New Headers Advice

[Mavericks Choice]

would you fit chinese parts to your aussie commodore , stay away from them

You do understand majority of VE & VF Commodores were built with Chinese parts! Right down to the ally wheels!!

 

[.05]

I'm not so sure they are Chinese, how do you know they are?
https://empireperformance.com.au/collections/holden-headers

ask them seller where there made chinese junk, plenty of horror stories about those , stay away,

 

[Milo 6.0]

The factory cats are the most restrictive part of the exhaust, if you can get some hsv tri ys with some 200 cells custom made you'd be good to go, I always see headers and full systems on faceback marketplace, there was a full difilippo system I saw the other day for $2500, that would be my pick.

People think the factory the cats are restrictive but they arent,compared to a high flow cat yes they are slightly more restrictive in comparison,tbh high flow cats do more for noise than hp.
The rear mufflers are the most restrictive part of the stock exhaust by a long way,they are reverse flow and designed to cancel out most of the noise and also seriously restrict flow in the process,second to that is the 40mm bottle necks in the flex joint before the rear mufflers.
I dont know why people think the cats are a major restriction because they arent.
Its obvious to see if you have a good look at a vf stock exhaust.

 

[Mattricho]

I forgot about the flex joint necking down to about 2inch if not more.

 

[426Cuda]

People think the factory the cats are restrictive but they arent,compared to a high flow cat yes they are slightly more restrictive in comparison,tbh high flow cats do more for noise than hp.
The rear mufflers are the most restrictive part of the stock exhaust by a long way,they are reverse flow and designed to cancel out most of the noise and also seriously restrict flow in the process,second to that is the 40mm bottle necks in the flex joint before the rear mufflers.
I dont know why people think the cats are a major restriction because they arent.
Its obvious to see if you have a good look at a vf stock exhaust.

From what I understand, it's more the angle at the entry point of the HSV cats. It's a sharp angle and inside the cat there is a ring to reduce the inside diameter. When I removed the HSV cats and added 200cpi bullet cats and had it retuned, I picked up 20 something rwkw on the already tuned L77.

 

[Milo 6.0]

From what I understand, it's more the angle at the entry point of the HSV cats. It's a sharp angle and inside the cat there is a ring to reduce the inside diameter. When I removed the HSV cats and added 200cpi bullet cats and had it retuned, I picked up 20 something rwkw on the already tuned L77.

I totally agree that the entry angle isnt ideal but 20 rwkw just from cats,I find that very hard to believe.
On a factory system which is what i was talking about,the reverse flow rear mufflers are alot more restrictive than the factory cats.
The body of my ve hsv cats are huge,there is no restriction ring just an inlet and outlet 2.25 inch pipe.
Dyno sheet?

 

[426Cuda]

I totally agree that the entry angle isnt ideal but 20 rwkw just from cats,I find that very hard to believe.
On a factory system which is what i was talking about,the reverse flow rear mufflers are alot more restrictive than the factory cats.
The body of my ve hsv cats are huge,there is no restriction ring just an inlet and outlet 2.25 inch pipe.
Dyno sheet?

Yeah I have dyno sheets. But they dont show that the reason for the increase was the addition of hiflow cats and a retune. Only I know what was changed (i.e. cats) and only the tuner knows what they adjusted. Probably a degree or two of advance here or there, amongst other adjustments. From memory it went from 229rwkw to 252.9. Or thereabouts. I'm the first to admit that the increase seems high. But the seat of the pants dyno certainly felt the change. The initial tune may have been conservative IDK? But the only hardware change was the 200cpi cats.
I could upload them. But they prove nothing and I have nothing to prove.

 

[Milo 6.0]

Thats fair enough,i just think other factors may have come into play there like you said with tuning the second time around,i can see a few hp from cats alone but to say 30rwhp is a big big stretch,look at project vf from street quick,they only gained 25 rwhp from a full exhaust,difillipo extractors,3 inch 100 cell cats and twin 3 inch exhaust,that was an already tuned vf ss with a bog stock exhaust with almost identical factory cats,those guys have an excellent track record,repeatable reliable dyno etc.
So to be saying that the factory cats are so restrictive that you can make 30rwhp once they are replaced with high flow cats and retuned is not correct and gives others the totally wrong idea,not sure whats going on with your tuner but the fact he believed the cats gave 30 hp with a tune tells me something is off.
Comparing dynos is a stupid thing to do and something that i absoultely hate to do but its the only way i can explain this situation.
Seriously if the cats were that restrictive and holding back 30hp a full exhaust would be netting close to 50hp with a tune after its already had a mafless otr tune,thats crazy talk.
The most obvious scenario is that maybe he did an average job tuning it the first time and actually did a decent tune the second time around,or the cats were fkd in the first place.

 

[blackve76]

From what I understand, it's more the angle at the entry point of the HSV cats. It's a sharp angle and inside the cat there is a ring to reduce the inside diameter. When I removed the HSV cats and added 200cpi bullet cats and had it retuned, I picked up 20 something rwkw on the already tuned L77.

Wow that's a big increase, early in The VE days I had pacemaker try us and std cats on my 06 VE SS, got a cam and later on got 4~1 packed and 100 CPI cats and retune got extra 7 kws and was from 4000rpm above. My tuner told me the std cats sent that bad look at the size of them.

 

[426Cuda]

Thats fair enough,i just think other factors may have come into play there like you said with tuning the second time around,i can see a few hp from cats alone but to say 30rwhp is a big big stretch,look at project vf from street quick,they only gained 25 rwhp from a full exhaust,difillipo extractors,3 inch 100 cell cats and twin 3 inch exhaust,that was an already tuned vf ss with a bog stock exhaust with almost identical factory cats,those guys have an excellent track record,repeatable reliable dyno etc.
So to be saying that the factory cats are so restrictive that you can make 30rwhp once they are replaced with high flow cats and retuned is not correct and gives others the totally wrong idea,not sure whats going on with your tuner but the fact he believed the cats gave 30 hp with a tune tells me something is off.
Comparing dynos is a stupid thing to do and something that i absoultely hate to do but its the only way i can explain this situation.
Seriously if the cats were that restrictive and holding back 30hp a full exhaust would be netting close to 50hp with a tune after its already had a mafless otr tune,thats crazy talk.
The most obvious scenario is that maybe he did an average job tuning it the first time and actually did a decent tune the second time around,or the cats were fkd in the first place.

I'm not trying to mislead anyone Milo. Just sharing the experience I had with my L77. Whatever the numbers, the second tune, after fitting hiflow cats, made a big difference. There were two things changed, the cats and the tune. The second hand 2.5" GTS exhaust I fitted was like new, including the cats. I didn't have stock rear AFM mufflers. I had J pipes. So, the cats were by far the most restrictive part of the exhaust. The first tune wasn't crap at all. It was a virtually brand new engine though and the plan was always to take it back for a retune and change the cats. So, maybe they factored that into the first tune, which metted about 24kw from memory. Either way, the hiflow cats and second tune brought it to life. That's a fact. I've had it tuned since too, but that made little difference.
As for the workshop, they're very experienced, reputable and widely used. I hardly think their dyno figures are overstated either. If anything, they are quite a bit lower than the results other tuners state.