TWIN 2 1/2 EXHAUST SYSTEM V's SINGLE 3 INCH ON A V8

[Not_An_Abba_Fan]

With the way the LSx heads flow and where they make their torque, I wouldn't fit a 3" single on one because you will be creating too much back pressure. Twin 2 1/2" at a minimum if you are not planning to cam it.

Single 3" has an internal area of ~12 773 sq mm, and twin 2 1/2" has ~17 392 sq mm. The flow charactersitics of the exhaust single versus twin is completely different though, so you can't just compare volume. With a single exhaust you are pushing 8 cylinders worth of exhaust gas through a single pipe, and with twin you are only pushing 4 cylinders through each. The pulses are further apart in a twin than single too, so the scavenging effect is different also.

 

[Rob_VT]

listen to not an abba fan..... knows his ****.
And he probably is one of the only other people here that could explain what a reynolds number is.
depending on your flow rate, a rough surface can give you better (turbulent) flow than a polished pipe of equal size and fluid pressure etc but this changes as your variables do...
So really, theres no point asking performance questions like this (unless your chasing numbers on a dyno)..... as long as its not too big or too small and is mandrel bent, just about every system will be better than stock. Go for note..

 

[petern64]

I ended up putting on a set Geniie Try Y's ,a pair of 2 1/2" Magnaflow cats and a 2 1/2" twin mild steel mandrel bent Redback exhaust system with the rear resonator, car sounds great and revs a lot freer,only other mod is an SS inductions CIA, but I get the powertrain alert , I've been told it's the after cat oxy sensors, looking at getting a tune or something to get rid of the alert ,need to sort it soon,any advise appreciated,

 

[Not_An_Abba_Fan]

The Reynolds number doesn't really apply to exhaust gas as the velocity, density and temperature are too variable and change with engine revs. The problem with exhaust systems is that a compromise has to be had for street use. What works well at 2000rpm will not work effectively at 5000rpm. So what exhaust manufacturers do is make what works at the engines maximum output and make it sound good. I would need two pages to expalin everything, but in laymans terms, pretty much do waht Rob_VT says and pick something that sounds good, as it won't really make that much difference to power unless you spend a decent amount on the engine.

As far as the engine light is concerned, the VZ 6.0L has two issues, one, the after cat sensors not reading the factory paramater O2 levels, and the common thing on all cars when fitting extractors, is the paint on them contaminating all the sensors when it burns off. New front sensors after about 3-4 weeks and a tune to switch off the rear sensors will fix it.

 

[petern64]

Thanks NAAF,I'm thinking thats the way to go, I'll do the changes ,I'll let all know how it turns out .

Pete

 

[lambsblood]

if you have a 5.0 ltr and going straight through tail pipe a single 3" is the go dual 2 1/2 are to big and make horrible
drones at 1500 rpm

 

[VESSVBLACK]

I had a over 3 years ago, had a LS3 swap into my then VTII HSV GTS---Formerly a C4B LS1 Engine. Mods to car when the LS3 went in was 90mm TB, Alloy VCM OTR, Pacemaker 1 3/4 headers hi flo cats and a xforce 3'' s/s catback, and maffless tune.
From driving the car everyday and having a few different catbacks on the car, im in a position to comment, rather than some know all who thinks they can do a few mathematical sums and say get that.. utter rubbish.
I had on the car whilst I owned it with the LS3
3'' Diffillipo catback
3'' XForce s/s and m/s catbacK. Remus 2.5'' Catback. and finally a SINGLE 3'' Caback YES A SINGLE 3'' WOW

Let me say the car went as hard and sounded nicer than any of those twin 3'' systems mentioned with the Single 3'' catback which is good for 500 horsepower....

 

[st3r3otyp3]

Lol single 3 inch will flow 500-600fwhp, twin 2.5 inch/3.5 single 700-800 fwhp and twin 3 inch 1000-1200 fwhp.

 

[senatorsignature1]

I have 3.5" single Sureflo cat back with Di Filippo 4 into 1 Extractors and 3" Hi-Flow Cats on my VY Berlina 5.7 Litre Auto and it sounds awesome, I have the quiet system but it also comes in medium and loud.

Had it Mafless tuned and is producing 235rwkw

Check out Youtube link below of a VY SV8 with the loud system.

https://www.youtube.com/watch?v=_a4Qnb2iHz4

 

[petern64]

I've seen plenty of big horse power racings with single exhaust !