Check this out, info I got from the Engines topic, from a link to Ford factory training information. It's about the 4.2's split-port induction (SPI) system:

4.2L OHV 12V V-6 (F-150 and E-Series)

This member of the F-150 and E-Series lineup combines quiet operation with responsive performance and load-handling power. Standard on F-150 and E-Series Van and Wagon models.

Major features and benefits:

The split-port induction (SPI) system uses an intake manifold with two runners per cylinder. These runners carry the air charge to the intake side of the combustion chamber. At lower engine speeds, the air charge is directed through a narrow pathway that squeezes the air through at a higher velocity, quickening engine response, optimizing fuel efficiency and reducing emissions.

As engine speed increases above 3000 rpm, the second, wider air path is opened. The increased volume of air allowed by this second path works to further enhance engine power and operating efficiency.
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I'm thinking: I seldom go over 3,000 rpm, though I cruise long distances at 2,500 rpm in 5th. That means I almost never get to feel that second air path. Maybe I'll go over 3,000 rpm more often and check this out.


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Black 2000 SC short-box XLT. 4.2 V-6, 5-speed, 3.55 limited-slip. CD, remote entry, factory side steps, FORD box liner, rear fender inner splash shields (TSB 00-09-05).

My third F-series ordered new. The other two: '73 F-100 Custom, 240 cube 6, 3 on the tree, tan, "West Coast" mirrors, step bumper, knitted vinyl seat, AM radio; and '98 F-150 SC short-box XL, XLS package, Pacific Green, 4.2 5-speed, 3.55 LS, FM-cassette.

GREAT trucks!

 

they left out something!

"along with increased power above 3000 rpms you'll also notice your gas guage drop right before your eyes!"

lol

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97 F150 XLT: Two-Tone Green and Tan,V6 4.2L auto 4X4, 3.55 gears
MODS:Airaid FIPK, Superchip, Ravin Z55 exhaust SI/SO
GOODIES:12 disk cd changer, jvc 4ch 560watt poweramp, Bazooka tube, Boston Acoustic 5x9's, Tinted Back..

 

I'm looking at my ('98) shop manual and it says, "The 4.2L engine has:"..."a multiport, sequential fuel injection (SFI) system."..."a variable length induction system (intake manifold runner control)." The drawings that show upper and lower intake manifold removal definitely show two ports/passages heading into each cylinder. I don't see how one or both are selected...maybe in the throttle body? I don't think so. Maybe a computer-controlled valve that opens above 3000 RPM? Anybody know?

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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

 

on the lower intake there is a set of butterfly flappers, they act as duct work, by directing the flow , opening like throttle bodys,or rather i think by the pcm, which controls how the engine runs

 

i wonder if we could have both runners open at all times... more power down low???

maybe

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TRUCK
White 00' XLT 4.2 Auto Sport
Regular cab Styleside
3.55 non-limited slip
Superchip
Airaid FIPK
custom ported STOCK throttle body

PC
Thunderbird 1.1ghz @ 1.33ghz
Abit KT7A-Raid
384mb Kingmax PC-150 ram
60gig IBM 75gxp RAID array
Geforce2 GTS 64mb

 

It sounds great in theory, but I think it might bog the engine down too much

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1997 XLT Reg. Cab, 4.2L V6, 5spd, Superchipped, K&N Air Filter, Lund Deflector, Dash Mat, Clear Corner Lenses, MagnaFlow Muffler, Hellwig Rear Sway Bar, Edelbrock Shocks, Duraliner, Extang Saber Tonneau, Painted Tailgate Handle, Bell-Tech 2" Rear Drop, Amer. Rac. Atlas Wheels Clad in 275/60/17 Eagle GTII. Likes straightaways, loves twisties.

 

Perhaps, it would be possible to get the second, more open pathway open all the time?
Just an idea, but if it is computer controlled, maybe a chip or something could be developed just for this...

 

Ford knows what they are doing. The runners are controlled the way they are for a good reason. Longer narrower runners enhance torque but not horsepower. Once the engine is at higher rpm where torque is not so much the issue, the shorter and wider runners open to enhance breathing and increase horsepower. Having both runners open all the time would kill your bottom end torque.

 

Hey patrickj what size tires you running. Those aren't stock are they. Anyways like them. Would like to get some thanks

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2001 F-150 5.4L trition,
Regular cab with 8' bed
XLT with Black Clearcoat
4x4 3.55 limited slip
factory cab steps
class III tow package
Factory ordered: 12/5
recieved: 2/22

Current Mods: Ford Plastic bedliner, Bug Deflector II