Exhaust headers diameter

[Lego]

Hey guys,

I am going to build custom exhaust headers, and after a bit of studying I am considering my options.

Stock headers are 38mm outside diameter, and they are double pipes so i think inside diameter is around 35mm for example.

If I build custom headers from 43mm pipe with thicknes 1.5mm , so internal thinkness will be 40mm. I will be using baffles.
There is no good source for 38mm pipes in my location. So that why i am considering this option. Also i like the idea of thicker headers, it will look better with my build.

What do you think about the change of the tuning of the bike, will this be a big change. will i have to tune it too much? changing jets etc?

also my plan is to make 2 into 1 with merge collertor and one baffle. But in general, connecting both headers toghether should only help with back pressures.

 

[16VGTIDave]

There is a lot of science behind exhaust systems. It can't be ignored. You will need to do a number of calculations to determine what size pipes to use, and how long to make them. The carb tuning will be greatly effected.

I believe the internal diameter of the stock header pipe is closer to 25mm. At least on the slightly more powerful DOHC bikes it is. Bigger is rarely better. Otherwise the engineers at Yamaha would have done so...