How To Tell A Stuffed Cat

[toy515]

Hey guys got my car tuned today I've got -5 turbos made 400hp on 18psi so we done a back pressure test and it runs 6psi of back pressure I've been told 2.5psi is normal and every psi over is restricting roughly 10hp. I've got x force dumps pipes, blitz 2x2.75" into 3" x force high flow ceramic cat and trust 80mm cat back

let me know your thoughts

cheers

[PM-R33]

Did you drop the exhaust at the cat on the dyno to check? Simple way to test it.

[R31Nismoid]

^ exactly what i was thinking...

If you knew there was a restriction (im assuming you have pressure sensors in each dump?)... then a 5min job to exhaust drop would have been logical.

Interesing that 6-8 months later you are using -5's like everyone told ya from the start

[Cowboy1600]

Stuffed cat

Real cat

The differences are quite obvious.

Couldn't help myself

[PM-R33]

[toy515]

Lol I walked straight into that

[toy515]

^ exactly what i was thinking...

If you knew there was a restriction (im assuming you have pressure sensors in each dump?)... then a 5min job to exhaust drop would have been logical.

Interesing that 6-8 months later you are using -5's like everyone told ya from the start

Nah didn't get a chance to drop it, we only put a sensor in the rear dump pipe and on 16psi it had 6psi back pressure then went home punched cat out then put the sensor back in and went for a drive around and on 14psi and didn't go over 2.5psi back pressure Then on 18psi it hit 9psi in 2nd gear

does it matter what gear your in? Or am I doing anything wrong when testing it?

[FineLine]

Heres another pic of a stuffed cat.

http://www.thedrunkenkitty.com/freecat.jpg

[XRATED]

It looks real... but it dosn't meow

[Adriano]

Put an 80mm pipe between the merge on the dumps and the catback and see if it is better. Seems to be a big restriction increase when only increasing the boost a little, however punched out cats tend to cause a lot of turbulance

[Adriano]

Or even better get a 3.5inch cat now that you have stuffed your old one

[toy515]

Put an 80mm pipe between the merge on the dumps and the catback and see if it is better. Seems to be a big restriction increase when only increasing the boost a little, however punched out cats tend to cause a lot of turbulance

Ok I don't know where exactly you mean? And should I replace the cat with 3 inch pipe? Tuner doesn't think it's worth me putting in a metal cat because I could end up and the same spot I am now

[R31Nismoid]

Ideally you want a 4-4.5" cat, 3.5" might not get to 380rwkw and could pose a problem... hence going that bit bigger while you are at it might be a safer bet.

[toy515]

Does anyone know if Im 100% right about what the back pressure should be and what hp you loose per psi over?

[XRATED]

It's not that simple..

Every psi over X psi of exhaust pressure dose not equal an exact HP... ha ha ha

3psi is generally reguarded (by the tuning community) about the limmit for exhaust back pressure. You find the restriction by removing exhuast components one at a time.

Install one pressure guage just before the cat... if you measure it in the dump pipe you can get a false reading due to turbulance. Then install a pressure guage after each exhaust component. The difference in the guages will show you where the restriction is.

Cheers

J.

[Adriano]

Having said that at your power level anything 3 inch is posing a restriction

[soturi]

Bit OT, but this is the rb26 in the s15 yea? post up a pic of the monster!!!