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Re: GM 4 bbl intakes

To: list@marketvalue.net
Subject: Re: GM 4 bbl intakes
From: Greg A Myer <motorhead45@juno.com>
Date: Tue, 6 Jul 2004 12:56:49 -0400
Cc: buick-rover-v8@autox.team.net, mgb-v8@autox.team.net
Reply-to: Greg A Myer <motorhead45@juno.com>
Sender: owner-mgb-v8@autox.team.net
Good question Larry,
           I also have two   4bbl manifolds.  Both different.
Intake casting # 1349520 has primary bore size of 1.35 inches
                                                  the secondaries are :  
1.55 inches
I will be using the stock Rochester carb                  1.310 primary
throttle bore
                                                                         
                1.450 secondaries

the other manifold is casting # 581830X      Primary    1.450
                                                                        
Secondary    1.700

I believe either will feed a 215 just fine. I've port matched the smaller
one for my
Buick 215 going into a B GT.  The other will eventually go on a stroked
215.
The theory is that for street motors, smaller ports maintain mixture
velocity
thereby aiding low and midrange power ( that's where we play mostly )
   If the bores are larger than the carb sitting on them, opening them up
more
may hurt not only velocity, but distribution as well ( wet fuel falling
out of suspension
and onto the manifold walls as droplets )
          With larger cubes and lower gear ratios in the rear the motor
needs more
mixture, thus the larger manifold would probably work better under these
circumstances.
         Why 2 different manifolds ? I don't know. Any Historians out
there with the answer ?
                                                                         
                  Greg

On Mon, 5 Jul 2004 23:05:23 -0600 "Larry list account"
<list@marketvalue.net> writes:
> I have a couple of GM stock 4bbl intake manifolds that fit the 
> 215/3.5
> aluminum V8.
> 
> Each has four intake holes on the top; but one of them has smaller 
> primary
> holes and smaller secondary holes than the other.  When I compare 
> the
> intakes with the venturi holes on a Carter 400 and a Edelbrock 500 
> carb;
> even the intake manifold with the smaller intake holes has larger 
> holes than
> the carb venturi holes. (are you still with me here?  Even if I got 
> all that
> right you might need to read it twice!)
> 
> Are there any advantages of the manifold with the larger holes; or 
> perhaps
> the manifold with the smaller holes?
> 
> Does anyone know why there is a difference?  What they may have come 
> off of?
> 
> Thanks in advance,
> 
> Larry Hoy


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