ABY and ADU DP Design Expert help needed

[orsum]

There are some clever people that designed our down pipes, why did they split it into two at the bottom of the DP.

Why did they not just do a single 3" from day one?

Due to the cooling effect two pipes would obviously have over a single pipe would it be a benefit the cars performance?

The volume of air possible in the two 2.5" pipes is more that the single 3".

Is it possible to over cool the exhaust gases?

I am looking to use the standard exhaust system and connection it to a 3" DP hybrid with 2 X 2.5" outlets.

At the bottom of the DP the 2 X 2.5" outlets will take the same OEM route to the existing stock system. (cats removed)

What do you gas guys recommend? Is there a benefit?

[4WDrifter]

Temperature is probably not the only consideration.
Pressure is important too

[orsum]

Thermo dynamics and gas flow are not high up in my skill base.

What I think I know is hot air is less dense than cold air.

Hence my thinking that you will get a pressure drop due to the cooling effect which should help the turbo performance.

[Error404]

They needed to get two catalysts in to meet emissions regs.

[LHD_Kid]

They needed to get two catalysts in to meet emissions regs.

Yeah, in those days they didn't have the technology to program the engine management for test scenarios...

[orsum]

They needed to get two catalysts in to meet emissions regs.

Good point

[mcandmar]

Yeah, in those days they didn't have the technology to program the engine management for test scenarios...

As above, a single cat converter suitably sized wouldn't have physically fitted, hence the need for two.

[orsum]

So what about the gain due to the increased cross section area to the first box?

1 x 3" = 182.4 sq cm
2 x 3" = 364.8 sq cm
2 x 2.75" = 306.5 sq cm
2 x 2.5" = 253.3 sq cm
ABY Total cross section area for 2 x 2.5" pipes to first box = 253.3
RS2 Total cross section area for 2 x 2.75" pipes to first box = 306.5
ABY Hybrid Total cross section area 2 x 3" pipes to first box = 364.8

So having two 2.5" pipes from the 3" DP Y section would give you a 253.3sq cm area to the back boxes. Sounding better than one 3" pipe with the cross section area of 182.4 sq cm.

I would think taking into account the losses of the Y split and the increased inner wall area I still think having two pipes vs one would still be better to the first back box.

Would having two 3" pipes taking the standard route to the first back box fit?

And would that be any better??

So far I have been unable to locate any 2.75" exhaust pipe in SA.

[mcandmar]

The s4/s6 has a twin pipe system all the way to the tips, and I believe it does flow better. On the 80 chassis space is limited around the back axle so I am not sure if it would be possible to run two pipes..