255, no afpr, but I have emanage. Am I ok?

[HighPSI TSi Guy]

I really would like to hear your plan for tuning around regulator overrun. Please include consideration of the part throttle engine dynamics and discuss how the fuel trim time constants in closed loop compound the problem. Maybe a little discussion on how the tuning might interact with coasting injector cut and load variations cause by random external forces like terrain and wind loading would make it interesting.

Or you could just install a fuel pressure regulator that doesn't overrun and ignore these nasty little details.

I guess you could also just run a sloppy fat tune to avoid running lean when the regulator decides to track. Which of these is the "too ignorant to tune around it" case?

Steve

I don't think you understand how fuel delivery works. Tuning for higher pressure is just like tuning for a larger injector. Fuel volume delivered is a product of duty and pressure. Therefore the fuel volume delivered can be adjusted by EITHER pressure OR duty. I'm not sure what you're point is about the coasting injector cut, as the injectors are closed during cut. Bottom line is that volume is volume, change it how you want. If you don't know how to do it in the map, and find it easier to just add a regulator and turn a screw, go for it. But if you know how to tune a car properly it's not a necessary component. Lots of cars run perfectly fine with non-linear fuel curves, a lot of cars don't even have 1:1 regulators, and guess what, they run perfectly fine, because the fuel map corrects for the non-linear pressure. LS1, Ecotecs, etc are all this way from the factory. Non-linear fuel pressure compensated for by the fuel mapping. I guess the engineers at GM are idiots though and need to join DSMtuners so they can learn how to tune a car from from the wiseguys

With a MAP or speed density system it gets even easier, since you're tuning the fuel map by manifold pressure, which is in direct relation to fuel pressure.

 

[steve]

I don't think you understand how fuel delivery works.

That's rich.

Tuning for higher pressure is just like tuning for a larger injector. Fuel volume delivered is a product of duty and pressure.
Therefore the fuel volume delivered can be adjusted by EITHER pressure OR duty.

Correct but they need to be consistant and predictable to tune from.

I'm not sure what you're point is about the coasting injector cut, as the injectors are closed during cut.

When the injectors close the regulator overruns and the fuel pressure spikes. It stays that way for a while after the ECU turns the injectors back on. How do you propose to tune this out using a MAFT or SAFC. Even in the ECU you would need more than a change to a MAP.

Bottom line is that volume is volume, change it how you want. If you don't know how to do it in the map, and find it easier to just add a regulator and turn a screw, go for it. But if you know how to tune a car properly it's not a necessary component. Lots of cars run perfectly fine with non-linear fuel curves, a lot of cars don't even have 1:1 regulators, and guess what, they run perfectly fine, because the fuel map corrects for the non-linear pressure. LS1, Ecotecs, etc are all this way from the factory. Non-linear fuel pressure compensated for by the fuel mapping.

I guess the engineers at GM are idiots though and need to join DSMtuners so they can learn how to tune a car from from the wiseguys

When you get as smart as the engineers in Warren, we can debate the subject. Though, I doubt any of the ones I've met there or the guys at Ford's tech center in Dearborn or the Chrysler center in Auburn Hills would argue that a predictable linear fuel pressure is prefered or that not having one makes tuning difficult. One of the benefits of opening the Detroit office selling Apollo engineering workstations in the early '80s was you got to meet all sorts of interesting people and discuss the problem they were working on.

Until then, the point you missed is fuel pressure overrun is dynamic and not predictable by the existing hardware, software or piggybacks. Changes in engine load cause the regulator to work on not. The magnitude of the pressure change depends on how much the return port is being overrun. Like most systems of its time the DSM ECU software chose to eliminate all the work of reading the current fuel pressure and factoring that into the base injector activation code. The problem isn't easily bounded by RPM, throttle position, or engine load.

While I haven't looked closely at the LS1 or Ecotec, I expect to find some sort of fuel pressure regulation and their ECU software expects some predictable behaviour even if they don't run a constant differential pressure or a rising rate (>1:1).


Real bottom line, fuel pressure overrun is a problem you can't tune out.

You can either ignore the problem, try to tune out the worst of it and live with the lean conditions caused when you expected overrun and it didn't happen, or eliminate the problem with a regulator that doesn't overrun.

Are you done calling me an idiot?

Steve

 

[nanokpsi]

Does the ecu not "tune out" the problem on its own?
The point the fpr will no longer overrun the stock reglator is also pretty constant. When ever the volutme of fuel consumed is equal to the ammount the the stock regulator return is being overrun by, or the manifold pressure is equal to the overrun pressure. A combination of the two starts to make it a non issue IMHO.
I'm cetainly not suggesting that having one is worthless, as idealy you want fuel pressure to be as consistant as possible. I'm mearly suggesting that the $200 to get one set up would certainly be better spent on other things, especially for anyone still stuck using an AFC or a MAF-T as their sole tuning method.


Good stuff in here by the way

 

[Rice Over Wheat]

Why the hell would anyone compare tuning in modified cars to a stocker straight off the factory line? Maybe if that C6 was pushing 600 hp instead of 400 it would require more than linear fuel pressure from GM. Last I checked I've been upgrading everything in my dsm because Mits never intended for the car to exceed 210 bhp. Put the apples and oranges back in their respective crates.