I have just bought an sti7 which i am well pleased with,it miles better than my 01wrx,I have a scoobysport de-cat centre in my
garage off my old car and was wondering if i will get much
benifit of fitting it on my sti,difference on old car was minimal.
thanks
Steve

It won't make a lot of difference - the backbox seems to be the most restricted bit on an STi7.

And it probably won't fit anyway - the shape is different on an STi7 decat centre pipe to clear the wider diff.

Thanks dave,saved me wasting an hour.
Steve

DTS,d'ont you mean down pipe?

Nope. At first, the WRX system didn't fit the STi7 properly - it either banged on the diff or hit the transmission tunnel (well, ours did one of each). I think Hayward & Scott changed *both* the centre and backbox jigs slightly to fit.

Steve, sorry I forgot to mention in my first reply - you might be able to get your centre modded if you really want to fit it:)



[Edited by Dave T-S - 6/10/2002 8:59:50 AM]

Dave, are you sure that the back box is the most restricted bit on the STI7? Looking into mine, I see a straight thru pipe with an open chamber at the upstream end. Looks pretty free flow - certainly better than the old GC backboxes!

Yes thats what I meant.

Whose been playing with their 6 inch ruler then?
At least it justifies me replacing the back box then!

DS

Worse than that - I had to run out in the middle of posting and drag the exhaust system out of the garage roof to measure it:D

Does reducing the back pressure slightly lose low down torque,
giving a benifit higher up the rev range?
steve.

Dave T-S,

That is excellent info !

Effort like yours on the posts and info you supply makes ScoobyNet such a valuable asset to have access to !! :)

Thanks again for all on Scoobynet who take the time to get the facts sorted !

Cheers,
Ray :)

Ray

Thanks. I don't always get it right, but I do try and get my facts correct:)

Steve

That's a good question, and one I considered. Unfortunately I do not know the answer LOL. It will depend on what combination of exhaust bits you are running. Subaru put the restriction in the back box pipe for a reason - it may have been one of getting through the noise regs, or may have been to increase back pressure, as you say.

Dave
when my 01wrx went to the dealer as p/x,put the centre cat and standard b/box back on.On my drive to the dealers it seemed to
have more torque pulling away but was a bit flat between 5-6000
revs.It seems most mods you do have a minus effect somwhere as well
as a plus.Maybee subaru do know what there doing after all.
Steve

Ah, right, with you now - sorry!

The internal diameter of a STi7 OEM exhaust centre section is 58mm. The back box flange is also 58mm ID. Immediately inside the mounting flange, the backbox pipe ID is reduced down to 50mm, all the way into the backbox. If a 8mm reduction isn't a restriction, I don't know what is!:)

In perspective, that's also a 11mm or so smaller inside diameter than a Scoobysport backbox pipe.....

[Edited by Dave T-S - 6/10/2002 9:22:47 PM]