exhaust manifold sizing
Turbo Mini Forums

Hi,

I am considering building my own manifold for my standard 998 12G295 head turbo engine.

Reason is I want the turbo on the clutch.

My favorite yellow book (the one with very few phone numbers) states I need 1"1/4 ID for outers and 1"3/8 D on centre branch.

That is for N/A engines with a power expectancy of 70 to 110 HP.

But exhaust valve is 1" wich is 64 % of the exhaust area, assuming 100% efficiency of the valve.

I am trying to avoid lag without compromising maximum bananas

So what size would best apply in your opinion ?

Thanks in advance

Rusty by nature

I think the optimal sections are the same for NA and FI engines because the expelled volume is still the same, it's a matter of pressure.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

So long as they are as big or bigger than the exhaust ports where the manifold meets head I would say it will be fine. I am sure there is some maths out there that can work it out, but remember that the turbo is a masive restriction.

http://www.twin-turbo.co.uk
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A man without a project is like a like a woman without a shopping list.

This was discussed a couple of weeks ago.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=253314

The sizing in the Vizard book is totaly irrelevant for a turbo application. Keep the branches small.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I thougt so !

Thanks Paul

So it is small before turbine and big afterwards.

I'll go for small bore size before turbine

Rusty by nature