vulnax999

iTrader: (7)

Hi all

After fitting first SS backbox ( bit more rumble, nothing exciting ) and then SS centre ( no real change ) and finally a H&S d/pipe with splitter ( WOW, loud and rumbly! ) I went and fitted OBX headers ( v.nearly equal length tubular steel, ceramic coated, and up-pipe).

Then car was Too Loud; simple gentle acceleration in traffic queue was very loud and "barky". Not fussed over losing the scooby beat, but a question on the noise and back pressures, etc. This is in a Wagon, looks very standard ... and I drive through a lot of villages and towns so draw too much attention! And noisy on the move as soon as any load placed on engine / throttle used.

Fitted a 2nd hand STi back box, quiet as a mouse!!!! But it has a rattle between 2000 and 4000 rpm. Any ideas where from, seems like either baffle inside or the chrome bit overthe actual exhaust pipe.


So, to the main Q.
What is the back pressure difference / power loss / torque loss / spool up delay between the STi back box, and a H&S Scoobysport back box?

Also, I guess the resonant frequency / octave band of sound needing to be deadened by the back box is changed after fitting the OBX headers, and the SS/H&S back box is not the right internal design for this,? yet the std STi one does a good job?

Any ideas appreciated,

V

Jay m A

iTrader: (2)

I have read a few threads in the past that suggests the STi BB doesn't flow any better than the OE twin pea shooter. Its just an aesthetic(sp?) change.

I too have a wagon and as a result of a bit of research I have bought the Revolution centre and BB to go with a H&S DP. I will be wrapping the DP also to keep cabin noise a minimum yet have max flow. All components are 3".

Alas i can't tell you how effective this combo is as its still sitting next to me in the study

micared

Changed from standard b/box to sti, ( 'cos it was cheap s/hand and nicer looking ), don't think it makes an atom of difference over standard tbh.

Chaddy

Funnily enough, we tested the standard 'Peashooter', both 00MY, and 01 MY, which by the way are different internal designs, and the STi rear systems, on our flow rig, and the Sti system does have substantially lower backpressure than the 00MY, and the 01MY, (which have the same backpressure), and therefore should give a bit more power. A good performance rear system should have a straight through absorbtion box, and give almost the same backpressure as an open pipe, and hence more power, but also more noise !

pbee

MRT make a centre section with a resonator and H & S will custom make one for you, that will dampen the noise.

On the 03 cars I have both the standard wrx and STi8 backbox, they have exactly the same part number on the the actual box so i think it is just the exit pipe that is different.

cheers


Peter

Turbo Herbie

I have a decatted magnex d/p and c/s and a 2nd hand STi BB.
I was led to believe the decat would be a lot noisier than standard but no difference other than more turbo noise.

I have exactly the same problem with the rattling at 2-4k revs. I thought the baffles were gone but it only occurs if the car has already been used that day!! Sounds so nasty I am considering putting the pea shooter back on.

Could it be something to do with condensation or is that just stupid ??

JIM THEO

The STI backbox ISN'T the same internally with the standard WRX but the resonance you hear may be is from the underside aluminum shield above muffler, at least this gave me some strange noises in the past until I put some noise deadening material in the boot, after all wrap your system you'll reduce remarkably the noise and droning.
JIM

ozzy

I've ran an STI BB on my MY99 RB5 for 4 years without any problems whatsoever. I prefer to run it with my TSL DP & centre because it's much more subtle and quieter than other BB's.

Stefan

Turbo Herbie

Sounds like the back box IS dead then

Chaddy

Hmm, sounds like the rattle could be caused by the fact that those of you who have the rattle have changed the system upstream i.e. taking out cats, changing pownpipes, and headers etc. this can drastically affect the noise entering the back box, and it maybe suffering from a resonance that would not be set up with the standard front end. These kind of noises can often sound like loose baffles, even when thry are not actually loose. It can often be the baffles, endplates, or even the case itself simply vibrating in sympathy with the incoming frequency, which would normally have been attenuated by the upstream components, or not even generated in the case of changed headers. I suppose the bottom line is, if it rattles, then it isn't suitable for your set up....'Mick' has the Sti rear system that we tested on his otherwise standard 97MY and that doesn't rattle, which maybe supports my theory about the upstream changes. By the way, 'pbee' says that the 03MY and Sti have the same box Part No, I don't see how they can if one is twin outlet, and the other is single ! See 'Jim Theo' comment.

micared

Changed u/pipe, d/pipe, also have sti b/box....no rattles!!

vulnax999

iTrader: (7)

Thanks guys, H&S seem to agree with most of this.

Best suggestion seems to be get a silenced / resonated centre then...

Cheers

Neil

JIM THEO

Just to add that I have same configuration and same noise issues with you mate I believe is something internally on STI back box!
"Only" 8-9ps difference between STI and Scoobysport (same with H&S) back box and bear in mind I already had decated the rest...
JIM

pbee

what car do you have ?. if its a newage the original 2nd part of the centre section has a resonator that you could swap back in. this greatly reduces in cabin noise.

saves you buying yet another part with a resonator. will be in 2.5" and non stainless but will give you some idea of how much a resonator will change the sound.