The exhaust also has an SSR which heavily influences how well the port can flow.
This mould shows the kind of condition the factory leaves the heads in.
A finger prodded into the port will expose a sharp edge which creates major restriction and turbulence just as on the intakes.
Once youve addressed that and modified it to more closely resemble the next photo, apply a similar finish to the exhaust port surfaces as the intakes using the methods youll now have developed.
You can finish these to 120 grit as itll help to reduce carbon buildup than a rougher surface which can alter the flow of the ports over time.
Modified exhaust port shape.
If youve done a good job, you should have ports that are closely matched for both flow and give a good improvement over stock.
Typical bare port flow for a stock 3vzfe is 204cfm@28", the result of your efforts if you work diligently should enable an improvement to approx 230cfm.
Typical exhaust flows are 154cfm@28" on exhausts, yours should rise to at least 165-170 after mods.
At this point in time, ive done limited tests regarding valves and seats, so its far from clear what the ultimate seat angle, width and number of cuts plus optimum valve shape is for these ports, that will come later when I have more time to spend on them.
I hope this article is useful.
Copyright 2009 T.Warren ( 4v6)