F.A.S.T. Nitrous set up

[55Belair]

I am getting ready to set up my nitrous system for the first time. It is a dry system, custom port set up using the injectors to add the needed fuel. My question is,

Is there a rule of thumb of so many pounds per hour of fuel per X amount of horse power nitrous jets?

example: I have always heard subtract 2 degrees of timing per 50 horsepower + 1 degree for good measure.

Is there a base set up for the fuel part of the equation?

 

[Craig Smith]

Sounds like your timing theory lines up with what I have heard as well.

I see a lot of people start off with 1 lb/hr of fuel for every 2 horsepower. It's generally a little rich this way but can be leaned out accordingly and serves as a safe starting point for most.

 

[55Belair]

Is this 1# per 2 hp divided by 8 injectors? I am going to start with the 150 hp jets which would equate to 75 # of additional fuel.

The nitrous demo screen on the wp software starts at 6#'s and gradually goes up. Do you know what hp this demo was based on?


I've got the bugcatcher on and it is running great. As soon as I get pictures, I will send them up.
I hope to get to a chassis dyno next week to get a baseline on the motor only. I will try to send that info also.

 

[TurboTR]

>I am going to start with the 150 hp jets which would equate to 75 # of additional fuel.

You are correct sir. Be careful that you add a continuous 75 lb/hr of fuel vs rpm, since the spray is also ~ continuous with rpm. Rather than getting a weird fuel curve drawn up that tapers off with rpm or something is what I'm trying to say And you do have enough injector headroom to supprt that extra 75 lb/hr at no more than about 90% duty cycle, right?

On the chassis dyno, and with a very conservative starting approach like you described above, I gained ~ 125 rwhp with a 150 size jet, on top of some 30 psi boost no less. Turns out it was a bit conservative, but better to start that way of course. IME the FAST wb system works awesome with the hose.

TurboTR

 

[55Belair]

Do I need to divide the 75 by 8 injectors for the input? ex. 8.5 #'s per injector equals 75# for the nitrous fuel table in the FAST ecu or will it do that automatically?


I was talking with the guys at Compucar last night and the only help they could give me was that 100# of fuel and 100# of nitrous per hour = 100 horsepower. With their logic, that would be 1# per hour per 1 horsepower.
They have not done any dry nitrous systems like this in the past. The only dry system they have experience with is a standard add on for a factory system.

Your hands on experience and Craigs experience proves your numbers.

Thank you for your response.

 

[Craig Smith]

I'm not sure how to equate xxx lb/hr of nitrous to a particular hp level, but 100 lb/hr of gasoline is sufficient for over 200 hp.

So, I do not agree with the numbers you posted from Compucar.

If you want to add 75 lb/hr of fuel while on the hose, just set the graph for the first stage to 75 all the way across the RPM range. The ECU will figure pulsewidths from there. Just make sure that the injector flow rate you entered in the fuel calc parameters is accurate and the nitrous fuel will be just as accurate.

Like I said, I think you'll wind up leaning it out from the 75 lb/hr by the time you are done.

Let me know when you've got scuff marks on the underside of your rear bumper.

 

[91cam447]

OK, timeout!! I'm confused now. I was told that the engine ran off of the nitrous fuel chart when the nitrous was activated. In other words, the nitrous fuel graph is not just for fuel enrichment for the nitrous. If this is true, you wouldn't want to set the graph at 75 across the board. Would you datalog fuel lbs/hr on a motor pass then set the graph at what it shows at that rpm plus the 75 lbs? Or have I been told wrong?????

 

[TurboTR]

Told by whom?? The nitrous fuel table is an additional fuel table, in other words it adds that fuel on top of the normal fueling calculation. It's just there to support the additional air introduced via the nitrous.

Bottom line is you have to tell the ecu how much extra fuel to add based on how much extra air (nitrous) you are hosing in. It's exactly analogous to sizing a nitrous fuel jet for it, only in terms of lb/hr of fuel flow rather than just hole size

The older sw versions just had an additional pulsewidth table, not in convenient terms of lb/hr like the current sw Easy enough to get a good 1st guess on though.

Looking at an engine as a "black box" with fuel coming in and power coming out, historically you need to supply fuel in the range of about 0.5 lb/hr to get 1 hp out. This hold true in general, regardless of how the air is being supplied. So 75 lb/hr for 150 hp is a good first guess, but you might even want to start a little richer initially just to be safe.

Do you have enough injector headroom for this?

TurboTR

 

[91cam447]

Look at this picture of a nitrous graph that I got from a well known FAST tuner and nitrous guy. Am I reading this wrong? That is alot of spray if it is just a nitrous enrichment. I have C-Com WP. Please steer me in the right direction. This is not my setup but I will be programming my own I would like to know the correct way of going about this. Don't want to blow stuff up!!

Shoot!!! Can't post a picture. Anyways, at 7500 the graph is set at 565.0 lbs. Now at lbs/hr fuel divided by .5 BSFC, that would be that he is spraying 1130 hp on the 1st stage alone. Hope you understand what I am saying.

 

[TurboTR]

>Please steer me in the right direction.

Already done, per all the posts above.

TurboTR

 

[91cam447]

TurboTR, we had a post overlap

 

[TurboTR]

Yes I understand. That car must have an additional set of 160 lb injectors on it and about 4 bottles

Sounds messed up to me. If you want to send me the pic feel free, as long as it's a reasonable size .jpg. I'm at home on a dialup acct.

TurboTR

 

[91cam447]

I'll send the picture your way. Is 640x480 too big?? Might have a hard time making out the numbers but you will get the point.

 

[TurboTR]

Anything less than about 100 kb should be fine. turbotking@hotmail.com.

TurboTR

 

[Craig Smith]

Alright guys, you're BOTH right!

TurboTR is right, in SPEED/DENSITY mode. N2O table is additive fuel.

In ALPHA-N mode, the ECU switches to the nitrous fuel table exclusively.

 

[91cam447]

LOL!!!! Thanks Craig. That is a really important factor to know. Would really suck to melt stuff right off the get go. LOL!!!!!!!

 

[TurboTR]

Well there ya go! Always nice to know little details that get left out, like running alpha n rather than speed/density...

TurboTR

 

[Ricky Trussell]

I just installed my nitrous today and need some clarification on the post from Craig.

I have speed/density and wb 02. Will my fuel page be set at 70 -75# all across the rpm range for 150hp?

The demo page shows 6# at 0 then goes up the chart. I think mine should be set at 70-75# across the rpm range but need to be sure.