The time is coming when I'm considering a dyno run, just to see what kinda numbers getting.

Question is, how do you dyno an A4 (stock converter)?

In a stick, you just leave it in 4th (or whatever gear gives you a 1:1 ratio) and floor it to redline. However, the same technique in an A4 will make it downshift. Also, how do you account for T/C slip... is this included in the 20% driveline losses number that is typically used?

What about low-rpm numbers (below stall speed)?

Thanks for any info :)

 

You leave it in 3rd so it won't shift into overdrive. They run through the gears (1-2) and hammer it in 3rd. The chart usually starts at about 2700 RPM. All losses are taken into account as the numbers come off of the rear wheels.

 

:confused: How do they avoid a downshift if they hammer it in 3rd?

So there's no way to get RWHP / RWTQ numbers <2,700rpm? :(

Wouldn't it be easier to just do the whole run in 1st-gear and factor-out the multiplication effect of the gear ratio?

 

I hosted a Dyno Day for my club last year and here's what I learned. The process is the same for both the A4 and MN6. Once strapped to the dyno:

Turn off the T/C
For A4 cars place selector in 3rd gear
Start to accelerate (it'll feel funny the first time)
Depending on when you'll start your run (set before you start) usually somewhere between 2500 and 2700 RPM's get the car into 3rd or 4th if a manual and MASH the throttle to the predetermined cut off point. Some guys stopped short of redline others played the hero and held it until the rev limiter kicked in.
Peak HP/TQ will occur just at 5250 RPM's or there bout’s and fall off after that. That's why some shut down before redline.

Now as far as calculating drive train loss. There are many numbers floating around. A4's have more parasitic loss than MN6 some say about 2% more. The widely accepted figures are:

A4 = 16%
MN6 = 14%

The reading the dyno provides is known as Rear Wheels HP or Torque. To calculate the HP/TQ at the crank you divide the dyno numbers by .84 for the A4 and .86 for MN6. These are not hard and fast numbers - some folks use other factors, depending on how much power they want to CREATE.

So if your RWHP is 300 (about right for a stock C5 your crank HP would be about 349HP. The same car with a NM6 would probably dyno in slightly higher around 307 RWHP.

In the for what it's worth department, the day we dyno'd we had over 15 C5's many with the usual minor bolt on mods. The numbers ranged from a low of 288 RWHP (me) to a high of 321 (a 2001 MN6). What was the major factor involved - one word AFR's. We tested on a wide-band dyno which sniff's your exhaust to see how your car is using fuel. Some cars were RICH like me (my AFR's were down to below 11.0:1 and actually dropped to 10:1:1 from 5500 RPM's) and others had almost perfect AFR's (between 12:5:1 and 13.0:1). I was just a matter of how well your cars PCM were doing its thing. Cars like mine can benefit from the LS1 Edit tune. Other's are lucky and come from the factory tuned just right.

Good luck and have fun. Hope this helped you.

Tom
USAF Retired

 

Tom,

Thanks for the very detailed reply, but how does the dyno operator stop the car from downshifting when they mash it in 3rd? :confused:

Interesting comments re. A/F ratios... had the people with less-than-ideal A/F ratios recently added mods? If so, the fuel trims may have been off. Also, a MAF Translator could cause it.

:cheers:

 

I believe it DOES matter which rear end ratio you have. For instance When I had the 2.73's we left it in 2nd and ran the Dyno..With most other rear end ratios we used 3rd... :yesnod:

 

Thanks for the very detailed reply, but how does the dyno operator stop the car from downshifting when they mash it in 3rd?

Determine ahead of time, at what rpms you car will no longer downshift to 2nd. Floor it after that point. Unless you don't have a choice it is best to lock the TC after you get your rpms up to, say about 2000.