Look at the cross sectional area

for example; two 2.5" squares have the same area (slightly larger) as a single 3.5" square.
two 3.5" squares have the same area (nearly) as a single 5" square.

hmmm... four 2.5" squares would have the same area as a single 5" square....

I used squares, not cubes, as an example because i cant remember the equation used to work out the area of a circle.

im just throwin ideas at ya

but I liken exhaust flow rates to water in a pipe and more water flows thru a larger diameter pipe.

area of 2.5" = 19.63 sq (4.43)
area of 5.0" = 78.53sq (8.86)
area of 3.5" = 38.48 sq (6.20)

Get the twin 2.5 " exhaust as it is better all round for legalities and performance. Get a set that flows too much and you lose the scavenging properties which eat into the slight performance gains. Its also a pain in the a** to after spending money on a exhaust to have to get it looked at again cos a certain Mr Plod thinks its too loud. By law (last time i checked) states that adr complient vehicles exhaust to be no louder than 90 DB at 1 meter at a 45 degree angle from the rear of the vehicle. Just ask all the corolla, excel owners who thought they'd put a milo tin on the back to make it sound "tough" ( cough cough ).

This would be an even better thread with some sound clips of your exhaust setup. Feel free to upload!



Isn't it also about air speed as well as decent airflow?

i like your idea of the sound clips Vic, so if anyone has one let us hear

well i think i've gone off the idea of hotdogs, i might just wait til i can afford a full system (which shouldnt be too long) but what to get?

mild steel vs stainless
herrod vs difilipo

any opinions or feedback from owners with either exhausts?

[quote="Vic"]Isn't it also about air speed as well as decent airflow?

Agreed, the quicker its out the better :lol:

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[quote="schnoods"]Get the twin 2.5 " exhaust as it is better all round for legalities and performance. Get a set that flows too much and you lose the scavenging properties which eat into the slight performance gains. Its also a pain in the a** to after spending money on a exhaust to have to get it looked at again cos a certain Mr Plod thinks its too loud. By law (last time i checked) states that adr complient vehicles exhaust to be no louder than 90 DB at 1 meter at a 45 degree angle from the rear of the vehicle. Just ask all the corolla, excel owners who thought they'd put a milo tin on the back to make it sound "tough" ( cough cough ). "

Agreed 2.5" for most,

With the performance, I disagree with any power loss with big pipes, I had only noticable gains throughout the rev range and whilst I agree that 3" may be slightl overkill and cross pipes etc make a difference in performance results I dont believe you would notice it much at all once you alrerady had the big pipes, though in saying that I will consider them when my new pipes are made.

look at the manta range i run one on my xr8 and it souonds very nice twin 2.5" cat back didnt want it to loud as mr plod starts lookn a set of hi flo cats will make the beast sound and perform better as well

i think twin 2.5" is the way im gonna go... looks better too

is it worth getting stainless?

I went stainless on my XF 6 and its a waste of money. With an 8 theres even more of a waste of money going stainless especially if you run twins the whole way.

why's that? i've always been told "get stainless, better sound, last longer" and that crap

Last longer but that's about it. Have no idea where they pull sound from unless they are audiophiles.

anyone else got any comments about stainless?

waste of money ask the same question when i had mine done bloke said if you want it to last longer then spend the money theres no difference in performance or sound otherwise

don't get stainless.........i don't think its worth it. spend the rest of the money u save on the blower ....dw i won't tell es about it

hahahaha ye the blowers a long way off there phong

just a thought, is it legal to put side exhaust like the v8 supercars?