North American Turbocoupe Organization

Full Version: Fuel pressure adjustment spec
You're currently viewing a stripped down version of our content. View the full version with proper formatting.
What is idea fuel pressure at idle with vacuum line on. Stock motor, turbo , etc... put a kirban on and I set it at 39. Just wanted an opinion on it . Thanks in advance
39 is good on a stock motor.
Thanks for posting this, as I am about to place a Kirban on my '88TC with big turbo and aftermarket fuel rail. It will come in handy when I get the car up and running.
With the vac line ON the FPR, 39 is too high on a stock or nearly stock engine, and may be too high even on a somewhat modified engine. Stock pressure is 39 psi with the vac line OFF the FPR. Assuming you have around 20 in Hg vacuum at idle, which corresponds to roughly a 10 psi drop over atmospheric pressure, the fuel pressure should be around 29 to 30 psi. Removing the vac line, the pressure will pop back up to 39-40 psi. the most important thing is for the pressure to increase 1:1 with boost. At 15 psi, pressure should be 54 psi if the base pressure is 39 psi with vac line off.

Unless you are shooting for 450+ Hp, an aftermarket fuel rail is a waste of money. The stock rail can support 500 Hp.
A friend is making me the rail, so who am I to say NO!
I am also of the mindset that a larger inside diameter fuel rail will help at elevated fuel requirements/higher rpm as it will act as both a fluid damping device AND a reservoir so I don't run the risk of fuel starvation.
Thanks for the reply
Larger diameter rail will not help with damping at all, as gasoline is not compressible.
I guess damping was a poor choice of wording, and I am aware that liquid in not compressible (well, it is but at 3000psi it only compresses .001% of its volume). I was referring to the effect that each injector firing has on the volume of the fluid. Even under pressure, when an injector fires, there is a momentary release/drop of pressure, and when it closes, a momentary spike in pressure. Magnify that by the firing of all 4 injectors and you have a 'harmonic' of sorts rippling through the rail. With a higher volume, this effect is lessened (not that it really matters with our small of a delivery amount). I am just using the rail increased volume to prevent starvation at elevated delivery levels and at higher rpm of the engine.

(Fluid and Thermal dynamics are a portion, albeit a very small portion, of my job fields required base knowledge)