2.5" & 3" Exhausts please explain!
 

Hi Folks

After having my 2nd scoob for about 8 months now, i am loving every minute of it :D but! :(

I have a V2 v-ltd wrx (previous had a V1 wrx) now the mod's & engine's are the same but my current scoob had come over into this country with a Fujitsubo 3" cat back system. Not loud but a very nice sound.

mods/info for both cars:
std 2L 5 spd,
scooby ecu
k&n panel filter
3" open neck de-cat
ngkpfr6b plugs
new coil packs
filters etc etc
std td05 turbo
*old scoob had l/weight pulleys & flywheel - new scoob to have l/weight
flywheel in a couple of weeks & then pulleys at a later date.

Now then as it has exactly the same scooby ecu chip in it as my 1st scoob, but the mpg is really really shocking :rolleyes: i know scoobs are not mpg king's & im not after good mpg, but im 99% sure its using a lot more fuel than my last one, yet has the same set up apart from the zorst.

I had & have a 3" open neck decat, but on my last scoob i had a 2.5" ninja silenced centre & 2.5" vortex angled back box & this was a lot louder & felt more torque'ier (spelling!?!?)

so does the 3" bore play a part in the using more fuel (it does pop & grumble alot when slowing down in gear!) & is it too much bore for running 280/300 ish bhp & would I be better off with the 2.5" from the decat back to get a better build up of pressure as well?

Thanks people :thumb:

You don't need a 3" exhaust for max power. I run a 2.5" system on my car with 500bhp. The reason behind going for the larger bore is that the back pressure is reduced allowing exhaust losses to escape more freely. Given the up-pipe to the turbo is a smaller diameter than a 2.5" exhaust then you will always have less pressure after the turbo, maybe not as much with a 3" exhaust, but not that much to worry about.

Andy

wont make any difference to the fuel mate what size exhaust you have. What it will be is the car is running rich thats why you are getting alot of popping on overrun.

2.5 will be torquier on a standard system :)

Yep is torquier on 2.5 then 3. I have a TD04, and went from 2.5 to 3, and it lost a bit of low end but made better top end.

Is that with your 321t?

Yes with 20% E85. I am now using meths due to lack of supply of E85.

cheers for the info people, i was sure that with a car with only 280/300bhp is easy for a 2.5" standard & 3" was for big power. To be honest i think i prefer the 2.5" system for a bit more torquier drive & really miss my vortex back box, by eckkers that sounded great !!

B13bat, i was wondering about the plugs, but always had issues with 7 rated ngk's as i dont do alot of miles & many of them the car does not get warm & i was always cleaning the plugs, so far with this scoob the ngk6's have been working well. That seem about right or am i imagining it!?!?!