3SGTE turbo manifold runner sizes?

[Jimmee1990]

Hello,

Looking into possibly making a manifold sometime down the track for my 3S-GTE Caldina as the standard one is developing some cracks and being fairly old cast iron will most likely keep cracking. I'm interested in what internal diameter tubing people have run and had good success with, I was thinking 35-40mm but unsure on what would be best?

It would definitely be mild steel steam pipe and a very simple design (not a log type), mainly interested in sizing and runner lengths at this stage. Keep in mind it's east west and space is at a premium in this engine bay.

[Skylar]

1.25" sch. 10. but that might only be available in stainless. When I last looked, you could only get 1.5" mild steel bends in sch. 40.

Don't go to 1.5" unless you are going to make stupid power.

Keep runners same'ish length but not critical. Some say, do radial fire for open collector, others say it doesn't matter. Twin scroll is better than single scroll (you probably know that much).

[Hen may possibly be a nut]

I can't add much constructive, and while welding your own manifold could be fun, I wouldn't write off repairing your cast manifold.

I had cracks in an old mani (from early 90s) but drilled the ends, ground a bit of a V along the crack, pre-heated it then welded it with a stick welder and electrodes that allegedly suited. I'm no pro welder but it held without issue for the few years I kept the car.

[Jimmee1990]

Will be for a basically standard engine, possibly a set of mild cams and a little more boost later on but nothing else. The main reasons I want to go away from the cast manifold is that it has cracked and been welded before, secondly that the turbo exhaust housing is part of the manifold and the whole thing is a terrible shape.

Fabrication isn't an issue, I have several professional fabricators in the family. I will go with 1.5" and single scroll for cheapness and try a few different collector types back to back and see what happens.

Thanks for the input guys.

[Hen may possibly be a nut]

Ah yes, the old turbifold. They always seemed annoying.

[Skylar]

Maybe I shoulda been little more clear. You can get 1.25" pipe in mild but it will be sch. 40, not sch. 10. It's no biggie aside from it weighing a little more than it needs to. You can get away with 16ga if you wanted to.

For the collector, you basically want the minimum convergence angle you can but packaging comes into it and the design becomes a compromise between space and performance. I think I have loss factors for converging pipes at work if you want an idea of how much difference the angle makes.