36lb SVO injector tune....
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From: Phoenix, AZ USA
36lb SVO injector tune.... Check over my adjustments to the injector flow rate table.
I have a 97/98 Vette fuel rail (return line style) with an aftermarket vacuum referenced pressure regulator. I also have 36lb SVO injectors and am running 64lb fuel pressure (+6 over factory 58).
I calculated that the 36lb SVOs would be like a 46.03lb at my pressure:
(square root (64lb/39.15lb) * 36 = 46.03 lb)
Then I calculated the difference between the factory 28lb and my 36 SVOs:
46.03lb/28lb = 1.644 (164.4%)
so now I take this 164.4% and multiply the factory flow rate times that.
Now…….According to this site: http://ls1edit.slowcar.net/tuning.html
”If you are using a vacuum referenced regulator (some supercharger setups, etc.) then you will simply fill in a constant value across the range”
As I understand it, all the cells (besides the 0 kPa) are to make up for the factory fuel rail not having a vacuum referenced regulator. It makes up for the fact that as vacuum increases in the intake, the injectors will flow more.
Now I have a vacuum referenced regulator. As vacuum increases, my fuel pressure decreases. As I get pressure (boost), the fuel pressure will rise.
I no longer need this “computer compensation.” If I keep it, the computer will pull fuel (shorten pulse rate) while the regulator is also pulling fuel (lower pressure = lower flow rate).
I just use my calculated value for the 0 kPa cell and copy it all the way across.
I have a 97/98 Vette fuel rail (return line style) with an aftermarket vacuum referenced pressure regulator. I also have 36lb SVO injectors and am running 64lb fuel pressure (+6 over factory 58).
I calculated that the 36lb SVOs would be like a 46.03lb at my pressure:
(square root (64lb/39.15lb) * 36 = 46.03 lb)
Then I calculated the difference between the factory 28lb and my 36 SVOs:
46.03lb/28lb = 1.644 (164.4%)
so now I take this 164.4% and multiply the factory flow rate times that.
Now…….According to this site: http://ls1edit.slowcar.net/tuning.html
”If you are using a vacuum referenced regulator (some supercharger setups, etc.) then you will simply fill in a constant value across the range”
As I understand it, all the cells (besides the 0 kPa) are to make up for the factory fuel rail not having a vacuum referenced regulator. It makes up for the fact that as vacuum increases in the intake, the injectors will flow more.
Now I have a vacuum referenced regulator. As vacuum increases, my fuel pressure decreases. As I get pressure (boost), the fuel pressure will rise.
I no longer need this “computer compensation.” If I keep it, the computer will pull fuel (shorten pulse rate) while the regulator is also pulling fuel (lower pressure = lower flow rate).
I just use my calculated value for the 0 kPa cell and copy it all the way across.
TECH Regular
Joined: Feb 2002
Posts: 426
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From: ohio
Re: Need help with injector tune.... Why is it that you have a vacuum regulator? It will be a bit more difficult to tune with this. If it is for FI then maybe just reference the boost and not the vacuum, and if not then maybe disconnect the vacuum line and run constant pressure like the stock system does?
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Joined: Nov 2001
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From: College Station, Tx
Re: Need help with injector tune.... (square root (64lb/45lb) * 36 = 42.9 lb)
Right, except the SVO's are rated at 39.15 psi, so it would be sqrt(64/39.15)*36, or 46.03 lb/hr
(this is assuming the 64lb value is the value you see with the vacuum reference line disconnected/vented to atmosphere)
Then if I want to set it with an 80% duty cycle:
1.536 (153.6%) * .8 (80%) = 1.229 (122.9%)
This is probably what's tripping you up -- there is no "set it to 80% duty cycle" step or technique you can really perform. You would be effectively underreporting your injector size to the pcm, so you would always be flowing 20% more fuel than intended if you do this. You just need to tell the pcm the correct size
As I understand it, all the cells (besides the 0 kPa) are to make up for the factory fuel rail not having a vacuum referenced regulator. It makes up for the fact that as vacuum increases in the intake, the injectors will flow more.
Now I have a vacuum referenced regulator. As vacuum increases, my fuel pressure decreases. As I get pressure (boost), the fuel pressure will rise.
I no longer need this “computer compensation.” If I keep it, the computer will pull fuel (shorten pulse rate) while the regulator is also pulling fuel (lower pressure = lower flow rate).
Do I just use my calculated value for the 0 kPa cell and copy it all the way across?
yep, you got it 100% - you will put 5.8 in across the board in your situation for your injector flow rate (that was just a quick back of the napkin calculation - so double check it, but I think that's right).
