Hog out 2 hole Intake Manifold

[john02md]

Is there any value, or harm, to hogging out the 2 holes into 1 for use with a Weber 32/36.  I know it is recommended for the heavier breathing 38/38. 

Thanks,

John '74 Polaris

[Mark92131]

As long as there is no restrictions to the opening of the throttle plates on the Weber 32/36 with the 2 hole intake manifold, you should be good to go.  There certainly is no harm in hogging these out, unless you don't properly flush out the aluminum shavings and they end up in your combustion chamber.  Any value, possible improvement to the flow of gas/air mixture through the intake manifold.  This was an BMW OEM modification in the "Peanut" manifold, so someone at BMW thought it was a good idea.

 

Mark92131

[jireland2002]

No harm.  In fact it is a good modification.  It increases the volume of the plenum and should have a small improvement in performance.

['76mintgrün'02]

I asked this question a while back and got the opposite advice... which I took to heart.

 

[jimk]

I wasn't going to post.  Got tired of trying to discuss the topic and why the effort doesn't accomplish much if not the opposite of what was expected.  Nobody seems to have any dyno results of only the pre and post grinding effort to prove their point.  Hole size matching is one thing, Creating a sudden expansion is another.

[rstclark]

The other worthwhile improvement is to take the manifold off the engine and port the intake runners to match the intake ports of the head which are larger that the manifold. Taper them back in the intake runners about an inch and a half  Don't make them bigger that the head ports as that could be counter-productive. After removing the manifold, look at the intake manifolds gaskets , you will see the impression of the miss-fit.