SF Forester larger diameter exhaust

Austas75

Forum Member
Joined
Feb 20, 2018
Messages
17
Location
Tasmania
Car Year
1999
Car Model
SF Forester
Transmission
5spd Manual
Not sure if this is in the right section?

But I am looking at replacing my exhaust and was toying with putting one on with a larger diameter has anyone done this and was there any performance gains?
 
I have a modified exhaust system; can't remember the diameter but it's a little larger. You don't want it to be too big as the engine relies on back pressure. I have aftermarket free flowing cat and resonator and I think they would make more difference than any increase in the pipework. Performance gain - possibly but hard to gauge unless it was dynoed before and after.
 
Ok Thanks, Kevin, I just want a little extra power to help with towing. I will look into a free flow cat and resonator.
 
If your SF is non-turbo, it won't help.

But you can go into low range even on road, that helps alot as you have a 1,447:1 ratio.

Another option is to fit an EJ22 if you have an EJ20/122hp engine or an EJ25 if you have an EJ20/125hp engine because of harness compatibility.
 
[MENTION=15842]Austas75[/MENTION] BTW - I only replaced the exhaust system because it needed replacing. If your exhaust is in good condition then I wouldn't bother.
 
I put an oem 04 sti catback on my na 04 sg forester. Feels like a picked up a smidge of hp in higher rpms, in exchange for a smidge less torque in lower rpms
 
A larger exhaust diameter can reduce restrictions in the exhaust system - but too large will loose the scavenging effect where the exhaust acts like a chimney and pulls exhaust gasses out of the combustion chamber. At a certain point in the rev range this is lost, even on a stock exhaust.

Too large and the exhaust loses its scavenging effect until a lot later in the revs, this can lose the low down performance for around town driving.

While replacing the exhaust it’s a great time to get what you want - less restriction, maybe more noise ;) ;) ;)
UELs will give you the Subaru burble but the extractors or “Y” pipes rarely need replacing, and this is the section of exhaust that makes this happen or not - it’s in how they’re built.

Cheers

Bennie
 
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