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De-cat truth

L

lasimone

Car  Ph2 172
Hi, i have been thinking about getting a de cat pipe for my clio 172.

I already have a full cat back system and wondering does anyone know the actual bhp increase you get from a de-cat?
 
Difficult to say as it will change from car to car but its viewed as a supporting mod, as in it will help make the most of your exhaust system. On its own maybe 5bhp which is deemed a good increase on the clio tuning scene.
 
MonkeyKnifeFight said:
Difficult to say as it will change from car to car but its viewed as a supporting mod, as in it will help make the most of your exhaust system. On its own maybe 5bhp which is deemed a good increase on the clio tuning scene.
Click to expand...

I've been told up to 10 bhp increase if you have a decent exhaust system in place
 
Decat on its own was worse for my car gave it flat spots all over the rev range was s**t taken off quite quickly
 
chale989 said:
Has anyone on here got a print out o power run with and then power run with a de cat
Click to expand...

Here's mine without a de-cat so if someone has got a dyno of a car with de-cat then we could compare them!! Win.

Screenshot2011-11-21at214323.png
 
Going for a dyno run on Saturday with Decat, espace v6 airbox and full yozza system on a 172 cup.

I'll post up the results when I get them.

The Decat sounds good and seems to make the engine rev more freely but as I only use mine on track I haven't noticed any flat spots.
 
If it gives you an increase in bhp - you won't notice it. All you WILL notice is a slightly sharper throttle response and an engine that is abit more free revving.
 
Just frees up the revs abit lower down but does very little power wise. I had a blast with a mate with the cat on and the decat on. Sod all difference in both blasts.
 
Thing is you cant compare RR graphs, because each one will be setup slightly different.
So unless you did it on the same rolling road, exact same car, near enough exactly after each other, wouldn't be an accurate comparison.

In reality I don't think you'll get any noticable increase. Certainly not 10bhp, wouldn't have even thought 5bhp tbh.
Just compliments other breathing mods if remapped imo.
 
I preferred how my car drove with the cat on so i put it back in. No power increase at all, just noise.
 
Iirc it can induce flat spots also. I know the 197 had problems

My car already had a small sports cat on it so there was no adverse affect apart from more noise and pops really. It also never became intrusive at normal speed/revs.
 
interesting to hear stories from the other side of the coin - decats are usually recommended but the downsides not normally mentioned.
 
btb do a modification on the 172/182 cat to the front joint radius as it slightly restricts flow in standard form wont see any real gains unless running over 200bhp.

as from the first of january every car fitted with a cat from 1992 onwards must have a cat to pass its mot.
 
If your looking at a decat to transform the car will be out of luck. If you want a better noise imo, get one.
 
Helpful if your trying to get big power but fairly pointless otherwise, I think I got around 2-5 extra torque with one fitting but no extra bhp, just ALOT of noise and the car felt like it wanted to rev move, although this was probably just down to the noise.
 
lasimone said:
I've been told up to 10 bhp increase if you have a decent exhaust system in place
Click to expand...

LOL, I have a 'decent' exhaust system, but I know for a fact I wouldn't get anywhere near 10bhp more with one fitted, more like 0-1 bhp. I would love to know what genius told you that, obviously not someone that owns a 1*2.
 
ITBs or cams and map are the only way you will see any noticeable increase in my opinion. Don't bother with getting it dyno'd. You will get more from the car taking the back seats out!!! I prefer the sound with a decat though!!!
 
i just bought it with the exhast system because it saved money on postage lol seems a little nicer to drive and sounds nice tbh but no major claim to fame for putting out more performace from me though lol
 
Probably the best value new engine mod on the market for a Clio. You can notice the difference. Spins up noticeably quicker
 
my 182 used 2 pull past my boys 172 easily,id be in front of him by the end of 3rd gear....since he put a k tec system an de cat on though,....same stretch of road where i used 2 fly past him, now i get half a car in front by 4th gear and the comparison was made same day....massive improvement on his car....fact
 
All this talk of "spins up quicker" and "revs more freely"

are you guys talking about in neutral?

Cause if you are talking about in gear, then the ONLY way an engine will do either of those things is with a significant increase in torque at the points in the rev range that its now "spinning up quicker" or "revving more freely"
So to say it does those things but doesnt increase power is a bit of a contradiction.
All sounds like a load of nonsense to me as a placebo effect you are thinking that you can feel brought on by a change in engine sound.
 
B19WAW said:
my 182 used 2 pull past my boys 172 easily,id be in front of him by the end of 3rd gear....since he put a k tec system an de cat on though,....same stretch of road where i used 2 fly past him, now i get half a car in front by 4th gear and the comparison was made same day....massive improvement on his car....fact
Click to expand...

The problem with that test, is how much of the difference was the exhaust and how much was the decat?
When you change 2 things at once its hard to know which has had the more significant effect, so its a fundamentally flawed experiment.
 
Chip-mk1 said:
All this talk of "spins up quicker" and "revs more freely"

are you guys talking about in neutral?

Cause if you are talking about in gear, then the ONLY way an engine will do either of those things is with a significant increase in torque at the points in the rev range that its now "spinning up quicker" or "revving more freely"
So to say it does those things but doesnt increase power is a bit of a contradiction.
All sounds like a load of nonsense to me as a placebo effect you are thinking that you can feel brought on by a change in engine sound.
Click to expand...

Your removing a restriction not buring more air and fuel
 
Andyman said:
Your removing a restriction not buring more air and fuel
Click to expand...

And what does removing that restriction do exactly?

Do you think you are gaining power purely from reduced pumping losses in the engine?
Cause if so then seriously people need their heads read thinking thats going to make 5-10bhp of difference! 0.05 maybe, lol

The reason that removing an exhaust restriction works to gain power, is that it reduces the EBP, and then because of the reduced EBP the cylinder pressures near to TDC and EBP stay further away from equilibrium which means that as a result the engine manages to empty the cylinder better, then because it has emptied the cylinder better it means that on the next intake stroke it does a better job of filling the cylinder with fresh intake charge, which means it swallows more fuel and air.

Try and think through the WHOLE combustion process, not just look at one part of it or you'll just keep making schoolboy errors mate.
 
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