V8 Exhaust

[Mont5.0]

morning All,
Replacing Exhaust on fairmont, which would be better twin cat back all the way, or a cat back, "y" into single all the way. Any one found any noticable gains from either design, its for V8. Not looking for too noisey.
Cheers.

[WoodysXR6]

Not sure about the montys but my xr8 has twin cats standard which i will be replacing very soon with high flow, couldn't say about any power gains.

[Mont5.0]

yeah its not the cats, the design of exhaust from there back!

[WoodysXR6]

yeah sorry mine are
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Thats a twin mandrel it flows very nicely, If that makes sense

[Mont5.0]

so yours are twins all the way,as mine ends in a single pipe.

[WoodysXR6]

yeap all the way

[Mont5.0]

is yours noisey?

[WoodysXR6]

Not at all, But i'm waiting on headers, it doesn't drown in the car like some i've heard.

[Fireblade]

Originally I had a single 3" cat back, it made reasonable gains but the drone was terrible.. I now have comp. headers, twin 2 1/2" high flow cats, and twin 2 1/2" high flow system with high flow mufflers.. NO DRONE which is great and the gains were incredible.. First dyno done I made 127.6rwkw with TS50 intake, K&N and catback 3", Second dyno netted 155.7rwkw with SS CAI, K&N and full zorst so I made some great gains from the zorst then made 169.3rwkw with the flash tune. IMO go for full header back twin system you won't regret it..

[WoodysXR6]

Originally Posted by GR8WITE

Originally I had a single 3" cat back, it made reasonable gains but the drone was terrible.. I now have comp. headers, twin 2 1/2" high flow cats, and twin 2 1/2" high flow system with high flow mufflers.. NO DRONE which is great and the gains were incredible.. First dyno done I made 127.6rwkw with TS50 intake, K&N and catback 3", Second dyno netted 155.7rwkw with SS CAI, K&N and full zorst so I made some great gains from the zorst then made 169.3rwkw with the flash tune. IMO go for full header back twin system you won't regret it..

Thats quiet a good gain there!

[Mont5.0]

yeah, mine is auto- so i am looking for something that isnt to loud at idle or under 2000rpm. if its loud after that no problems, but something thats loud and droany aint really what i am after, as i use motorway 99% of the time .

[Mont5.0]

cheers for that.

[Fireblade]

no problemo, my exhaust was the most favourite bit on my car until I got my F6 19" but I still love it.. I credit the exhaust with all the gains made on my car so you might as well do it right the first time I say..

[Mont5.0]

agreed. so 21/2" pipes and cats etc.

[Fireblade]

I have PH4006's, twin 2.5" cats, twin 2.5" mufflers and 2.5" piping all the way through topped off with twin 3" tips..

[galaxy xr8]

How about a factory exhaust from an AUII XR8, vertually brand new, I have mine sitting in the shed looking for a new home.

[HLC]

wont fit Mont5.0's car, as his fairmont is live axle.

twin 2.5" system from the cats back Heath. cant go wrong.

had a 3" on my dads old EL 5L. sounded grouse but it did drone a bit.

[b2tf]

Ill go against the grain a bit here and ask you first what are your plans for the car? If you just want a nice cruiser then a 3" off the shelf system may suit your needs and they're quite easily had - and relatively cheap too.

If however you want to get a bit more go out of it and are happy to spend a bit more money on it, then yes go a twin system. On a stock engine I would suggest a twin system may actually lose you a bit of power but on a worked one it is a must.

[WoodysXR6]

If however you want to get a bit more go out of it and are happy to spend a bit more money on it, then yes go a twin system. On a stock engine I would suggest a twin system may actually lose you a bit of power but on a worked one it is a must.[/QUOTE]

Thats a big call right their!

Not trying to have a dig at you lol, just come across wrong after i read it lol.

[Fireblade]

Originally Posted by b2tf

On a stock engine I would suggest a twin system may actually lose you a bit of power but on a worked one it is a must.

A 2.5" twin is probably a good size for good gains from a stocker but big enough for future mods too... now a twin 3" is probably going too big for a stocker as well as having size fitment issues with an AU

[5.0 ED]

I just went from a single mandrel bent 3inch system with straight thru mufflers to a twin 2.5inch, and it has picked up a lot of extra power, it sounds heaps better, and no drone at 100, actually cant even hear it, with 3inch annoying drone. Yet to fix the tune, but it is already up 10kw's at the tyres from 170rwkw, did 180 with twin and same cats/headers and was running lean/low fuel pressure, now i with pacey's as well so can't really compare anymore.

[5.0 ED]

A twin 3inch is going pretty overbored IMO, unless your planning 600hp+

[b2tf]

Twin 3" will have your plumber wondering where your downpipes went

[Mont5.0]

yeah twin system sounds the go. If the only diffrence between mine and a series1 XR8 (175 V 185kw) is the induction and exhaust, then would putting a twin system on pick up these extra kw's? I already have extractors fitted and run a K'N'N panel filter, just looking for a larger intake snorkel (xr6T?)

[b2tf]

Originally Posted by Mont5.0

yeah twin system sounds the go. If the only diffrence between mine and a series1 XR8 (175 V 185kw) is the induction and exhaust, then would putting a twin system on pick up these extra kw's? I already have extractors fitted and run a K'N'N panel filter, just looking for a larger intake snorkel (xr6T?)

well it definitely wouldnt hurt, put it that way. the biggest issue is the stock headers - they are 90% of the problem straight away but i see you have extractors on so you've overcome that.

[5L]

definately go a twin, when i first got my exhaust the exhaust place stuffed up, and put a twin 2.25" into a single 2.5" and it droned really really bad and didnt sound very nice for a v8 sort of sound.

so i took it back and got what i paid for twin 2.5"system, now it doesnt drone at highway speeds but you can notice a nice v8 rumble, and at full throttle it sound insance. i even get all the holden boys giving me thumbs up and have had many of them asking what mufflers and stuff im using because that is how they want there car sounding.

[MRJUCY]

Twin all the way is the only way to go on a V8, a single will never sound right.

[Sox]

I reckon twin 2.25" is the go on these 5L's, particularly if they're pretty standard.
Unless you're spinning them over 7000rpm, and making over 400hp, anything bigger is a not needed and leads to potential droning.

Mont5.0, did you contact Bruce?

[Fireblade]

Originally Posted by Sox

I reckon twin 2.25" is the go on these 5L's, particularly if they're pretty standard.
Unless you're spinning them over 7000rpm, and making over 400hp, anything bigger is a not needed and leads to potential droning.

Got no drone out of my 2.5" twin, I put a twin 2.5" on thinking of the future mods I will do so I don't have to replace the exhaust twice because decent twin setups from extractors back cost a lot of $$$$

[Sox]

Originally Posted by GR8WITE

Got no drone out of my 2.5" twin, I put a twin 2.5" on thinking of the future mods I will do so I don't have to replace the exhaust twice because decent twin setups from extractors back cost a lot of $$$$

Your're lucky, many dual 2.5" systems drone to buggery.
Dual 2.25" pipes actually flow over 900cfm.
Considering a 70mm T/B flows approx 700cfm, the dual 2.25 pipes are actually way over the ~75% intake to exhaust ratio required for good performance.

A 5L even revving to 8000rpm only requires 700cfm of intake, and that's based on 100%VE.

In other words, a dual 2.25 system is more than capable of providing a restriction free exhaust for any N/A street car.

The muffler quality is far far more important in an exhaust system.