3" downpipe to 2" exhaust stupid idea?

[sam80quattro]

after putting the 1.8t into my b3 90q ive had a 3" downpipe made and bought a reducer thinking the original exhaust was 2.5" only to find it was 2". will 2" flow enough for 300bhp
its a nicely tig welded stainless system and a shame to get rid of it but if it wont flow then its got to go.
my other option due to lackof funds would be to use a 7a exhaust as there 2.5" aren't they????

[driftin jo]

NO,it's got to go , just not big enough , even if it only cost you say 20 HP your egt would go way high and you would kill your motor, not worth the risk even trying it . A friend of a friend did this years ago just until he could get time to get a full exhaust made , drove it hard for 3 weeks then the head came off one of his exhaust valves and went through the piston , totally destroyed the motor.

[sam80quattro]

thought that might of been the answer.
2.5" will be acceptable though???

[quattrostyle]

2.5" will be acceptable though???

I'd say yes.

[driftin jo]

Yes it will be ok , you have to remember 2.5" dia has 4.9" cross sectional area, 2.0" dia has only 3.14" cross sectional area, so as you can see it has a lot more flow capability .
That said go for 3" if you can as if you tune it more later with a bigger turbo you won't need to upgrade and I cant see it costing you much more .
:

[sam80quattro]

has anyone successfully put a s2 coupe exhaust onto a b3 80/90 quattro? mainly from under the handbrake lever back over???

[GazzaG60]

which bit of the system is 2".

if its the back box. yes just about big enough.

2.5 will do over 300 but will be building back pressure and heat.

[sam80quattro]

its from were the cat would be back over

[GazzaG60]

250hp then

[sam80quattro]

im sure i could live with that untill i find something more suited.

[driftin jo]

You seem to be experiencing goldfish memory syndrome

Read post #2 again !

[Paul McCleary]

Read post #2 again !

What he said! My little 1.8T A4 had a 3" downpipe from the K03 to a 2" Stainless system when I got it. The EGT's at full load were very high and mechanical failure was on the horizon. With a 3" system, the EGT's were much lower and the car felt like it could breathe again. This was at a measly 250bhp!
A 2.5" system will do the job, but a 3" system would be future proof for similar money.

Paul.

[GazzaG60]

i still belive that 2" will do 250 hp with a bigger downpipe. also no cat helps get them out faster. whats a 2.5" flow with a cat for instance. and depending on cat type. put it this way a 200cell 3" cat in a reasonable size is 300hp. thats cat restriction.

ive seen close to 400hp on subaru with 2.5. no cats.

its in the tuning.

how bigs the exhaust flange on a k03? thats a good indicator.

whats very high egt.

[M_GORDON]

Hi, I have SuperSprint DP in 70mm and at last the OEM mufflers with 65mm
And it goes fine.

[driftin jo]

i still belive that 2" will do 250 hp with a bigger downpipe. also no cat helps get them out faster. whats a 2.5" flow with a cat for instance. and depending on cat type. put it this way a 200cell 3" cat in a reasonable size is 300hp. thats cat restriction.

ive seen close to 400hp on subaru with 2.5. no cats.

its in the tuning.

how bigs the exhaust flange on a k03? thats a good indicator.

whats very high egt.

A 2" system will flow enough for 250 HP granted, on a normally aspirated engine I wouldn't worry about it at all, the point is this turbo motor and is tuned to produce 300 HP not 250 .
If the motor was only tuned make 250hp it would not be a worry but still not great .
If you put a 2" system on this the motor it is still trying to make 300hp and that's not good at all.

As for the Subaru , as I said on an earlier post a 2.5" dia has 4.9" cross sectional area, 2.0" dia has only 3.14" cross sectional area , so the 2.5" has almost 1.6 times the flow capability and guess what
250 x 1.6 = 400 , so there you go you can get a Subaru to nearly 400hp with a 2.5" pipe .
The question would then be how long would your Subaru last at full throttle with a 2.5" exhaust compared to the same set-up with a 3" . I wouldn't want to be making 400hp with any turbo motor on a 2.5" exhaust.