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Tuning Tips for the 5X Racing Adjustable Fuel Pressure Regulator

While we haven't done any personal dyno testing for the regulators, we do all of our testing on track to both prove the reliability of the part and gauge the performance of it while in race conditions. So, we don't have any hard fact numbers on the torque curve, but we can attest to what the adjustment of the fuel pressure does to the air/fuel ratio while under full load on the track. Here is our best advice on tuning with our regulator:

  • A couple of things need to be considered before you start tuning with our regulator. 
  1. The first is having an air/fuel ratio gauge/fuel pressure gauge combo. This is a must! Otherwise, you are tuning in the dark at the track, which is what this regulator is best for. You might be able to pinpoint your best hp and torque on the dyno, but what happens when it is rainy, cold, hot, or you go to a track with hills and need more torque? 
  2. It is beneficial to document what fuel pressures did what while on the dyno, a good roundabout starting point is the stock range of 35-38 psi, but I think you will ultimately end up in the low 30's or high 20's on fuel psi. 
  3. 1.6 Cars: The other is whether or not your air flow meter is already tuned to try to achieve a leaner ratio. For instance, if you have an air flow meter that is already professionally tuned, most likely it is giving you an air/fuel ratio of around 13:1. Also, the trap door in the meter should be loose enough to not restrict air flow, and most likely this would be done already by the tuner of your meter. If your meter is tuned already, keep it in the car, tilt it on it's axis to allow the door to open easily ("d" portion facing down) and use our regulator to dial in your desired ratio. If your meter is stock, you can mess with the spring to loosen up the door and allow better flow, but this will richen the mixture quite a bit, so use the regulator to lean it back out. Adjusting the stock air flow meter is like a black art and I would be careful, always keep a known good one on hand if playing with this as the experimentation can throw it out of wack very easily and it might not be returned so easily. 
  4. 1.8 Cars: You have it easy! Since you have no air flow meter to adjust like a 1.6, the only thing you need to concentrate on is adjusting the fuel pressure to achieve the desired air/fuel ratio. That's it! A good air/fuel ratio for the 1.8 that has worked well for us is 12.8:1. 

The biggest gains we have experienced have been on the tracks that require a richer mixture to yield more low end through the mid range torque. We have found that tracks that require more torque and have 2nd gear turns like an air/fuel ratio of 12.8:1 rather than the preconceived notion of 13.2:1. The extra richness in fuel gives more pull in the lower RPM range, helping you out of corners. On tracks with high speed turns and no 2nd gear digging will like a leaner ratio around 13.2:1 or maybe 13.5:1 for the extra high RPM horsepower. Before the adjustable regulators, we were pretty much stuck with the 13.2:1 ratio our professionally adjusted meter came with, and it left us lacking torque in the low and mid RPM range.

It is hard to say exactly what will work for you and what works for us might not work for you, but one thing is for sure for all cars and that is air/fuel ratio's. Remember, 12.8:1 for low RPM torque and mid range, and 13.2:1 for high RPM horsepower tracks. This is where the dyno is deceiving, as you are trying to achieve the best HP, which is good for HP tracks but not torque tracks. While at the dyno, try to find what air/fuel ratio yields the best torque and you'll be ready to go when you get to the track!

UPDATE! Due to all commercial pump gas containing 10% or less ethanol, we've found that richening the mixture yields more power out of the corners. On our 1.8L SM, we've found that air/fuel ratio readings in the 11's (ie: 11.5 to 1) on the Innovate A/F ratio gauge in the higher RPM range has felt stronger coming out of the corners. We are yet to determine what is "too rich" as we have not been to the dyno, but we definitely felt a noticable loss in power by leaning out the mixture to 12.5 to 1, which is what was the previously the best known "roundabout" number. Once again, please visit the dyno to figure out what's best for your car and applications!