NOS & Fuel Pressure

[Kibster]

Kinda confused...

With an NOS kit that supplies fuel via the fuel rail/schrader (sp?) valve - how do you
maintain the fuel/NOS ratio?

As the fuel pressure in the rail varies with the boost (the1# fuel per 1# boost rule) -
so at 15# boost, you'd have an additional 15# fuel pressure in the rail - which would
also be supplying the fuel solenoid for the NOS system. Assuming that you never want
to be lean, so you'd be rich to begin with (no boost), wouldn't the additional fuel
pressure push the mixture even richer?

It seems it would be hard to "tune" the NOS system with the fuel pressure fluctuating
with the boost.

Am I missing something here or is the extra fuel pressure having a negligible impact on
the overall mixture?

 

[wilkinshc]

Kibster,


You are right, it runs richer the higher the fuel pressure goes (lossing hp). You might want to consider adding a fuel reg. to hold a constant fuel pressure say at 38lbs so it doesn't change. Nos system usually comes rich new also. I think they jet it for the stock boost level of 12-14 so if you are running 18-19 it is even worst yet. Another more expensive idea is to run a separate fuel cell, fuel pump, and fuel reg. That way you can run race gas in the fuel cell so when you use the nitrous you have a little better fuel rating.

Chuck

 

[ITSAV6]

psi

The fuel psi is also going up in the intake also. Thats the purpose of the rising rate reg. As the psi in intake rises,the fuel psi has to rise a proportional amount to supply the same amount of fuel from the injectors,same for the NOS. If the fuel psi doesnt rise w boost it will run lean out

 

[wilkinshc]

>As the psi in intake rises,the fuel psi has to rise a proportional >amount to supply the same amount of fuel from the >injectors,same for the NOS. If the fuel psi doesnt rise w boost it >will run lean out


That is true for the boost (air flow) but the Nitrous is constant (one size jet or jets) so it will richen up with the fuel pressure. So putting a fuel reg in between the fuel rail and the NOS fuel solenoid will allow the fuel pressure to stay at a constant pressure for the nitrous setup.


Chuck

 

[ITSAV6]

?

I see what your saying,but if you run a constant psi to nos solenoid wont the mixture change w/boost levels. If constant 40 psi minus 15 psi manifold =25psi fuel psi?
I under stand about the NOS not being regulated will change the mixture but that also happens as bottle psi goes up and down. Also w/bottle psi @ 900 and manifold @ 20 would be a small% difference(due to hi psi of nos)making it be like 880psi.
Make sense? Just my understanding. Anyone else wanna chime in? We could use a little input!

 

[wilkinshc]

I understand what your trying to point out (get less fuel because of the intake pressure). My experience has been that as long as the fuel pressure is set higher then the boost level it stays constant but if the fuel pressure drops lower then the boost psi then you have a problem. For example take the alky setups the pump has a set psi not a increasing psi with the boost level. They would run into problems with the higher the boost levels also. Another would be the injectors, you are increasing the fuel pressure (1 to 1) the same as the boost to increase fuel delivery not just maintain it. So if you were correct it would only maintain the injector rate instead of increasing it. I am not big in physics but that has been my experiences.

Make sense?

Chuck

 

[ITSAV6]

fuel constant

I read a post a few months ago abought "fuel constant". I always thought that the psi rose w/boost to add fuel til I read that thread. Thats why when adding a blower to a Mustang you get a high rising rate pressure regulator to spike the psi 6:1 or so. I searched but didn't find the thread,it was very informative for me. Helped me understand my fuel system a little better.
I know that the NOS kit for the TR is set up for 40psi,since I have one and had to call them for jet #s and fuel psi reccomendations.
Wonder if you could regulate the NOS psi some way?

 

[wilkinshc]

Itsav6,

Be careful on the jet sizes they tell you, they usually just quote it with what they send the kits out with. If you check the charts for hp vs nozzles (1 or 6 which every kit you have) vs fuel pressure it is 1-2 sizes smaller on the fuel side then what they send it out with.

Botlfed had the factory jets in and we adjust it down to what the charts show and he picked up 2 tenths at the track. No problem lean out at all.

Back in 87 with my first kits mine was so rich for NOS it would backfire like it was leaning out. Everyone said fuel delivery was not up to power, ended up with ATR double pumper, more fuel in chip, more fuel psi on reg and still popped. Talked to a local guy (guru with nitrous) told me lean it out and BAM ran like a champ. Since then I have went by charts and no problem except when I got greed and tried 175 hp jets and blew a headgasket. . my fault.


Chuck

 

[wilkinshc]

Oh yea with 175hp jet the headgaskets didn't go till the end of the quarter and I ended up with a 11.3 et on a slightly mod 87 gn with 5600 miles. (Thanks for warranty work) and it was both headgaskets.

 

[ITSAV6]

jets

Guy I got my kit from had same prob! Backfired and took out air flow meter more than once! They replaced the nozzle w/Top Gun nozzle and worked fine. Car was stk w/125 and went 7.20 1/8mile,150 it went 6.9** but it kept breaking axles.
I broke the nozzle and bought a new one from summit and got a chart for the jets,didn't tell them what it was for,just what fuel psi and what hp I wanted. Never sprayed at the track. But it's been on 3 mustangs,my old Fiero,and a 95 V6 camaro!

 

[Kibster]

Thanks for the comments and dialog. Still not sure if I'll put NOS on the car or go with an
Alcohol kit instead. I'm interested in a "street fast" combination vs. "strip fast".

Thanks again...Kibster