Best Bore Diameter for Performance?

[Spykee]

hi all,

i have been reading through the forum for a bit now after purchasing my lovely 172 Cup on the weekend and have not been able to find any information on the most effective bore size to go for on an exhaust system.

im after something that obviously keeps enough back pressure so that power isnt sapped from the engine but also one that wont be restriceted if i choose to get the power above 200bhp.

from previous cars that i have owned with this sort of engine size im guessing about 2.5" is the most appropriate? is this right or can you go bigger?

im also after an exhaust that is a bit different to a mongoose or magnex system, im liking the look of the supersprint or the one on yozzasport, about a 2.5 to 3" tail pipe but was wondering how deafening it would be with an un-silenced mid section?

any opinions or recommendations, even sound clips would be appreciated!

thanks,

Alex

 

[thedoc]

I'm sure I've read somewhere 67mm is the optimum...

 

[sh33n]

67mm, isn't the exact bore of the supersprint system? The one that makes peoples ears bleed?

 

[David_Snaresbrook]

If you cant get a supersprint for the 172 anywhere, then from what i've heard it will be stupidly loud.

 

[Spykee]

supersprint do a 63.5 and a 70mm system from what i have found out so far....... dont want ears bleeding though but dont mind loud! Sh33n's magnex is too quiet for me with a silenced mid section :rasp:

 

[ben_p]

lol supersprint is foooooooooooking loud!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[u33db]

Backpressure is mainly defined by the manifold...you could weld a wheelie bin on the back of the car and performance won't be degraded. Just get a system with no silencers other than the rear box.

 

[The Hoff]

Around 60mm i think was the best diameter from concensus, go down to prospeed in cardiff and charlie will knock you up whatever you want, and you can even customise how loud you'd like it, fitted for about £270.

 

[ant]

my blueflame sounds nice, very deep rumble to it - think subaru.

 

[haitch]

to match other mods (eg 200bhp+) 2.5" minimum, if you can handle the noise 3" is ideal.

 

[Neil G]

3 is definately only for heavily tuned cars....big bore isn't necessarily the best route for mildly modified cars....may find back flow going on

 

[Spykee]

cheers for the replies guys,

i will probably tune it to around 200bhp ish tops, looking at getting some cams and the omex 600 ECU or equivalent at some stage but i dont want to have to change the exhaust to accommodate...

does anyone have the race system from Yozzasport? that looks prety nice and there are plenty of options, ie. with/without b pipe silencer.

otherwise any other recommendations?

 

[wide]

2.5" bore is optimum for standard to well modified, if its going to be really modified you could go upto 2.75", but that'll be seriously loud lol

 

[lawrence]

the supersprint i had is 63.5mm and was very loud but i loved it, ask run115 if he has any soundclips, all i have is this http://media.putfile.com/watchthisdad58, from what yozza has told me their system is based on the supersprint and to me sounds exactly the same

 

[Spykee]

the supersprint i had is 63.5mm and was very loud but i loved it, ask run115 if he has any soundclips, all i have is this http://media.putfile.com/watchthisdad58, from what yozza has told me their system is based on the supersprint and to me sounds exactly the same

thats great, thanks lawrence!

how much did you pay for it and where did you get it from?

sounds bloody loud, wondering if the cops would pull me for it?! :evil:

 

[Spykee]

lol supersprint is foooooooooooking loud!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Ben, my Corrado G60 is fookin loud so im pretty used to lots of noise, it sounds like a V8 drag car with a gear drive!

also heard the supersprint on a Civic Type R when i had one of those and it was loud but not stupid comparred to some of the systems you could get for it like the Tanabe SuperMedallion or the GReddy Evo! lol

Alex

 

[lawrence]

thats great, thanks lawrence!

how much did you pay for it and where did you get it from?

sounds bloody loud, wondering if the cops would pull me for it?! :evil:

lol i never got pulled once, but just got the occasional glare hehe,

i bought it off a guy from this forum and sold it on to run115,

 

[John DNA]

Everyone is talking about diameter, but I've yet to hear anyone mention length of pipework anywhere in relation to harmonics and exhaust gas scavenging.

The diameter of your exhaust will at the end of the day be a trade off, for top end bhp you want it big, for low end torque you need back pressure and a more conservative size will provide this.
however at some point between this this is a sweet spot for a set rpm where harmonics aid combustion chamber scavenging and can provide an increase in performance, this is true on both inlet and exhaust headers as you will see on some systems that have variable length intake headers, why do they need to vary in length? Well as the rpms change then so does the sweet spot for this effect change, so on a fixed length system this will again be a compromise.

 

[cK]

2.5 is adequate

 

[Neil G]

Ben, my Corrado G60 is fookin loud so im pretty used to lots of noise, it sounds like a V8 drag car with a gear drive!

also heard the supersprint on a Civic Type R when i had one of those and it was loud but not stupid comparred to some of the systems you could get for it like the Tanabe SuperMedallion or the GReddy Evo! lol

Alex

Agree....my car is silent compared to some of my friends cars.

Think the 'worst' for noise is a fully decatted Subaru running a Blitz exhaust....just deafening

 

[MarkM]

I have 2.5" on my 200bhp car the sound is fine IMO

 

[sh33n]

Have you decated or put on a sport cat Mark? Or is it standard cat?

 

[MarkM]

Have you decated or put on a sport cat Mark? Or is it standard cat?

sports cat

 

[izibizi]

Just for info:
Orbisoud gr.N: 67mm (gr.N exhaust camshaft)
Supersprint mk2: 63.5mm
Supersprint mk1: 70mm
Orbisoud 182: 60mm

And ofcourse they all use different material thickness.
I am going for custom made ss 60mm outer diameter with only 0.8mm thick walls.
I will post the results once fitted and optimised.