TURBHOE

iTrader: (4)

ok, i think i am confused. or maybe not. if you convert from a returnless style system to a return style with a regulator up front, and that regulator hooks to you manifold for vacuum. when there is vacuum it lowers fuel pressure just like stock 99-03 trucks. correct? but when the same regulator is boosted or has pressure applied rather than vacuum won't it raise the pressure? so there for the older nbs truck have a vacuum/boosted referenced fuel system. correct? and then there are mechanical regulators that have no vacuum to them and have a constant pressure, and FMU's will work like a regular vacuum'd regulator until pressure is applied then raise the pressure at a set ratio ie: 2:1 or higher rather than 1:1 in a normal vacuumed regulator.

am i right or no? i'm thinking of going return style to help my 5.3 idle and cruise on the street better with the 60's that are installed for the turbo. so i'm trying to make sure i got this right. i have found a few regulators that have a vacuum port on them but don't neccarly say "boost referenced"

MIGHTYMOUSE

iTrader: (59)

our cars are not retunless, there is a return line half way under the car and goes back to a regulator in the tank

the regulator in the tank is pressure referenced, its just that normally the inside of the tank is around the same 1 atmosphere all the time

fmu's raise fuel pressure as a multipe of manifold pressure

it can boost referenced as soon as the car is no longer n/a but if the car is sold n/a it is ony vaccum referenced

if you run an aftermarket regulator AND stock one you can raise the press but not lower it as the other regulator in the tank will catch it on the way down

DanWS6

iTrader: (5)

Next time I dyno I'll ask for the uncorrected numbers just for you.

Corrected numbers is how we make up for our terrible track times.

Schantin

iTrader: (6)

I'm actually running a boost-referenced regulator on my "lowly STS" at 5PSI. Even have big ol' 60lb MotoTron injectors and they work fine (58% duty cycle at WOT). What I DIDN'T do was hook the boost reference to vacuum. That creates a lot of work mapping the fuel model on tuning. In the case of super big-a$$ed injecotrs (think MightyMouse was hinting at this), it would be beneficial, but 60lb'ers are not "big-a$$ed injectors". So what I DID was hook the vacuum reference to the INTAKE. It measures boost, but not vacuum. End out running a constant 60PSI fuel pressure at all boost levels, as the 1:1 of the regulator compensates for the rise on boost pressure working against the injectors.

Is it needed.......no. But I like to overbuild the $hit out of everything (especially while I still have the stock shortblock) It would be a useful mod considering that you wish to run 10+ PSI. That's just my $0.02.

BTW, I'm using the Aeromotive 1000 regulator.

gametech

iTrader: (1)

I don't follow what you are saying. Hooking the reference to the intake manifold to sense vacuum and boost keeps a constant pressure delta regardless of KPa. This makes tuning EASIER, not harder. The only way I see vacuum being a problem is if the regulator has enough mechanical delay to not properly change pressure if you have wild vacuum fluctuations with a large cam.

Schantin

iTrader: (6)

If you hook to a vacuum source, it will pull the pressure down under normal idle/part throttle driving when the engine is in vacuum. How much depends on how much vacuum your cam produces at idle. As an example, if you have a cam that produces 18inches of vacuum at idle, your fuel pressure (if set to 58PSI at atmospheric pressure) will be about 43PSI at idle (due to the vacuum pull). At WOT it will read 60-63PSI. If you reference from the intake, either you're in boost (positive pressure) or else the pressure is atmospheric (neither vacuum or boost). I stated the intake pipe, NOT the intake manifold.

Trust me, my car is a rolling example that this is a correct statement

gametech

iTrader: (1)

It SHOULD pull pressure down at idle. This maintains the same delta P under all circumstances. BTW, 18" of vacuum is nowhere near 15psi. I do, however, acknowledge that your real world experience with whatever particular regulator you are using may cause erratic fueling. This does NOT mean that the regulator should ignore vacuum, it just means that your setup has some minor mechanical issue that you have tuned around. The bottom line is that sometimes the ideal tuning theory won't work with the allowed hardware. This doesn't mean the theory is wrong, it just means that the mechanical parts aren't perfect. As long as your motor works, who cares?

Schantin

iTrader: (6)

Word to that

Lonnies Performance

iTrader: (16)

There are 2 methods of thought here & neither are wrong, but both have a distinct advantage.

Boost referencing to the intake mainfold will lower the idle pressure to below the base (vac line off) regulator setting to approx. -.5psi per inch of vacuum. This can help idle quality with large injectors. This setup is standard with the LT1 cars & they should use this method for ease of tuning.

Boost referencing to the intake tubing (going to the throttle body) will not lower the idle pressure as there is no vacuum here. This is a good way of tuning an LS1 car that has already been set up (tuned) with a stock regulator. This way the idle/part throttle tune will still be the same & you only elevate the fuel pressure under boost. If you are having problems with idle problems due to larger injectors, this is not the way to go. This is also a good way to boost reference a carbureted application. If I had to name each properly, I would deem this method as "boost referenced", whereas the other is literally "engine referenced" in a truer sense of the term.