'66 300hp Holley Carb

[Alex Gilmour]

All, I just received my brand new 3367 Holley for my '66 327/300hp. My question is which base gasket is correct for the carb? (The car had the incorrect base gasket so comparisons are useless).

Holley provided 2, one with 4 holes (1 for each barrel) and a long slot near the end that spans the width of the gasket.

The other has 2 holes for the primaries and 1 common slot for the secondaries, and no other holes.

Thanks, Alex

'66 A/C Coupe

[Alex Gilmour]

Re: '66 300hp Holley Carb (More)

All, Holley also included a metal plate with 4 holes. I assume that it goes between the carb and the base gasket??

Thanks, Alex

'66 A/C Coupe

[Joe L.]

Re: '66 300hp Holley Carb (More)

Alex----

Your 1966 300hp/327 should be equipped with cast iron intake manifold GM# 3872783. This manifold should have 4 equal-size holes for each carburetor barrel. At the front of the carb mounting pad, I believe you will find a groove about 1/4" wide which extends nearly the width of the carb pad. At each end of the groove are two holes which access into the manifold heat cross-over passage. This "feature" is designed to provide "pre-heat" to the carburetor during engine warm-up, supposedly for better fuel atomization.

For your application, you should use the gasket with the four holes. If your manifold has the groove I described, then the long, narrow groove in the gasket should mate to this. The gasket goes on the manifold first, then the stainless steel shield. The shield is there to prevent exhaust GASSES which pass through the "pre-heat" groove from damaging the carburetor. So, to summarize, you install the gasket first, then the shield, then the carburetor. The original GM part number for the gasket was 3890495 and for the shield it was 3884575. Both are now discontinued from the GM parts system.

As a point of further information and advice, if your manifold is equipped with the "pre-heat" groove, I recommend that you disable it. In my opinion, this system is responsible for more carburetor problems than anything GM ever did to a car. The stainless shield does prevent exhaust gasses from getting to the carburetor, but the heat on the carburetor causes untold problems, including warped carb castings and accelerated soft part wear. The "pre-heat" system can be disabled by drilling and tapping the two holes to accept the smallest size pipe plug which will fit(1/8"pipe, as I recall). Don't worry about "losing points"; no one will be the wiser once the carb is on the car. GM used this system on most 66-69 V-8s. For 1970 and beyond, they decided that it wasn't "necessary" anymore. Or maybe it was all those carburetors they were replacing under warranty.

The only thing that you might "lose" from this modification is a little cold start performance. I think you will find the difference negligible. Primarily, the mod will preserve your carburetor if that's important to you.

[Alex Gilmour]

Re: '66 300hp Holley Carb (More)

Joe, Thanks for the tip. Since I live in Phoenix, I am going to do this. Is there any problem with drilling the intake on the car? ie filings going into the engine? Or will the filings just get blown out the exhaust?

Thanks Again. Alex

'66 A/C Coupe

[Joe L.]

Re: '66 300hp Holley Carb (More)

Alex---

Theoretically, if you were to perform this operation with the manifold on the engine, the filings should wind up in the exhaust. I'd still be a little hesitant to do it this way since they could still find their way past the exhaust valves on the left side of the engine. If you do, I'd be very careful to minimize the chips falling into the passage. Use grease on the tap to retain as much as possible. When you're done drilling and tapping, insert a magnet into each hole to try to collect as much of the material as possible. One of those pencil-like tools used to start screws on one end and a small magnet on the other end should work great for this.

[Alex Gilmour]

Joe - One more question - Base Gasket

Joe, Thanks for all the help so far. Now that I have the holes plugged, couldn't I use a normal Holley gasket (one without the cutout at the front for the exhaust crossover)? The people at Long Island Corvette sent me the wrong metal baffle plate (one for an AFB!), but without the crossover functioning, wouldn't a standard 4-hole Holley gasket work just as well now? I should be able to pick one of those up locally tomorrow so I won't have to wait for the metal plate...

Thanks, Alex

'66 A/C Coupe

[Joe L.]

Re: Joe - One more question - Base Gasket

Alex----

Yes, I believe that you could dispense with the stainless baffle with the "pre-heat" holes plugged. However, there is more than one "standard" Holley gasket. I'd try to find one that is IDENTICAL to the one you have, save for the pre-heat cutout. Also, most stock gaskets are a relatively thick, steel reinforced "asbestos" type gasket. This is the best type to use for two reasons. First, it helps insulate the carb from heat. Second, the thickness may be important to the proper functioning of your divorced choke.

A lot of aftermarket Holley gaskets are the thin, non-insulated type.