Wondering what the members thoughts are on the use of a spacer between the carb and manifold? My stock Rochester on my stock manifold on my 79 L-82 has a 3/8" spacer but I am not sure if the spacer was added by one of several previous owners.
I am replacing with a Holley 670 cfm to set on top of an Edelbrock RPM Air Gap. I understand hood clearance issues and that's not a problem. 

 Different design spacers provide different "advantages". You have the open hole spacers, where the center is completely open, and you have the four hole spacer that has 4 holes presumably the same approximate size of the carb throttle plates. The open hole spacers help with higher rpm(hp) gains, while the 4 holers provide a slight torque increase at lower rpm. The height of the spacers is equally important....changing the height will move the HP/torque curve up/down the rpm band. Going from a 1/2" spacer to a 1" spacer makes a definite change on dyno tests...usually the taller the spacer, the more top end HP, up to a point.
The spacers also will provide a bit of insulation from engine heat that is transferred from the intake manifold to the carb base, but here the material the spacer is made of makes the biggest difference. Metal(aluminuminum) spacers will still transfer heat, just not as much. Phenolic(plastic/resin) type spacers provide much more heat insulation, and are normally the best choice if heat is an issue.
The design of the intake manifold needs to be considered when choosing a spacer plate. An open plenum intake will work best at higher rpms with the open hole spacer, but an open plenum intake with a 4 hole spacer will increase the torque all across the board.
On a stock type, 4 hole intake, an open hole spacer is basically useless for anything other than heat insulation...the combination of open spacer/4 hole intake will not provide ANY performance gains, and in most cases will loose both torque and horsepower.
4 hole intakes need to use 4 hole spacers....this combo will help hp AND torque in the mid range rpm, but will usually drop hp in the higher rpm ranges.

There are also adapter/spacers that adapt from a spread-bore carb to a straight bore intake, and versa-visa. The only real benefit, if any, of those things is the heat insulation properties.


I'm spaced out now.....


Well...almost...
bcousins said:"My stock Rochester on my stock manifold on my 79 L-82 has a 3/8" spacer but I am not sure if the spacer was added by one of several previous owners."


Are you sure what you see is not the normal, stock gasket? The base gaskets for quadrapukes are normally aboot 3/8" thick, and are made of a fiberboard-like material....mostly for heat insulation, but also for a good seal to the intake.  
Doesn't really matter since your are changing both intake and carb...just wonderin.


|UPDATED|6/26/2014 10:07:07 AM (AZT)|/UPDATED|

Joel,

Bcousins am I to understand that you are installing an Edelbrock 

Thanks for the info about the heat transfer Sal. The L-82 stock manifold is 4.75 inches high. The Edelbrock RPM Performer Air Gap 7501 is 5.25 inches high, a difference of 1/2 of an inch. I know it will not clear the stock hood with the stock air cleaner but I believe it will with the Edelbrock Low-profile air cleaner that is reportedly 1 inch lower. 
Any other members have experience with this combo?




|UPDATED|6/27/2014 8:27:53 PM (AZT)|/UPDATED|

I was having hot start issues with "The Toy" several years ago.  Turned out the carb was getting too hot to touch and boiling the fuel.  I bought a Mr Gasket spacer kit which was a mix of aluminum and fiber layers.  I added as many layers (alternating the fiber and aluminum) as I could without bumping the hood.  The hot start problem went away and the carb stays WWWAAAYYY cooler than before.  The only modification I had to do was to make a slightly longer choke linkage (I used an old clothes hanger - yea I know - can you say "BUBBA"!).

Jim,
Thanks for the info about boiling fuel. By my calculations, and I used some of my grandson's Play-Do to measure, I have about 3/8 or so to play with so I can use a small spacer before having to spring for a new hood that will accommodate all the goodies. 
Any idea how much spacr you created using the layers?

I admire your ingenuity by using the coat hanger to solve a problem. Always helpful to be creative!