QUOTE(rick 918-S @ Feb 18 2021, 10:33 AM)
Probably don't have to tell an experienced engine guy like you about this but for others that may not be aware, cam shaft lift and duration are key with EFI. At least with CIS as too much pulse in the intake makes for wacky reactions to drivability. Maybe you can expand on how it effects more modern EFI stuff.
There are 3 types of fuel injection.
1. Mass Airflow. This is CIS, L-Jet and it's descendant, DME. It uses an air flow meter or mass air meter to measure the incoming air volume and meter fuel to match. The Vane air meter on L-Jet and CIS is terrible for high performance camshafts. The reversion of the cam overlap makes the air meter flap oscillate back and forth, affecting mixture and eventually breaking the vane air meter. Also, vane air meters are a restriction in the intake tract that reduces horsepower. A Mass airflow meter is better because it doesn't have a flap, but it still is affected by reversion. But careful software programming can tune out the effects of reversion.
2. Speed Density. This is D-Jet and a lot of modern injection systems like GM fuel systems. It measures manifold vacuum to determine the air flow requirements of the engine. It is also affected by reversion, as the cam overlap lowers available manifold vacuum at idle to the point where the ECU is unable to control the mixture effectively.
3. Alpha-N. This is the Bosch MFI system used on early 70s 911s and cars like the BMW 2002Tii and the Porsche 917 that ran at LeMans. It doesn't measure airflow at all, so reversion cannot affect it. It just looks at the position of the throttle and the RPM and uses that to determine the required fuel amount to inject. It will work with any camshaft. But it is horribly inefficient, and it gets lousy fuel mileage. But it has extremely good throttle response and performance. And it has that incredible scream when it is up on the cams and producing horsepower. :shiver:
Modern aftermarket EFI setups like Megasquirt and it's derivatives, can be setup in a hybrid mode, where it will use Alpha-N at low speeds due to reversion, and at higher speeds it will switch to Speed Density or Mass airflow. This allows the engine builder to us radical cams, and still get much better fuel efficiency and performance. The modern EFI can also make a radically cammed engine Idle like a mildly cammed one.
Frankly, the computer chip was the best thing to ever happen to gasoline engines. You can get more HP out of a 2.0L engine that was ever thought possible in the 1960s from a 7.0L monster Chrysler Hemi Elephant motor. As I see it, learning and using modern EFI is the only way to go for performance, drivability and reliability.
My future plans are to megasquirt the 4.0 motor, using the current harness and parts. I will change out the throttle body for a larger one, and to support an integrated idle air motor and throttle position sensor. I will also add wheel speed sensors to the rear wheels so I can use the traction control module. I have considered the idea of ITBs, but I think just a bigger throttle body will be better for street use.
Clay
Clay