyno run in the next week or two. Steve also volunteered to have Dinan help me diagnose the problem, and if it's not something obvious I'll take him up on the offer. Until the cause is known, however, I don't believe anyone can draw conclusions about the Dinan CAI or ECU software. So far, I have had nothing but positive experiences with Dinan products for both my M3 and M5, and I have no reason to believe it will be any different with their M5 CAI.

I will post new results & information as soon as it becomes available.

Cheers,
Ben

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