I need to shorten my fuel line on my nitrous kit, but I don't know how short of a line to get. I run my kit at 950psi. How much shorter does the fuel line need to be?


thanks

 

If you are tring to do away with a lean spike then you can shorten the hose a couple of inch's. We can make or cut down any size line that you will need.

-Chris

 

I am trying to do away with the lean spike, but How much shorter is enough.


The fuel is at 60 lbs and has 16 inches to travel before it reaches the nozzle.

The nitrous is at 950 lbs and has 16 inches to travel through the same size line.


It seems like the fuel line would have to be at least half the length of the nitrous to get rid of the spike.


I was just wondering if anyone had done a calculation to see just how much shorter fuel would have to be so that they both reached the nozzle at the same time.


Thanks

 

We don't have any engineers that want to take a shot at this question??

 

 

I'll take a shot at it, but I'll put a huge disclaimer that this is completely theoretical and has lots of assumptions. I'm not responsible if you do damage to anything based on my ramblings.

I used the Bernoulli equation (which assumes many things, including that there are incompressible liquids) and simplified it to P = 0.5*density*velocity^2 which is applicable for both the nitrous and fuel:
(nitrous pressure) = 0.5*(nitrous density)*(nitrous velocity)^2
and
(fuel pressure) = 0.5*(fuel density)*(fuel velocity)^2

The major assumptions here are that there are no significant differences in elevation between the solenoid and the nozzle and that friction losses in the line are not significant.

I also used: velocity = distance (aka hose length)/time, and the time for each is the same, and so the ratio of the hose lengths would be:

(fuel hose length)/(nitrous hose length) = Square root of ((fuel pressure)/(fuel density)) * ((nitrous density)/(nitrous pressure))

So if fuel pressure is 58 psi (nominal value for LS1), fuel density is 0.76 kg/L (I found a range from 0.72 to 0.80 and it varies with temperature), nitrous pressure is 950 psi (normally 900-1100), and nitrous density is 1.22 kg/L (I assumed it was liquid and it varies with temperature), the result is a ratio of 0.31. So if the nitrous hose was 16", the fuel hose would be 5". That is ridiculously short, but then again the nitrous has a significantly higher pressure so it's not that surprising. Realistically, I think that many people have used nitrous hoses that are about half as long as the fuel hoses and had pretty good luck with it.

 

That ratio sounds like it would be correct given the large pressure difference between the fuel and the nitrous.

I do have another option...............A timer that will delay the nitrous solenoid in 1/10 of a second increments. This way I wouldn't have to do a lot of experiments with line length.

Thanks for the calculation

 

Using the formulas above, the velocity of the nitrous would be about 340 ft/s, so it would take 0.004 seconds to go 16" from the solenoid to the nozzle and the velocity of the fuel would be about 106 ft/s, so it would take about 0.013 seconds to go 16" from the solenoid to the nozzle. The time difference is only about one hundredth of a second.

 

And that's why you always have a lean spike upon activation when you're using lines of equal length for the nitrous and fuel jets.

 

I am not sure how small of an increment I can adjust the timer. I will have to check into that before I purchase it. I am about to hard line my nitrous kit, so, I will run the fuel line about a third of the length of the nitrous line. When I get it all done I will see If I still have the spike and go from there.

I will let everyone know how it turns out.

thanks

 

I am sure running a 3/16th hard line will change the calculations a little bit, but at least It won't cost much to go back and change the line lengths.

 

Just remember that the above calculation does not take into effect the difference in jet sizes. This effects the speed of flow to the engine as well.

.01 seconds will not even likely show up at the o2. How many samples per second are you logging at & how long is the lean spike?

Did you ever try to purge your fuel system by bringing the rpm up to about 3k & hitting the activation switch with the bottle off? Try this with no pressure in the nitrous line. How long does it take to bog the motor.

Do this first, then immediately open the bottle, purge the nitrous & see if it still has the lean spike.

 

I wonder how this equation would work with a progressive controller. I would hate to think of the nitrous and fuel lines being so different in length that it would cause nitrous and fuel lines to be "Out Of Phase with each other causing a rapid rich to lean condition while the progressive controller is activating? any thoughts on that?