Something to make you think..Fuel pressure, lets discuss!

[turboglenn]

Okay, So every post about fuel pressure leads to the manufacturers stated pressure. So here's my points of discussion.

A.) Why are these pressures the values that they are, or what is the main reason of the base fuel pressure value?

B.) What is the catalyst in the 2g that required an additional few pounds of base pressure?

C.) How many of you have a decent form of fuel management, and don't run the factory recommended pressures and why?

And here's the kicker of all questions If you run a 1G 6 bolt motor in a 2G car AND HAVE SOME SORT OF MANAGEMENT.. Which fuel pressure do you choose? 1g or 2g and WHY?

Please explain your answer on this one to me, because for a while I've wondered why fuel pressure is so important to be at factory spec even when you have fuel management..personally i don't think it's that important to the overall performance of the engine.

I will post my main thoughts that brought this up later in the thread... Now lets discuss fuel pressure *YEY!!!!!!!!!!*

 

[snowborder714]

If you run a 1g 6 bolt motor in a 2g, you run 43.5psi (which is the 2g pressure). You run this because the air/fuel mixture is based off of the ECU, which in this case is the 2g ECU.

Also, I'm not sure about the difference between 1g and 2g pressure, but there is also a difference in just the 1g pressure. My guess for this might be the difference in injector size between the auto and manual cars. The 1g auto turbos had 390cc and the 1g manual turbos had 450cc

1G auto - 43.5psi
1G manual - 37.5psi
2G - 43.5psi
(all with vacuum lines off, obviously )

 

[turboglenn]

If you run a 1g 6 bolt motor in a 2g, you run 43.5psi (which is the 2g pressure). You run this because the air/fuel mixture is based off of the ECU, which in this case is the 2g ECU.

That's why i stated having fuel management

Also, I'm not sure about the difference between 1g and 2g pressure, but there is also a difference in just the 1g pressure. My guess for this might be the difference in injector size between the auto and manual cars. The 1g auto turbos had 390cc and the 1g manual turbos had 450cc

1G auto - 43.5psi
1G manual - 37.5psi
2G - 43.5psi
(all with vacuum lines off, obviously )

That is interesting because the 390cc auto car has 43.5psi, where the bigger 450 manual car has 37.5.. You would think it would because the pulsewidth is near the same in both ECU's, and they are compensating for injector size. But, we know that's not true...So, why did they have different pressure values being they are so alike in the motor dept. except for injector and turbo sizes? More good stuff It feels like eventually a lot of us are going to learn or figure out something pretty cool before the thread dies. (or maybe not )

 

[pneumo]

43.5psi is 3 bar, 36psi is 2.5 bar, so these pressures aren't totally arbitrary.

I'm not sure why Mitsu would choose 36psi base pressure for the 1G turbo while other cars use 43.5. Maybe it was due to emmissions? Lower fuel pressure reduces deadtime slightly, which improves accuracy at low flow levels. Or maybe it was simply to reduce the flow capacity of the injector to, again, improve accuracy at low flow levels, which can improve emissions.

Base pressure went up from 36 to 43psi in the 2G because a stock 2G has 15HP more than a stock 1G. (210 vs. 195) and more fuel was needed.

 

[turboglenn]

43.5psi is 3 bar, 36psi is 2.5 bar, so these pressures aren't totally arbitrary.

I'm not sure why Mitsu would choose 36psi base pressure for the 1G turbo while other cars use 43.5. Maybe it was due to emmissions? Lower fuel pressure reduces deadtime slightly, which improves accuracy at low flow levels. Or maybe it was simply to reduce the flow capacity of the injector to, again, improve accuracy at low flow levels, which can improve emissions.

***Base pressure went up from 36 to 43psi in the 2G because a stock 2G has 15HP more than a stock 1G. (210 vs. 195) and more fuel was needed.

#1 ( i italicized) Is good info, i didn't even think of or know that.

#2 (bold) Also did not know that about the deadtimes related to pressure

#3 (*** in front) Makes sense to me.

Let's hear more!

EDIT:Based on #2, i could get a better ( more consistant ) idle from running a lower fuel pressure in theory. And better control of light to mid range fuel control, but at the cost of running out of pulsewidth up top.

 

[pneumo]

Based on #2, i could get a better ( more consistant ) idle from running a lower fuel pressure in theory. And better control of light to mid range fuel control, but at the cost of running out of pulsewidth up top.

That's the trick, improving idle and low flow accuracy tends to compromise high HP.
To be honest, lowering pressure won't have much effect on deadtime. If you wanted to make a difference in idle quality, you'd have to lower pressure to the point of hurting the spray pattern which would hurt idle quality too.

C.) How many of you have a decent form of fuel management, and don't run the factory recommended pressures and why?

I burn my own EPROM chips, so I can set injector size, deadtime, and airflow comp wherever I want. I use 45psi base pressure on my 1G simply to get a little more flow out of them.

 

[turboglenn]

*shrugs* I figured more people would have had theorys or facts to chime in with. Must only be interesting to me