Exhaust port size - HELP

Hi Guys,
 
so im toying with the notion of trying to fabricate my own turbo exhaust manifold (lol), and i want to try and buy the relevant steampipe today to start playing over the weekend.
 
Problem is i dont quite know what pipe size to buy.
 
I believe the two common sizes used are 32mm, and 40mm. But i also understand that the sizing if steampipe is a little strange, in the they talk about nominal bore sizes etc.
 
So, my question is (and im hoping to nut this out this morning so i can go down to the shop and buy the pipe).
 
1) What is the exhaust port size of a standard pinto head?. I want to make sure i dont get pipe that is too small for the port.
2) Is anyone able to (in laymans terms) briefly explain the way the sizings of steampipe actually works?. Is 32mm referring to the inside diameter of the pipe?.......
 
Thanks for any help guys.
 
Dave

thanks Knightime.......
 
Appreciate the help.
 
Dave

No spigot,
 
The only difference is in the designation. Both are manufactured to an 'actual' od.
eg. 25mm tube is 25mm od.
25mm (old 1") NB pipe is 33.7mm od. The actual id varies due to the wall thickness, & thus
the bore is nominal. (you could call it 33.7 tube) 
 
Gregg
 

The id and od varies with regard to the schedule, this is why it's called nominal bore. The "nominal" bore dimension remains constant, the wall thickness is given per schedule. You then have to actually calculate the id & od.

As I said ask a steel merchant!

Thanks to all for the info and guidance provided. I now have the info i need.
 
Dave