340 headers VF2

[Nico36]

Awesome! Did you use the HSV cats aswell or go with 200 cell hiflow replacement? Apparently some good gains to be had in replacing the HSV cats too.

Yea just used the HSV cats that came with the headers. There may be but I couldn't imagine it would be much of an increase.

 

[Nico36]

Great result. Without the WP price too!

Yes absolutely, considering I paid about 2000 all up for eveything! Considering WP quoted me 7000 for the 375 lol !

 

[arronm]

I have been advised that stock cats are good for under 400rwhp (300rwkw).

 

[monstar]

most of the hsv headers i see with cats are sold advertised with no size of exit flange pipe size, 340kw are 2 1/2inch what size are the other hsv header pipes 2 1/4 inch ?
is there any difference between 325kw hsv headers to 340kw hsv headers power wise
everyone seems to only talk of the larger 340 ones
for street traffic light drags would i notice much difference between the two
or is it just you can pick them up for the the same price, might as well get the 340kw ones

Yes 2.25" is standard for the HM exit ID.
Whether you notice the difference depends on the tuning as most tunes are not really customised to the setup. What you notice is the trade-off 90% of the driving time when you want torque but seems less (doughy, laggy) when tuned for the larger diameter to make peak power up top. So to be clear you don't hardly feel 10-20 fwkw (15rwkw) screaming its tits off up top, but you certainly miss the wider torque spread that comes with higher velocity and scavenging low to mid.
FWIW I've never been an advocate for larger diameter short throw headers on our car, I did some calcs then dyno trials took the choke off using varying diameter (hence tuning velocity) of the stock downpipe just after the header flange: 2.25" is ideal for HP and TQ balance with a (near) stock engine.
The two tonne wagon (all variants really), gear ratios, V8 and chassis character all responds better to more torque than unproductive screaming HP.
Unfortunately for most owners (at least on Facebook) there is one number to describe all the detailed facets of engineering and factors affecting state of tune, that being (estimated) peak engine power.
BTW I posted results of investigation into LS3 pipe lengths and diameters using PipeMax and Engine Analyser Pro somewhere here will link if I can.
In other words yes there is a trade-off to get more peak power.

 

[426Cuda]

Yes 2.25" is standard for the HM exit ID.
Whether you notice the difference depends on the tuning as most tunes are not really customised to the setup. What you notice is the trade-off 90% of the driving time when you want torque but seems less (doughy, laggy) when tuned for the larger diameter to make peak power up top. So to be clear you don't hardly feel 10-20 fwkw (15rwkw) screaming its tits off up top, but you certainly miss the wider torque spread that comes with higher velocity and scavenging low to mid.
FWIW I've never been an advocate for larger diameter short throw headers on our car, I did some calcs then dyno trials took the choke off using varying diameter (hence tuning velocity) of the stock downpipe just after the header flange: 2.25" is ideal for HP and TQ balance with a (near) stock engine.
The two tonne wagon (all variants really), gear ratios, V8 and chassis character all responds better to more torque than unproductive screaming HP.
Unfortunately for most owners (at least on Facebook) there is one number to describe all the detailed facets of engineering and factors affecting state of tune, that being (estimated) peak engine power.
BTW I posted results of investigation into LS3 pipe lengths and diameters using PipeMax and Engine Analyser Pro somewhere here will link if I can.
In other words yes there is a trade-off to get more peak power.

Thanks Monstar. A view of both curves would be great if you have them?

 

[VF_CalaisV]

most of the hsv headers i see with cats are sold advertised with no size of exit flange pipe size, 340kw are 2 1/2inch what size are the other hsv header pipes 2 1/4 inch ?
is there any difference between 325kw hsv headers to 340kw hsv headers power wise
everyone seems to only talk of the larger 340 ones
for street traffic light drags would i notice much difference between the two
or is it just you can pick them up for the the same price, might as well get the 340kw ones

The difference between them is only somewhere between 5 and 10kw. The other power increase to get up to the 340 mark was from using the supercharged airbox. From what I understand there is no tune difference betwen the 317kw and the 340kw its just part swapping. I am slightly porting my clubsport 2.25" headers. You can open it up a bit at the collector maybe about 3mm increase in diameter. Also at the top of the entry to the header runners there are half ground off welds from the flange welding. I am grinding the rest of the internal parts of the weld off to make it smooth at the top of the runners. Should help the flow a little. I will then use a 2.5" dia bend into a set of VFii cats and a 3" out to suit the catback that came with my car. I'll hopefully eventually get a dyno run and give the results.
Its just hard to find some cheap VFii cats..

 

[kleanphil]

Its just hard to find some cheap VFii cats..

I've got a pair for sale , what do you call cheap ?

 

[.05]

The difference between them is only somewhere between 5 and 10kw. The other power increase to get up to the 340 mark was from using the supercharged airbox. From what I understand there is no tune difference betwen the 317kw and the 340kw its just part swapping. I am slightly porting my clubsport 2.25" headers. You can open it up a bit at the collector maybe about 3mm increase in diameter. Also at the top of the entry to the header runners there are half ground off welds from the flange welding. I am grinding the rest of the internal parts of the weld off to make it smooth at the top of the runners. Should help the flow a little. I will then use a 2.5" dia bend into a set of VFii cats and a 3" out to suit the catback that came with my car. I'll hopefully eventually get a dyno run and give the results.
Its just hard to find some cheap VFii cats..

thanks for the info , i wondered the difference in power output between 317,325,340kw headers and engines tune ect
i will be fitting some pacemaker 5377 headers i think there hsv340kw clones and will be making up some 200cel cats with smooth pipe bends to cats and hsv 2.5 cat back with stock bimodal mufflers and rotafab air box
its my misses car shes a traffic light bandit so its just for a bit more squirt for her
when i,m making up the short cat pipes i dont want to fry the computer , damage anything when doing tack welds under the car
anyone have any advice on what to do , i have always tack welded on older cars with battery connected before and never had a problem
i don't want to stuff it up or i will be in big trouble

 

[VF_CalaisV]

Just an update on the size for the smaller collector (VE) version. There is really 3 dimensions to measure:
1) Pipe inside diameter, this is only a mm or two over 2"
2) Flange inner step diameter, this is 2,1/4 "
3) Flange surface(mating to cat flange) inner diameter is 2,1/2"

I measured the outer diameter of the pipe going into the flange as 60mm
So when porting the inside of the pipe and step I will go up to about 2,1/8" inner diameter and flare out to the step at 2,1/4"

It would be interesting to know those dimensions for the so called 2,1/2" 340kW collectors.

 

[426Cuda]

Aftet having fitted the Roto-Fab CAI, and previously a Gen-f2 2.5" centre section I'm about to book my Motorsport in for a tune at Gentech in Canberra. At the same time, I will have the 340 headers fitted.
So, my questions are about the cats. I understand the VF2 cats are 400cell? But, it appears they flow quite well up to beyond 300rwkw, which is my upper target. I like the look of the stock cats and would.like to retain them if I can. Has anyone used these with the HSV 340 headers and if so, what were your results? What mods were required to fit them to the HSV headers?
Any advice appreciated.
Thanks all.