How a Geek prepares for Dyno Day...

Oy oy.

 

After the last dyno day, it was pretty obvious that I had some serious fueling issues.  I am in the rare, but enviable position of having too much fuel delivery. My a/f ratio dipped into the 9s -- about the only way my car will get into the 9s unless I'm running an 1/8 mile dragstrip. ;)

 

The other bit of good news is that I've got plenty that I can do to get things tuned properly.  Here's how it all played out:

 

1)  The easiest thing to do when you have too much fuel and not enough air is to add more air.  I've got 2 charger pulleys that are smaller than the one I was running last weekend.  I ran the 68mm (15psi) pulley on Saturday.  I've got a 65mm (17psi) pulley that I installed last night, a 62mm pulley (19psi) and a 58mm pulley (21+psi).  I'm not going to run either of the smallest pulleys because they would require me to limit the RPMs at which I peak so that I'd have to shift before the head flow was maxed out.  While I'd probably get more horsepower and torque, it would be only stuff I could use on the dyno. Drivability would suffer. 

 

Eventually I'll put a Lysholm charger on this thing.  Hopefully I'll do that this winter.  Once broken in, that charger can comfortably put out 20+ psi all day long.  If the A/F is right, then the bottom end can take that kind of boost without a problem. 

 

2.  Leaner Chip:  When SNS sent me my Stage V+ chip, they sent me three chips.  The idea is to install the richest one and check the A/F.  If all is well, then go to the middle chip and check the a/f.  If that still shows up rich, dance a happy dance, drop in the leanest chip and check the A/F.  Last weekend was on the middle chip.  I installed the leanest chip on Tuesday night.

 

3.  Lean the mixture.  VWs of that vintage used a CO Potentiameter to test the fuel mixture.  The signal from the CO-Pot tells the ECU how much air is going by and an idea of its composition.  By adjusting the resistance in the CO-Pot, you can adjust the signal that is sent to the ECU.  More resistance = leaner mixture.  This is an adjustment that you can do on the dyno.  It takes only a moment with a volt meter and a flathead screwdriver.  I set it at 600ohms and I can go as high as 800 before the ECU reads "out of range" and assumes that the CO-Pot is dead.  (500 is the stock setting). 

 

4.  Add Timing:  While this isn't an ideal way to deal with excess fuel, it is something that you can do when you've got too much fuel.  If you've done all of the above and your still running a little rich, you can run a little more timing.  This will use a little of that fuel and adjust your performance accordingly.  Normally as you increase timing advance on a G60, you lose a little low end torque and gain a bit of high end horsepower.  I'm not really sure if I like that trade-off.  Torque is fun.  It is a good way to take up a little extra fuel. 

 

Stock timing for a G60 is 6 degrees of advance in relation to top dead center.  I currently have it set at +10BTDC.  Again, I can adjust this while the car is on the dyno.  I'll just use the adjustable timing pulley. :D

 

Last week I knew I was running rich.  When I got on the boost, I was easlily 6 bisquits into the rich part of the dial on the A/F meter.  After the changes this week, I'm running 1-2 bisquits in the rich.  I've got potential to run it leaner than that if I need to.  

 

We'll see how it runs this weekend. 

 

Take care,

 

Pete