FAST nitrous settings [Craig]

[Ricky Trussell]

I read you post about fuel table for nitrous but need clarification. I have seed/density so will my nitrous fuel setting be flat across the fuel additive table in lbs.?? I am running 150 hp shot so I will be set at 70-75# across the table??

 

[Old442]

Ricky,
You are correct. Some will recommend that you add one lb/hr (pph) for every anticipated horsepower of nitrous strictly as a check against running lean the first time out. Typically, as Craig has stated, you can look forward to running considerably leaner, or approximately .5 pph fuel per horsepower. However, err on the rich side for safety.
Also, you are correct in your use of the table. For a 150 horse shot, your first run could be set with the fuel at a straight 75 (or slightly richer 80-85) across the table. Log the data and read the plugs, then readjust from there.
Good Luck!!

 

[Craig Smith]

If you add 1 lb/hr of fuel for each anticipated hp, you are probably entering much more dangerous territory than running too lean!

A little rich on nitrous is OK. Extremely rich on nitrous is a great big explosion waiting to happen.

I don't mean to sound argumentative, but don't run that rich. Engine damage is likely - been there, done that. 75 lb/hr for 150 hp of nitrous should be conservatively rich and can be tuned down from there.

And yes, in speed/density mode the nitrous fuel is additive so set it flat across the board. In some very old ECU firmware versions it doesn't work this way though - look on the back of your ECU at the firmware version and post it here if you would like. I'll tell you if it works any differently. It's been quite a while since we've shipped anything like that though.

 

[Old442]

Craig,
I do not disagree with your statements. My personal experience has shown that a .5 pph per horsepower is a pretty good number.
Interestingly enough, a year ago I had similar questions about how to use the nitrous tables, and called several "big name" nationally known engine builder/tuners (this was before I found this board!). Their consistent recommendation for a 100-150 shot was to start with a 1 to 1 ratio of fuel pph to horsepower, and lean out rom there. Also, all three that were willing to talk recommended against running closed loop.
I have since run the car several times with a 100 horse kit, and found no problems running closed loop, and have ended up at the .5 pph/hp number, so I'm not sure where they were coming from. I do remember that they were all very concerned about running lean, and not one voiced any concern about running too rich.
I have been following this forum for some time, and have great respect for your input, so now I feel lucky that I did not have a big "bang" running too rich. I can remember running strong with an indicated a/f of about 10:1, but am now running at about 11.5:1.
Thanks for your feedback.
Vince
PS. Was it bad form to answer a question directed at you? If so, I apologize.

 

[Ricky Trussell]

Thanks guys for taking the time to reply.

Old442 you refer to my next question. Should I run in closed loop with the nitrous and if so is 11.5 a/f ratio a good place to start?

What would be the best way to get the VE table to 11.5?

1] Use the A/F target page in closed loop and leave my map alone.
2] Run my engine off nitrous and change my map.

11.5 is rich off the nitrous but is only a little over 1% richer than my map now in that rpm range.

 

[Craig Smith]

Please don't apologize for replying to any post here. This is a public forum so any and all feedback is appreciated and encouraged.

The reason I said what I did is because running too rich on nitrous can also cause damage. I pulled my 327 apart once and found broken rings on 6 of 8 pistons with no signs of ring butting. After I did some checking around with several people, the damage was most commonly attributed to excess fuel burning between the top and 2nd rings.

Closed loop is OK for small shots of nitrous, maybe, but I would avoid it. An oxygen sensor simply isn't designed to measure the stuff that's coming out of your exhaust on the spray. When the nitrous shots get larger, you actually start shoving more and more raw nitrous right out the pipe. This can create false O2 readings. Your spark plugs always were, and always will be the best source of information on how to tune your engine, especially when using nitrous.