Drac recalibration

[George Blake]

I'm trying to see if a drac can be recalibrated so that the speedo in our stock clusters can be modified to read higher, say 150 to 160 mph. I'd like to keep the stock drac the same so the ecm reads right but modify another drac just to feed the speedo. Am I looking at doing this correctly? Is there a better way?

 

[MikeRenz]

Re: Drac recalibration

only if you want 120mph on the speedo to actually be 150mph. I assume you'd get some gauge overlays? I think the odometer would also spin accordingly though.

Modding the drac is simple...its just some jumpers that you change. You could just make the drac think you have smaller overall tire height...that should do it for you. You'd have to do the calcs to figure out the tire ratio thats .8 of our stock set.

 

[George Blake]

Re: Drac recalibration

Correct. What I'm doing is having a custom setup done. I actually have to peel off the original film and put the new ones on. The company doing them for me actually recommended doing this while I had it apart. I'm doing a carbon fiber setup to match the autometer carbon fiber gauges.

Here's the gauge look:

I'll go through the Helms and see where the wires hook in and see how I'll have to do this. I know the Drac can be adjusted, but didn't know if it would accept such a large change.
http://www.autometer.com/img/products/4763_d.jpg

 

[JSM]

Re: Drac recalibration

As mike said drac recal is easy, but the odo and trip will then be off.

You would need to adjust signal in to just speedo but I don't know exactly how speedo works.

 

[MikeRenz]

Re: Drac recalibration

The DRAC receives the AC input from the speed sensor and changes the AC sine-wave signal to a DC square-wave signal. It provides a signal on wheel speed to the anti-lock ECU, the cruise control controller (if equipped), the vehicle electronic control module and the speedometer.

 

[George Blake]

Re: Drac recalibration

I went through a stock 100MPH speedo and the syty 120MPH speedo and there is no difference. It is definitely in the DRAC.

 

[George Blake]

Re: Drac recalibration

Well. Here's what I came up with.
According to this document:
http://614streets.com/drac.html
and this pic:

and this CGI calculator:
http://www.philter.com/cgi-bin/drac.pl
I can do this.
What I did was solved for our stock 80.55 tire diameter and got an input ratio of .8407 which equals a DRAC value of 48.
I then set up a ratio of the 120 mph speedo to a 150 speedo which gave an input ratio of 1.05 and a DRAC value of 68.
I did the same thing for 160 mph speedo. Input ratio=1.1211 and DRAC value=74
So it's very possible. I'm gonna see if I can get a DRAC module from a local junk yard and make this happen. I just need to isolate the signal to the speedo.

Here's the DRAC setup if anyone is interested:
120 MPH speedo
7 not connected
6 connected
5 connected
4 not connected
3 not connected
2 not connected
1 not connected

150 MPH speedo
7 connected
6 no connection
5 no connection
4 no connection
3 connected
2 no connection
1 no connection

160 mph speedo
7 connected
6 no connection
5 no connection
4 connected
3 no connection
2 connection
1 no connection

Should I just go with 150MPH? Anyone care to double check my math?

 

[MikeRenz]

Re: Drac recalibration

well this is how you should mod your drac - it'll make life way simpler for you:

makes for easy toggle switching between settings. :tup:

 

[MikeRenz]

Re: Drac recalibration

I then set up a ratio of the 120 mph speedo to a 150 speedo which gave an input ratio of 1.05 and a DRAC value of 68.[/QUOTE]

How did you get 1.05 here? Don't you mean 150 / 120 = 1.25

 

[MikeRenz]

Re: Drac recalibration

nevermind...i see INPUT RATIO now.

so you're right:

.8407 * (150/120) = 1.050875 input ratio :tup:

 

[George Blake]

Re: Drac recalibration

EXACTLY!! Sorry, I should've put the formula up of what I did. I set up a ratio of 120 to 150=1.25. Then multiplied the 1.25 by the stock 120mph speedo input ratio. And then I just worked my way up from there.
Is there a part number for that DIP switcher?
I think I saw something like that at PartsExpress when I was there getting my radio stuffs.

 

[MikeRenz]

Re: Drac recalibration

that jumper was bought in a bag-o-jumper switches from ebay. no part number, sorry.

You can find them if you search for them though - its nothing special piece-wise

 

[MikeRenz]

Re: Drac recalibration

$0.75 at http://www.cascadesurplus.com/catalog/product_info.php/products_id/1107

 

[George Blake]

Re: Drac recalibration

Thanks very much Mike for double checking me.
What it looks like I may have to do is run a speedometer (the circuit board) with the stock drac to keep the odometer straight and run the visual speedometer with the piggyback drac to keep the true new scaled speedometer correct.
You think 150 is enough? I can do 160. It's just as the MPH goes up, the scaled numbers either get smaller or spread out more and quick look resolution goes down. I don't see a lot of guys doing 160 though.

 

[George Blake]

Re: Drac recalibration

Hopefully others can use this thread when they go to larger wheel/tire combos too to keep their stock instrumentation correct.

 

[MikeRenz]

Re: Drac recalibration

considering the 8second trucks aren't touching 160mph....i'd think 150 is plenty. You really wanna drive these bricks that fast?

 

[George Blake]

Re: Drac recalibration

That's the mind set I was in. The reason I ask is all the aftermarket speedos go to 160 for whatever reason and I just wanted something comparable to them but your right. 150 is faster than I would ever want to go.

 

[mmp142965]

Re: Drac recalibration

George, I have an extra DRAC from Jeff at JS if you need one. Let me know!

 

[George Blake]

Re: Drac recalibration

considering the 8second trucks aren't touching 160mph....i'd think 150 is plenty. You really wanna drive these bricks that fast?

Looks like Robert's just went 155+MPH. If it looks right, I'm just gonna do 160mph gauge. Robert's set the bar. Anyone running 8's or slower will have an accurate gauge if I do the 160.
Unbelievable.

 

[JSM]

Re: Drac recalibration

Yea I was going to send George one, then forgot.

This is becoming pass the DRAC game.