What Difference (Kw) Is A Cat Back Exhaust Really Going To Make?

[dragonf6]

I've got a fg f6 currently with a 4" dump, outlaw high flow cat, standard exhaust from cat back and VCM HP tune running 11 psi. It's running around 300 - 310rwkw at the moment. After much research on this site and asking lots of questions it's going in for a process west stage 2 intercooler & retune shortly, as that's probably the best bang for the buck.

I'm not chasing big numbers, probably around 330 - 340rwkw.

My questions:

1. With the above parts, is there a real/genuine need to put a cat back system on the car & what kw gain will that actually have verses leaving the exhaust standard from cat back? (will it make adiffernce at all)

2. If I go for a cat back exhaust I thought a mild steel twin 2.5 as don't want any drone or noise or perhaps a 3.5 single. Thoughts? (mild steel because I'm turning the car over in 3 years)

Out of interest, this is what's been quoted: :

$2200.00 fitted for the stage 2 PW IC.

$600.00 for the retunetune (vcm hp)

Varying numbers on exhaust: 1. $2100 for 3.5 single custom SS cat back exhaust, 2. $795 for mild steel twin, 3. $900 for mild steel twin, 4. $1200 for 3.5 single Xforce - which to go for if I go that way?

injectors (If there's a need) - buy from ebay & local mechanic will fit for $100.00. Tuners quoted $800.00 for this - go figure?

Any comments thoughts on my questions would be appreciated.

[Wenier]

Doing the catback will allow the exhaust to flow easier which could in turn give you the power you want at a lower boost, or more power at the same boost. As for what to get everyone has different wants, I have stainless steel dump connected to mild steel catback and really like the noise it does have when booting it, general driving you can still sneak round.

[Gasman]

I would guess the $800 price tag for injectors includes a dyno tune. Not sure if Larger injectors are "plug & play" ?

[Henz]

for 330-340 you don't need it, but at my level its worth about 40rwkw if I upgrade the catback.

[dragonf6]

How is a cat back exhaust, regardless of configeration, 3.5 single or 2.5 twin etc etc, going to add 40kw? I thought that other peformance add ons like intercooler, dump pipe, cat, tune and turbo psi that make the most gains kw wise.

Of course everyhing works together.

There are cars on here runing relatively high rwkw's with standard cat back exhausts. I thought I could do the same and that an exhaust, kw wise, would add modest gains to the existing rwkw.

Anyone know what kw gains a cat back exhaust on it's own will actually add?

Thoughts?

Oops, the $895 quotes for injectors actually was for purchase and fitting only. Tune was extra.

[Henz]

Because I have done pretty much everything else, the catback is that much of a restriction that it is holding it back. When I do the catback it should go from 360 to wherever the turbo max's out, hopefully 400.

On its own without a tune there wouldnt be much of a gain, maybe 10kw?

[Lazz1007]

I just recently bought a 2008 fg turbo. I drove out of the dealership and drove straight to Genie exhaust and Dyno, in Perth WA. They fitted a 2.5 inch X force, stainless cat back exhaust and K@N panel filter.It was dyno'd @ 264 rwks and 355 rwhp. Due to a double booking they couldnt do a pre fitment dyno unless I re booked for another day. So, I said fu$k it, and just do the final dyno and see where I stand " I didnt want to wait". Going by what most people say, the fg xr6t puts out about 220 to 240 rwks stock standard. So...... I reckon that's a pretty good result for a non tuned car.

[riptide]

Non tuned? So you upgraded the exhaust without a tune and made good gains? If that's the case does it mean the engine is getting more air so running leaner?

Just wondering because I upgraded my exhaust recently and was told not to go hard for long periods until it was tuned.

[MurdoK]

^^^I think with standard FG dump and cat still in place it would be fine. Stock restrictive cat would help prevent overboosting and wont mess the ECU around thinking it needs to lean out to meet emissions.

[sexual harrassment panda]

How is a cat back exhaust, regardless of configeration, 3.5 single or 2.5 twin etc etc, going to add 40kw? I thought that other peformance add ons like intercooler, dump pipe, cat, tune and turbo psi that make the most gains kw wise.

There are cars on here runing relatively high rwkw's with standard cat back exhausts. I thought I could do the same and that an exhaust, kw wise, would add modest gains to the existing rwkw.

The most restrictive link in the whole system is what will net you the most gains. For example if you have a bog stock BF.

1st thing holding it back it the tune, but if you just tune it then the 2nd thing holding it back would be injectors, change them and retune and it will be your cat convertor or fuel pump or standard intercooler, change them and it just shifts it to another link in the system.

If you look at henz's sig than he's got a lot of supporting mods, debatable on if just a good 3.5 - 4" system would net him 398rwkw but the stock cat back would definetly be the restriction in his system.