Manifold design considerations

[Lurker27]

Relative runner length - As I see it, this is primarily going to affect the cylinder pressures - if a given runner to the turbo is short, you're going to have more backpressure in the cylinder, which means that cylinder will run richer. This is why top mount turbo BMWs detonate on #6 - it has the longest runner and therefore runs leanest.


Thoughts? I'll be welding my mani up soon.

[kylekrueger]

Just make sure all the primaries are the same length. Are you doing a bottom mount turbo or top? Are you going to fab up a whole new manifold or are you going to add turbo primaries to the stock manifolds? Also are you going to run a twin scroll exhaust side or single as this will affect how you run the primaries and to which scroll housing.

I suggest reading this:

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_systems_tech_center.html

That helped me a lot.

[Lurker27]

Top mount

New manifold (hopefully true divided t3 w/ single wastegate)

[kylekrueger]

Ok well if you are going to run a divided then I would definitely set up the manifold to support the benefit of the divided scrolls. Im not sure exactly how to do it because I am pretty confused on how firing orders work but here is an example from garrett.

If you have a 4 cylinder engine with a 1342 firing order, when 1 is finishing the combustion stroke 2 is in overlap. And therefore 1 and 4 are complementary? and 2 and 3 are complementary? That is what they say but I am really confused on how that works but that is what you want to do.

[Lurker27]

its 123-456

[Jaxx_]

the shortest runners will always be best, giving the exhaust gas the least amount of time to cool down, which in turn will keep the turbine speed up.

pick up max boost by corky bell if you want some good baseline advice (take some of it with a grain of salt)

[ChrisM]

if this is true does my log mani detonate on cyl 1 since my turbo is in the rear?

Relative runner length - As I see it, this is primarily going to affect the cylinder pressures - if a given runner to the turbo is short, you're going to have more backpressure in the cylinder, which means that cylinder will run richer. This is why top mount turbo BMWs detonate on #6 - it has the longest runner and therefore runs leanest.


Thoughts? I'll be welding my mani up soon.