Thread: nitrious
View Single Post
Old 07-18-2013, 07:38 PM
Senior Member
TheRabbit's Avatar
Join Date: Jan 2007
Location: Augusta, Ga.
Posts: 2,295

Originally Posted by Swiley383
Somthing I have wondered is what why do a motor purge if you have purge valves is it to clear the solinods out or plugs I see all the guys around here spray big hits do it
You motor purge to get the air out of the fuel lines. The first motor purge is really weak. Usually by the 2nd purge the air bubble are gone. You line purge to get the pressure down. The nitrous is at 950-1050 depending on your tune. The fuel is at 4 1/2 to 5 1/2 depending on your tune. The lower the nitrous pressure the less pressure drop you have while going down the track. I go to the line as close to 1,000psi as I can, motor purge only what I have to make it have a crisp hit then line purge if I need to. You really shouldn't need to motor purge on your 2nd pass, but most people do just to make sure everything is working. I've also forgotten to turn on the 1/4 turn valve. It pruges like a turd pretty quick.
And you do need to motor purge every stage.
A street car that always has gas in the tank / fuel lines really want have air in the lines or need to motor purge. Almost all race cars / trucks drain the gas out after a race. I say drain out, but all I do is cut the fuel pump off, run the carb out of fuel then stick my drum pump in the fuel cell and get out what I can get out.

Originally Posted by chevynovaman
Not sure if everybody knows that Nitrous Oxide systems changed the jetting chart not to long ago. The new charts have dropped the jetting on the fuel side of the plate. Make sure your using the new chart as I still see old charts on the net yet..
I've never seen an NOS jet guide, but i can tell you Speedtech's guide is WAY FAT and will burn your stuff up quick!! Theirs is only a 4 jet spread. I run a 10 jet spread, but every motor is different so you simply can't tell somebody they should run a 4,6,10 etc spread.

What I mean by jet spread is the difference between the nitrous jet and the fuel jet size. Example is 32 Nitrous jet and a 28 fuel jet. That's 4 jet spread.

Let me also tell you most people will LIE to you on their jet spread and hope you try it!!!!

Originally Posted by wazup
Thanks Bj. I have 31/10.5 15w and going to the 33s.

This is my input on nitrous is every engine is different as for the cams, comp,heads ect. The first thing is to get a good tune on motor and then work with what ever system your going to use following there guide lines.
That's true to a point.

It's really hard to run the car / truck on just a motor pass with such a tight converter and tall gear and get a good read on the plugs.
I changed the jets in my carb to lean it out. I went from 95 to 90's square which is too lean if I were to run on motor alone. Leaning out the carb is a huge debate that not everybody agrees with. Some will tell you to leave the carb alone and tune the nitrous / fuel, but most guys like me that have a dedicated nitrous motor (meaning I don't run without nitrous because of the really tight converter and tall gear) lean the carbs out a good bit.

I totally agree with your post for a car that runs nitrous some of the time and on motor some of the time.

Getting the timing correct and phasing the distributor are important things to do too.
TheRabbit is offline