jebia

I've got an intermittent (doesn't depend on an exact rpm) noise that lasts for a second or two every so often, while accelerating under load. It most occurs when you accelerate sometimes at 2000 rpm and sometimes around 3000 rpm, depending on whether your in 2nd, 3rd or 4th gear.

The noise sounds like the exhaust or intake is resonatting (sounds like a "waaahhh"), then after a second or two it stops even though the motor is still accelerating. The noise doesn't affect the engine performance, the car doesn not stumble or surge.

I don't remember this happening before I installed a cut out air box cover, so maybe this is enhancing a sound that was always there (before I removed the stock cover and snorkel tube).

Has any body heard a similar noise? Its almost like a valve is opening and then closing very quickly. Or maybe some sort of resonant frequency in either the intake or exhaust system (I've got the fabspeed bypasses).

Thanks in advance.

Jon

jebia

Found the problem (imtermittent intake howling noise).


Turns out The last time I removed the intercooler (for a boost sensor replacement), I forgot to re-connect the air temp sensor on the intercooler . I re-conected it yesterday, when I was re-installing the stock airbox cover and snorkel (turned out the cut away air box cover didn't give me the NA sound I was after, I guess the intercooler blocks that sound or maybe my fab speed bypasses are too lound to hear anything else).

The car now runs as normal.

Rob 97 993c2

jon-
may i ask why you did the cut away air-box? ive heard this works in NA cars (similar to motorsport sound) but cant see why this would work in a turbo when the noise is so muffled by the turbos and the intercooler. Did you have any luck? Im amazed how quiet my TT is, but im afraid to take mufflers off as i dont want to offend the locals.

jebia

I wasn't after the exact same sounds emitted by the NA car ("wosh" sound of air coming in thru the filter and being dumped into the intake manifold), I though, I would be able to hear the "wosh" sound of air being sucked into the turbo, and perhaps some turbo whine (sounds made by the turbo's spooling up).

I also wanted to see if the cut out air box, made a difference performance wise (I couldn't tell the difference on this either, perhaps the intake pulling in warm engine air, counter acts any increased intake flow). No harm, no foul, the cut out box I picked up on ebay for about $30 used, I did buy a BMC air filter for this experiment, and that stayed in the car.

My idea came from my truck, a dodge cummings turbo diesel. When I installed a K/N instake on the truck, out came the beautiful sound of the turbo spooling up (just like a big rig). This worked because the turbo is up high near the engine hood, and with in about 2 feet of the air filter.

As far as the exhaust, I had the same feeling (fear of it being too loud) when I installed my fab speed bypasses. The bypasses are very loud at start up and at Idle they sound like my friends jet boat. I didn't like so much the loudness (my neighbors don't car, they all have harleys), I didn't like the "type" of sound. I ended up installing (welding) a couple of CC inserts (baffles) in the by passes to change the sound (the sound is more refined, less gurgle) a bit at idle and to get rid of a irritating rosonance (booming sound about 60 miles per hour). Now its just right (you can fine tune the sound by drilling out holes in the baffles) for me.

Don't be afraid to try things, that's the fun of it.

Rob 97 993c2

jon-
thx for the help. not sure what i should do, ive read all the posts here on cat bypass and muffler bypass,etc. i dont want loud sound at idle, but want to hear the motor and turbos at speed. I loved how the varioram NA 993 sounded at 5k rpm, and i love how turbo track cars sound when u can hear the turbo spool and then let the air out when they brake. Not sure how to get this.

boostid

I too would like a bit more sound from my TT. I made a CD copy of the Fabspeed bypass sample at their Website, fired it up on my old stereo and B&O speakers in the garage, turned it up and decided that with the garage door open, firing up the car would create a giant Chris Craft subwoofer experience in my neighborhood and have every dog within a mile howling like wolves. I'm old and half deaf, so I don't care, but I do try to be a good neighbor. I'm starting to look at mufflers. I want a decent sound (not too loud), but don't want resonance. Suggestion today from one of the local shops was they favored B&B. They've tried B&B, GHL, Fabspeed, and Dansk. Any comments or suggestions?

Hal
97TT Arena/Cashmere, RUF19s, SRDs, PSS9, RS Sways