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U2NDyno.com Tuning Tips

Old 27-Apr-2007, 10:49 AM
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U2NDyno.com Tuning Tips

Hey guys,

I've started jotting down just some basic tuning tips that some of you may be interested in. Let me know if there are any specifc questions and I'll do more tuning related write-ups.

Tuning Tip: Correct Fuel Injector Sizing

Tuning Tip: Affects of Increasing Fuel Pressure
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Old 27-Apr-2007, 03:28 PM
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Good stuff HAPPY.

About fuel pressure....simply raising the fuel pressure in an attempt to deliver more fuel, is a very crude way of doing so. When you increase the fuel pressure you are increasing the amount of fuel being forced into the engine (like you said in your write up HAPPY) but, it is doing so ALL OF THE TIME, not just at WOT. So an increase in fuel pressure adds more fuel at idle, partial throttle/cruise and at WOT....so like i said, its a crude way of delivering more fuel. This works the same way when decreasing fuel pressure, it will deliver less fuel all of the time.

As you increase the fuel pressure, you are decreasing the efficiency of the STOCK fuel pump (aftermarket pumps are a different story) and increasing the wear and tear on the injectors and fuel pump and increasing the chances of the pump failing. We're talking about a good increase in pressure here, not just like a 5-10psi increase.

Also, if you get your car tuned, the tuner will set the fuel pressure to whatever PSI and tune from there. So if you go increase/decrease the fuel pressure you are going to change the tune. So if you've had your car tuned, DO NOT change the fuel pressure without having the capabilities to fix the tune.

From my experiences, installing a higher volume fuel pump (such as a walbro 255lph) usually results in an increase in fuel pressure. When i installed my 255lph pump i noticed a 4-6psi increase in fuel pressure (without changing anything else). Now, 4-6 psi isn't enough to dramatically change how the car runs, but i did notice the AFR (air/fuel ratio) at idle went from about 15:1 to like 14.5:1....not a huge change, but definately a change. So all i did, was get an adjustable fuel pressure regulator (the B&M command flow) and turned it back down to the stock settings....problem solved.
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Old 27-Apr-2007, 09:59 PM
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Yeah, I am in no way advocating doing it at random. In fact, that was the conversation I had with my customer. I was explaining to him that he had plenty of injector and with the PowerFC (what I happened to be tuning) I had complete control over fuel...so there was zero need for his expensive FPR.
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