I recently read on the F150 message boards that the 4.2L V6 in the 98 F150 uses two sets of intake manifold runners that are separated by a butterfly valve which opens at 3000 rpm to allow greater air flow. Has anyone experimented with ways to control the point at which the butterfly opens so that it could be tuned to any engine modifications that have been made?

 

Most places like Supersixmotorsports that deal with modifying the intake manifold discard the IMRC plates in the lower manifold to greatly improve airflow. They do this on stock and modified engines. Just porting and throwing out the IMRC plates will net gains of close to 10hp to the wheels, not peak but through the entire powerband.

 

What does IMRC stand for?

I don't think I'd want to remove the valve/plate thing, unless I was only concered about max power. If it's computer/electrically controlled, it might be nice to add a three-position switch so you'd have complete control over it. One position would be stock operation, another would be always open for max power all the time and the third position for always closed for max MPG (if you "accidentaly" rev above 3,000 RPM for a short while, it wouldn't open).

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Danny
'98 F-150 Std., RC, SB, 4x2, 4.2L, 5-sp, 3.08, AC, speed control, rear slider.
Mods: Mobil 1 engine oil, Red Line D4-ATF trans fluid, Edelbrock IAS shocks, 50 Series Flowmaster, K&N with airbox mod, Perma-Cool electric radiator fan, Superchip, ASP underdrive pulley

 

Thanks for the replies. What I was thinking was that the rpm point and rate that the butterflies open at could perhaps be controlled or modified like you would do with the secondaries on a four barrel vacuum secondary carburetor (remember those?). Do the butterflies open fully and instantly at 3000 rpm or are they controlled by the vacuum level in the intake? If anyone knows how they are controlled I would like to hear from them. I agree that running with them open all the time would make a fairly stock motor pretty sluggish at low rpm's

 

IMRC-- Intake Manifold Runner Control THe runners are controlled by an on-off vaccuum soleniod. they are open or closed...nothing in between. The benefit if this system is at low rpm's you want torque. LONG intake runners make torque at low rpm's, but loose efficiency at high rpm's. At higher rpm's short intake runners make hp, but at low ones torque sucks. therefore the change to the SPI setup. Basically it provides 2 intakes in one, with the butterflies making it possible for short and long runners. Simply removing them will kill the usage of the proper runner. They don't really work like secondaries in a carb and I am not sure there is going to be gained anything by modifying the runners' controll, but I could be wrong. In modification you must remember that the valves are monitored by the PCM for position, so any mod made must include some way of fooling the PCM into thinking that it still has control of the valves, or you will get a MIL.

[This message has been edited by Nomopar4me (edited 04-21-2001).]