Preface:

Quote:

Originally Posted by parish8

most of this was said above but it is worth saying again. if you have a return line then the fuel presure is refrenced off of the intake presure. the BASE presure is around 58psi. if you pull the vacume line going to the regulator you should see around 58psi. the regulator seems to add about 1psi of fuel presure per 1psi of boost. when i am over 20psi i see about 80psi of fuel presure.

As the FPR is not boost referenced, the only way that the returnless fuel systems have to compensate for decreased injector flow under boost is to keep the injectors open more. Hence those of us with this setup should see higher duty cycles and max out the injectors sooner if properly tuned.

If 1 psi of boost equates to a loss of 1 psi of FP and my actual FP also drops 5 psi under boost, that is like losing 13 psi of FP at 8 psi of boost! From my calculations that works out to at least +13% duty cycle at the corrected flow rate of 37 lb/hr(Radix injectors).

Now, I don't see anything in the tune where I can correct the IFR for boost or the line pressure drop. Magnuson has the IFR set to 5g/s for all MAPs pre boost but there is no table for boost. So as there is no feedback in Open Loop, I assume that there is no compensation for the decreased IFR other than programming a richer "PE modifier based on RPM" or “Boost VE” table of EFILive's custom OS than what you actually want to achieve if you go MAFless. Does this mean AutoTune is not an option?

 

I ran some crazy numbers in my PE table to try to drive my PE fueling richer. I was never satisfied with my results. Bigger injectors made me happy finally. I didn't have to go or attempt to go mafless.

 

I ended up going with the Magnason Magna-volt setup for my truck.

I was runing out of injector above 5900rpm at a AFR of 12.1 at 11psi boost.

Now with the magna-volt I have more than enough injector and I can run a
AFR of 11.8 with injectors at 98% at 6200rpm at 12psi boost.

The Magna-volt senses BOOST and RPM and increases the voltage and current to the fuel pump when it see's BOOST above 3psi and above 3000RPM,
this thing works like a champ as does all of magnasons products.

 

What's your fuel pressure? Does the voltage booster get it up to at least 70 psi and hold it there at full boost. It looks like that's what would be needed(at 11 ps1 of boost) to fully compensate for the "returnless" issues.

 

I don't know what the fuel pressure is at but I do have an AEM Wide Band
and I know if it leans out.

I'm told that the Magna-volt increases the Voltage to 17vdc and increases the amps to 20amps any time your above 3000rpm and 3psi boost.

When I first installed it I had to Lower my PE Tables because the AFR's where
getting in the lower 11.0's and before the Magna-volt the AFR's where in the
mid to upper 12's from 3000rpm to 5900rpm then the lower 13's above that.

I think there is plenty of fuel pump with the Radix kit its just that the injectors
max out above a 100% if you up the boost above 10psi and try to run an AFR
less than 12.5.

 

I have the older style kenne bell voltage booster. It runs off a "Hobbs" switch that closes the circuit at a preset boost level. Does you Magnavolt work the same? If the Magnavolt is better maybe I will trade up. I was going to put the voltage booster on the inline pump (255lph from Magnuson) that I am installing. Is this what you did?

 

Mine is a 2005 ,and Magnacharger supplies a new in tank High Flow pump with
the Radix kit.
The Magna-volt is all internal electronics, you just supply a boost line to it
and pick up the RPM signal going to the Tachometer, there is also a B+ and
a ground and it is tied in between the fuel pump relay and the fuel pump.
It supplys a regulated 12vdc to the pump untill 3psi and 3000rpm then it
increases it to 17vdc @ 20amps.

 

Doesn't sound like enough difference to warrant an upgrade from old to new. With a 3 psi turn on for the old one they will operate basically the same.

 

Looks like Auto VE tuning will still work but it will just give me higher than actual VE values under boost in compensating for the decreased fuel flow. Won't help with the high injector duty cycles though.

 

Your injector duty cycle is still on the high side. Is your vehicle a 1500 series?

Just looked at my FP gauge markings and realized that my FP drop is worse than I thought. It drops to 51(not 55) psi from 60. So my effective pressure loss is actually 8+9=17 psi giving me an injector flow rate of 35.6 lb/hr(depends what Magnuson means by "42lb at GM pressure"). I called Magnuson today about the Magnavolt but they said that if their replacement pump couldn't handle my fuel needs(we were only talking like 350 RWHP), then the Magnavolt or both together wouldn't help either! Maybe they know something I don't. I've seen crazy IDCs way over 100%. They suggested that maybe larger injectors would help.

Also, take a look at the tiny inlet size on my stock pump. The replacement pump is the same. Now compare that to the inlet on the 2500 pump in the pic from Magnuson's 2500 series install manual. I would guess that the 2500 returnless guys aren't having as many problems unless they are really moving a lot of air.