Hi, John.
Most [remotely modern] heads have intake valves larger than exhaust.
The reason is that the differential pressure available to move the
charge into the cylinder is much smaller than that available to move
the combustion gases out. So more area is allowed for the charge to
pass through.
Further, the incoming charge cools the back of the intake valve, so a
larger surface area-to-perimeter ratio is allowed (exhaust valve is
heated through both front and back surfaces; the heat is rejected to
the head through the valve seat [primarily. Some does go out through
the valve stem to the guide] while the valve is closed, and only
through the area in contact with the valve seat, proportional to the
perimeter.)
So, the year the head came from shouldn't matter much as long as it
fits, has no cracks, is level, has rockers, springs, valves that fit,
manifolds. Combustion chamber size and shape will affect performance
but that gets into the realm of [somewhat-more] advanced engine design
and engineering issues.
Donald.
> From: "John & Tracy Knox" <jknox@erie.net>
> References: <001201bef9ee$6064bd20$f936fea9@w7dqq>
> Date: Wed, 8 Sep 1999 21:12:58 -0400
>
>
> Ok list, I have a 1970 1300, and I know the engine is coming out and like to
> make it better than it was. I also have an extra head, sans valves,
> springs, etc. It is a raw head that was given to me. I do not know what
> year this head came from. How do I know what year the head came from? Does
> it matter what year the head came from? Someone just mentioned that one of
> the heads has an intake valve bigger than the exhaust, It seems to me that
> this head is the same way. How to know for sure as I will have to fit new
> valves to this head.
>
>
> Thanks
>
> John
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