Staring down the EFI rabbit hole again, /6 intake design, Which way around for the 964 plenums in a 914? Options

[Mark Henry]

One of the locals fell on some hard times, his plans changed and his 930 was sold, so he offered me a smoking deal on an EFI system.

SDS EM5-F /6 system with twin plug coil packs, Siemens 55lb injectors, cold start valve, crank trigger and /6 trigger mount, extra relay outputs (had meth injection), Beru plug wires X2, manuals, base maps, dizzy hole block off, Bosch one wire (Djet) head temp sender plus all the cabling, fuses, etc that are not included with an SDS system.
I already have a Wabro 300hp FI pump, a Djet fuel pressure regulator, 14point7 wideband O2 meter and an O2 bung in both headers.

This is not a discussion on which Aftermarket EFI system is better, etc but rather on plenum based intake design.
I'm not new. I've been playing with a SDS EM4-F /4 system since 2003-2004 that's now on my '67 bug T4 2600cc conversion, I know that ITB's are better for peak HP, but I'm after overall improvement, usable vacuum signal for MAP, drivability, fuel economy and etc.

FYI I have also asked this on the bird board here for some more info on the build.
This thread shows my /6 conversion a few years back and has all the engine specs here. Plus I've built my own motorcycle ITB's before here.

Please I only want to discuss a single TB plenum based intake for performance EFI.

[rick 918-S]

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.

[ClayPerrine]

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