So I plan on building a manifold out of mild steel weld-els. The flange I have has 1 5/8” holes. It looks like I can get pipe with either 1 3/8” ID or 1.65” ID. Is it better to go smaller or bigger than the flange hole?
So I plan on building a manifold out of mild steel weld-els. The flange I have has 1 5/8” holes. It looks like I can get pipe with either 1 3/8” ID or 1.65” ID. Is it better to go smaller or bigger than the flange hole?
What's the size of the exhaust outlet on the head? That's more important. I would go with what most closely matches the head.
Bigger. Always bigger.
The flow through the manifold is already restricted, so anything you can do to help keep flow up is important.
Headers are routinely made with pipes diameters larger than the cylinder head outlets with no detriment to power output.
In reply to Stefan :
Good to know. Will bigger hurt response or nah?
Maybe tell us what motor your putting the turbo on would help and your power goals ?
LS motors have made crazy power with stock truck manifolds..
On a log manifold? No. No it won't.
I’ve though about this a lot. I have friends with 4 cylinder motors that have made 400hp on a log manifold with sub 2” internal diameter.
My instincts tell me that once the manifold is pressurized by back pressure created by the turbo the diameter of the manifold bends isn’t super important.
Ad stated by scottdownsouth ls guys flip stock manifolds and those things get real small inside when you cut them up (just ask my sawzall).
In short my advice would be, run what you can fit unless your chasing every last horsepower.
Disclaimer: I’ve turbod a few cars but have no science to back this up.
I’m turbo’ing the 4age in my ae86. The SC is dying and I’ve been craving more power (don’t we all?)
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