stand alone with rising rate fpr?

[niner11]

I have been reading but can't get a definite answer as to why I should run a vacuum line on my aftermarket fuel pressure regulator with my turbo setup. I understand a stock setup running more than stock boost can benefit but If I tuned my l280 et with a wideband and datalogs does it matter?

 

The more I read it sounds like you disconnect the vac line and set pressure to 43psi so that under a vacuum psi I drop to something in the neighborhood of 35. I am running MSII with a pallnet fuel rail and 440cc injectors. The injectors are a little on the large side so I can only guess that I may have more control of a low pulsewidth idle having slightly lower fuel psi. Any info would be appreciated. Chuck

[gregkring]

you keep the vacuumn line on to raise fuel pressure 1 to 1 with boost pressure. Think of it this way. 20 pounds of fuel pressure and 20 pounds of boost in the intake would mean no fuel would spray when the injector opened. Therefore you need to raise fuel pressure as the boost raises. The opposite is also true. Zero fuel pressure and vacuumn in the intake would still suck fuel when the injectors opened.

 

On the flip side I think you are confusing rising rate fuel regulators with stocj fuel pressure regulators. Rising rates will raise fuel pressure more than 1 pound per pound of boost to push extra fuel than would normally flow. Some do 1.5 to 1 pound of boost, some do 2, etc.

 

A few searches here should clear up the mystery. Good luck

[niner11]

That makes sense, thanks. I'll do some more searching but am I correct in setting fuel pressure at idle with the vacuum line removed?

 

Also, here is a pic of what I'm using

[ktm]

That makes sense, thanks. I'll do some more searching but am I correct in setting fuel pressure at idle with the vacuum line removed?

 

Yes.

[niner11]

Thanks, I think I understand better now after reading some other threads. What I have pictured is an adjustable fpr that references boost 1:1 not a rrfpr. Makes sense now.

 

It should be pretty easy to readjust my fuel pressure correctly and then do a few datalogs to correct my VE table.

[Tony D]

It all depends on what fuel pressure your injectors are rated at...

Generally they want 'Static' fuel pressure for the flow rating---which is fuel pressure key on, engine not running (or running with the vacuum line reference to the regulator restricted/blocked/removed.)

 

What this accomplishes is effectively decreasing the 'size' of your injectors by some ammount at idle due to the vacuum, allowing a longer pulsewidth at idle which most standalones can handle easier.

 

This resolution issue may not be an issue with modern electronics, but in the old days, decreasing the fuel pressure 10psi at idle could mean the difference between a 170cc/min injector and a 150cc/min injector, effectively. It helps get resolution at idle for emissions for sure. And with an old processor....

 

But all FPR's should be 1:1, meaning they reference manifold pressure and keep the same relative pressure drop across the injector regardless of vacuum, or boost present. This makes calculations on the ECU much easier as it's dealing with a set value for possible injection delivery, and it's basically a linear scalar.

 

This is why most MS setups show VE's very low at idle: you have 'decreased' the size of the injector by manifold referencing the fuel pressure, and at 36psi there idling you are X% in flow delivery below what the internal algorithim shows as delivered by a straight-static referenced 3 -Bar injector with 3 bar on the fuel delivery line. On an N/A engine, you can run straight static fuel pressure, but you run the risk of leaning out slightly at speed (versus dyno runs) if you have any sort of dynamic pressurisation of the inlet manifold from your intake positioning.

 

You will notice on an N/A engine if you simply run static fuel pressure to the injectors, that at idle and cruise portions of the fuel map, you will see a different VE in the bin once it's tuned to run the best than if it's a manifold-referenced FPR.