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Fuel pressure

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So just read Andres articles on speedhunters in regards to pre dyno checks such as base ignition timing and fuel pressure etc.

So one thing I didn’t know about, prior to reading, was the fuel pressure differential. I.E if you have 45 psi of fuel and up the boost to 45psi you will essentially have not one drop of fuel come out of the injectors. Now I assume the 5.3 lm7 I’ll be building will be a return system at 4 bar. If I run 1 bar of boost will I have to increase my fuel pressure to 5 bar to maintain the same 4 bar of fuel pressure?

Or does it work differently in a return style system?

Thanks in advance,


They key is to have your fuel pressure regulator referenced to the manifold pressure (you'll see a little 1/8NPT vacuum port on proper regulators to allow this). As long as you do that, the differential pressure will remain constant.

AH!!! Makes sense, yes i was thinking of going with the aeromotive FPR. Thank you for the Reply! By the way, why cant i see this course in the course purchasing link?

Hi Damen, you've nailed it with the differential pressure issue. You can still run a constant pressure returnless system with boost but you just need to make sure your injectors are big enough to supply the required fuel at the actual differential pressure you're running. On a more serious build it would be normal to add a return line and use a manifold pressure referenced regulator.

This course is now called our 'Practical Standalone Tuning' course. I'm not sure if that's the issue but it should be visible in the courses page.

Makes sense, so then the "boost" referenced FPR as they list them here for aeromotive, would then take care of that pressure differential with out having to increase the actual fuel system pressure, am i correct on this thinking?

Also, one more question Andre, if you don't mind, where or how can I learn to scale all sensors and know how to do "start from scratch" type of tunes? Does the practical standalone tuning course provide this information? I'm playing with the new Holley Terminator X software and just going through everything but now sure how I'm supposed to scale the sensors and or where to find the scaling information at.

I apologize, I do have even one more question, last one I promise. So the new Holley terminator X standalone ecu for LS motors, only gives you the ability to tune in AFR not lambda (-1 for holley IMO). Can I use the innovative windshield mounted wideband to tune in lambda then? Or would I need to learn how to tune with AFR (which i'm not a fan of). It's just such a great deal to have a 3.5" lcd screen, standalone ecu, AND engine harness all for $1000 to get this project up and going. Thanks


Hi Damen - Yes, a 'boost referenced' FPR simply maintains a fixed differential fuel pressure irrespective of boost or vacuum.

I haven't used the Holley system, however I'd be very surprised if they didn't have an option to select from a list of common sensors for most of the inputs. Irrespective of this though, our Practical Standalone Tuning course does cover this. We show you how to start from a freshly installed ECU with no base map and calibrate everything yourself from start to finish.

If the Holley won't allow you to convert the AFR target tables to units of lambda then you could use a separate wideband displaying lambda, however to be honest I'd just work in AFR units for this application. It's not that big of a deal and it's probably more beneficial to have the AFR values on your laptop screen anyway.

Yes, this comes with the Bosch 4.9. And they don't have the lambda option to change the readout too. I'm just rather confused as to know how much fuel to add or subtract when needed. Where as from being taught by your course and never had prior tuning experience. I really can only figure out lambda qute easily now.

So just a little nervous about it. Also ill be running e85, im not sure the bosch 4.9 can read down to 7.8 (.80).

The LSU 4.9 lambda sensor will have no issue reading the lambda values you'll see with E85. Remember that the sensor reads natively in lambda values and then converts to AFR values based on the stoich setting. You can still use the same correction technique taught in the EFI Fundamentals course. Take your measured AFR and divide it by your target AFR. This will give you a correction factor to multiply your fuel table value by.