exhaust back pressure needed. a myth? :poke:

[STEEV888]

after watching this episode it makes me think is back pressure really needed ?

Oz Garage S02E09 Online - Exhaust Comparo | OzGarage

i know there are alot of variables. but for your stock commodore v8 it seems pretty straight forward.

 

[IMCRZY]

Velocity is what is needed, to big and u will loose & to small u will loose, just need to fing the right setup

 

[GenReaper]

I dropped my exhaust to straight collectors on the dyno and it lost stack of bottom end torque.

 

[soop]

As the first guy said.
You don't need backpressure. But that doesn't mean you can run 5" pipes and it will be a missile.

You need a balance between exhaust gas flow and gas speed.
Genreaper would have lost a fair what of torque because the exhaust system wasn't there to continue drawing the spend gas from the manifolds. So it essentially slows it down making the engine work harder.
In very basic terms anyway.

 

[edals]

Well Ever since i put a exhaust on the VX, Its only a 6, It cannot make its mind between 3-4th, so goes in between gears at about 75kms going up a slight hill, never did with the old restricted exhaust so i have lost some torque down low.

 

[AirStrike]

As the first guy said.
You don't need backpressure. But that doesn't mean you can run 5" pipes and it will be a missile.

You need a balance between exhaust gas flow and gas speed.
Genreaper would have lost a fair what of torque because the exhaust system wasn't there to continue drawing the spend gas from the manifolds. So it essentially slows it down making the engine work harder.
In very basic terms anyway.

With a turbo setup being the exexption to this.

 

[soop]

Yeah well, thats a whole other kettle of fish

 

[STEEV888]

i know about velocity and everything.
which is why i was planning on getting a 2.5 instead of a 3 when i went exhaust shopping.
but this opened up ideas that a 3" system would be better especially considering this car was stock and mine will have mods slowly done to it over then next 2 - 3 years.
one of the first being exhaust otrcai tune etc
and when i took my cats out i got more power all through the rev range as well as a faster 0 - 100

 

[AirStrike]

i know about velocity and everything.
which is why i was planning on getting a 2.5 instead of a 3 when i went exhaust shopping.
but this opened up ideas that a 3" system would be better especially considering this car was stock and mine will have mods slowly done to it over then next 2 - 3 years.
one of the first being exhaust otrcai tune etc
and when i took my cats out i got more power all through the rev range as well as a faster 0 - 100

From what I have seen and read about the LSx series of engines, a mild 5.7lt is best with the twin 2.5", only go twin 3" on the 6lt+ engines or if you are running FI, etc.

 

[soop]

That or a really big cam in a 5.7.
They just don't physically move enough gas to warrant a twin 3". Lots of people will argue till they're blue in the face about that though.