Hey guys,

I am in the process of rebuilding my setup and this time around I am a few years older and now want to reinstall my AC and PS and other creature comforts as well as be able to drive the car whenever I want and have full race gas boost available without running around town burning $12/gallon fuel. I was running E85, but the nearest station that sells it is 3 hours away from me and it just isn't practical to keep making 6 hour round trips to pick up a few 55 gallon drums.

So I have been thinking about doing a dual fuel system and running 16 injectors, something like some 24 pounders off boost and my 160lb injectors when boost comes in. I have plenty of inputs for switching on fuel pumps and each set of injectors would have its own tank and pump. could it be as simple as follows?

I was thinking about using a relay to switch the positive voltage from each set of injectors at a certain set point? so essentially, each pair of injectors for a particular cylinder would have the grounding trigger wire from the ECU jumped or Y'd so both injectors would be seeing a trigger voltage. the change would occur when the relay was triggered changing the 12 volt positive to the secondary set. so the same fuel map would be utilized and for all intents and purposes the ECU wouldn't know any difference.

now the only down side that comes to mind immediately is the time for the relay to activate. because there is no transition such as would be seen in a overlapping dual map staged injection setup there may be a blip during relay activation that caused a lean condition. not sure if it would be damaging as I would set it to be triggered at 1 lb of boost and anything over 60% TPS which would happen around 2800rpm MAP wise.

Any thoughts or suggestions on this or another way to do this? the DFI offers the staged injection but only in 4 cylinder mode and I think that could also be managed somehow by using a batch fire mode, but I don't know if running it in 4 cylinder mode would play havoc on the ignition system.

Thank in advance guys!!

Chris

 

A couple of issues, you will have to pair the trigger wires to two injectors for each trigger out of the Gen 7, So you have to make sure their drive can handle the 160s and a smaller injector... I am not sure on this but I would think it will be fine. Second issue is the ecu is doing the math based on 8 injectors so your VE map will be larger in the area where only one set is turned on, then go back to normal when the second set is turned on. You third issue is by triggering the first set of injectors the 12v power will also bleed into the ground side since it is a coil and the power will go into the ground side of the second set of injectors if you don't deal with that also. The time it takes for the second relay to turn on is no big deal and can be delt with in the VE table.

 

I have been doing a lot of reading and planning and I think unfortunately unless I could use the nitrous auxiliary fuel map from DFI to run the fueling strategy for the 160's and switch settings for activating the change to the secondary injectors.

as for the box handling the injectors... I am not sure if it can or cannot. it may be that it doesn't like swapping between high and low Z injectors that fast and I need to run the same resistance injector. beyond that it is just a matter of a pretty hefty sized pulse width change in the box which it is designed to handle. so maybe need to run some ID injectors that are high z or find some low z smaller injectors.

for the grounding issue... the ECU is triggered by ground not positive voltage so the circuit is open until the ecu fires it.. shouldn't be an issue if there is no place for the injector to bleed anything through too I would imagine.

I also found this guy who is doing exactly what I was thinking. I was concerned that a electromechanical relay wouldn't be fast enough but he says there is not even a miss or hiccup during the transition. he is also running the same size injectors on both rails though so the ecu isn't noticing any change and the map is going to be pretty fluid between the change as again.. same size injectors... maybe that's the easier way to go even though you would loose the benefit of a smaller injector to tune with for the lower RPM cruising and idle areas.

Have some more to look into with the DFI gen 7 nitrous stuff to see if it could work somehow to make the smaller injectors work, if not I am definitely at least doing the same size secondary injectors.. push comes to shove it just making a bigger fuel system for down the road and more power..lol

Chris

 

I've done this and the bleed thru is an issue. Your right they trigger ground but it is a coil and there is power coming through the other side

that will bleed into the secind set of injectors you have hooked up. We verified this with another setup just make sure the second set isnt always turning on.

The nitrous output function also works but wont give you the control that the ve table will.

 

This is what you are think of doing.

http://www.turbomalibu.com/turbomalibu/SDFI.gif

I had to find it again, because I remembered this system from an old post on Turbo buick.
He has been running this way for a long time.

http://www.turbomalibu.com/dualfuelsystem.htm

Lots of real world information, on his site, about what you are thinking about setting up.

 

When you say bleed through can you explain that a little more? If the secondary injectors are disabled from the positive voltage source by the relay being mechanically disconnected and the primary set outs connected then where does the bleed through occur?

Both sets are paralleled by the ground trigger wire from the ecu but the secondaries would have an open ended circuit would they not? Not doubting as wiring is not one of my best strengths just want to verify and avoid pitfalls.

Thanks

Chris

 

Ok, I just looked closer and saw the "blocking diodes" where or what type should I get for this?

 

How hard will it be to tune with drastically different sized injectors?

 

The blocking diodes is the only way it will work. The power from the first set will loop into the second set without it since the wires go through the injector like a coil.

 

It's not hard although you will find if you keep all 16 on the VE table will have large numbers in it where the second 8 isn't turned on. Then it goes back to normal when they are all on. If you are just switching one on and one set off then it really isn't going to be much different. I would use a solid state relay if it was me though.

 

....2 different fuel maps, one pump gas outside of boost, and soon as it reaches boost it has to switch over and run the race gas, 2 different VE tables overlayed if im not mistaken. I hate to push people to other sites but you might want to run over to LS1 tech and give maxxmitchell and skinnies a shout. maxs thirdgen had a non intercooled twin set up on a ls doing the same thing you want to do, ran 87 outside of boost on 80# injectors and then when it started to go into boost it switched to the large injectors and E98. Im not sure how they did it really, but I know they were having issues transitioning from 87 to E98, it would hit hard.

 

I think I would get an ecm made for staged injection.

 

Well the easiest I think is too use the same size injectors and stay with 87 and race gas. That way the volumes would be very close and you would not need any drastic map changes.

If I were going to run gasoline and e98 or e85 as my secondary fuel, I would size the secondary injectors roughly 30% larger... that way the map could remain relatively smooth and the volume change would come from the injector flow rate increase.

I have run both race gas and E85, my map remained the same,I just changed the injector flow rate for a global fiddling increase without having to tune the whole thing again for the ethanol.

Just a thought.

Can someone give me some specific information on the blocking diodes such as part number or place to purchase.

Thanks,

Chris

 

You will need a blocking or one way diode at each trigger wire to the second set of injectors. The size depends on what injectors you are running but they can be had at any Radio Shack or Digikey.

You can also run one map depending on how you are using it. If it is a pump gas low boost and race fuel hi boost it will be in different parts of the map anyway.

 

Hi, just saw this thread, First let me say, that the Gen. 7 will fire 16 injectors, but if you hook them to the same driver, you will get bleed through, as mentioned before. The correct way to fire 16 injectors with a Gen. 7 is to us the injection harness and V/E to fire the main set, and use one of the PWM channels and fire the second set with a Crydom relay. In the PWM table you will be able to control the #2 injectors by duty cycle. Also you can turn a second fuel pump on using the NOS control or the V-tec control. I would try to match the injector sizes to maske tuning alittle easier though.

 

Can you elaborate on the pwm table? Where is that located in the software, I have been through about every table and have not yet found anything like that. Unless you mean the nitrous fueling table? I would want to run two different fuels, most likely pump gas on they primary and racing methanol on the second fuel system for added power and lower cost. I have 160lb secondary injectors and was planning on sizing the primary injectors according to the difference in volume required by the two fuels to keep the map somewhat normal looking and let the injector flow rate differences make up for the added required volume of methanol.

 

Under Configuration, at the bottom, is PWM Outputs or Ctrl+M, they have 3 different ways or all 3 controllers to activate the table. Then there is a duty cycle page to operate the injectors... Then I would use the NOS control feature to turn your second fuel system pump on.... By the way, I don't follow the site rules about vendors.

 

Under Configuration and the bottom of the drop down, is PWM Outputs, or Ctrl+M, these have a 3 separate or a combination of all 3 window switch to activate the table. The tables are set up for duty cycle, so you can tune the second set of injectors. You can use one of the NOS stages to turn on the second fuel pump, by it's 3 separate or combination of all 3 window switch. So when your first stage injectors (pump gas) go static at lets say 5 psi. Youi would use the 1stage NOS window switch, select 2 of the 3 switchs, let's say RPM enable at 2,000 rpm, disable at 1,500 rpm, MAP enable at 1psi and dis able at -2psi. Then go to your PWM screen, set your window switches at the same, but enable MAP at 3 psi, disable 1psi, then go to your duty cycle table and add fuel in as needed for the fuel you are running. Now remember you should be able to run about 600 horse power on pump gas, so I'd run a 55 lb injector. Now for your second fuel system, see how much horsepower you are going to need to fuel, and then select that injector. ie 1200 hp max, that would be a 55 lb for pump gas and another set of 55 lb for the race gas, unless you want to run methanol, then you would need a 120 lb.. Also, remember if you run a different fuel for the second system ie; ethanol or methanol, you will not be able to use your wide band for tuning, different stoich...

p.s. I am about to be banned because I can't follow the rules about vendors.

 

sorry for the repost, my computer is freeking out, and won't let me edit