M5 Dyno

[Wicked 3800 V6]

Note: I want this to stay here, where there are more experts, and so that it won't get buried in general tech, please.

I'll probably be dynoing my car at the Terrapin Motorsports Event on May 3rd (see the regional events or www.terrapinmotorsports.tk for details). I have an M5. After reading the last issue of Grassroots Motorsports, which talked about lots of dyno stuff, I learned that different gears affect the dyno readouts because of rotational mass / inertia / etc. Don't ask if you don't know, but instead go take a physics course or be an engineer like me. Simple explanation: spinning stuff takes energy, lots of it. Ignoring gears and tire sizing, and no I haven't been up to the speed limiter to find out if it's there or not, and I have a 97 so there is no HPP3, SCU, or anything. ... I figure I have a few options:

1. Do it in 3rd gear, where I shouldn't reach the limiter, but experience slightly lower numbers due to rotational stuff.

2. Do it in 4th gear, where I might bounce off the limiter at 4800rpms or so and waste an entire run.

3. Do it in 4th, after jumping underneath and disconnecting the speed sensor. No, I have no idea where it is, nor if fluid will spurt out at me when I do. [img]smile.gif[/img] Any tips?

Eager to hear ideas!
-Rob

[ April 05, 2003: Message edited by: Wicked 3800 V6 ]</p>

[Dominic]

#3

[01camaro]

the speed sensor is on the tailshaft of the transmission, driver side, one bolt holds it in place, 15mm i believe, it's just a sensor.

[Only4U]

<blockquote>quote:</font><hr>Originally posted by 01camaro:
the speed sensor is on the tailshaft of the transmission, driver side, one bolt holds it in place, 15mm i believe, it's just a sensor.<hr></blockquote>

will the tach still work though?

[raxxus]

Not until you plug her back in a believe [img]smile.gif[/img]

[AZ3.8Camaro]

Why would the Speed Sensor mess up the tach?

I don't think they are connected except for the speedometer.

Dunno..

[justforfun]

I have been told that when you unplug the vss sensor the pcm limits the car to like 4000rpm.

The guy was telling me he the car would not let him rev above 4k for a launch on drags.

anyone else tried this & does it apply to 4th?

[justforfun]

ok word from huff is that you disconnect the vss & the rear abs sensor.

[Wicked 3800 V6]

I'm thinking I'll just stick it in third ... Sway me another way?
-Rob

[viper98885]

<blockquote>quote:</font><hr>Originally posted by Wicked 3800 V6:
I'm thinking I'll just stick it in third ... Sway me another way?
-Rob<hr></blockquote>

Stick in third with a manual tranny?!? Computer won't control which gear you are in with a manual tranny.

[Dojo2000]

<blockquote>quote:</font><hr>Originally posted by justforfun:
I have been told that when you unplug the vss sensor the pcm limits the car to like 4000rpm.

The guy was telling me he the car would not let him rev above 4k for a launch on drags.

anyone else tried this & does it apply to 4th?<hr></blockquote>

only on an automatic tranny

[jonny985]

I may sign up to dyno my car there too, we'll see how we compare, I have a similar setup.

[imported_admin]

Dyno in third. Save yourself the headache.

What's 2-3 hp going to matter? There's more of a difference due to temperature and atmospheric pressure than that.

Dyno tuning is a ballpark of how your car is doing, not an absolute.

And yes, your power curve WILL drop to 0 immediately as soon as you hit about 4800 rpm in fourth gear... I've done it. The chart kept going up and up and up and then--DOH! [img]graemlins/crybaby.gif[/img]

[Amped96]

Ok...so does anyone know for sure if unhooking the speed sensor will work on an M5? I am dynoing this saturday and am just curious. I may unhook the vss and make a speed run and see for myself. I have had friends that have unhooked it on other vehicles and it worked.