Big Valve question

[TurboFource]

Were the ports or valve seat inserts any larger on a Big Valve head?

[Kendo]

According to Wikipedia, https://en.wikipedia.org/wiki/Lotus-Ford_Twin_Cam ports were enlarged for the bigger valves. They don't mention seats. I was recently reading Vizard's book on the Ford 4-bangers, and he showed the heads not having seat inserts, which I found odd. His book covers more than the Twin Cam, though.

[jbcollier]

"Big" Valve heads have 1mm larger intake valves.  But that's not all, revised cams and ports is where the power really comes from.

All aluminium heads have valve seat inserts.  Virtually all the seat inserts are hard enough stock for unleaded fuels.  It's cast-iron heads that often have seats just cut into the head material.  Cast iron is not hard enough to run in anger with unleaded fuels.

[cwtech]

I can't speak to port sizes/changes.

All T/C's used Exhaust valve #B026E 0200Y which is 1.322" (33.5 mm).

Early T/C's used Inlet Valve #A026E 0019Y which is 1.530" (38.8 mm).

T/C Federal, Special, and Special Federal models used Inlet Valve #B026E 0019Y which is       1.563" (39.7 mm).

An aluminum OHV head needs to have valve seat inserts.  ....Valve seats are different for Big Valve and "small valve"  engines.

[EuropaTC]

Now I'm not 100% on this but I thought the inserts were the same for both standard & the bigger valves.

I know from personal experience that you can fit up to 1.62" inlet valves on the standard inserts because I've done it. From memory the valve seat was at the edge but Paul Ivy, an engine tuner back then, told me about it and sold me the larger valves when I went to him for some of his guides & 1.56" valves. After the change the engine (in the Elan) ran for years without any problems.

I know that you can get larger diameter inserts but thought these were for replacements should you damage the head removing the old inserts and need to re-machine before fitting the new ones, they only go up to 0.015"

Brian