dyno power runs procedure - any thoughts???

[dickster]

i'm changing the stock cat. and muffler for dansk premuffler and sport 1 in 2 out muffler and for anyone interested i have booked in for next thursday for 3 power runs:

1. without mods
2. change either the cat. or the muffler
3. change the remaining cat. or muffler

what order should i go in??

does it matter??

does anyone care??!!!!



the dickster
('86 3.2 US)

Well first you should do a run with stock setup. Then you should do a run with the new pre muffler and rear muffler.

At least that would be of interest to me.

[Steve W]

dickster, do you have a chip in the car presently? When you do the dyno runs, especially when you do the run with both the premuffler and muffler, make a run with the Motronic fuel quality switch in position 2 and position 3 to see if there is any difference in power, and make up for the possibly lean fuel condition that may be caused by the reduced exhaust backpressure. Otherwise the power gains differences may seem little because full throttle acceleration will switch to a fixed fuel map, and inject the same quantity of fuel on all runs.

[dickster]

steve, only the std. chip.

how do i do that??

i'll only be able to do 3 runs (cost) so do i change the settings with the exhaust changes?? (say position 2 with the first change and then no. 3 on the final change??)

the dickster

[juan ruiz]

Stock numbers will be the plataform for future upgrades, possible heart attack when shes running wide open!

[dickster]

no particular order then.

guess i'll record the sound files when its on the rollers flat out!!

[Steve W]

dickster, there is a small hole on the side of your Motronic box under the driver's seat that is plugged with a small plastic plug. If you reach under the rear side of your seat, and feel the side of the box facing the rear of the car, you will feel the plug/hole on the left side. Pop that plug, and low and behold will be a blue seven position rotary switch that is an adjustment for fuel quality. Postion 1, full counterclockwise is stock, postion 2 one click right, increases fuel delivery by 2-4%, and position 3 increases fuel delivery by 4 to 7%. The hole of the switch is actually a little triangular hole, but I use a small flathead jeweler's screwdriver which fits in there fine and I can turn it.

Being that a premuffler is supposed to increase power by 4 to 6 hp over a cat, that theoretically works out to a 3% increase in fuel required. A combination of a premuffler, along with a sport final muffler is supposed to increase peak power by 11.78 hp a la Bruce Anderson, that works out to something like 6%. So your methodology about the dyno runs should work. However theory and reality are two different things. It's like putting on SSIs without putting in a chip programmed for it. The car will run lean. You might gain 12 hp with the new exhaust tuning, but loose 6 because because it is running lean, netting you only 6 hp gain.
The only problem I have with the method of runs is that it does not completely follow the scientific method. For example, though position 1 is programmed stock for a stock car, just flicking to position 2 or 3 would probably give you more power anyways without making any exhaust changes. So when you start comparing results, it gets confusing. You'll start wondering how much of the gains came from the exhaust changes, and how much came from enrichening the fuel mixture. Get the drift?

The switch is easy to flick by reaching under the seat. I know dyno time is expensive and I admire you for performing the runs for the sake of science. But I guess you will set history and end this myth once and for all. Better would be on run three, make a full throttle run at postion 2, turn off the car, flick to position 3, and make another full throttle run. If the runs are done quickly, I think the additional dyno time should be minimal. Good Luck!!!

[ChrisBennet]

I would leave the fuel quality switch alone.

From an old post I save (refers to 944 Turbo):

Subject: Re: DME Settings
From: "David J. Hardee"
Date: Wed, 02 Jun 1999 01:18:42 -0400
X-Message-Number: 3

An additional point for those who might care...
On our 88 951S race car, we tried all positions of the switch over 2
race/DE weekends. Before we did it, a good friend and great car
builder/racer told us to leave it at stock.... Then a motronics engineer
at Sebring told us to leave it at stock. We found every position other
than stock caused to car to be somewhat slower/worse performing. This
was measured with lap times, segment times, a good A/F meter w/injector
duty cycle indicator and with our Vericom computer. Go figure! The
factory does know best sometimes. It is back at stock. By the way,
this was with stock chips and with 3 sets of custom chips done by Al
Collins at Autothority. His chips were from mild to wild and he said to
leave the setting alone.
Dave

[dickster]

appreciate your (conflicting!!!) thoughts guys.

NOW I'M TOTALLY CONFUSED!!

i have negotiated a good deal for 3 runs only (i may use my charm to get a quick forth), so really need to be sure of a way to go.

now i understand that with both the cat. and muffler replaced full power may not be realised until further "tweaking" is done..........but is this necessary for the purposes........(i may get more power from stock with tweaking - don't intend doing it as under time presure here)

anyone else got an opinion/thought on this??

times a running out