I have a Stock 2000 4.2 RegCab 2WD 5 speed. At 2500 RPM I get a boost of extra power that feels like about 10 HP. I have come up with 2 ideas as to what this could be, and figured you guys could help (Jimmy Dean, HorizonHuskies, Busa01, BrianA, Strick4.2 and True4.2).

1. The fuel is being limited by the engine until 2500 RPM. Which could be solved with a chip.

2. After reading through the Haynes manual, chapter 4 page 13 section 15 says:

Intake Manifold Runner Control (IMRC) system (V6 Models) general information.

"The IMRC system controls the air intake charge by opening or closing the butterfly valve on the secondary intake valve directly at the intake manifold. By closing the butterfly to the secondary intake valves under 3000 RPM low end drivebility is improved (Meaning limited power??). Yet above 3000 RPM the butterfly valves open to INCREASE HIGH-END PERFORMANCE (!). The butterfly valves are controlled by the IMRC actuator and cable assembly".

Question #1. Do you experience the same boost in your truck? If so what RPM?

Question #2. Does this boost go away if you install a chip? (for those who have one).

Question #3. If it is the IMRC restricing the airflow, can it be removed/tuned/changed/etc.?

I have learned a lot about my truck from you guys. Thanks for the info. I hope I have discovered a way to get 10HP cheaply for all of us 4.2ers!!

 

umm or maybe you just hit the torque curve at 2500

 

The IMRC blocks the air from going through the short runner at low RPM's. Since the short runner is blocked the incoming air has to go through the long, thin runner. Doing this helps give you more low end torque. At a certain RPM the IMRC opens allowing the air to go through the short, fat runner = good for high RPM horsepower.
But I agree with drizzt, you're probably just feeling the peak torque kick in at around 2500-2700 RPMs
The butterfly valve itself doesn't become a restriction until you're past the 300rwhp mark.
My car starts pulling hard around 2500 RPMs and I have no IMRC's

 

I don't think you'd have much luck trying to "cheat the system".
As mentioned, the switch over from intake valves/runners is done in an attempt to maximize low and high rpm perfomance.
Everything is a compromise, you don't get something for nothing. Dual intake runners are an attempt to mitigate the trade offs.
Intake charge velocity and density, like exhaust velocity, has an impact on performance. What's good at low rpm ain't always good at high rpm.
I'd avoid trying to one-up the Ford engineers. Look elsewhere for your HP.

 

What you are feeling is the squirrel under your hood being fed more acorns,thus,making him run faster on the rubber band!

 

chipmunks under my hood, I whip them past 2500 rpm that's when I get my power.

 

I had some solinoid on the intake manifold seize.I lost bottom end performance .I had tons of midrangepower,but my fuel economy dropped drasticly. ford had told me this solinoid had seized in the open position,turning my check engine light on. telling the computer the throttle was in w.o.t..My mpg dropped almost half.My repair bill was about $600 canadian.

 

Ditto what all the above stated. They are absolutely right (except for the squirrel statement ). You aren't feeling any kind of 'boost' as a SC would give you, but you are feeling the high end of the torque curve at that point. That's why your truck 'all of a sudden' starts going much faster.

 

I just thought i would put my two cents worth in. that solinoid controls some sort of vanes in the intake for low end and open up at w.o.t. i didn't want any body to make a costly mistake.like i said my bottom end performance suffered dramatically.but top end wasn't to shabby,except for fuel economy.

 

Wow, thanks for the info everyone. Hey I'm getting ready to do a 2"/4" drop on my 2000 short bed regular side (2WD). Anyone have any suggestions on which kit to go with?

 

I have the auto tranny and at about 2500 it really starts to come alive. However the peak torque for this engine is at 3400 (252ft.lbs). So I believe you are feeling the onset of the vanes opening at 2500 rpm, and the troque curve rise. I agree your mpg will suffer if you try to defeat the system.

Tim