RX8 dead time + small pulse, controversial results.
 

I used the best part of a weekend sniffing fuel vapor while measuring the yellow RX8 injectors. I like to think I did it the proper way:

-Megasquirt in output mode.
-Fuel rail and injectors out of car squirting into bottles, weighing the contents after every set of a specific pulse length.
-I extrapolated (linear regression) the dead time from several pulse lengths between 10ms and 75ms.

I had an adjustable power source which admittedly was sagging just a bit under pulse opening as viewed from my oscilloscope. However, I also did measurements straight from the car battery at ~12.7V with no noticable sag and the results were well inline with the ones done with the power source. I also used the oscilloscope to check megasquirt was actually outputting what I was asking it to.

Results are somewhat controversial. Quite long dead times! I think most are using about half of what I got.

http://img220.imageshack.us/img220/4...adtimerx8c.png

As reference I got 2.85ms@12.7V for the stock Miata 265cc/min injectors.

I also measured small pulse responce. There seems to be a characteristic hump in the output right at the shortest pulses. Same at all voltages.

http://img51.imageshack.us/img51/5427/smallpulserx8.png

Output was ~440cc/min at stock fuel rail pressures.

Hmm... Maybe the megasquirt was adding the dead time you already had set? Thats the only thing I can think of to make the numbers look that good but be that much higher... There's just no way modern injectors have that much dead time, imo.

I measured one of my yellows at .490 ms @ 13v. (Have a ghetto diy injector test bench, was actually using a basic stamp to drive a tip120, using mineral spirits through a 1.6 fuel rail)

Sounds too long. I reckon more accurate results can be had by varying pulse time from 1-3 ms or so.

ian, what was the flyback clamp voltage of your test setup? You will get different dead-times if your clamp voltage is different than that of your ECU.

Hell idk, Not really a hardware guy... I put a diode across the the tip120, but couldn't tell you what kind other than 'a physically large one that was laying around'

Edit: How much does flyback clamping really matter? At this point I'd be pretty happy to be within 25% of correct, lol. It may be worth it to use j-po's voltage curve and my number though since brain contends that the stock ms3 curves are off. I was only able to measure @ 13v since the battery I test with is basically dead (I run a battery charger on it while running the tests, voltage stays pretty consistent but its definitely inelegant.)

That will make them close very slowly.

Any idea of the ballpark for 'very slowly?' If anything, I was worried that my number was too small, as its one of the smaller numbers out of the pool of mostly guesses I've seen for rx8 injectors.

My WAG is > 500 us of error, making dead-time look shorter than it is. Maybe more.

The correct way to test it is to use the same drivers as the ECU, or use the same clamp voltage. (33V is common)

Here is the plot for my RX8 Yellow injectors using Jason's method.

Measured dead time is 0.75ms.

https://lh5.googleusercontent.com/-I...252520time.png

j-po, can you post the actual numbers for your first plot?

Thanks.
-Raj

Here is the screen shot of the lag time map for a stock RX8 setup. I found it on the RX8 forums.

The yellow injector is the secondary injector. (lower table)

https://lh3.googleusercontent.com/-I...or+latency.jpg

Can someone cleverer than me translate that into a MS2/3 settings for the RX8 yellows?

I have problem understanding the chart for RX8 injectors dead time. Would someone also translate that for me in terms of adaptronic settings please?
https://www.miataturbo.net/attachmen...ine=1312448687

So... Just ballparking here, but the baro reading is relative pressure from rail to IM? so if you're running stock rail pressure of 3 bars, thats 2 bars over IM pressure = the 1.99 line? I'm probably thinking about this wrong...

I've asked the RX8 guys for some help. Let's see what they say.

-Raj

BTW, I found this document which is a manual on how to use access tuner for rx8.. It makes me think that they're referencing a map sensor, So in that case does 1 bar = atmospheric = WOT? I'm thinking thats probably what you want to use for a turbo miata w/ rx8 yellows... But then again maybe it'd be better if you had your normal cruise cells optimized? VE values and EGO will adjust for everything else. IDK, either way we only get to pick one row.


http://www.google.com/url?sa=t&sourc...UNgS8g&cad=rja

We should probably pick the lowest pressure column.

1 bar = 14.5psi, not atmospheric

I don't see why MS2 doesn't have a correction table for non linear injector regions, considering they added such support to MS3

Memory space at a guess.

Plus MS3 is the new hotness. The devs have stated many times that new features won't be added by them, only bug fixes.

I'm sure they'd welcome you writing it yourself though.

I wish I could, my programming experince is not up to par
I may look into it later.

what richy said.

1 bar = 14.5 psi = 100 kpa = WOT (if you're na) = atmospheric.