[Fot] Intake / Exhaust manifold mating surfaces to head

[Duncan Charlton]

My book sources indicate that it's fine for the intake manifold runner 
to be slightly smaller than the port entrance on the head, and the 
opposite goes for the exhaust port/manifold junction. Pulsing pressure 
waves revert upstream due to valve closure and leaving a lip at the 
outer edge theoretically blocks the reversion wave to some extent.  It's 
OK to have a "downward" step for the gases to fall over but you don't 
want an "upward" step for the gases to have to pass over.

Duncan
(Texas)


On 10/7/14, 9:49 PM, Tony Drews wrote:
> You're very liable to make things worse by opening up the manifold.  
> Having the manifold port somewhat smaller than the head port isn't a 
> big problem.
>
> Tony Drews
>
> At 02:46 PM 10/7/2014, Dan wrote:
>> I am preparing my TR4a head to accept the intake and exhaust 
>> manifolds and
>> there seems to be a rather significant difference in the diameters 
>> between the
>> intake ports of the head (1-1/2" dia.) and the intake manifold (1-3/8 to
>> 1-7/16" dia.). In addition, the two mating gaskets I measured come in 
>> with a
>> dia. of 1-23/32nd, just under 1-3/4".  The literature I have consulted
>> recommends that the intake ports of the head and the manifold match up
>> perfectly including the dia. of the mating gaskets.  Not so critical 
>> on the
>> exhaust  as a "notch" to the upside on the exhaust port apparently 
>> aids in
>> extracting gases.  What have you all found in your engine building
>> experiences?  I could carefully enlarge the intake ports to match the 
>> head,
>> but the remaining intake  (TR4a long runner) shell would need to be a 
>> opened
>> up around 7/32nds thereby perhaps weakening the runners? Thoughts?
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