So, if I put 12A irons on a 13B motor what header do I use?
Can I use my 12A header and oval the bolt holes?
Thanks,
Vin

 

13b header

 

Ahhh the header bolts to the housings not the irons LOL.

 

no. you can use a 13b header on a 12a but from what ive seen you cant go the other way.

 

Guys the header bolts to the aluminum houseings, this is what chages between a 12a, and a 13b, the width of the rotor houseing. the width of the side and center irons has not changed since they first came out with the 10a. all of the sid and center irons are of the same external dimensions, thats why you can swap them back and forth!

if you have 13b rotor houseings, then you need a 13b header, and for 12a houseings a 12 a header.

any other configuration witll result in you haveing to cut and modify the header to get it to work.

kenn

 

what i was saying is that you can modify a 13b header to fit onto a 12a engine,atleast others have said they have been able to do so. but you cant modify a 12 header to fit a 13b, or atleast the 12a header i have cant be made to fit. theres just not enough metal on either side of the mounting holes.

 

That clears that up.

I wish I could just cut the header flange and spead the pipes. I just welded the oxygesensor boss on and now I have to get a new header

 

you can!

Sorry if I seemed grumpy was not meaning to jump on anybodies wheaties back there.

If you are willing to cut it, then either will work, you simply slice the header in between the pipes, this allows you to lengthen, or shorten as required.

ovaling the bolt holes is a bad route to take, as it will not seal for ****.

for a 12a header to fit on a 13b, regardless of the irons you use you would need to slice the manifold flange between the primaries and then cut the rear primary about 2 inches before the collector. Shorten it about 3/4 of an inch (measure yourself to find exact difference) and then weld it back, this will spread you primaries apart the required amount to make it fit. it does require welding though so if you do not have acess to a welder you can't do it.

the flange does not have to be one piece. Many of the orignal early 70's headers used two flanges that were not connected, they just found out that it was easier to manufacture and sell it with a one piece flange.

(also currently anybody who races a periport with the mazda factory race <mazda speed> housings uses a header with split flanges)

kenn

 

That's great.
I'll give it a try.
Thanks,
Vin

 

i have -se housings and 12a irons, im using a 12a race header. i cut down the center of the flange that bolts to the motor, and added a short section of pipe to the far end of the front rotors exhaust runner.

 

Thanks,
Vin