I thought I would share my manifold project with the group (pics included):

I thought about the intake manifold for my 20B for a year.  Initially, I knew
I would ditch the factory original one because it is so heavy and has all the
extra junk I don't need like the air valve, etc.  I participated in numerous
discussions within this group about the design and fabrication of intake
manifolds, but no matter what I heard or saw, I kept going back out to the
garage to look at the beautiful cast aluminum intake manifold that came on
the engine.  How nice it would be to use this perfectly shaped and ready to
bolt on manifold that has already been proven to work wonderfully on this
engine!!!  Then I would go back to the drawing board and consider other
options again.  Finally it occurred to me:  Why not just modify the original
lower manifold that I have and then possibly build the upper portion if
necessary.  The upper portion of the manifold would be easier to fabricate
and doesn't need to be as strong as the lower portion which still requires
structural strength.  As I looked at the manifold, it was the lower portion
which was heavy and bulky with all the emissions junk anyway.  As I closely
inspected it, I became apparent that much of the lower manifold could be cut
away thus leaving a small lighter manifold without the air valve, heat
jackets, etc.   So, I took a deep breath and a firm grip on my hacksaw and
went to work.  I still have a lot of work to do to finish making it lighter
and look pretty, but I have already cut the weight down from 15 pounds to 9
pounds, and I believe I can actually get it down to 7-1/2 pounds without
weakening the structure much.  I've attached some pics of the work I've done
so far, and I'll post more pics next week after OSH when the servers is back
up.

I haven't completely planned out the upper portion of the manifold yet but
I've been thinking about building runners from carbon fiber sleeves.  I've
already played with some foam tubes that could be easily used as a form over
which to lay the carbon fiber.  These foams tubes are cheap and easily
manipulated into shape.  I've seen some higher temp epoxies starting to come
on the scene over the last year that would probably work well considering the
cooling airflow within the runners.  I'd appreciate any comments on this !!!

Thanks,
Don Mitchell

Ken Powell wrote:

Don,
   I know this sounds like heresy, but I have a 'budget' of an extra 10 pounds that I am willing to build into my engine in order to save dollars.  I have never discussed this before (or even admitted it) but it is a very pragmatic decision.  My motor mount will weigh 1 - 2 pounds more than necessary because I am building it out of 4130 that is probably too heavy.  The oil pan will be another 1 - 1.5 pounds - again 4130 (0.035") because I can weld 4130 but not aluminum.  This is 3.5 of my 10 pounds - hopefuly this is all I will need.
   With that being said, I think that your intake is a good compromise considering the difficulty of building one from scratch.  Seems like a 2 - 3 pound weight penalty is reasonable.  The compromise that I do not want to make is a major performance penalty.  Will this manifold be tunable for the RPM range that you are looking for?

Ken Powell
kenpowell@aristotle.net

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