540i w/bolt ons Dyno run

[topaz540i]

Testing performed at Pro-Fab Chassis in Whitehouse, NJ


2001 540i 140k miles w/ all typical bolt-ons

3" cat back to straight thru muffler
m60 intake manifold
afe intake
Ess Tuning m62tu w/m60 manifold software
JBR LWFW (may not affect dyno results)

Test was performed as suggested by mechanic in 4th gear 2,500 rpm rolling start to 6,00 rpm. Data appears valid from 3k-6k rpm only.
The difference in the beginning and end of chart is due to user error missing the 2500rpm mark to stab the throttle w.o.t on the second run and holding the throttle a little longer at the end on the first run. The difference in the drop off at the end is where I let off the gas pedal. The rev limiter is actually closer to 6,500rpm but this is a street car not, a dyno king so there was no point stressing it further for a small handful of hp to brag about. The point of this testing is a "before headers" vs "after headers" with the real story being in the "drivable" rpm range as this is a street use daily driver machine. After Schiedmann headers are installed I hope to have the charts overlaid to see any difference in the mid range section of the chart.

2 runs were performed resulting nearly identical charts negating need for further testing.


IMG_0913.jpg

[Msport540]

awesome, thanks for posting. I have the same bolt-ons as you but with a DUDMD tune, would love to see the difference if any.

[topaz540i]

Im almost putting down stock flywheel number at the wheels.


does anyone have a stock 540i chart that we can overlay?

[jicaino]

Why in 4th and not in 5th which is 1:1 ?

[topaz540i]

Idk. I had never done it before and that's what the guy suggested.
The machine has an RPM pick up off of one of the coil packs so that it compars your rpm to the speed the dyno drum is turning.
if I'm not mistaken that should make the dyno results the same the matter what gear you use. The way the guy explained it was basically " how fast do you want your wheels to be spinning when it falls off the dyno and goes into the brick wall 5 feet in front of us ?"

if the actual gear you use does in fact change the outcome it shouldnt matter because I intend to do the next test using 4th gear again so that it's still a relevant before and after as far as the change caused by headers is concerned, even if it can't be compared head to head with to other peoples cars done in a different gear

Does anyone know if the actual gear you use matters? I'm curious about this.
btw i have an m5 3.15 rear not the stock 2.81

[jicaino]

Lower gearing tend to produce artificially high tq curves down low and hp curves up the chart. And even if compensated (gearing) it will reflect anything but the actual "oomph" the engine has when pulling 1:1 on real life.

I find the explanation your dyno guy gives a little on the ludicrous side, to be honest. With that mindset, might as well mount the car backwards and pull in reverse...

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Since you'll be playing on the dyno again, you could do another pass in 5th and compare it to 4th instead doing 2 passes in 4th next time.

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And FWIW if your car goes off the roller you'd be worstly f**d if you'rem in a lower gear, pulling stronger on higher tq multiplication factor. You'll hit the wall with more force.

[jp5Touring]

My Son's shop has a dyno and they do pulls in 3rd or 3-4 gear pull. Has something to do with the ecu.Mostly turbo stuff.

[topaz540i]

I found this, which seems to explain it well:

"What an inertial dyno measures at the rollers is rear wheel torque based upon the time required to spin up to a certain RPM. The dyno also MUST measure engine RPM. It then computes over all gear ratio and uses this number to calculate the final HP and TQ numbers. When you change to a lower (numerically higher) axle ratio you will increase rear wheel torque. The dyno will compare engine RPM to the rear wheel RPM and see the gear change. The dyno program will then use this higher ratio number to compute the final numbers. While the switch to 4.10 gears (for example) will show higher torque as measured at the rear wheels it will also result in a larger correction factor. This change in the correction factor will offset the increase and then some. Part of the problem is understanding the terms. The maximum rear wheel torque as measure by the dyno is not real world RWTQ, but a computed number useful for comparing one engineto another. A 4000 RPM clutch drop in a Z06 in first gear will generate over 4000 pound feet of initial twist at the rear wheels. :crazy:"


ok after a little more digging it seems the answer is based on the following criteria:

you want a gear that isn't going to break the wheels loose on the dyno which is why you don't use 1st

you want a gear that will make the run last long enough to record meaningful data.

but... the higher the gear the more load you are putting on the engine so you probably wouldn't want to use overdrive (6th). The change in load can affect the car's performance. It seems you want to do the testing in the gear you use most. For example a street race car might do testing in 3rd.

People that get extreme swear by the gear closest to a 1:1 ratio not because it effects the dyno as much as the way the trans works. the 1:1 ratio gear is passing the power straight through the trans, any other gear would have more moving parts equaling more rotational inertia working against you. 5th gear is typically the closest to 1:1. If it was because the dyno needed a 1:1 ratio to be accurate you would be off by a mile since you still have a final drive ratio in the rear multiplying everything so therefore there is no 1:1 gear by the time the rubber meets the road. The dyno does not know what your gear ratio is. It doesn't need to. It measures rate of change in rpm to rate of change in roller speed to come up with a correction factor automatically displaying as if it was 1:1 on the screen

[philly98540]

Nice results! Top end keeps pulling and nice flat torque curve. I think there may be a mph limit on some dyno's too, so 5th will be way up there. Should not change result too much in either 4th or 5th gear.

[DJ12341]

That much from bolt ons? Didn't know that

Sent from my N9132 using Tapatalk

[topaz540i]

the m60 manifold really opens up the top end. Without it the curve usually hits a brick wall way earlier.

[jicaino]

the m60 manifold really opens up the top end. Without it the curve usually hits a break wall way earlier.

Yes, I have the M60 Mani (velocity stacked ;-) ) decated exhaust, Alpina tune, improved slush box and engine cooling, and the 3.15 rear end ratio too. It feels a lot more powerful than a regular 540i.

My critic on the 4th gear dyno pull was about th e tranny not being in 1:1 as to eliminate it out of the equation. I understand about the rear end ratio and all. Usually when you pull in 1:1 there's a lot of debug potential for the fuel/timing maps whereas pulling in a lower gear means less load on the engine, sometimes you mask up too much timing or other artificially lean/rich under load conditions... Not to mention the vanos not being used as much (since yours' a TU too)

I don't think the numbers would change more than 5/7% but if you're data logging in order to see if you can come up with a better tune, I would also make a run in 3rd and one in 5th to compare fuel/timing/vanos duty/O2 readings.

It does look like your engine is healthy and Fun to drive! Congrats on that.

[DUDMD]

Nice results! Top end keeps pulling and nice flat torque curve. I think there may be a mph limit on some dyno's too, so 5th will be way up there. Should not change result too much in either 4th or 5th gear.

Most cars also have a speed limiter as well.
I dyno all BMWs in 4th gear on my dyno. Sl65 in 3rd gear, because it's so long that 4th gear would max out my dyno speed limiter, and not good for the bearings/etc.

On a load bearing dyno like a dyno dynamics, differences between gears doesn't really affect max hp/tq, just a bit under the curve maybe.

[merlindavis]

I did a couple baseline runs not long after I picked up my 540. Both pulls were done in 5th.
Attachment 590906

[geargrinder]

IME 3rd or 4th are usually used for dyno pull to load the engine well but not overspin the hardware as Dima says.

[JimLev]

When I had mine done years ago the guy asked me what the tranny gear ratio and diff ratio was so he could put it into the settings on his software. I used 5th gear. His roller weighted 10K Lbs.
I need to get it done again now that lots of parts have been changed.

[geargrinder]

Yeah. That is mostly for rpm calc I bet. Real RPM tap on the motor is sooooo much better and separates the above average dyno ops with the hackers. So much better data than the "meh calculated RPM from drum speed" junk...

[tptrsn]

I need to get it done again now that lots of parts have been changed.

You definitely do Jim, or hit the 1/4 mile black dyno for a trap speed. Since you are THE MAN when it comes to the nitrous powered e39 540s, it would really be a nice data point.

[JimLev]

Thad, I intend on doing a dyno as well as taking a stroll down the strip.
It'd be nice to see what Topaz comes up with for additional HP when he added the headers.