exhaust

bigcatdazzer

bigcatdazzer

Well-known user
Oct 28, 2013
231
36
Cambirdge
if im going for 3" cat back exhaust and im going to decat it and get new manifold should I make that all 3" too,seen some on ebay cheap but 2.5" decat pipe? meny thanks Darren (y)
 
No need to go any bigger than 2.5 on your system, if you do jump up to 3 then I would bank on you losing some power
 
And the headers shouldnt go any bigger than that, otherwise there would be NO back pressure tp speak of which would be a major reduction in power
 
With a turbo application the bigger and shorter the exhaust the better, once its spun the blower up it needs to be gone as quick as possible!
 
So is our exhaust the same as mk 2 v6 mondeo? Meaning i cant find cougar decat but can the mondeos can get that and just fit it if its the same?
 
The tailpipes are closer together on the Cougar.

The art of exhaust design is a dark one. Back pressure in pure terms never helps, but exhaust tuning relies upon partial vacuums travelling up individual tracts to the exhaust valves of other cylinders. If the wave arrives as the valve opens then the exhaust gases are sucked out, meaning that the crankshaft doesn't need to exert force on the piston to push it out.

Timing is of the essence, as is momentum in the exhaust gas. It's the momentum which creates the partial vacuum behind a slug of exhaust gas. Bigger pipes reduces the speed of the gas inside it, and the scavenging effect is ruined.

To make negative pressure in one place you create positive pressure somewhere else. The art is keeping velocities high without costing too much kinetic energy, and placing the high pressure somewhere that will generate low pressure where you want it and at the right time.
 
Is a sports cat not more recommendable ? Your CAT creates back pressure and helps with power, without one surely you would lose power and get a drone rather than sporty sound !
Thought de-cats main application was going turbo, probably totally wrong as normal :beer:
 
I've driven a V6 both with and without a main cat. Power difference is negligible, however....the car drank more fuel with a cat in place. Don't know why but there you are. I like the sound of a V6 with a decat though - the precats and silencers take care of the back pressure (y)
 
according to mondeoSTOC, the all but very latest ST24's were all 2 bolt flange cat, where as late and ST200s were 3 bolt, and then obviously most cougars from 99 on were 3 bolt also


if its performance you want, leave the main cant, and ditch the headers for the Racebits/Toyosports headers as they will delete the precats too

not saying the BHP sum will hike massively, but the difference in hwo the engine feels and revs is second to none! it transforms the feel of the car, and for later improvements to its power will only be better if you already have a free flowing manifold (pair)
 
Easiest way to see if you have two or three bolt cat is to poke your head under there

If you have a braided flexi pipe it's three
Spring bolts = two

Two bolt stainless y pipes are proving hard to find now, mine has been changed to a three bolt setup.
 
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