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De-cat truth
- Thread starter lasimone
- Start date
Well its the end of it if you dont want to ever actually understand how an engine works properly.
So seen as your the resident Clio expert is the Clio 172 decat not restrictive in any way? Just asking
Yes it is restrictive to an extent, but on the standard exhaust and standard engine its not a big restriction though.
The more air you are trying to flow in the first place, the more of a restriction it becomes, so the gains from removing it will be linked to what else you have done.
Unless yours is actually getting blocked up with carbon deposits or from it breaking down, then on a standard car the gains are going to be very small indeed.
Evo 5 RS
You'll see hardly anything, the twin barrel cat on the ph1 especially. You'll see better gains from the newer stealth systems (or any uprated system instead)
Coupled with matched inlets my decat on a standard exhaust and standard air box and filter on my 182 made 187bhp..was very strong pulling engine. Then I got a custom exhaust made and it used to get flat spots all over the place and with a knackered lambda it really did slow down.
If you have breathing mods done already then I would go for it. It's not exactly like they are expensive and you can always take it off.
If you have breathing mods done already then I would go for it. It's not exactly like they are expensive and you can always take it off.
Its either restrictive or it isnt. It doesn't become less restrictive on a standard engine, it just becomes less noticeable.
I was running a IK and exhaust at the time when i fitted mine. It made a noticeable difference probably because it was in conjunction with the other 2 mods, yes. Didnt turn it into a fire breathing dragon but for 130 sheets made well worth improvement for this mere handful of pennies it cost. IMO a good power vs ££££ mod.
Ermmm clio's arent turbo'd - you're talking s**t
De-cats lose power if anything due to the lack of back pressure. Worst mod ever unless all you want is noise
Yozza'd Blue Bus
Yes m8 back pressure loss :S
LOL whattttttttttt
KTM 990 SD / S60 D5
Changed my decat for a sports cat made no difference to power.
As flow increases, so does resistance.
At idle for example, it is to all intents and purposes not restrictive at all, flat out at high rpm it starts to become restrictive, improve the breathing of the engine with other modifications and it becomes more of a bottle neck.
If you want power you want VELOCITY of exhaust gas. The standard exhaust is designed to do this.
The reductions in pipe size around the cat that people think are bottle necks are more likely designed to increase the speed of the escaping gases.
People think increasing the bore of the exhaust and removing the cat etc.. means it's easier for exhaust gases to escape so you get more power - but what actually happens is the gases slow down which is worse for performance
BOTTOM LINE is that de-cats do f**k-all for a standard engine. THey make it sound louder and make you fail the MOT
If you've fitted cams, bodies, charger or turbo then it might help - but on a standard car it's £130 that you'd be better off spending elsewhere
The reductions in pipe size around the cat that people think are bottle necks are more likely designed to increase the speed of the escaping gases.
People think increasing the bore of the exhaust and removing the cat etc.. means it's easier for exhaust gases to escape so you get more power - but what actually happens is the gases slow down which is worse for performance
BOTTOM LINE is that de-cats do f**k-all for a standard engine. THey make it sound louder and make you fail the MOT
If you've fitted cams, bodies, charger or turbo then it might help - but on a standard car it's £130 that you'd be better off spending elsewhere
When I fitted my decat, like I said in the post above, it pulled a lot better and smoother at lower revs. It probably didn't increase the power but it improved the delivery of it.
182
I would listen to people who know their stuff when it comes to engine tuning, not just the marketting stuff you get all over the internet, car comics and especially on the forums.
Designing an exhaust is more in-depth than just removing all restrictions to improve flow. Plenty of manufacturers design their factory exhaust to have "steps" or bore profile changes at specific points to pulse-tune (in order to help scavenging pent gassess from the cylinders), this is typically done in the area of the exhaust imediately after the manifold, i.e where the cat is. So it is perfectly conceivable that the clio could perform better at certain revs with the cat in place. Needs proving on back-to-back dyno runs but I would expect to see a very slightly different shape to the torque curve.
edit - not saying a decat won't make more power, I've no opinion either way (I've always had my cat in place) but I felt no perceivable gain from fitting a scorpion stainless exhaust, and wouldn't expect anything different if I swapped the cat for a straight pipe.
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The standard exhaust and cat is designed to meet EU regulations on noise and pollution levels.
This rubbish about back pressure and loosing power as a result doesn't happen with a mere 2.5 inch bore exhaust on a Clio. If you went beyond this then yes.
Removing a cat on a 172 does aid performance. It might not get you anything in the way of raw gains but it free's the engine up due to loosing the restriction of the internal cat material.
Can you back that up with LITERALLY ANYTHING?
I took my decat off and put my cat back on after running the decat for a year and gained a couple of seconds per lap at the same track last year - it had more torque and pulled better out of corners
I've not seen a single rolling road graph on here that shows they make any power at all
Only reason I'm not running one now is because the ITB's tend to pop and bang and knacker the cat
As for freeing the engine up - utter utter utter b****cks
There are cars on here with over 220bhp running very fast quarter miles still on ph1 172 cat's. The 182 cat is practically a sports cat it flows so well
The inlet on the 172 engine is far more restrictive than the exhaust system
Velocity of gas is useful for increasing scavenging effects but this is quite a narrow effect, so while it might improve midrange torque to do so, a larger exhaust diameter in turn will typicall be better at higher rpm. Its impossible to come up with an exhaust that is optimum for the whole rev range.
But bare in mind that the moment they then go back to the full bore diameter it will of course then stall.
So its really key the distance is optimised to get the effect at the desired points in the rev range.
A single pipe of the required diameter would do this better than a complex structure like a cat which will typically destroy the sort of pulses you are aiming to maintain.
I agree to a certain extent when dealing with a decent flowing cat like the 1*2's have, but once you are dealing with a 100K old cat that is either breaking down or carbon'ed up, the same is not always true, and on some other cars where the car is more restrictive its more beneficial to remove it.
Welcome to most of the tuning industry, the land of "UP TO" claims that are backed up with f**k all in most cases!
Fluid dynamics is a very complicated subject, and when combined with pulses from an engine, its very difficult to second guess, trial and error is the only way most of us will find out if a change has worked or not, its very hard to predict in advance accurately.
Lol at 2 seconds quicker a lap after refitting a cat, because it gives you that much more torque! Priceless that!
Phil, step away from the computer with all your Internet reading, you actually make yourself look like a complete idiot! Lol
Phil, step away from the computer with all your Internet reading, you actually make yourself look like a complete idiot! Lol
The 182 is now a ''sports cat it flows so well'' to quote you yet the 172 cat happens to be a waste of time changing? How does this work? :S
The 182 cat is good because its only 180 cells (or something) which makes it more free flowing and less restrictive than a 172. So taking this theory into account, removing the cells altogether = no internal restriction, maximizes flow even further.
Its a good stealth tactic, but its still divergent-convergent in shape which creates a buffer volume and not particularly aiding velocity. It's probably better with the cells left in!
I'm not an exhaust tuning expert but I know enough about fluid dynamics and the behaviour of gasses to know that most of this 'restiction' chat is tosh.
When people say that less restriction = more flow, thats partly correct. There is the POTENTIAL for more flow (actual flow relying on a number of factors) this is why turbo engines respond better to bigger bore free flowing exhausts.
Consider a garden hose pipe with water flowing through it powered by a small fish tank pump, and then couple it to a drain pipe. The drain pipe will be so underwhelmed and take ages to fill up to the point it 'stalls' as mentioned.
In terms of a turbo engine, imagine emptying a swimming pool with a A) a hose pipe and B) a drain pipe. The drain pipe would be better for obvious reasons.
Thats the simplest way I can think of explaining it. :S
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This thread is brilliant. A lot of threads are doomed to fail but this one has it all (well apart from "M3" or a horrific ebay modded clio):
* People who appear to know the theory/practical implications very well.
* People who don't understand (NOT saying that I do) the words they're throwing around - most people on here don't actually get what "power" is nevermind thermofluid dynamics.
* People who are talking about completely different cars (as if comparisons aren't mostly flawed as is)
* People with absurdly flawed reasoning to back up their opinion/experiences (I'm sure if you stop and think about the number of variables involved in laptimes you'll realise how impossible your "2 second improvement" is to verify).
Get one on a rolling road. Remember that a 100% "fair" comparison is impossible. Compare the shape of the two graphs. You now have an estimate of the "answer" for one exact car in it's exact mechanical state at that exact point in time.
* People who appear to know the theory/practical implications very well.
* People who don't understand (NOT saying that I do) the words they're throwing around - most people on here don't actually get what "power" is nevermind thermofluid dynamics.
* People who are talking about completely different cars (as if comparisons aren't mostly flawed as is)
* People with absurdly flawed reasoning to back up their opinion/experiences (I'm sure if you stop and think about the number of variables involved in laptimes you'll realise how impossible your "2 second improvement" is to verify).
Get one on a rolling road. Remember that a 100% "fair" comparison is impossible. Compare the shape of the two graphs. You now have an estimate of the "answer" for one exact car in it's exact mechanical state at that exact point in time.
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PH1 twin cat 132 CFM
182 cat 110 CFM
Magnaflow 59926 200 cell metallic cat 215 CFM
KTEC 172 decat 300 CFM
@10" H2O
Lots of generic science on this thread but leaving velocity, flow rates and Google search classroom calculations behind, the question is, on a Clio 172 does fitting one make a difference?
The majority who have fitted one (most maybe in conjunction with other breathing mods) say yes.
The majority who have fitted one (most maybe in conjunction with other breathing mods) say yes.
I literally couldn't give a flying f**k what you think though
I put a decat on my car - it was possibly a bit quicker at the very top end - but as there isn't a single track in the UK that I can hit 140mph on that was f**king pointless
Coming out of corners it was down on torque - and slower
It also made it impossible to pass half of the noise tests and was a royal f**king pain in the arse
I put a cat back on, there was a noticeable increase in low down torque which made the car quicker on track. End of
It's called personal experience - that's what the OP was asking. I might be completely wrong about my theories but from what I've read it matches the actual real world results I've seen on my 172
Trying different things is fine - but the actual question the OP asked was if a de-cat would get more power - and let's be honest if it does it's only 1 or 2bhp and you won't f**king notice it - therefore a waste of money
Still maybe we should all be sheep and whack some eibachs on our cars and an RS2 manifold and claim we've got 190+bhp eh?
f**king forums...
This is the main problem
MOT law is changing next year so even if your car was lucky enough to pass emissions tests without a cat they have to check the presence of one - so it's a fail
The 172 cat is a b**ch to change as the bolts are right up at the back of the engine
So it's £100-150 out of your pocket for a bit of metal tube that IMO loses you a bit of torque and gains you about 3mph more at the end where you'll lose your license. It takes you 2hours every MOT to swap back and if you get stopped for a road side test you're fucked
If you want a loud exhaust then fair enough - but if you're chasing BHP figures then keep saving your money
MOT law is changing next year so even if your car was lucky enough to pass emissions tests without a cat they have to check the presence of one - so it's a fail
The 172 cat is a b**ch to change as the bolts are right up at the back of the engine
So it's £100-150 out of your pocket for a bit of metal tube that IMO loses you a bit of torque and gains you about 3mph more at the end where you'll lose your license. It takes you 2hours every MOT to swap back and if you get stopped for a road side test you're fucked
If you want a loud exhaust then fair enough - but if you're chasing BHP figures then keep saving your money
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