Header Diameter
Turbo Mini Forums

I'll be making my own set of headers, and am wondering what diameter of header stock I should use. Does anyone know how to determine optimum diameter?

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1967 Cooper 's' Turbo build @ www.drjing.com

For a turbo application you need to keep the header as small as possible say around 1.5 to 1.75 inches depending on power output this way the gas velocity is kept high as it exits the port on it's way to the turbo. Doing this should help reduce the amount of lag.
If it were me I?d be going for a 32mm exhaust valve sat along side a 36mm inlet.

Edited by Doodmeister on 4th Feb, 2005.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

These valve sizes suggest the use of offset exhaust valves which is very expensive and fragile. I would not have used such big valves in a turbo engine.

yes personally for turbo use I think std MG Metro valve sizes are a good compromise, 1.4" inlets and std sodium exhausts.

MG Turbo as std has 1.3" inlets.

Each to their own chaps but speaking to Brian Slarks he tells me he gets great results from the 36/32 combination and used them on many top winning engine and head combinations for the groupA turbo metro days.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Thanks for the info, guys!

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1967 Cooper 's' Turbo build @ www.drjing.com

I have done two head with offset exhaust valves. Cost of mods: nothing. Time spent: a little more than nothing.

Here?s what I did: press out guides. Drill the guide holes to 15,8 mm in pillar press. Ream the hole to 16,00 mm. Machine a 20 mm counterbore 4 mm deep. Then turn 4 sleeves with 16,10 mm diameter (and 19,9 mm top) to fit into above drilled guide holes. Now the trick part: fit the sleeves offset on a lathe chuck and drill the guide holes to 11,7 mm. Ream the guide hole to 11,85 mm. This gives a pretty tight fit with bronze guides and they need to be reamed to correct running clearance. When fitting make sure that the offset it the correct direction. Takes about one day to done one head. Worth it ???? Who knows ! Why ??? Call it an engineering challenge...

As for reliability, I have not had any reliability issues with big valves close together. Cannot say the same about valve seat recession though... Next head will be unleaded and run 36 mm valves with std sized exhausts. Done enough head carving to my liking...

Thanks, guys. I think I've decided to just go with the standard header pipe, and then just run one single pipe from the header outlet over to where I'll be locating the turbo. Easier, cheaper, and it takes the guess-work out of it. I had just assumed that the standard header was a compromise piece (since it is stock), and thus thought that I should build my own...

Thanks, again!

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1967 Cooper 's' Turbo build @ www.drjing.com