That's correct. this is part of the EGR (Exhaust Gas Recirculation)
system. On the Tigers, and other cars of that period, it was used mostly to
just heat the Intake manifold as described below by Bob. In later cars of
the 70's and 80's, they had a valve that would feed some of the cooled
exhaust gases (the ones being passed through the intake manifold), back into
the carb base to be re-burned. Part of the clean air systems. This is also
when Air pumps showed up to pump fresh air into the exhaust manifolds to
help finish the cumbustion of the air/fuel misture. Shortly after this came
the big heat shields to keep the cars from burning up from the Super heated
exhaust manifolds and down pipes...!!!
Rich
>Dave,
>
>These are the "heat riser" openings that allow exhaust gases to circulate
>under the plenum chamber. Heating the plenum improves gas/air mixing and
>speeds warmup of the engine. If you are more interested in horsepower than
>economy, you may want to use the intake manifold gasket with these openings
>closed off. I use this type of gasket on my Tiger and have for the last
>twenty years. Can't remember what it was like the other way, but I have no
>objections to the way it works.
>
>Bob
>
>At 05:24 PM 10/15/98 -0700, Dave Binkley wrote:
>>This is a little hard for me to explain, but here goes. I have the
original
>>intake manifold off and am in the middle of installing an Edelbrock F4B.
>>Valve covers are off. Looking down at the cylinder heads it is pretty
>>obvious that the forward and rear ports are for water. The four ports
which
>>mate up to the intake manifold for air/fuel are also obvious. What is the
>>port in the middle for? This is the smaller one sandwhiched between the
two
>>middle intake manifold bolts.
>>
>>Here's why I ask. I have two intake gasket sets (both say they are for
>>260/289/302). One gasket set has no hole where this middle port is. The
>>other gasket set has a round hole where this middle (rectangular) port is.
>>I'm guessing I need to use the set with the hole in the middle and
probably
>>need to cut the hole out to match the shape of the rectangular port.
>>
>>So, what's going on here?
>>
>>Thanks,
>>
>>Dave
>>
>Robert L. Palmer
>Dept. of AMES, Univ. of Calif., San Diego
>rpalmer@ames.ucsd.edu
>rpalmer@cts.com
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