Exhaust diameter?

[Klutch]

I have a bog stock 12a engine, recently picked up a 3" exhaust, resonator, magnaflow muffler, no cat for cheap

I've gotten told by a few people the exhaust is too large and i'd be losing power. And others are saying i wont lose power and/or it'll just shift the rev-range up higher a bit.

i figure it has to be better than the one i have now...but yeah, people saying different things, so im a tad confused on the matter

views and opinions?

[MRO]

Too many different views and opinions on this one but i think bigger is always better. I am sure many will disagree.

Just bolt it on and rip a skid.

[Rantopotamus]

bigger = better! If 6 inch Milo tin pipes can make lancers go than im sure itll be good for yours!

[Butcher]

I was taught 1" per liter then + 1" for boost was a good basis to work on.

[Pav]

Yeah i'm in two minds about it aswell. Maybe just give an exhaust shop a call and ask for some insight?

Even if you do loose a bit of 'power' from your stock 12a. Who gives a fuck? Atleast it's gonna sound off tits! (Well better than the pea shooter). And really isn't that what driving an NA rotor is all about? The noise!?

[RICEY]

I was taught 1" per liter then + 1" for boost was a good basis to work on.

So I should have a 5.7" exhaust? LOL

[joshg123]

So I should have a 5.7" exhaust? LOL

Dont you have 2x2.5 inch pipes mounted side by side?

[RICEY]

Yes Ive come up short by .7" !!!!!!

[mc68]

I was taught 1" per liter then + 1" for boost was a good basis to work on.

those boosted ls2's must run awesome with those 7" exhausts

[Butcher]

Look at all the modified 6ltr holdens just about all of them are running a twin 3" system 2 X 3" = 6 why do you think my reasoning is fucked up

[Butcher]

those boosted ls2's must run awesome with those 7" exhausts

Nice piss take

[Tocchi]

noooooo

its not like that.

do some simple mathematics :)

pi x (radius of exhaust) ^2 = surface area of exhaust
and if its twins etc, add the multiplier to that.

much better way to work it out

[Lonewolf]

do it, rotors move a lot of air.
Came to the same issue with my car, proven to have gains going to 3" thanks to high flow and high rpm.

If your serious about making top end power (and having the porting etc to suit), then go 3". It will be farking loud however haha

[Klutch]

Yeah, i've decided to go ahead and chuck it on. Has to be better than what i've got on it now anyway haha :P

[Butcher]

Whats the official work shop methodology for working out the most appropriate size to suit application.

[mitchy]

So I should have a 5.7" exhaust? LOL

then you'd have an exhaust bigger than your dick :P



Look at all the modified 6ltr holdens just about all of them are running a twin 3" system 2 X 3" = 6 why do you think my reasoning is fucked up

fail... 2x 3" pipes is not even close to a 6" pipe.

3" = 7.07 square inches
2x 3" = 14.14 square inches

6" = 28.28 square inches

[Lonewolf]

Whats the official work shop methodology for working out the most appropriate size to suit application.

there isnt a hard and fast rule.
turbo basically bigger is better.

n/a exhaust sizing is a lot tricker, depending on the motor, power output, rpm, what headers (eg how good they merge and scavenge), length of exhaust and what mufflers are being used.

most good exhaust places will be able to make a recommendation, but may get it wrong.

[Butcher]

there isnt a hard and fast rule.
turbo basically bigger is better.

n/a exhaust sizing is a lot tricker, depending on the motor, power output, rpm, what headers (eg how good they merge and scavenge), length of exhaust and what mufflers are being used.

most good exhaust places will be able to make a recommendation, but may get it wrong.

Fair enough Thanks for the explanation, so i guess its a case of go to the exhaust shop and hope he gets it right. So theres no official formula

[Lonewolf]

im sure there are calculations that can be done to take some of the factors onboard (gas flow physics etc), but a lot will also come down to personal experience too.

[Miggy]

Every engine is different you could have one exhaust that works really well on a 2L N/A 4 pot then put the same exhaust on a different 2L N/A 4 pot from a different manufacture and you could lose power.

[RICEY]

then you'd have an exhaust bigger than your dick :P




fail... 2x 3" pipes is not even close to a 6" pipe.

3" = 7.07 square inches
2x 3" = 14.14 square inches

6" = 28.28 square inches

You do realise you just complimented me as the inch measurement of exhausts is diametre not length you clown.

[mitchy]

You do realise you just complimented me as the inch measurement of exhausts is diametre not length you clown.

oops, lol

good luck fitting it in anything :lol:

[RICEY]

Ya mum took it without any lube no probs