GTI Exhaust Questions/Options

[McDub]

nice, will probably be able to get one from the wreckers if that's the case.

tbh i can't really see the drone going away on it's own. had it for over a week now (about 500km's) and no change in drone.
got it flashed with Custom Code on Sat, and it's great when you're giving it some, but slow driving at low rpm still annoying drone.

i still think it's either the downpipe is made poorly, or it's because i have downturned tips, but so do most gti's...

i'm waiting to hear back from Billy Boat to see what they say about my downpipe

[BI65ND]

I was reading about the downturned tips creating a heap of drone in aftermarket exhausts on one of the exhaust manufacturers sites. Think it miteve been the 42 Draft Designs site.... but dont quote me on that. But anyway what they were saying was that the sound bounces off the road and back up through the chassis. So that company had modified the design of their exhausts where the downturned tips were also angled slightly to the side of the car to deflect the majority of the noise away from the car.

[McDub]

yeah this w/e i was actually suppose to try putting something solid on the ground just under the tips at 45deg to see what effect it would have on the sound, but forgot.

I'm now thinking stock box with resonator delete... Bad idea?


edit: just tried then, put a granite slab under to try deflect sound away like straight tips would... didn't seem to make a difference, though it doesn't really drone much without loud on the engine... dury is still out

[Speed]

Also does stainless make a sound different to mild steel ??

Sure does. Is much crisper and is usually louder.

McDub, I would have thought that the new tune would have cleaned up the drone a bit.

If keeping the new system and it still bothers you, put a bigger resonator in or an additional one to the one you've got.
Magnaflow are pretty good.
That way you still keep the noise without the drone.

[McDub]

yeah im thinking of going with a bigger resonator.

still trying to get an official response from billy boat about my downpipe

ecs are claiming that it's normal and shouldn't affect the flow.

can't say i agree, here's what i said in response:

They "think" it looks like the other downpipes?
It protrudes outwards, creating a somewhat decent sized cavity between the outside edge of the downpipe, and the inside surface of the flexible joint.
Imagine going for a run, and running into a step you didn't see coming.
What happens? you fall over or stumble because it is impeding on your path.
In a simillar way, as the ehaust gases are expelled out of the turbo, part of the flow will hit this lip sticking outwards. Most of the flow runs above this, and continues down the exhaust pipe. Some of the flow will become trapped in this void creating a high pressure zone that will generate turbulance that will in turn impede on the rest of the exhaust flow. The whole point of the exhaust piping is to be free flowing to extract good power out of the motor. The affect of this turbulance on sound, well your guess is as good as mine, it could have any sort of affect. Whistle, drone, who knows. And the amount of power you might be losing out of this, once again, who knows.
You need to understand that right out of the turbo is the most critical part of the exhausts air flow, so to say that it shouldn't affect the flow is far from the truth.

Did you guys forward the pic to Billy Boat, or your supplier? I would be very surprised if they descibe this as "normal".

here it is again


what do you guys think?

If it's normal, then yeah i'm fine with it, just wanting to make sure.

[McDub]

apparantly billy boat "think it looks alright"... not very comforting!

[McDub]

for while there i thought the drone was getting worse, turns out when i've got a full bootload (was just dropping off my car full of suspension goodies then for installing ), the drone gets twice as bad! hate drone
problem is i've got so many options to try and fix it,
- bigger/better resonator
- change tips on existing box to straight and get bora valance with cutouts (1J6807521C)
- buy different back box with straight tips and get bora valance with cutouts
- remove catback completely and sell it, pipe in old stock muffler with 2.25" piping (delete old resonator)
- sound deaden boot

though with all that, i'm hoping that the dodgy looking downpipe isn't what is causing this drone!
I don't want to waste money trying to fix it with one or some of the above methods, only to find that it is the downpipe at fault...
I really have no idea what to do...

[Speed]

for while there i thought the drone was getting worse, turns out when i've got a full bootload (was just dropping off my car full of suspension goodies then for installing ), the drone gets twice as bad! hate drone
problem is i've got so many options to try and fix it,
- bigger/better resonator
- change tips on existing box to straight and get bora valance with cutouts (1J6807521C)
- buy different back box with straight tips and get bora valance with cutouts
- remove catback completely and sell it, pipe in old stock muffler with 2.25" piping (delete old resonator)
- sound deaden boot

though with all that, i'm hoping that the dodgy looking downpipe isn't what is causing this drone!
I don't want to waste money trying to fix it with one or some of the above methods, only to find that it is the downpipe at fault...
I really have no idea what to do...

I don't think that the straight tips will make much of a difference.
A baffled "back box" may kill the drone but also the power.
Selling the cat back and going back to stock will also reduce your power and I suspect you won't be happy with it.
Sound deadening the boot might help a little - That is if that is where the drone is comming from?
I'm sticking to my previous suggestion of putting in a bigger resonator.

What you could try is have a flange plate made up just before your rear muffler and the same on your standard rear muffler. Bolt it in and try it too see what you think re sound/drone and power.
If power is lacking you could then bolt the new rear muffler back on and do the resonator.

Anybody else got any ideas???

[Water Boy]

Noise is good!