340 headers VF2

[Paulie81]

im thinking of doing this myself. Aside from the 340 headers and cats, what do I need? Does it make sense to add the HSV centre pipe as well?

 

[Rikster71]

im thinking of doing this myself. Aside from the 340 headers and cats, what do I need? Does it make sense to add the HSV centre pipe as well?

I think so just need to make sure you get the 2.5" centre pipe, there seems to have been a 2.25 centre pipe early on. Biggest issue will be finding the header and cat which is what I am finding and everyone has said.

 

[Nico36]

Hey Nico, just catching up on all these posts, great result, which cats did you use, an also what 2.5 mid section did you use, and im guessing that was into the standard bimodal cans

Hey mate, I used the stock standard HSV cats that came with the headers. The 2.5 mid section was from planet parts, bolts in and out very worth it. Correct mate straight to the stock bimodal mufflers. I also got walkinshaw 3.5" tips welded on to keep that oem look but without the price tag!

 

[Nico36]

Alright guys, I want to go down the path of cam now that I'm over the 385 package. If I go down this route would I need to re-do the exhaust again? or would new extractors/ high flow cats combined with the 2.5" HSV centre/ bimodals suffice? I do love the sound of xforce but everyone says its drony AF, and Im not about the drone life!

 

[Nico36]

Im assuming it would sound similar to this (probably louder with the 2.5" section and the extractors/ cats if got them)

 

[Nico36]

At this stage im looking at getting the rex (gm Motorsport) 1 3/4 headers with 3" cats to the 2.5" exhaust? Would that be an issue bolting it up going two difference sizes? My plan is later down the track if the 2.5" HSV system sounds **** then upgrade it to a 3" aftermarket so I would prefer to get a 3" cat now and tuned if that makes sense? Please I need some clarification as this is doing my head in lol

 

[paulgar]

I know the threads a bit old but....
Would there be any benefit/drawbacks of matching the HSV 340 (2½) headers with the stock (2¼) midsection in preference to the gts 2½ midsection?
It has been said a few times on this forum that most of the exhaust gains are from the headers and cats.
What about the HSV 325 (2¼) headers and stock midsection? Aren't the narrower pipes meant to keep the torque higher in the lower rev range, better for daily driving?
Any suggestions would be appreciated.

 

[paulgar]

‘Bullet cats’ by themselves are $125-$150 each x2 so yeah around $550 the pair ready-made is OK.
View attachment 198433
Dimensionally if you have the 340 set with 2 1/2” outlet at the merge then may as well stick to a 6100+ top end tuning target for max HP. 3” downpipe is just too big for this engine.
Otherwise the 2.25” outlet of R8 is better TQ/HP balance for everyday, matched with 2” downpipe gets you more torque 95% of the driving time.
The main thing is space restriction longitudinally to the stock catback flange location of course. Ideally you want the length of downpipe 9” measured along the centreline before entry to cat. The HM (left), HSV (right) are easy cos bolt-on ready-made but downpipe is way short:
View attachment 198428 View attachment 198432
So grafting the required mandrel bend moves HSV cat all the way rear, then just flange your cat’s butt
As you’re taking a hacksaw to it could do same with Holden VF cats (below), doesn’t matter.
View attachment 198436
Can hardly see down there, stainless won’t stay shiny at cat temps, silly to waste money on shiny branded stuff that is technically incorrect.
Deng Xiaoping famously said that it doesn't matter if a cat is black or white so long as it catches mice, here doesn’t matter which (bullet) cat as long as it has a 200+ cpi steel substrate.
Short fat barrel cat is better than long skinny for fit and theory, possibly not emissions.

If you are still monitoring this thread, are you saying that HSV 2¼ headers would be better for most daily driving? and stock midsection vs 2.5?
Thank you.

 

[426Cuda]

If you are still monitoring this thread, are you saying that HSV 2¼ headers would be better for most daily driving? and stock midsection vs 2.5?
Thank you.

The 340's and 2.5" will make a bit more peak torque and power. But the difference will be negligible and both are great for daily driving.

 

[paulgar]

The 340's and 2.5" will make a bit more peak torque and power. But the difference will be negligible and both are great for daily driving.

Thanks for the info.