Turbo Manifold Design

[Nick-G]

I'm working on some turbo headers for my 3400 and I'm looking for some opinions.

First of all I am going to have 1 5/8 equal length primaries. Now my first question is would it be better to have 2" collectors or 2.5"?

FYI these will be going into a divided t3 housing.

[MidnightriderZ24]

go wit 2''. it will keep velocity up and help with spool time.

[Nick-G]

go wit 2''. it will keep velocity up and help with spool time.

Thanks! That's kind of the answer I expected to get but now I know for sure.

[RedZMonte]

I agree especially on a T3 Divided housing. 2".

My LQ1 im going to redesign my turbo kit one of these days and im going to move down to a 2" x-over and a Divided (twin scroll) housing T4 (keeping my same turbo. do a search for one of my posts a bit ago there are a few ideas for turbo manifolds.

[ForcedFirebird]

2.5" is too big IMO. Specially if you are going into a 2" (equal to 2") diameter housing. If they made triple 1.65" to 2" collector, that's what would have been on my car

As the heated gasses pass through a smaller area, they become MORE excited, thus creating more velocity, Think about blowing on a pinwheel - first try it using a paper towel roll center, then a straw - what moves the pinwheel (turbine) faster? Just make sure the transition is a smooth as possible.

Divided housing, eh? Ever consider a quick spool valve?

[RedZMonte]

Quick Spool Valve


so how exactly does that work? it looks like it would restrict the flow not increase it for faster spoolup.... what am i not understanding?

[ghrarhg]

It's the same idea that Forced was talking about. In order to keep the same amount of flow (cfm) when reducing the area, velocity has to increase (to a point, then back pressure becomes an issue).

Insert pinwheel analogy here:

Before back pressure becomes an issue, the valve opens.

[Nick-G]

Quick Spool Valve


so how exactly does that work? it looks like it would restrict the flow not increase it for faster spoolup.... what am i not understanding?

Someone correct me if im wrong but isn't that for use with a divided turbo with non divided manifolds?

If I am thinking of this right then that would do me no good because I am going to have divided manifolds.

[IsaacHayes]

Yeah I would have to say that would have to work only with a single common exhaust feed. That would not work if you have each bank feeding each divided scroll or whatever. In other words if you had two manifolds, the one going to the closed valve there would basically be like welding the exhaust ports shut on one cylinder head... lol

[ForcedFirebird]

Correct. You have to use a single collector/Y into the turbine housing, while using a divided unit. That is a very expensive piece of equipment for something you can accomplish with two large waste gates

Essentially what you are doing is: at low boost you are operating on a turbine 1/2 the physical size, as the boost rises, you are opening up the second half for the top end, increasing/decreasing the back pressure created by the compressing of the exhaust gasses. Guys have been doing this for many years on cars that use JY diesel turbos. Diesel turbos generally have a huge turbine in comparison to a gasoline engine - both with the same compressor - they would just use 1/2 of the turbine

EDIT: If you search theturboforums, you will see the posts go back to early 00's. They started with only closing off one side of the divided housing.