Exhaust Diameter - Why 2.5 inch?

[RichCup]

I thought that 2" was good for about 190bhp before it came restrictive and that you'd need about 220bhp to warrant a 2.5" exhaust? If you were only running 190ish bhp wouldn't 2.25" be better? Surely a slightly smaller diameter is better than a bit bigger due to back pressure etc?

Probably talking rubbish but it was just a thought...

 

[davM]

Lol here we go again

When I got my exhaust done at AAS, I asked the guy about this and he really knows his stuff. He said it has been tried and tested that 2.25 bore is the best for performance on a 180ish bhp car. Then went on about another RS that they had dyno'd and the 2.25 came out tops.

Cant see much difference between the two tbh, although 2.5 will be louder.

 

[ben_p]

back pressure is a bit of a myth, pulse timing is where its at! most of the high power N/A clios run 2.5"

 

[RichCup]

back pressure is a bit of a myth, pulse timing is where its at! most of the high power N/A clios run 2.5"

Meaning heavily modded I take it rather than because of the exhaust lol?

If I was only going as far as breathing mods (inc matched inlets) and remap would I be better off with something like 2.25?

 

[172bagss2]

Me ever calling Baggers back is a bit of a myth, ignoring the poor bugger is where its at! tbh his 2.5" girth is pretty impressive though

 

[bmh.01]

Unless your mega tuned clio wise its all much of a muchness as you'll not be a big gain from either, 2.25" is too quiet imo but its horses for courses.

Also I wouldn't say you can just stick a horsepower figure on an exhaust size as i'd think its all down to the engine that the exhaust is being stuck to and how its designed and how it makes its power. The miltek i've got on the meggy is a 3" system and the standard one wasn't much smaller either.

 

[RichCup]

Well if the standard system is 2", surely for a slight increase in power a slightly bigger exhaust (i.e. no bigger than 2.25") would be ideal? Renault can't have got it that far off with the standard system.

 

[bmh.01]

You'd be surprised they've done far worse lol, basically unless your going for mega power you go for what you want. Most aftermarket systems are 2.5" I believe, i've heard a 2.25" Janspeed and its hardly any louder than standard.

 

[Black_clio]

have 2.25 janspeed on mine with sports cat and took off resonator box and fabricated new pipe .... its loud believe me lol

 

[Gaz_]

Imo the Renault exhaust (although made from kitkat wrappers!) is bang on. You never see big gains with aftermarket systems, so that must tell you something imo.......

 

[SBV116]

Me ever calling Baggers back is a bit of a myth, ignoring the poor bugger is where its at! tbh his 2.5" girth is pretty impressive though

I actually lol'd!