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NT Mods - Removing the Resonator

'How-to' by Bob Forrest


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Overview


This is the easiest modification you can do...   It takes less than 5 minutes, and it does result in a noticeable 'feeling' of faster response.  I use the term in quotes because it has been debated as to whether or not it makes a difference.  I believe it does.  It is totally harmless to remove the resonator.  Further, since it actually restricts the smooth flow of air to the intake when it's in place, removing it may actually prolong the life of your engine by allowing it to "breathe" more easily.  And any slight difference in the air-fuel mix will be adjusted for by the ECU. 

The intention of the resonator (and why it is called by that name) is to change the resonant frequency in the intake for a quieter sound.  It has also been claimed to change the frequency of the intake 'pulse', which may actually be saying the same thing.  While it's installed, it does exactly that - it make things quieter.  Once you remove it, you'll notice the audible difference from the way it had been, and I think you'll also notice the difference in response.  In the May '98 issue of Popular Mechanics, 'Care Care' column, writer Mike Allen identifies it as a "Helmholtz resonator to reduce intake air resonance at some engine speeds.  It works by bouncing a pulse of air back into the intake path exactly 180 degrees out of phase with a noise pulse reflected by the closing intake valve.";  The article doesn't say what it does to the engine's horsepower.

I didn't dyno it, but my 'butt dyno' tells me the car IS 'peppier' by a scoche after removing the resonator;  my logic tells me the same thing.   Anything that interrupts the smooth movement of air along the intake path MUST slow it down, and slower movement of intake air robs you of power, although by only a small amount.  But the whole idea of modifying a system is to squeeze every last iota of power out of what you've got.  This is just one more 'iota' to squeeze out.

It seems to have more effect on the base (SOHC) models than on the DOHC's, (it's not applicable for turbos - there's no resonator), and yes, it is a noticeable boost in low-end power.  There's also a slightly louder intake sound at WOT, which is totally logical, since that's the reason it's there in the first place--  to lower the pitch of the intake sound to make the car 'Stealthier'. All you need is a Phillips screwdriver, and there's really nothing to screw up, unless you forget to plug something back in...  The concept is simple: below the intake hose, between the engine and the battery, is the resonator, which resembles a kind of squarish 'bottle'.  Your mission, (should you choose to accept it), is to remove the bottle and plug up the hole it leaves, then reattach everything.  Here's how...






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Details


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    1.  Unscrew the intake hose clamp just past the Mass Air Sensor box attached to the air filter, and pull the hose off.

    2.  Lift the hose up and you'll see the resonator bottle.

    3.  Loosen the clamp around the neck of the resonator bottle and pull the bottle out; (there's also a little nipple at the other end of the bottle that plugs into a hole in a plastic bracket on the underside of the hose--  pull that out too).

    4.  Stick a vitamin bottle cap, or anything that makes a snug fit into the hole where the resonator was, and tighten the clamp back up.  Make sure it's a good seal-- you don't want any unfiltered air getting into the throttle body.  And please, be logical - put the cap in 'top-first' so as to smooth out the wall of the intake tube!

    5.  Reattach the intake hose to the MAS box and tighten the clamp.  Note: you don't have to plug where the nipple was attached - it's just a fastening point.  That's it!  You're done!





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Dissenting Opinion: Erik Gross


{{{ unless you dislike hearing that slight "slurp" of air at WOT enough to give up that performance benefit, there are no negatives to removing it.}}}

I don't have the capability to test this specifically in the 3000GT engine, but in a generic system with an accumulator/resonator in the intake air path...

{geek mode = ON}

... the accumulator also lessens the hammer shock effect of the intake valves' closing and tends to dampen the oscillations in overall intake velocity due to the non-linear vacuum created by the motion of the pistons.  This is in addition to providing noise cancellation at certain RPM ranges by generating out-of-phase sound waves properly tuned to offset the existing intake noise.

{geek mode = OFF}

Thus, in lay-terms, having the resonator installed would be easier on your valves (and probably throttle plate), make your engine quieter at certain RPM, and cause your intake airflow to be smoother.  The "smoothing out" function is very similar to a capacitor in an electrical circuit if you are of the EE persuasion of have experience with big car stereos.  I'm not sure whether a "smoother" airflow offers more total airflow (and thus more HP) in this case.

AFAIK, this would depend on whether the hammer shock effect from the valves could cause the pressure inside an adjacent cylinder to rise above ambient pressure.  If so, removing the resonator could generate more power by raising the average intake pressure at a cost of larger fluctuations in that pressure.  Otherwise, removing the resonator would cause the engine to produce *less* power because the oscillations in intake pressure would have larger amplitude and the same maximum value.  Thus you'd have a lower average pressure.  I can go into more detail if people are interested and I have some old discussions on this topic from the Starnet list, but I don't want to clutter the list unnecessarily.  Since we're talking about miniscule amounts of change in HP here, and there's a possibility that the Mitsu engineers put that resonator in for reasons other than noise reduction, my resonator stayed intact.

P.S.:  in the above, I referred to "pressure." This does not mean I am referring to a forced-induction (turbo) engine.  Pressure/vacuum depends on your perspective (and how much you like negative signs) and for this discussion I thought it'd be clearer to refer to everything in terms of pressure, even though sometimes that pressure is negative.

My 2HP...

--- Erik





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Diagram provided by Max Cottrel.
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