I'm not really interested in running a piggyback PCM but would like to add additional fuel via injectors instead of doing a wet shot. Based on the way the MAP, MAF and O2's work together couldn't I place a resistor or capacitor inline with one of those sensors that could be switched on/off to increase fuel when nitrous is hit?
There should be a fairly easy way to figure this out so that I can spray evenly through all injectors.

The downside is I can't just add a small fuel tank and only do the high octane fuel for the nitrous setup....

Hmmm, wonder if there would be a way to Y the 2 fuel systems together.... That's for a different advanced tech question.



Mike

 

That's exactly what I don't want to do.
I also can't raise the fuel pressure enough to compensate for a full 250HP shot but I can force the injectors to give more fuel.

Somebody has to know how these circuits work in the feedback loop in order to be able to fool the PCM.

Mike

 

I read in a mustang book once on the 4.6 they put bigger injectors in it and din't change the computer, ran rich as hell on motor but great on nitrous... Just a thought, sorry it's late here and i'm thinkin

 

There is one major problem with adding fuel with your existing injectors: you will run out of duty cycle on the top end!

Why?

The stock injectors typically are running a 15-18 msec pulsewidth on the sequential fuel injector cars (half that on bank fire cars). At 6000rpm, there is only a maximum of 20msec available on a sequential setup to cycle the injector ((60sec per min/6000rpm)x2). Since it takes at least 1.0msec just to cycle the injector, the maximum pulsewidth you could add might be only 1 or 2 msec... This equates to a very small fuel enrichment...maybe enough for a 25HP shot.

On the other hand, if you step up to large injectors (remember, they have to be big enough to supply fuel for your total HP with nitrous...a 250 shot will require injectors large enough for about 550HP assuming your engine is still stock), you will be able to add the fuel you need. The only problem is that you will be flooding the engine with fuel whenever your nitrous is off!

Solution: run nitrous all the time!

Honestly, though, there are not a whole lot of options to manipulate injector pulsewidths in an on/off manner. In other words, there is nothing out there that I can think of that will safely run your injectors on one pulsewidth, then step up the pulsewidth when the nitrous is applied. The reason for this is that injector pulsewidths need to be extremely accurate, or else the car will lean out the instant the nitrous is applied (bad), or the car will bog down from being too rich from the fuel being applied slightly too early before the nitrous.

For a 250 shot daily driver, I highly recommend a standard fogger, or even a direct port. Direct port setups are safer IMO...no cylinder-to-cylinder imbalances.

Don't forget to run a good fuel pump...the HP is almost being doubled!

Pete

 

Currently I have 42lb Lucas injectors.
Fuel pumps - Walbro 340 in tank and NOS (Bosch) inline fuel pump.
Car makes 380HP/430TQ to the ground.

In thinking about this further (was at work yesterday) I didn't think about the fact that the PCM goes into "WOT" mode so no feedback from O2's.

Is MAF still interactive?

I'll continue to puzzle on this....

 

Well, O2's are pretty much useless when running NOS anyway...the way that an oxygen sensor works, with the outside air being the comparision gas, NOS tricks the sensor into thinking the mixture is different. In other words, the gases entering the engine (outside air & NOS) are not the same makeup as just the outside air.

The MAF is all that is used at WOT for fuel metering...in addition to the various smaller enrichments from TPS, MAP, CLT, MAT, etc...

With your injectors, I am calculating that you can probably add about 20% more fuel, right? This is assuming you don't change the fuel pressure... What are your current pulsewidths?

Perhaps as an interesting alternative, you could run two fuel pressure regulators...one with a higher spring setting than the other. Tune your car to run the 42lb/hr injectors at high duty cycle, and low fuel pressure on one regulator. Then, when you want to engage NOS, switch to the other regulator which will have very high spring pressure. Just a thought...

Pete

 

Say'n "tricking" the ecm to me would be a maftranslator.
Setting up the ecm:
*you need bigger injectors first.
* set the constant setting to the correct value for the injector size.
* run higher fuel pressure [50~60 psi] and tune in the afr your looking to run in the openloop afr page...read the plugs or use a wideband box to confirm where your actualy at for afr.
I use injector balance [idle] table to tame down the blm values you may see. Most likely it will be subtracting fuel to bring the Block learn to 128.

Remember 128= zero correction and on target 14.7:1 afr
108= 24% subtraction in correction trying to reach 14.7:1
160= 24% addition in correction trying to reach 14.7:1

so if blm is showing 120 @ idle in closed loop you are seeing a 18% reduction in the injector by the ecm.
I adjust the idle balance table by 16% over all, reflash and go test drive. You can tame any idle issues like this and run say 50 pound injectors and get all the fuel you need.




:quoting pete:
Perhaps as an interesting alternative, you could run two fuel pressure regulators...one with a higher spring setting than the other. Tune your car to run the 42lb/hr injectors at high duty cycle, and low fuel pressure on one regulator. Then, when you want to engage NOS, switch to the other regulator which will have very high spring pressure. Just a thought...

Pete
:End quoting pete:

^^^^^^^Reguarding ^^^^^^

This dual fp reg set up is what NOS systems set you up with in there dry systems.
I ran 280hp dry shot with cheater noids in place of the small superpower shots on 36 pound injectors.
I ran 80 pounds rail pressue when on the hose and off the hose the engines fp reg ran at 60 psi with the above tuning to the "Idle" INJ BAL table.

I'd just run the NOS fuel pressure compensator and dial in the pressure with the jet fitting in the "tee fitting".
A dry system jet change in the compensator [fuel pressure] works like this:
Smaller jet= higher rail pressure.
Larger jet size= lower rail pressure.

word
This is not a typo reguarding how the jet change effects the rail pressures in the "tee fitting"

 

While playing with the fuel pressure seems to be workable on the 5176 kit with a 125-1150 shot, not sure that I'd want to tune that way for a 250-shot. "Tricking" the PCM doesn't seem all that promising either... sort of hit or miss.

One idea that always stuck in the back of my mind from back when I was running the 5176 dry kit was to use a separate source of gas pressure to alter the FPR setting.... a small bottle of high pressure air, with an adjustable gas pressure regulator, applying the pressure to the vacuum compensation port on the FPR. All you need is a solenoid operated 3-way valve to switch the FPR from vacuum signal (normal driving) to the regulated gas pressure supply (nitrous use) when you are spraying.

And, I'm not sure why you say you can't raise the pressure to compensate for a 250-shot. It isn't that hard at all. Let's say you use a Bosch injector, flow rated and operated at 2.7bar (39.15psi) for your normal 500HP stroker..... you could run a 42#/HR injector, assuming a 0.45BSFC and a 67% duty cycle. When you run the 250-shot, you are going to need a flow of 62#/HR, assuming an 0.53BSFC, and no more than 80% DC. That means you need to raise the pressure by a factor of 2.25.... so 39.15 X 2.25 = 88.3psi..... not unworkable.

Thoughts?

PS: This should probably have been put in "N2O Tech".

 

Fred I two stage'd a dry system almost the way you mentioned in 2000. No co2 system was needed, just a air system control valve.
{My plastics Injection molding maintance experance gave me this idea}

I used a MAC 2-way control valve. The deal had 1/8 npt threaded ports so fittings for lines and dual fuel jet fittings for two stage fuel pressure control was easy. When no power was present the valve defaulted its supply port thru to a Blocked port. This is where you drill it open so it's a drain port.
...this supply to drain port was for normal non-nitrous fp [passthru].
Three vac lines ran from three ports of the mac valve with each line having a one-way check valve [gn parts] between the small 4 port manifold and the control valve. This was a three to one line if you will connection to the FP regulator.

This MAC control valve {a/b control noids} triggerd as follows:

a-noid switched vac thru fp jet for first stage fp off the wot switch which also triggered a digiset timer set to bring in the second stage nos noid along with the switch to the b-side of the MAC control valve and port [B] fp jet for higher fuel pressure.


it's small and adds under 2 pounds to the car and worked well.

Why I'm I posting this info????

 

OK so if I go back to a fully dry setup and use my 5176 components then my only problem is that I was told that the Lucas injectors (disk) will NOT handle high fuel pressure.

So sell the Lucas injectors and swap for some SVO 42lbers and go back to a dry setup with increased FP....

I could use the 3 way air setup to do a 2 stage shot this way as well...

I guess I could do that, just need to drill out the NOS 58MM to handle the larger shot.



Mike

 

Hot Rod Hawk is THE man when tuning this setup. He has helped me a great deal.

Just as a little helper my Nossle points at my IAT senser

 

Hmmm... I smell a IAT timing adjustment....