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Old 02-21-2021, 03:50 PM
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eschaider eschaider is offline
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Location: Gilroy, CA
Cobra Make, Engine: SPF 2291, Whipple Blown & Injected 4V ModMotor
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Quote:
Originally Posted by Lightingrod View Post
The LS3 is FI Ed and I only dropped it 3 psi, 60 to 57! All looks good with HP Tuners Scanner! It will be tuned before any trips to the 1/4 mile!

Some good points on carb tuning Ed. Tuned a few myself! Love me some Weber's, used dual 2 and 3 choke Weber's on air cooled VW's and Porsche's. With air cooled engines you BEST have the F/A ratio RIGHT!

There are few induction setups with the raw sex appeal of an eight stack Weber setup. It sort of sets the high watermark for cool, sexy and any number of other check marks for the really cool gee-whiz stuff.

My commentary assumed carburetors and not EFI. None-the-less my fuel pressure admonition is still valid but to a much lesser extent. EFI based fuel system pressure is used in the calculation of the mass of fuel that is injected into an engine when the injector is held open for a specific period of time. The ECU can’t control the incoming air mass but it can control the incoming fuel mass by adjusting injector pulse widths. Because the fuel flow through the injector is linked at the hip with fuel mass, the ECU manipulates injector pulse width (the injector on time if you will) to hit the commanded AFR the tuner has programmed into the system based on a number of metrics, one of which is base fuel system pressure.

Once we introduce closed loop operation where the ECU looks to the oxygen sensor for rich / lean guidance, the engine fueling event becomes a private party between the ECU and the O2 sensor. At the private party, the accuracy of the fueling event is determined by the accuracy of the calibration data for things like, base fuel pressure, injector flow rate at 3 BAR differential pressure, fuel specific gravity and a host of other wonky considerations. Not withstanding these other metrics the EFI system will continuously adjust the mixture predicated upon the guidance it receives from the oxygen sensor.

Because things like engine load, which is used throughout the fueling model for calculating the appropriate injector pulse width and therefore fueling shot, can be affected by things like base fuel system pressure I would suggest embracing the GM standard for your engine (60psi) and controlling the fueling through the various fueling tables in the ECU, whether they are Ve based or AFR based.

Just the injector flow characteristics alone can be quite entertaining. In the following link you will find a pdf about an injector attribute most people may hear about but never get to really understand. It impacts low speed and part throttle fueling at the smaller injector pulse widths (read idle and off idle) where you end up frequently driving the car. Quite interesting, possibly helpful for you going forward. Here is the link => Injector High / Low Slope Information

Greg Banish is sort of a modern day Paladin (if you ever saw the old '50/60's series) whose Have Gun will Travel moniker was used to offer help to those who need it but could not get it. Banish's unpublished moniker would probably read similarly but be in reference to EFI calibration. He is a contract calibrator for Ford, GM and Chysler.

Not withstanding his wonky work and skills, he speaks in plain English so mere mortals like us can understand it. He also offers a tuning school for interested aftermarket enthusiasts to whisk away the fog of how to tune with modern EFi systems. At the very least his publications and the few free papers he has published are quite good. I think you'll like them.



Ed
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Last edited by eschaider; 02-21-2021 at 11:00 PM.. Reason: Spelling& Grammar
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