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Old 07-03-2002, 09:02 PM   #1
Amir
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Queston on how to dyno a step car

Hey guys, I'm going to be dynoing my car this Friday at Pro Technik here in Houston. Anyway, my question for those who have steptronic....how did you dyno your car?? I mean, what gear did you put it in when you dynoed....and if there were any problmes you incurred....

Thanks


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Old 07-03-2002, 09:50 PM   #2
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Ideally, you should dyno a car in whatever gear equals 1:1.

Most modern 5-speed manual transmission cars have an overdrive 5th, and 4th gear is the direct drive.

In many automatics, you should also dyno in the gear just below top gear for the same reason. However, there can be a problem with low-redline engines where that gear may hit the top speed limiter before it gets to redline, so you will not get a full-range dyno run. In those cases, use the next gear down. Even though it may not be 1:1, the innacuracy (or correctly "false power due to excessive torque multiplication) is only a few percent, and your results are still meaningful.

Actually, any results are meaningful when testing the same car to determine the benefit of a modification. You're simply looking for a delta, not necessarily the accuracy of the numbers in comparison to another car tested under different circumstances.

- Rob

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Old 07-03-2002, 10:19 PM   #3
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Amir: I had problems running mine...

1st run:
Put car in M4 (tranny is now @ 1:1). Floor it at low revs (about 2500) to try and get a complete run over full rpm range. Problem: At these low revs, the Step. downshifts when pedal engages the kickdown button, shifts down to 3rd & blows the run.

2nd run:
Same start as above (M4), but gently take revs to about 3500-4000 while in 4th and then floor it. Step. doesn't kickdown to 3rd so run is completed in one gear to redline, but you only get data from 3500 or 4000 to redline (6500-6700 depending). So, no good data on low-end performance. :sad:

Comments:
1) You could try a run as in 1st example above, but instead of flooring it, depress throttle to just short of kickdown to get a complete run in 4th (@1:1) from low revs. This would give you a good picture over full rpm range, however, the engine would be at something short of full throttle (WOT) and so I think it would give you results that would not depict the car's full capability. Just an educated guess on this. I don't know how close the engine really is to WOT at this point.

2) You can make a clean single-gear run from lower revs if you start in 3rd, but this isn't a 1:1 ratio. I asked the dyno guy if he couldn't just correct for the gear ratio difference with the dyno software (btw, this was a dynojet 248 setup). He said no, the trans had to be in a gear that was direct-drive or 1:1. Struck me as odd at the time since I know not all transmissions, manual or auto, have a 1:1 ratio so wtf? I began to feel that the dyno dude wasn't the brightest bulb in the chandelier if you get my drift. And it seems that the dyno software should be able to correct for whatever your ratio is during the run.

Anyway, when I went through this, the place I used seemed a bit baffled by the Step. setup, even though a lot of the cars they test are your garden-variety slushbox. (This was a place that mods big American iron). So they seemed pretty baffled by the "foreign intruder" & the Step tranny.:tongue:

Having said all this, Sam should know what to do with the car since his shop is a Porsche specialist and the Tiptronic would behave same as the Step. If there's a way to get it down, they'll know how to make it happen.

Don't know why I didn't go there myself. Just been out of Porsches for too long I suppose. How about letting me know when you plan to get out there on Friday. I'd like to stop by & see what happens & run mine too.
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Old 07-03-2002, 10:29 PM   #4
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Rob...

Quote:
Ideally, you should dyno a car in whatever gear equals 1:1.

Most modern 5-speed manual transmission cars have an overdrive 5th, and 4th gear is the direct drive.

In many automatics, you should also dyno in the gear just below top gear for the same reason. However, there can be a problem with low-redline engines where that gear may hit the top speed limiter before it gets to redline, so you will not get a full-range dyno run. In those cases, use the next gear down. Even though it may not be 1:1, the innacuracy (or correctly "false power due to excessive torque multiplication) is only a few percent, and your results are still meaningful.

Actually, any results are meaningful when testing the same car to determine the benefit of a modification. You're simply looking for a delta, not necessarily the accuracy of the numbers in comparison to another car tested under different circumstances.

- Rob
Agree with you 100% on using the test to measure relative changes. Unfortuneately, my car had the mods installed before I got it, so I can only compare to other published data for stock engines.

Also: "False power due to excessive torque multiplication"

Wouldn't this be more than a few % between 3rd and 4th?

Oh, and can I get one of those 313 ft-lb engines in my 323 for les than $6K?

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Old 07-04-2002, 12:15 AM   #5
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Stealthwagon and Rob, thanks for the awesome information and insight .....Stealth, what are your comments on Pro Technik?? I'm assuming you have been there since you know Sam. I'm going to have them try to rig up the unichip to my car when i switch to the 24 lb injectors for my s/c. Hopefully they can tune everything right w/o problems.
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Old 07-04-2002, 12:38 AM   #6
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Re: Rob...

Quote:
Originally posted by Stealthwagen
Also: "False power due to excessive torque multiplication"

Wouldn't this be more than a few % between 3rd and 4th?

Not a whole lot. There is just a small amount of error introduced from being in the wrong gear due to the lower load (in lower gears) of the motor's power requirement to spin itself, seperate from all other drivetrain frictional losses and actual load at the wheels.

Quote:

Oh, and can I get one of those 313 ft-lb engines in my 323 for les than $6K?
You know I'm always ready for a new project. Would cost just a little more than $6K, and I think we can skip the gullwing doors - too hard to use in a parking lot, ya know.

I'll be dynoing that motor again soon with the 6-speed in place, we shall see what the numbers are like then. After that, I start considering power mods.

- Rob
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Old 07-04-2002, 01:24 AM   #7
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Re: Re: Rob...

Quote:
Originally posted by Rob Levinson * UUC Motorwerks



Not a whole lot. There is just a small amount of error introduced from being in the wrong gear due to the lower load (in lower gears) of the motor's power requirement to spin itself, seperate from all other drivetrain frictional losses and actual load at the wheels.



You know I'm always ready for a new project. Would cost just a little more than $6K, and I think we can skip the gullwing doors - too hard to use in a parking lot, ya know.

I'll be dynoing that motor again soon with the 6-speed in place, we shall see what the numbers are like then. After that, I start considering power mods.

- Rob
Rob, what car is that dyno run for??
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Old 07-04-2002, 03:10 AM   #8
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Follow the URL below to hear my thoughts on dynoing, including the 1:1 gear ratio...

http://forum.e46fanatics.com/showthr...threadid=10133

Rob, your thoughts?
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    Old 07-04-2002, 03:19 AM   #9
    KromeX
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    I've had my car on the dyno numerous times and between 3rd and 4th gear, there seems to be very little change, maybe 1-3 hp but it may be due to small errors between runs or just heat soak. I did notice that overall, 4th gear does produce slightly higher numbers than 3rd even if I dynoed in 3rd gear first or 4th gear first.
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    Old 07-04-2002, 12:28 PM   #10
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    Quote:
    Originally posted by JawKnee
    Follow the URL below to hear my thoughts on dynoing, including the 1:1 gear ratio...

    http://forum.e46fanatics.com/showthr...threadid=10133

    Rob, your thoughts?
    Different types of dynos have different characteristics which can introduce greater or lesser accuracy factors (some older dynos using ancient computer controls have an inherent sampling inaccuracy of at least 3%). Likewise, there are even variations in runs done consecutively due to a variety of factors, even some as small as a 10 degree change in oil temperature (which I have documented myself). With all of these inevitable inaccuracies, you do what you can to minimize them.

    The idea behind another inaccuracy caused by a dyno run done in other than the 1:1 gear has to do with the "minumim no load spin up rate" of a motor. Imagine your car is stopped, not on a dyno, and in the neutral gear. You floor the motor and time how long it takes to go from idle to redline. There is a period of time there, the amount of time it takes for the motor to generate enough power to overcome its own basic inertia. All of its own energy was being used to accelerate itself, without any drivetrain losses as part of the situation.

    Now we put the car on the dyno. At this point, the majority of energy is being used to turn thr dyno components. The time from idle to redline is much longer than when the car is in neutral.

    Since the engine rpm is increasing at a much slower rate, much less of the actual energy output is used to accelerate the engine itself.

    The conclusion to the theory is that a lower gear allows the idle to redline time to be shorter, and redirects more energy to actually moving the engine compoents.

    It's a very small amount, but (depending on the motor), potentially as much a factor as tire pressure, oil temp, humidity, or air temp as an inaccuracy factor.

    But as I stated previously, it's not how you dyno the car... it's how consistently you perform subsequent dyno tests to validate the accuracy of comparisons from different sets of results.

    - Rob
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    Old 07-04-2002, 12:51 PM   #11
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    Re: Re: Re: Rob...

    Quote:
    Originally posted by Amir


    Rob, what car is that dyno run for??
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    Old 07-04-2002, 02:43 PM   #12
    Stealthwagen
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    Rob:

    Thanks for the details on dyno theory & practice. Your explanation of the torque multiplication/gear ratio effect was quite clear and makes perfect sense. As an engineer, I find a lot of the data people offer about mods to be poorly or un-supported by fact. It's always nice to get technical information from someone who understands the physics &/or engineering fundamentals behind the issue. Again, much appreciated.

    Todd Horst
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    Old 07-04-2002, 03:02 PM   #13
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    originally posted by Amir

    Quote:
    Stealthwagon and Rob, thanks for the awesome information and insight .....Stealth, what are your comments on Pro Technik?? I'm assuming you have been there since you know Sam. I'm going to have them try to rig up the unichip to my car when i switch to the 24 lb injectors for my s/c. Hopefully they can tune everything right w/o problems.
    Amir: Pro Technik is a solid shop. Been in business for, oh, close to 20 years I guess. Sam was a dealer tech. (think they were called mechanics back then :tongue: ) before he opened his own shop. He has campaigned a string of 911's and now a GT3 Carrera in a variety of series including IMSA, Daytona 24 hrs, PCA club racing, and of course our locally sponsored PCA drivers ed events at TWS. He was doing engine management systems (Motec, Zytek & so on) long before they became known to the street-car crowd.

    You running an ESS or RMS blower? We'll have to get together sometime so you can fill me in on the install/performance/etc. What's the unichip? An add-on to the stock ECU? Does it mean you avoid reprogramming the OE ECU?

    Amir: check your pm for another question re your dyno run tomorrow. Thanks.
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