What's the better exhaust design?

[BottleFed70]

Because my car is a classic, I want to keep the dual exhaust look.
I'd like an exhaust system that will support up to 600HP and is agressive sounding without being too loud.
It's a street car with a single T70, 3" downpipe.

So what is the better chouice?    Dual mufflers with a Y upstream, or a single muffler with a Y on the output?  Either way the plan is to use a 3" Y with 2x2.5" outs.

[brianj5600]

While you are at it, if you could fit 3.5 right out of the turbo it would be good.  I turned mine down and split it in front of the engine.  There is not much room to get a decent size downpipe out, as you know.  Splitting up front gives you smaller pipes to get past the crossmember and drag link.  I have the Hooker version of ultraflows on mine just in front of the axle and a lot of people say it is too quiet.  I like it quiet.

[Drac0nic]

2.5" dual will flow a little more than a single 3" will. To me this means do it as early as possible. JMO on it, your routing may also dictate this as well.

[Dangerous Dan]

not flow numbers but crossectional  area of the pipe ,assuming 16ga
3.5" = 8.941 sq"
2.5" =4.427 sq" or 8.854 sq" with duals
3" = 6.488 sq"

[brianj5600]

A P-trim needs all the flow it can get on a 351w too.

[BottleFed70]

Hmmm so sounds like a tossup and the routing, etc will be the largest factor in determining the configuration.

I doubt I will go with the 3.5" downpipe.  The 3" is already too tight IMO and I already have ground clearance problems due to lowering 2.5"   Plus the 600HP mark is a bit of a pipe dream.. it will likely never see more than 14PSI/500HP.

I will need to get under the car and take a good long look at the clearances, potential routing, etc.

[brianj5600]

Can't fit 3.5"?  This is 5" in a 67.  It splits into twin 3" and one goes down each side of the engine.  I hear there is more room in front of the engine on a 70.  I could fit 3.5" and keep my sn95 electric fan.  I will be using a pusher now.

[BottleFed70]

LOL.  Anything is possible with enough time, money, and effort.

I don't believe there is more room in front of the engine, but there is more room in front of the radiator for an intercooler, etc.   My Taurus fan just barely clears the water pump pully. 

[TomServo]

Here is a 3.5" downpipe in a '69 with a 351c.  Splits into dual 3" as it goes down next to the firewall, all the way back to dual 3" hooker max flow mufflers at the back.  Sounds amazing.  I had to dent my valvecovers and the downpipe just a little bit to fit it under the shock tower brace.



Here you can see what I did with the radiator.  Gives more room for the turbo and stuff up front.  If I had stuck the turbo off to one side I probably wouldn't have needed to do that, but if you're running out of real estate up front, its an option.