## DASH2 Boost Conversion - Autronic SM4

MickAshby
Posts: 5
Joined: Tue Jul 20, 2021 3:31 am

### DASH2 Boost Conversion - Autronic SM4

Greetings...
Apologies in advance for the long-winded explanation...

I have the DASH2 linked up to an Autronic SM4 ECU (v1.09).

I have everything working fine, all the data channels passing data through from the ECU to the DASH2. However, I have an issue with showing the correct boost pressure. I'd like the DASH2 to show the psi, but the ECU outputs pressure in Kpa (absolute).

I've seen another forum post (viewtopic.php?f=2&t=3656&p=13813&hilit=boost#p13813) which details how to convert Kpa to PSI via an equation in the DASH2 config software. I can see I can enter the equation via the ECU Interface option against the Boost pressure data channel. The equation is in the format (<value> x input) + <offset>

So in the above forum example, this would be... (0.145 x input) + 0
So...
10 Kpa converts to 1.45psi
45 Kpa converts to 6.5psi
70 Kpa converts to 10.2psi
100 Kpa converts to 14.5psi
170 Kpa converts to 24.7psi etc...
I think this assumes you are converting atmospheric pressure in Kpa to PSI.

However, the Autronic ECU measures the absolute pressure in Kpa... so ~100Kpa above atmospheric.
So if I use the above conversion, on testing the actual outputs from the ECU and DASH2, I get the following...
@45 Kpa ECU absolute pressure (car idling), I see ~0.06 (psi) on the DASH2
@170 Kpa ECU absolute pressure (~10psi shown on the mechanical boost gauge), I see ~0.2 (psi) on the DASH2... so not what I need.

Now if I do a manual conversion of absolute to atmospheric and then apply the Kpa to psi conversion (using the tested pressures above), I get the following...
@45 Kpa ECU absolute converts to -55Kpa atmospheric, which converts to -8psi
@170 Kpa ECU absolute converts to 70Kpa atmospheric, which converts to 10.2psi ...which is correct.

So the conversion I need is, ((input - 100) x 0.145)

Is there any way of defining this format for the equation?... essentially subtracting a 100Kpa offset before doing the Kpa to PSI conversion?

Many Thanks!
Mick

Tech Support (D)
Posts: 13
Joined: Thu Jul 26, 2018 7:01 am

### Re: DASH2 Boost Conversion - Autronic SM4

Hello mick - you can enter equations in the Variable Source section on the DASH2 PRO config utility. Read back the current config from the dash > open Variable Source section > scroll down to the General variable 1 and select the 'calculate from a combination of inputs using equation' box > in the new window select custom > enter the desired equation for boost pressure - (VAR_3504 - 100) * 0.145

MickAshby
Posts: 5
Joined: Tue Jul 20, 2021 3:31 am

### Re: DASH2 Boost Conversion - Autronic SM4

Hello mick - you can enter equations in the Variable Source section on the DASH2 PRO config utility. Read back the current config from the dash > open Variable Source section > scroll down to the General variable 1 and select the 'calculate from a combination of inputs using equation' box > in the new window select custom > enter the desired equation for boost pressure - (VAR_3504 - 100) * 0.145
Many thanks for the reply... however, when trying to read the DASH2 using the DASH2 PRO config utility, I get the message "System can't identify connected device".

Cheers
Mick

Tech Support (D)
Posts: 13
Joined: Thu Jul 26, 2018 7:01 am

### Re: DASH2 Boost Conversion - Autronic SM4

Sorry Mick misread the post. For the DASH2 standard running latest software you can enter the equation in either the Other Data Sources section or the ECU Interface section, depending on where the channel has been enabled.

Set the Boost Pressure units to Custom then multiply by 0.145, I've attached some images to show how to enter the equation.

Other Data Sources:
Other Data Sources section.JPG (18.18 KiB) Viewed 7081 times

ECU Interface:
ECU Interface section.JPG (15.31 KiB) Viewed 7081 times

MickAshby
Posts: 5
Joined: Tue Jul 20, 2021 3:31 am

### Re: DASH2 Boost Conversion - Autronic SM4

Hi, yes, that seems to be my problem. The data channel is via the ECU interface, and as in your last screenshot, this equation doesn’t seem to allow me to subtract 100Kpa from the value before I convert it using the 0.145 multiplier.

Cheers
Mick

Tech Support (D)
Posts: 13
Joined: Thu Jul 26, 2018 7:01 am

### Re: DASH2 Boost Conversion - Autronic SM4

You can minus the 100 after the multiplier by typing '-100' in the lower box, however I don't think you'll need to do that. Try the 0.145 multiplier on it's own firstly then subtract the 100 if still reading absolute pressure.

MickAshby
Posts: 5
Joined: Tue Jul 20, 2021 3:31 am

### Re: DASH2 Boost Conversion - Autronic SM4

Hi
Unfortunately that's not going to work... (input - 100) * 0.145 is in no way the same as (input * 0.145) - 100 as the below calculations confirm...

Absolute (pressure-100)*0.145 (pressure*0.145)-100
Pressure PSI PSI
0 -14.5 -100.0
50 -7.3 -92.8
100 0.0 -85.5
150 7.3 -78.3
200 14.5 -71.0
250 21.8 -63.8

If the only equation available to me is (multiplier * input) + offset then it can't be done... I was looking for an alternative to this ECU channel custom units conversion.

Many Thanks
Mick

Tech Support (D)
Posts: 13
Joined: Thu Jul 26, 2018 7:01 am

### Re: DASH2 Boost Conversion - Autronic SM4

Mick email your DASH2 configuration to daniel AT race - technology DOT com and I will make the changes you require.

MickAshby
Posts: 5
Joined: Tue Jul 20, 2021 3:31 am

### Re: DASH2 Boost Conversion - Autronic SM4

Awesome... thanks... will do!

Cheers
Mick

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