This note has to be for Ted -

It almost seems to me, after reading doen through the thread - that there is a particular length of straight tube that needs to exist under the butterfly shaft. The combination of that uniform passage - and then the "diffuser" opening below does the deed? Looks like the section of straight tube must be something equal to (or slightly over) the full diameter of the butterfly below the pivot centerline?

 
 Steve Metzger       Tucson, Arizona

Ted, just finished reading that YBM article on the spacers, very interesting and again thank you for the testing results. Is this 4hole/open base style available or did you make it? best regards bill.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

Steve.  It would be nice if it was as simple as you propose but it’s not.  The carburetor spacer is related to the specific engine combination and if simply changing a engine parameter such as the camshaft or the exhaust, then the spacer requirement also changes.  The carb spacer ends up being a part of the total tuneup where the intake tract length from the carb to the valve is working in tandem with the exhaust lengths and the camshaft overlap has a lot to do with the balance of those two lengths.  That’s an over-simplification but will have to suffice short of writing a chapter on the subject.

 

The tapered spacers do tend to work best in those instances where the engine is under carbureted.  The tapered spacer straightens out the air flow by reducing flow eddys under the carb itself thus permitting more air flow through the carb.  As a general rule, the better the heads are, then the more a tapered carb spacer tends to benefit engine performance in a particular rpm band.  There was thirty plus horsepower gain on my roadster engine in just playing with spacer designs.

 

I have Gary’s 312 stroker on the dyno right now and it’s in the process of testing nine different single four barrel intake manifolds on it.  All are ported differently.  With what’s been tested so far, it’s becoming clear that there is no particular spacer that’s going to be a fit all.  Certain intakes simply like certain spacer designs or spacer heights.  Once all the intakes have been run, then it’s a matter of sorting out the data and making some sense of it.

Lorena, Texas (South of Waco)

The ‘tapered’ carb spacers are available from several suppliers in a variety of heights.  HVH and Wilson are two companies that come to mind.  Lots of home shops with CNC machines are also now knocking them out.

Lorena, Texas (South of Waco)

Ted;

I think I know the answer to this, but to be more certain, here's the question; I plan on using the "B" manifold on a street, supercharged 331 cu.in. motor. So, would you elongate the holes into ovals and use a 1" spacer that was open or with holes?

Thanks,

Rono

  Ron Lane,  Meridian, ID

Here’s my two cents worth.  Anyone else is free to comment.

 

That’s a yes for elongating the carb holes into slots.  With the slotted intake you can go either way, four hole or open but my particular choice in this case would be an open style carb spacer if simply choosing from these two designs.  Because maintaining a separation under the carb (true dual plane) with the supercharger isn’t as important as in a normally aspirated scenario, then reducing any restrictions under the carburetor by using an open spacer would have its advantages.  Another option that would help to smooth the transition going into the ‘slotted’ manifold and still maintain a true dual plane design would be a spacer with dual slots that matches the intake holes.  Here are some more pictures including the dual oval or slotted spacer.  All these spacers are upside down and viewed looking at their undersides.

  

Lorena, Texas (South of Waco)

hi ted, does a 4 hole tapered adaptor ( large hole carb to small hole intake ) work better than a straight bore 4 hole adaptor and boring the intake holes to match the larger bore? does the venturi affect help the bottom end torque on a street stocker?

 lincoln/merc. y-blocks &mel's                                                               bucyrus, ohio.

Ted;

You asked for more input, and here's mine.  I tried a slotted front-to-back intake on my race car with the Paxton.  Ran .1 to .15 seconds slower with the slotted one compared to the stock F code manifold.  No other changes were made.  It uses the stock phenolic 1/2" 4 hole spacer under the teapot..

John - "The Hoosier Hurricane"

Here's a Quick Fuel 1" aluminum carb spacer that is for Holley 4150 type carbs. It may be what I'll go with for my build. It is machined with the 4 hole/square bore design and their comments about performance seem to be right in line with Ted's.

http://www.summitracing.com/parts/QFT-300-4150-1AL/

Rono

  Ron Lane,  Meridian, ID

John.  Thanks for the real world input.  Supercharging just seems to make its own rules.  What works for normally aspirated engines just doesn’t cross over cleanly to ‘blow thru’ stuff.

Lorena, Texas (South of Waco)