RallyDogRacing

I'm not known for driving with a light foot and while I don't go warp velocities at cruise, I do like getting to cruise speed as quickly as possible. Last night something new happened. 45deg, clear and normal humidity; I was making the turn from Addison Str onto the I-90/94 W/N onramp here in Chicago. All things normal with a heel-toe downshift into first and then romping on it at the apex. Little tail out per normal to give the tail-gaiting hoopty behind me something fun to watch (silly I know). Engine screams and I go shooting down the onramp. About halfwaydown 1st is wound out to redline so I grab 2nd to keep the grin factor alive. As the tach winds past 5k things suddenly got a LOT louder.

*oh crap* I thought to myself and begin looking in the rear-view mirror expecting to see the G-pipe and tailpipe bouncing down the road. I litterally thought I blew the back-half of the exhaust off.

But I didn't see anything...

So I put my foot back in it in 3rd gear and run past 5k again. Once again I'm rewarded with a new and voracious howl 2x louder than I've ever heard driving this car before. Again I look expecting to see something flying out the back of the car, but saw nothing.

Concerned I snick the shifter into 5th and go to brisk-cruise throttle settings on the way up I-94. THEN it hits me!

My resonance-flap is now working!
"All Hail the Italian Tune-Up!"

I always presumed it was working but I've net yet identified the various clicks and pops while the engine is powered but not turning. I tested it a few more times in 3rd-gear pulls and definitely 'round about 5500rpm the engine note changes from a peaved-off rottweiler growl, to a pack a rabid and boisterous pit-bulls that somehow form a mechanical symphony.

It didn't feel much different power wise, but things were already moving quite briskly at that point anyway. I enjoyed the raucious noise on the way home, exiting the highway only to get back on my favorite on-ramps just to hear the noise, and prevent my from trying to hit mega-rpms in higher gears on an open road...

This morning I found the resonance flap opening sound works much like a really loud exhaust on a Harley. At first no one knows you're there, but once it's on the boil they can't help but see you; and stop merging on top of you.

But I did check to make sure the G-pipe was still there when I got home

Jeff Curtis

"This morning I found the resonance flap opening sound works much like a really loud exhaust on a Harley. At first no one knows you're there, but once it's on the boil they can't help but see you; and stop merging on top of you."

I HEAR YA!! ...I know that all too well.

Good deal on the resonance flap, I check mine daily!

I have V&H pipes on the Deuce, sounds OK at idle, but when you hit it - ...really lets them know you're there.

GG Allin

I love that sound. I love those on ramps too. Addison, Lawrence... Especially when the light's green. I usually hit 'em from the middle lane.

Marc Shaw

An on-ramp is a terrible thing to waste.

Marc

greddy0

How do u know if the resonator flap is working or not. Does it open up at a certain speed? Does the exhaust pressure open it? What does it do? Can you see the "flap" open and close? Thank

C4Russ

<b>resonance-flap</b>

Where is this thing located? My car doesn't make any more noise above 5000 rpms, it just scoots along. Is this in the exhaust or intake?

RallyDogRacing

Can't see it unless you're looking through the firewall from the interior I believe and have xray specs. Here's what I gleaned from Adrian's book last night when I decided to see if I was imagining things. The resonanace flap is a vaccuum operated solenoid that is control by the DME. The flap is sent the "open up" signal when over 5500rpm. It is sent the "close-down" signal when those rpms drop below 5400. I believe the open doesn't occur unless also at wide open throttle, or the WOT switch is activated - but I could be WAY wrong there. When open the volume and runner length of the intake plenum changes to create ideal resonances in the pulse of the airflow to better attomize fuel. So the theory goes, think of it like propeller-head version velocity-stacks.

I've been told one of the clicks that you can hear when you insert the key and turn to poz-2 (not all the way to engage the starter) is the resonnance flap flipping open and closed as part of the system check. Since it's vaccuum I presume that any air-leaks on the vaccuum side would prevent this from happening. I think after I put all my air-filter stuff back on I solved whatever leak was there before (disconnected reservoir on the back of the housing methinks). Becuase that was the last change and now it works! I never heard the sound before, and didn't listen for it this AM.

I never knew it wasn't working in the first 6mos of my 964 ownership.
But with a cut-away airbox, and the G-pipe... there's no way to mis it.
And yes, the air-box mod and the G-pipe mod were on the car for 3 weeks before I messed around with the suspension and subsequently fixed wherever the vaccuum leak was. (theory).

C4Russ

I'll have to go find an on-ramp to check this out. I guess there are worse ways of trouble-shooting.

pete000

Are you talking about Varioram?

I was not aware of this technology in the 964?

lancaster

Do women have these resonance things too?

GG Allin

My car has a KN Cone filter, with that you can hear it. With a stock air box you cannot hear it.

hawk911

Wondering if I should throw the drilled box back on when I get my G-pipe. You say cut airbox- different than drilled?

RallyDogRacing

Hawk - you'll get to see it as soon as your parts are in and we're dunking the suspension. I got my airbox from JoeyBagadonuts who after driving my car said "I can't hear the engine! Here take this..." It's pretty much the airbox cover , dremeled away at the perimeter so that it's a frame holding the filter to the housing.

It's mucho louder.

hawk911

I have a drilled, so really I just cut away all the inner plastic so I'm left with an open square? Sounds pretty easy, but does it get rid of the jet-like sounds the drilled box makes?

btw- parts should be here next week, as he just got the rears in, but no fronts yet.

RallyDogRacing

Jet like sounds? Hmmm, I think mine doesn't sound like what you're describing if by jet-like you mean pitch. It sounds like a wide-open intake to me. A friend compared it to a euro-930 he's flogged a bit as saying "your's sounds like a scared wild animal" which insulted me a bit - but he followed with "one that the predator isn't going to catch" so...

I dunno - you'll hear it next week sometime. Don't cut yours yet.
I wonder - can we post sound files to this forum?
I'd do mine stock, drilled and then cut and post the comparo.