MFI Induction Chart

[RobFrost]

The bottom of the E MFI stack is 35mm and the intake therefore jumps to 38mm for the throttle body. Surely it'd work better if there wasn't a sudden step out at the junction? Just contemplating boring the stacks out to 38mm.

[Jonny042]

Originally Posted by RobFrost

The bottom of the E MFI stack is 35mm and the intake therefore jumps to 38mm for the throttle body. Surely it'd work better if there wasn't a sudden step out at the junction? Just contemplating boring the stacks out to 38mm.

The step serves a purpose and is there for a reason.

It jumps up to 38mm for the throttle plate itself, but necks down again at the throttle body exit to the smaller diameter.

The throttle plate and the throttle shaft both take up room in the bore and reduce the cross sectional area of the system. That "bulge" in the flow path allows for the air to go around the obstruction without having to speed up and slow down again.

If you want to improve the flow capacity beyond the "S" dimensions it's theoretically better to increase the diameter of all the parts of the system in equal amounts.

Originally Posted by Jonny042

After years of all this kicking around in my head, work has finally begun on the MFI system. I've been accumulating parts, documentation, knowledge, tools, and equipment to make this all happen (and work!) the system will consist of:

- 911"T" throttle bodies enlarged to 40mm throttle plates, tapered to 38mm at the head

- small port SC heads ported to 38mm intake port, machined for MFI injectors

- 911"T" plastic stacks taper bored to 38mm bottom exit

- 911"T" pump converted to RS pump specs and calibrated for the 3.2SS motor

This weekend I started to work on the machining for the throttle bodies. The tricky part is the taper from 40 to 38mm but I ground a tool to make it happen and it's working out:



There is a big difference between the "T" throttles and mine!! They are going to have to flow more than twice the air to support the 250Hp target.....



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