Turbo manifold sizing
Turbo Mini Forums

I built a turbo manifold previously, i am not happy with it so want to do another.

Last one was 1.5 inch ID but would 1.25 be better or stick to 1.5?

Thanks.

I can't claim to be an expert in any way, but . I've used 1 1/2" on mine as it covers the cylinder head ports and is pretty much the max to fit in flanges without making the tube ends square. The original cast turbo manifold looks pretty small tho, so there might not be a right or wrong, unless someone has tried both...

What size turbo and state of tune? Recommended size for a 1300 engine is between 1¼ and 1½", however you want maximum velocity prior to the turbo.
Use smaller diameter tubes for widest power band and larger size where top-end power is more important and sluggish throtttle response is acceptable

Edited by Steve220 on 9th Oct, 2021.

On a friends car, circa 2.4 or thereabouts, it would make close to 1000hp with 1.75" OD header tubes.


It's so easy to get caught up in thinking ports need to be big with a turbo.

Although it does make sense to have smooth flow, transitions etc etc

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

This is why I love this site, I'd have assumed bigger is better initially, but of course velocity is king.

You want high pressure upstream to drive the turbine and low pressure after the turbine to create a high pressure differential.
So don’t oversize the runners.

Phil.

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