toddk911

So how lean can you go in the low/mid for spool up purposes?

Also, is it better, on the ARC2, to lean out the mid and turn up the accel, or vice versa?

johntorg

Todd, I've owned the car for 3 days now so I assume that question is for the people who are responding to my ignorance. On the other hand., I'd be interested in the answer also.

jimbo1111

I had a sketch of the arc2 nobbs in the glove box. Check your paper work. It's not that easy to tune unless you know the concept. I remember the excel was at 1 o'clock. The idle adjustment does not effect the others. I think it was around 12 o'clock. The mid was somewhere around 5:30 or so. I remember having to set the mid very high to add fuel to the mid range. The high I believe was around 8:30 to 9:00 with the fuel pressure set to 34 lbs at a warm engine idle. Don't fully count on these setting. They are from memory. Believe it or not. The car ran perfect with the arc 2. Better than some digital mafs I have seen. The part throttle was very good. No jumping or bucking in any way. That car has had c5's and 996's for lunch. Now we are moving up to bigger game.

toddk911

"the fuel pressure set to 34 lbs"

Wow, that seems really low.

Was that with the 72lb injectors??

johntorg

Jimbo, Here's the way they are set now. I checked the AFR and its between 10.5 and 11 at high RPM. That's with the high end all the way lean as shown in the picture. the mid was all the way rich so I backed it off a bit. I haven't logged it yet, just used the onboard wideband.

jimbo1111

I hope you didn't install the WB on the crossover pipe. It will register rich when on boost.

Tom M'Guinn

Check out splitsec.com and look at the graphs that show how the ***** work on the ARC2. The basic idea of the ARC2 is that it takes the signal from the MAF and converts it to the 0-5v voltage that the DME expects to see from the AFM. The low **** has a large effect on voltages closer to 0, and a decreasing effect as the voltage moves towards 5. The High **** is the opposite. And the mid **** has the most effect in the middle (near 2.5 volts) and a lesser effect near 0 and 5volts. If you log the AFM pin of the DME (7 I think), then you have a better idea which **** is likely to have the biggest impact at any given point.

The accel **** is different than the others. On the 951, the TPS has a binary switch in it that tells the DME whether the throttle is closed or open. The accel **** does nothing at all when the throttle is closed. (If moving the accel **** affects your idle, then your tps is not working or is not adjusted correctly.) As soon as the throttle opens, the accel **** adds a fixed offset to the air flow signal, which remains the same across the signal range (i.e. it might add .25volts to all voltage levels at a particular **** setting, and .3 volts accross the range at the next higher level.) The accel **** is intended to take the place of the old accelerator pumps in carburators -- so that the car won't go lean when you first open the throttle. I generally leave the accel **** in its middle position, unless I need to add or subtract fuel from the fuel curve without affecting the idle.

johntorg

Jimbo, I didn't install the wideband. I assumed you did. I'll check to see where the sensor is located. Did you sell it to a guy in NJ named Amaf, or did it go to someone else first. Where is the best location for a widband o2 sensor? I have an LM-1 with a tailpipe sensor that I can cross check the readings with.

johntorg

Tom, Thanks for the information on the ARC2. I will go to the website and study the instructions. I did see that the controls interact. Does the accel **** increase or decrease the signal at constant cruising? It would seem that if it was to work like an accelerator pump it should add some fuel as you step on the gas and then go away.

Tom M'Guinn

Splitsec says it acts like an accelerator pump, but as you point out, that is not really true. The accel **** adds gas across the voltage range (when the throttle is open) and does not go away like an accelerator pump. Their graphs show this pretty clearly. Also, based on the graphs, I understand it only adds gas, never takes any away.

TonyG

>>>Oh God help you - I didn't know that was Jimbo's old car......
You'll be lucky to get a few good runs before that thing blows like a geyser <<<

Quite being an ***. Focus on your 8000 RWHP car.


johntorg... the a/f ratios are close enough to easily rectify with the ARC2 (turn up the low, and down the high a notch or two). This should fatten up and flatten the a/r ratios. Your best bet is to do this on the dyno.

The LOW controls the entire "map" up or down.

The mid bows the middle load range up or down.

The hight bows the high end of the map up or down.

The accel is tied to the TPS and functions somewhat like a conventional accelerator pump. You shouldn't need more than a couple of clicks here max.



If you want to get to the 400RWHP level, you're going to need larger injectors 72lbs), fuel pump (Lindsey Racing sells the proper high volume fuel pump), proper chips, probably a different turbo, a cam, and some intake work wouldn't hurt.

You could save a ton of money and just run it at 28psi boost with a huge turbo like some of the other dyno queens here :-), but don't expect to do that on a track where real sustained loads are the norm.

Make sure you have a wide band with a new sensor and a EGT to tune with.


TonyG

emwporsche

did anyone notice that his power lines didn't cross at 5252?

special tool

Hey Rico Suave - that guy is a personal friend of mine - I am allowed to say that.
You'd know about it if you had some of your own.

johntorg

I've got to go on a trip for the next 8 days so won't have time to mess with the arc2. Then I have to decide if its a new chip or installing a standalone to go with larger injectors is the way to go. I like the current turbo since it gives usable power in the mid range. So far it holds 18-19 lbs to the redline. I'll also check the duty cycle on the injectors to see how much headroom I've got. This will not be a "Dyno Queen" so I may just try tweaking what I've got to see how far it can take me. If it makes 350 to 375 WHP, that may be enough.

I paid $7000 for the car, which gives me some leeway for modifications. Of course I'll need some $ for the inevitable breakdowns (I need one rear axle already).

johntorg

Tony, Thanks I've got an LM-1 and the car has a dash mounted wideband. I also have a Greddy EGT from My VW turbo projects. ?Where do you mount the EGT bung on a 951