Does a catback exhaust add any power?

[Solone]

A friend of mine has a vx ss auto, absolutely stock standard (k&n filters only in stock airbox)
and in good condition. 144000km.

on Saturday he fitted a twin 3 inch cat back from xforce, still has standard headers and cats, standard intake (k&n only) and standard tune.

He comments that it has a heap more power. (there was nothing wrong with his stock exhaust so he is comparing to stock in good condition)

From experience on here does a cat back only add any power? Or just more noise?

I know it's a good supporting mod for a tune later or headers later etc etc but what about in isolation if there is no intention to add more mods.

The exhaust shop claimed they add 20rwkw.

[BLACK 346]

A friend of mine has a vx ss auto, absolutely stock standard (k&n filters only in stock airbox)
and in good condition. 144000km.

on Saturday he fitted a twin 3 inch cat back from xforce, still has standard headers and cats, standard intake (k&n only) and standard tune.

He comments that it has a heap more power. (there was nothing wrong with his stock exhaust so he is comparing to stock in good condition)

From experience on here does a cat back only add any power? Or just more noise?

I know it's a good supporting mod for a tune later or headers later etc etc but what about in isolation if there is no intention to add more mods.

The exhaust shop claimed they add 20rwkw.

When I took my VT2 SS in to Sams Performance for a tune back in 2003 it pulled 198rwkw with the only mod being a shitty redback catback and some dodgy airbox mods. He was surprised that it pulled such a high number. I was expecting around 170 maximum. So yes, I reckon a decent catback will make a difference on VT-VX, considering those models come with a very restrictive exhaust compared to VY and onwards.

[Toddler78]

With less restriction at both ends ie intake and exhaust the engine is more efficient at transferring air ( and fuel ) so yes more power or should I say response is going to felt. Obviously it goes without saying a touch up of the tune would unlock the full benefits of the mod


Sent from my state of the art commodore 64€

[Solone]

The week before I added full exhaust to mine, headers cats and 2.5 inch twin catback

My mate thinks that the catback gives 85% of the benefit and being a twin 3 inch will be even better up top than my setup

Sound wise they are different. Mine seems more noisy at idle, more noisy when you crack the gas but silent when cruising. His seems to get louder as he revs it but has more drone when cruising.

[whitels1ss]

The week before I added full exhaust to mine, headers cats and 2.5 inch twin catback

My mate thinks that the catback gives 85% of the benefit and being a twin 3 inch will be even better up top than my setup

Sound wise they are different. Mine seems more noisy at idle, more noisy when you crack the gas but silent when cruising. His seems to get louder as he revs it but has more drone when cruising.
What is your car buddy?
Have you compared the performance of the two cars?

[Solone]

mine is vt2 berlina and hus is vx ss.

cant really compare as mine is mafless tune and full exhaust.

he has only catback with no tune.

does anyone know what catback only would add to stock car no tune?

[whitels1ss]

The exhaust shop claimed they add 20rwkw.

I reckon that your figure would be about right for a decent twin 2.5 inch cat back system on a VT or VX buddy.
A twin 3.0 inch cat back on stock headers and cats would give no better performance than the twin 2.5inch because you still have 2.25 inch engine pipes
being restricted down to 2.0 inch inlet and outlet through the factory cats. :cheers:

[Lunchbox]

mine is vt2 berlina and hus is vx ss.

cant really compare as mine is mafless tune and full exhaust.

he has only catback with no tune.

does anyone know what catback only would add to stock car no tune?

My VX Berlina wagon went from 173 rwkw to 185 rwkw with just a twin 2.5 inch redback catback and no tune.

Cheers Lunchbox

[calais190]

I had a 2.5" KPM catback only and then a 3" KPM catback only and it 'felt' no different to stock. I didn't do any back to back dyno runs though. I think if it feels faster its because you can hear it...

[SSer]

I had a 2.5" KPM catback only and then a 3" KPM catback only and it 'felt' no different to stock. I didn't do any back to back dyno runs though. I think if it feels faster its because you can hear it...

That was my experience going from stock to 3.5" cat back only. Biggest exhaust related seat-of-the-pants gain I noticed was getting Pacemaker headers fitted, and the stock cats changed to 2.5". I didnt get dyno'd before and after for the cat back though.

[QldKev]

My VX with 2 hole mod, after market cat back twin 2.25" but restrictive rear muffler, then fitted up with full 4-1 Extractors/Cats/2.5" Cat-back, dropped 0.4sec 0-100. Driving it I though it would have been more than a sec change, good old bum dyno was too busy listening to the noise.

Be careful with some HP claims that you will be told. Often they are 'up to xx KW gain', which is their best case ever and then some b/s factored in. The best case could have been where a muffler had collapsed in the OEM system and was a restriction, hence making the prior dyno result even lower than a normal stock system. If you add up the claims for a catback, then extractors, then exhaust, then otrcai, then mafless tune they never add up the same in the real world. Don't get me wrong they all are excellent, but if you add up the claimed numbers then check real world they never match. It reminds me of the rice boy with his auto civic that has about 80kw. Then adds 20kw exhaust, another 10kw cause he change the rear muffler to a cannon, plus 25kw air pod (sucking hot air under the bonnet), vtec badge 5kw, run mobil 1 oil 10kw; and claims basically double the kw output of his engine.

QldKev

[Solone]

I would have thought that if the cats are restrictive with their little pipes what would a bigger pipe do afterwoods? not much.

If anything it would matter less the further back the restriction is as doesnt exhaust gas slow up the further it is away from the motor as they are hottest at the header (need a good flowing header) a little less hot at the cats and by the time they reach the cat back cooled off significantly and slowed up in velocity, not needing as bigger pipes to maintain flow.

so adding twin 3 inch pipes might slow the flow up more than it maintains it? (on a stock headers/cats car). maybe creating drone?

So you could slowly decrease the size of the system from headers to rear of the car to maintain the velocity?

[whitels1ss]

I would have thought that if the cats are restrictive with their little pipes what would a bigger pipe do afterwoods? not much.


A big thing in the stock (factory) cat back is that after the cats it reduces to a single 2.25 system
going through a big heavy restrictive muffler and resanator,

any twin spots cat back will help somewhat.

[whitels1ss]

so adding twin 3 inch pipes might slow the flow up more than it maintains it? (on a stock headers/cats car). maybe creating drone?



Yeah IMHO running a twin 3 inch cat back after stock manifolds, 2.25 inch engine pipes and stock cats is overkill and it often will cause drone.

[Solone]

so really its only if the stock mufflers are restrictive as the pipes wont be a restriction if the manifolds and cats are already that size to begin with.

So if looking for power output only changing the stock mufflers (assuming they are restrictive) would be as good as any catback upgrade when retaining stock manifolds/cats.

[whitels1ss]

So if looking for power output only changing the stock mufflers (assuming they are restrictive) would be as good as any catback upgrade when retaining stock manifolds/cats.

The stock system on a VX goes into a single 2.25 inch pipe fitted with a big muffler and resonator after the cats,
virtually any aftermarket twin cat back will see some flow improvement.;)

[planetdavo]

Size DOES matter...;)

[Wonky]

Size DOES matter...;)

Only to a point PD. :nyuk: Even if you only have 3" that's generally regarded as too big. :eek: (for stock)

[planetdavo]

Only to a point PD. :nyuk: Even if you only have 3" that's generally regarded as too big. :eek: (for stock)

Ha ha.
Bigger the better if you want to show it off to your mates though for a cream session...

[jaykay]

Only to a point PD. :nyuk: Even if you only have 3" that's generally regarded as too big. :eek: (for stock)

:lmao: Gaz....first time ever 3" is too big for you

[macca_779]

Does less than people think. But depends on what you start with.

My car completely stock vt HSV system upgraded to 1"3/4 pacie 4>1's. 100cpi cats. Dual 2.5 all pacemaker gear with a cam already done. 9rwkw 30nm gain. Sounds better though. And that's why you do it.

[zorro]

The placebo effect of hearing how noisy your car really should be is enough to warrant the $$$s spent. Really though to get any gain do the old PCM reset get a couple of tanks through it and then gauge on either a dyno, timed 0-100 or on the strip. By rights yes a gain is to be had, the real gain though needs to be measured before & after

[seedyrom]

Only to a point PD. :nyuk: Even if you only have 3" that's generally regarded as too big. :eek: (for stock)


:lmao: Gaz....first time ever 3" is too big for you
Well he IS talking diameter