I have a 1957 , 312ci, with G head pretty much stock set. My question is it came with the Summit open spacer gasket . Should I use it or use the 1” spacer ( 4 hole )? This is a car that is used for shows, and some street drive, but like to have a little giddy up go now and then. Not good at tuning but have been have been trying to learn but seem to get over loaded and mixed up. So any and all help and advise is welcomed. As this group is the best source for us that are note to bright. So thanks for all past help and for being there to keep the Y-Blocks forever going strong!

It really won't matter much but the 4 hole is best.



Lawrenceville, GA

The manifold vacuum at idle will be higher if using four hole carburetor gaskets with the four hole spacer.  To date I have not used the 1/4” thick open gaskets that are supplied with the Summit carburetors and instead have used a gasket that maintains a true dual plane scenario.  For the Blue Thunder and Mummert intakes with the dual slots, I will modify the four hole gaskets so that they are a dual slot configuration to match the dual slot carburetor spacer being used.

Lorena, Texas (South of Waco)

Oh, I didn't realize they were 1/4" thick.  Was thinking it was a regular gasket.  Definitely what Ted says in that case.


Lawrenceville, GA

Sounds like the 4 hole is what I will go with.  Thanks for your input.   Once I get it all in place is there any suggestion or tip i might get to fine tune?  Has anyone out there used one of these ?  and your feed back on it.  I chose the carb because it seemed to have good reviews and appears to be base off the FOMO 4100 carb. Hope its not to large for my setup. 

Your motor is similar to the engine in my Tbird.  My motor is a .060" over 292 with 312 heads, valve train and a relatively mild Isky cam.  I am running a stock 312 iron intake with a 465 Holley 4V.  500 cfm or so seems perfect for these engines.  My car idles smooth and accelerates smoothly with zero dead spots. The plugs are perfect and they never foul. Use a 4 hole spacer and you should be fine.  Be careful about which gasket you use under the carb.  Some of them are too wide causing interference with the secondary linkage.  This can cause erratic idle issues. 

The carburetor is based off of the Holley 4010 / 4011 series of carburetors.  The Motorcraft / Autolite is a much more common carb with a similar design, which is why lot's of people think it is based on that.

My tip, particularly for a novice, which is most of us, install an oxygen sensor to take out the guess work.  You can see in real time what is going on and get a lot more info in just one drive than you can with the old fashioned method of tuning.  You can do a temporary install if you don't want to leave it in the car.


Lawrenceville, GA

Well just hit the first bump in the road or maybe large pot hole..  It appears that 4 hole on the intake are approx.. 1.5" dia. and the Ventura butter fly's on the carb. are approx. 1.6" dia.  So maybe i will be stuck using the open spacer gasket.  Any thoughts on this?  would they make a 4 hole spacer that would work in this dilemma? .. . 

There are tapered spacers.

https://www.speedwaymotors.com/Plastic-Insulating-Carb-Spacer-for-Holley-4150-4160-1-Inch,614.html

and small diameter spacers that you can taper, so that the top matches the carb and bottom matches the intake:
https://www.speedwaymotors.com/Speedway-Phenolic-4-Hole-1-2-Inch-Carburetor-Spacer,79875.html
https://www.speedwaymotors.com/Speedway-Phenolic-4-Hole-1-Inch-Carburetor-Spacer,79717.html

I've also seen used, racing surplus, I guess, on Ebay in various top and bottom diameters.


Lawrenceville, GA

Most aftermarket four hole carburetor spacers will accommodate the larger throttle blades.  Another option is to take a die grinder to the original carb spacer and enlarge the holes accordingly so that the throttle blades open freely.  While doing this, you can put a taper on those holes so that any lip between the lower edge of the spacer holes and the intake manifold holes is minimized.  Later when the intake manifold if off of the engine, the holes in the intake can be enlarged or to take it the next level, the four holes converted to dual slots.

Picture of manifold with dual oval slots.
  

Link to article discussing how to modify the ECZ-B intake manifold.
https://www.eatonbalancing.com/2015/05/01/unported-iron-heads-can-still-make-over-a-hp-to-the-cubic-inch/   

Lorena, Texas (South of Waco)