Optimal Fuel Pressure

[Totally T]

What is the optimal fuel pressure for mechanical injection N/A?

Using your calculator on the FIE site we end up in the area of 69 lbs.

[Spud Miller]

More pressure doesn't mean more power...there's a point where more pressure doesn't make much of a difference. As long as you're seeing more than 70 or so PSI at the finish line, you're already enjoying most of the benefit of pressure. You're there.

 When I nozzle a system, I shoot for 120 PSI at the highest RPM that will be achieved, in the best air (smallest main pill) that will ever be run. As the air worsens, it will only be lower from there.

 I get a lot of calls from folks wanting more pressure and honestly unless you're looking for every last HP or only making 40 or 50 PSI at the stripe, it often isn't worth changing nozzles. Especially in a supercharged application.

 More pressure atomizes better of course, but the fuel is already blowing out into a hurricane in the runner.

 More pressure will make main pill changes more responsive, but it will make your main pill smaller. In some cases, that isn't good...small coarsely sized pills means less control and bigger steps between pill sizes.

 Spud

[Pipe Dreams]

My car really came around when my system pressure got around 100psi.  When I was testing for the optimum tune up on the car shortly after I changed to injected alky my car picked up .2 from going to a .029 to a .028 nozzle. My car just seem to like the higher pressure. Keep playing around with spuds tune-up calculator, I've found it to be a great tool. 

[Spud Miller]

 Since we're talking nozzles - especially if you're naturally aspirated, having nozzles matched is hugely important. Much more so than pressure. Even Enderle's "flowed" nozzle jets can be out 7% or more from one to the next. We see this all the time. I've seen the regular nozzle jets out 15% from highest to lowest. TERRIBLE! Your cylinders are  not making equal power and performance can really suffer.

 When we sell a "flowed" set of nozzles, we test each of them here at 100 PSI and make sure they are within 1% or better. The brass and the labor combined is usually $12-$14 each (depends on size, smaller than .026" cost more). They are identified ("A" through "H") and come with a report that shows the flow of each @ 100 PSI. If a person just wants a set that flow what they should within 1% and don't need a report or identification, they're $10 each.

 Kinsler nozzles are generally very good. Hilborn's are great at 30 PSI (that's where they test them) but sometimes at 100 PSI, they are out in the 3-5% range. The type that are soldered together can't really be messed with much for correction. We do make a nozzle body to replace them however that utilizes a standard Enderle nozzle jet that is quick and easy for us to fiddle with on flow.

 With an accurate set of nozzles, customers report improved ET and MPH (a lot in some cases), balanced EGT's and even plug coloring.

 Spud

[Zooman]

I'm going to have to get a couple of sets Spud!

[H.G. Wells]

Spud, I am guessing nozzle size/accuracy is even more critical with nitro than with alky?
Just thinking ahead here and making notes.

[Pipe Dreams]

I'm going to have to get a couple of sets Spud!

me to.

[dreracecar]

Treat the engine like 8 single cylinder motors tied together, nobody says that all nozzles have to be the same.
  With fuel(and port nozzles), if you have 1 cyl running hot, do you but a bigger nozzle in it? NO!, that reduces line pressure and they all go lean, you adjust other cylinders with smaller nozzles which raises line presure and more fuel goes to the hot cylinder with the same nozzle.

 IMO with normaly asperated injection, the only time matched/flowed nozzles are nesassary is when you drop one and screws up the flare end and you need to replace it, at that point any difference in flow rates will throw a curve in the tune-up that was already in balence . Blown Alcohol (thru the hat, no ports), once you get the entire system flowed and the nozzle area figured out for you combo, the nozzles never change