Exhaust Port Size

[ChinGy]

Hello

I'm new to the forum. First time posting. Long time reader. I have a UK 1NZ-FE Yaris T Sport. I'm looking to have a custom exhaust header (manifold as we call it in UK) made up with longer runners to hopefully gain more power out of the engine. I currently have an OBX header which has been running fine for years, but I just want more out of the car.

Does anyone know what the exhaust port size are? The fabricator is currently making the head flange and wants to know the measurements so that they could make the runner's diametre slightly bigger, and not too big.

[cali yaris]

Welcome to the forums. :smile:

That's the 1.8L right? Do you still have your stock header?

[ChinGy]

It's a 1.5L, NCP13.
I do have the stock header. It looks about 1.25" (31mm).
The gasket bore size is about 41mm (just over 1.5")
Which is rather odd as that would mean the runners are smaller than the ports.
Shouldn't it be the other way around? With the exhaust ports being smaller than the runners.

[malibuguy]

Smaller runners reach peak velocity sooner building torque

[ChinGy]

Great fact. But it would be nice if the runners were slightly wider than the port to stop reversion.
If anyone has a cylinder head out. Could you please confirm the exhaust port size?