Sinister Subaru

I have a question about whether this particular issue was just a mechanical issue or just the resonance from the exhaust.....

A buddy of mine picked me up the other day in his STi and he uh....decided to accelerate to well over 100 mph. (Yeah, I b*tched him out for going that fast on a public highway even though there weren't any cars present).

Anyway, when we hit about 100 mph, we noticed what seemed like a vibration momentarily until he accelerated a little bit faster. I couldn't tell if this was just the resonance level of the stock STi exhaust or another type of issue. The only time this seemed to happen was when he did runs up to just over 100 mph.

So, I ask any of you that makes habit of driving this fast if this was resonance-related or some sort of mechanical issue.

And before anyone says it, I'm going to answer. No, I'm not going to take my car up to 100+ to see if my car does it.

Anyone have any insight?

Thanks!

Wingless Wonder

iTrader: (7)

Does the resonance go away if he lifts off the throttle? Could it have been a vibration originating from somewhere other than the exhaust note?

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0==WW==0
"…axles of evil…" - george w. bush

Subie do

sounds rad, i hope he had to pee or somthing to be going that fast. But i can under stand when i come home from school i got to go like a s.o.b

Sinister Subaru

As soon as he heard it he lifted. Then got back on the gas and it happened at around exactly the same speed again.....I noticed it lasting for about 5 mph, and then everything went back to normal. The sound went away....

I told him just to leave it alone. I'm not one to like travelling at 100+ on public roads. I wasn't about to egg him on and tell him to "hold" his speed to see if it went away.....

Wingless Wonder

iTrader: (7)

I was trying to determine whether the resonance was speed-related or exhaust-related. If he went beyond the speed where you could hear the noise and then lifted off the throttle, did the noise still occur when the vehicle decelerated through that speed range?
Same here. Too much can go wrong 'testing' cars on public roads. If someone wants to drive their cars into the triple digits on the highway, they can just pull over and let me out first.

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0==WW==0
"…axles of evil…" - george w. bush

Sinister Subaru

As he decelerated or accelerated beyond that "point," the sound did go away. It was only within about a "5 mph window" that this occured.

This morning I took my car out and while not going 100 mph, I did bring the revs up pretty high before shifting and sort of cruised around at a high rpm in low gears, and I thought that I noticed the same type of "vibrations" or "noise levels" at certain speeds or rpms.

I'm personally leaning towards thinking that this "hum" was resonance from his exhaust......

In my Camaro at around 2300 rpm I notice that it gets really loud in my car, and it's a constant "hum." I'm just thinking it may be the same with the STi, and it is just hitting the resonance level of the exhaust.......

Wingless Wonder

iTrader: (7)

It could very well be exhaust resonance. I don't know if this is common to the STi or if it's just a case of manufacturing tolerances or a defective exhaust hanger. I don't get any sort of resonance in my WRX but haven't taken it over 100 mph for quite a while. I do get a slight vibration (but no noise) in the steering wheel at 80 to 90 mph but it could be that I need an alignment. The factory uses soft rubber exhaust hanger bushings to combat NVH and I've replaced mine with the harder Kartboy polyurethane bushings and haven't noticed a great increase in noise.

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0==WW==0
"…axles of evil…" - george w. bush

Sinister Subaru

Thanks for great replies thus far, WW. Also, keep in mind that the stock STi exhaust is a different exhaust than is on a stock WRX.