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I'm sorry but the pie cuts are gross. I don't doubt the gains of going from 3 to 3.5 but you can buy mandrel bends from ace race and not suffer the awful flow characteristics of pie cuts. For all the time that was spent on the pie cuts you could of just got some proper bends.
For what it's worth large down pipes will always be custom to properly clear everything on most cars but have always made a huge difference. On my 9174 I'm flaring out to 4" just because I have the materials.
I'm sorry but the pie cuts are gross. I don't doubt the gains of going from 3 to 3.5 but you can buy mandrel bends from ace race and not suffer the awful flow characteristics of pie cuts. For all the time that was spent on the pie cuts you could of just got some proper bends.
For what it's worth large down pipes will always be custom to properly clear everything on most cars but have always made a huge difference. On my 9174 I'm flaring out to 4" just because I have the materials.
3.5 inch pipe can flow enough for 1200hp. so loosing maybe 1% flow potential using pie cuts aint hurtin a dang thing. looks like he is having a blast making somethin different. looks fabulous to me.
If it were really 1% do you think I'd of said anything? Try 10-20%
Take a look at a CFD flow analysis of a bend;
As you can see it has extremely high velocity right around the angle of the inside of the bend with there being a lower speed boundary layer on the outside of the bend. Having rough corners introduces significantly more turbulence than you'd think which kills flow. I'm actually not sure how much you gain on going from 3" mandrel vs 3.5" pie cut.
Other than the kink bend which might of been a bit of a pie with some bends, mandrels would be better. This is 2015, you can get bends on the internets cheaply and not have to spend hours measuring cutting grinding welding repeat to do pie cuts.
When I get back home I'll do a model of both a pie cut and a regular exhaust section with mandrel bends in solidworks and show you the flow data. It'll blow your mind. Also I'm curious to see what the delta in flow and back pressure is on 3" mandrel bent and 3.5" pie cut.
All this being said, yes 3.5" is far better than 3" for pretty much anything turbo related.
The reason for pie cutting is because you can make a tighter bend. Where the DP snakes around the tcase, even if he had bought bends, he still would have had to pie cut the bends to achieve a tighter radius. Likely the same for right at the turbo outlet..
That bend around the case is definitely a pain, and would have to be a "mock it up and see" deal. That downpipe? That looks like you don't even need a tight radius.
I'm actually not sure how much you gain on going from 3" mandrel vs 3.5" pie cut.
I'm curious to see what the delta in flow and back pressure is on 3" mandrel bent and 3.5" pie cut.
I'm curious too, only I would have said it nicer
I've never run CFD software, I was always the guy who would make the surfaces in Catia, after the Aero guys had decided what they wanted. Making the shapes continuous in tangency (G1) was usually a bare minimum requirement, but whenever possible we would also make the shapes continuous in curvature (G2). When I retired 2 years ago we were starting to think about making shapes continuous in G3 (rate of change of curvature).
Mick O is running a 7670 and retaining AC. Even with the tilted manifold it would not allow use of a 3.5" DP. Off the back of the turbo is 3" short radius mandrel DP which then steps out 3.5". Can't get 3.5" short radius bends off the shelf either (at least that's the case here in Aus) so I guess he's making the best of a bad situation.
I've got a 7670 which will end up on a tilted manifold and no AC, *hopefully* with this added clearance a 3.5" DP can be done
Those welds are fantastic, but you should probably just remove that under brace and run the downpipe in a much straighter path. Kind of defeats the purpose of a big downpipe if you have that sharp of a bend in it. The last 20 Evo's I've worked on don't have that under brace, and while I'm sure it provides a marginal gain in stiffness, I highly doubt it's important enough to sacrifice turbo performance for. I'm also sure you could make something that would do the same thing and allow the downpipe to fit.
Those welds are fantastic, but you should probably just remove that under brace and run the downpipe in a much straighter path. Kind of defeats the purpose of a big downpipe if you have that sharp of a bend in it. The last 20 Evo's I've worked on don't have that under brace, and while I'm sure it provides a marginal gain in stiffness, I highly doubt it's important enough to sacrifice turbo performance for. I'm also sure you could make something that would do the same thing and allow the downpipe to fit.
