O.K. guys,

(Original Problem: Trying to get RC 310's to flow like stock 240's)

I talked with John @ RC earlier this week and he said to not lower the fuel pressure of the 310's below 35 PSI because the spray pattern of the injectors will go to crap. Also to increase the idle speed to keep the motor from dying at idle.

So, I lowered it to the 35 PSI mark and leaned out the VAFC 9% all the way across (based on the previously discussed equations).
Outcome: The car ran like crap, even with adjusting the VAFC to work out the problems. Bogging and hesitating throughout the RPM range. Conclusion, not enough fuel pressure.

Next, I raised the fuel pressure to 43 PSI and leaned out the VAFC 18% all the way across (again based on the previously discussed equations).
Outcome: The car ran so much better than before, but still had some hesitations and bogging in certain areas of the RPM range which could not be worked out by adjusting the VAFC. Conclusion, still not quite enough fuel pressure.

Finally, I raised the fuel pressure to the HELMS recommended 48 PSI and leaned out the VAFC 23% across the board.
Outcome: The car ran much better than it did at 43 PSI, but still had slight bogging and hesitation at a few RPM points. These problems were much more receptive to changes in the VAFC. 22% to 21% in those certain areas corrected the problems and the car runs very strong again. Conclustion, HELMS has 48 PSI in there for a reason.

Also, another interesting observation: with all the calculations I was doing with fuel pressure and injector percentages, I found that 1 PSI of fuel pressure is approximately 1% on the VAFC - give or take a few hundredths. The VAFC only changes injector pulse width, not fuel pressure (just a reminder). So, leaning out the VAFC 1% is effectively reducing the fuel injector flow as much as reducing the fuel pressure 1 PSI would have.

Just posting this to help others out who might need this information.

-Shawn

 

just to keep things in one thread, i locked the original one which was HERE

 

Wow, I'm surprised no one has anything to say.

-Shawn

 

You probably set pressure off vacuum.
Remember that he said pressure shold not go below 35psi, that means that
35psi WITH maximum vacuum. 310s are easy to run with just an AFC.
On my old setup i ran 310s at 80psi off vacuum with an SFC helping at idle
and the car ran normally and still getting reasonably good gas mileage(35+)

 

remember, the "hi" and "low" throttle settings are the key to proper partial throttle driving.........

 

the low-high transition settings in particular

 

The 35 PSI was set with the vacuum line off and pinched. I thought that was how fuel pressure was supposed to be set.

The Hi throttle is at 50% and Lo throttle is at 10%. Does this sound right?

I originally set Hi and Lo throttle fuel settings the same and then tweaked each to get the optimum driveability and power along with smooth transition from Lo to Hi. This took a good 45 min. of dinking with to get just right.

Occasionally the car will stall coming to a stop w/the clutch pushed in. No other problems though.

-Shawn