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Exhaust query

richardpalinkas

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Hey just wondering what the most restrictive part of the standard exhaust is on the ss? Is it the manifold, cats or catback section?

Reason I ask is because I have a full exhaust system with pacies, 200cpi cats and twin 2.5, but I want at the moment to have a stealth type system without losing too much power. What I was thinking is putting a standard ss catback back on the car but keep the pacies and cats. How much power would I lose because of this? I already have a mafless tune if that makes any difference. Cheers
 

maloo3063

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pretty sure appart from the 2 mega mufflers its the cats but i could be wrong
 

Big-Al

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Pretty much the entire OEM system is restrictive but if the VZ exhaust is anything like the VY, there is a section of pipe (I think it's before the cats) that is crimped so the pipe is narrower than 2.5". This is the most restrictive part.
 

richardpalinkas

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Yea no doubt he will write something here. Just wanted all the non professional ideas also.

I know what you mean about the crimp, I think it's in the cat section.
 

Munz

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How many mufflers on your catback and what brand?

Usually putting a pair of longer chambered mufflers in place of the 2 middle straight thru mufflers would cancel out alot of frequency
 

Surfwagon

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The best flowing/least restrictive factory exhaust is the HSV VZ setup, has straight through centre and rear mufflers.
You can pass a garden hose from the rear right through to the cats.
The rear has twisted perforated pipes but no chambers as in the earlier factory exhausts.
The VT2-VY2 HSV systems have dogleg centre mufflers and a chambered rear muffler but again these flow better than the Holden factory twin system which uses chambered and dogleg in centre and triple chambered on the rear.
Unfortunately it is a different centre shape to any of the Holden VT2-VZ or HSV VT2-VY2 so requires mods to fit.
System is straight pipes after secondaries not a "Y" like all the other VT2 on systems.
HSV VZ system.
2009-04-02-0551-35_edited.jpg
 

Surfwagon

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BTW if stealth with flow is what you want, I still run my Z HSV catback behind 1 3/4" extractors with 3" 100 Ballistic cats (HSV secondaries are 3").
Silent when cruising which is how I wanted it for Highway trips at night but still burbles nice and deep when you are up it.
 

richardpalinkas

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I have 2 mufflers, just the centre ones, unsure of brand as its a custom made catback that was on the car when I bought it. It has no balance pipes either. Il look into the z hsv exhaust, see what I can sus out.
 

Not_An_Abba_Fan

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Each part of the factory system is restrictive in its own way.

The standard manifolds are because thet are cast and all different lengths flowing into a 2" outlet. They are a vast improvement on pre LS manifolds but still restricts flow.

The cats are restrictive because they are 400 CPSI.

The rear muffler is actually the most restrictive part of the cat back as it is the actual muffler, the two front ones are straight through. But the whole thing has crimps at various points for body clearance.
 
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