Dyno question

[ZoneLaps]

I'm planning to install my ESS tune late next week, so I have a dyno appointment scheduled for Wednesday to do a pre-tune dyno. I've seen conflicting information here about whether it's best to dyno the DCT in 4th or 5th gear.

Apparently some people use 5th because it's 1:1, but some people use 4th for whatever reason (perhaps easier to control?).

What is the definitive way to do this? I want to be able to do a direct compare. I will, of course, share with the forum when I have numbers.

[FriedPiston]

Just ask the dyno operator nicely to see if they're able to do the pulls in 5th gear. That's how I did my recent dyno, and the car was clocking at around 168 MPH per pull.

If the shop you're going to has never dyno'd an F8x before, it's very important to point them to this thread for the RPM hookup: http://f80.bimmerpost.com/forums/sho....php?t=1096277 (thanks to Mike@N54Tuning.com)

[ZoneLaps]

Originally Posted by nars3000

Just ask the dyno operator nicely to see if they're able to do the pulls in 5th gear. That's how I did my recent dyno, and the car was clocking at around 168 MPH per pull.

If the shop you're going to has never dyno'd an F8x before, it's very important to point them to this thread for the RPM hookup: http://f80.bimmerpost.com/forums/sho....php?t=1096277 (thanks to Mike@N54Tuning.com)

Super helpful, thanks! I wasn't sure if perhaps the top speed limiter would kick in in 5th.

[FriedPiston]

Originally Posted by isaywhateveryo

Super helpful, thanks! I wasn't sure if perhaps the top speed limiter would kick in in 5th.

You're welcome! If your tune doesn't have the VMAX limiter removed, then your only option would be 4th gear.

[ZoneLaps]

Originally Posted by nars3000

You're welcome! If your tune doesn't have the VMAX limiter removed, then your only option would be 4th gear.

The tune will, but my original dyno to compare to won't. So in that case, should I do 4th gear now on stock and then compare it with a 5th gear dyno on the tuned one in a few weeks, or should I do 4th gear on both?

[FriedPiston]

Originally Posted by isaywhateveryo

The tune will, but my original dyno to compare to won't. So in that case, should I do 4th gear now on stock and then compare it with a 5th gear dyno on the tuned one in a few weeks, or should I do 4th gear on both?

I'm not sure which tune you have, or which flashing application is being used. I know with MHD and BM3, you can easily switch to stock tune to do a baseline run, and then spend 5 minutes for cool down and re-flash.

Heck, the shop I took my car to was cool with me sitting shotgun to administer the map changes, and allowed me to collect data logs for each run. These are all things you can work out with the shop prior to the dyno session.

[ZoneLaps]

Originally Posted by nars3000

I'm not sure which tune you have, or which flashing application is being used. I know with MHD and BM3, you can easily switch to stock tune to do a baseline run, and then spend 5 minutes for cool down and re-flash.

Heck, the shop I took my car to was cool with me sitting shotgun to administer the map changes, and allowed me to collect data logs for each run. These are all things you can work out with the shop prior to the dyno session.

Understood. I was planning to do a dyno run before installing the tune at all. I'll have an ESS Stage 1+ tune. So I guess I'll do a couple of 4th gear pulls stock and then a few weeks later when I dyno the ESS, I'll do a 4th gear pull (for comparison) and a 5th gear pull (for 1:1).

[F80Moe]

6M/T - (1:1) on 5th gear

4th gear pull: 485whp
5th gear pull: 501whp

Same mods & same day

So 5th will generally result in higher numbers

[drgmt]

Don't bother posting dyno graphs here - you'll likely be called a liar etc etc

[CanAutM3]

It all depends what you are after.

If you are simply interested in getting the highest number, 5th gear will most likely give you the highest result because it is a direct drive ratio. All other gears need to channel the power through 2 sets of gears, while 5th gear does not channel power through any gears inside the gear box, hence it has less drivetrain loss. However, the drawback of using 5th gear, is that you will likely hit the top speed limiter before your reach redline.

If you are mostly interested in understanding your full power curve and the gains provided by your mods all the way to redline, then 4th gear is the better choice.

What is important to understand, is that whatever absolute number you obtain from your dyno run is irrelevant (example: I pulled 450whp). Look for the relative gain you are getting from your tune and modifications (example: I got 10% more power with the tune). That is what's meaningful. It is critical to do a baseline run before the mods and the end run with the mods in the same conditions as much as possible to avoid variables. As an example, ensure you do the before and after runs in the same gear. Further, since the S55 auto-corrects for atmospheric conditions, it is preferable to use un-corrected dyno results for a more precise assessment of the gains.

[Rotzy]

Originally Posted by isaywhateveryo

The tune will, but my original dyno to compare to won't. So in that case, should I do 4th gear now on stock and then compare it with a 5th gear dyno on the tuned one in a few weeks, or should I do 4th gear on both?

It also depends on type of dyno. When I ran my X5 N63TU on a Mustand Dyno, the difference in output between 4th and 5th gear was 1HP. Dynojet will likely produce a much greater difference. Either way, I would compare before and after runs from the same gear on the same dyno.

[M4309]

Originally Posted by CanAutM3

It all depends what you are after.

If you are simply interested in getting the highest number, 5th gear will most likely give you the highest result because it is a direct drive ratio. All other gears need to channel the power through 2 sets of gears, while 5th gear does not channel power through any gears inside the gear box, hence it has less drivetrain loss. However, the drawback of using 5th gear, is that you will likely hit the top speed limiter before your reach redline.

If you are mostly interested in understanding your full power curve and the gains provided by your mods all the way to redline, then 4th gear is the better choice.

What is important to understand, is that whatever absolute number you obtain from your dyno run is irrelevant (I pulled 450whp). Look for the relative gain you are getting from your tune and modifications (I got 10% more power with the tune). That is what's meaningful. It is critical to do a baseline run before the mods and the end run with the mods in the same conditions as much as possible to avoid variables. As an example, ensure you do the before and after runs in the same gear. Further, since the S55 auto-corrects for atmospheric conditions, it is preferable to use un-corrected dyno results for a more precise assessment of the gains.

Hey CAN, great feedback, what tune are you running on your f80?