I am planning on running a Holley 1850 or an Autolite 4100 on my 312 build, and was wondering about carburetor spacers.  Do I need one, and if so what height and whether open or four hole?  Thanks for your consideration in advance.

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

What intake are you planning to install on the car?

Frank/Rebop

Bristol, In ( by Elkhart) 

I am using a stock post '57 four barrel intake.

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

A four hole spacer is best suited for your particular application.  An open spacer will hurt low end torque, have a slight decrease in manifold signal at the carburetor, and does present some flow turbulence where the fuel air mixture must transition into the holes at the intake manifold.  The hole sizes in the stock intake are smaller than the throttle bore sizes in most modern carbs which requires the intake holes to be bored to match.  Putting a taper in the bores of the carburetor spacer can also be a way around this but the main thing is to have a smooth transition from the carburetor bores to the holes in the intake.  Just measure your carb bores at the base of the carb and compare these to the intake bores and plan accordingly.

Lorena, Texas (South of Waco)

Cactus,

           If it was me. I'd stack up 4 or 5- 4 hole gaskets and try that. My car picked up mph in the quarter with more but you can run out of hood clearance rather quickly. Mummert and Feistrizer both have told me that Y's don't seem to like open plenums with an original manifold. Seems it hurts the low end without adding much to the top end.  

Frank/Rebop

Bristol, In ( by Elkhart) 

Thank you very much for the info. 

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

This picture shows a 1/2 thick phenolic spacer being fitted to an ECZ 9425-B four barrel manifold. The phenolic material is way less likely to transfer heat than aluminum and is a little better at preventing distortion of the carb base than a stack of gaskets. Avoid the poly "plastic" spacers as their heat resistance is usually poor on an exhaust heated street manifold - and like the guys have said, use a closed center that keeps the 180° manifold divided. These are predominently torque engines and open center spacers usually lend themselves more to a higher rpm range.

The spacer is available from both Speedway Motors and Moroso as an exact match to the original Ford manifold bores. After laying down some tape, transfer the throttle bore diameters of the bigger 600cfm carb (a proper size matching gasket works good) to the phenolic base. A small half-round file or other similar tool will make short work of enlarging the upper bores and tapering them down to the manifold size. Making the upper end slightly larger than the carb throttle bore insures there will be no impedence to airflow exiting the carb. The plan is to leave no abrupt edges that extend into the flow path at both upper and lower edges of the spacer - so take care not to enlarge the bottom holes. I usually finish the phenolic material with 400 grit paper to make things nice and slick.

At lower right you can see a small hole in the Moroso spacer - there is a second hole on the diagonal opposite. These are provided to allow "pinning" the spacer in an exact location on the manifold. There is enough clearance in the stud holes to slightly misalign the spacer over the manifold bores during assembly (and leaving a step). Moroso recommends drilling the manifold for two rollpins that always return the spacer to an exact match (I didn't). This is certainly good practice - but I put a slight radius on the top edge of the iron manifold and wrapped some tape on the studs (to improve the fit) instead. 

Don't talk yourself out of doing something to properly match the carb, spacer and manifold! The primary throttle blades of the carbs rotate clockwise as seen from the driver's side. Because the shaft centerline is by necessity above the mounting base - the blades may actually rotate open over the smaller bores with nothing more than a gasket adding to the space between. As the blade swings open from idle - it will actually begin to close the rear of the venturi passage by mating with the spacer or manifold bore radius below. This is a major disruption for part throttle operation as all of the airflow must abruptly transfer to the the front wall of the venturi and cross the upside edge of the throttle blade.

 
 Steve Metzger       Tucson, Arizona

Thanks, I think that I have found one of the Moroso spacers here locally, and it shows to have the roll pin holes already there.  I am going tomorrow to see if what I found is what I want.  Again, Thanks, everyone for your help

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

I had never heard this before. It's a good day when you learn something new.



I wonder if anybody has ever tried using D shaped throttle blades/ports to minimize this effect.



Regarding matching of spacers/runners, etc. It's my understanding that there are anti-reversion effects from making the downstream side slightly larger than the upstream side; the disruption of flow is much greater in the reverse direction when you're going from large to small than visa-versa.



Edit; By the way, that's outstanding looking work, Steve M. Very impressive!



Perhaps the carb mounting studs could be changed to something with an untheaded shank in the middle to help align the carb spacer.


Best regards,



Paul Menten

Meridian, Idaho

You guys are the greatest, thanks for the info

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland