I managed to score a 64 300 4bbl intake to stick onto my engine. I would like to use a holley 4bbl for carburetor (because its what i have). I also have an edelbrock 1406 but prefer the holley. My question is can the 1.4"-ish carburetor pad bores on the intake manifold be enlarged to the 1.68"-ish holley throttle bore size? I seem to recall a thread where someone took a 4bbl intake, and in an effort to "convert" it to an open plenum design found that the coolant passages are alarmingly close to the intake plenum walls I know some sort of adapter will still be necessary to accommodate the bolt pattern but i should be able to tackle that easily enough.
I would leave the bores in the intake alone and taper or simply step bore the adapter....you get a venturi effect....may be of a benefit....may not help but can't see it hurting
Or turn a tapered spacer upside down ...roll the edges on the intake to match the bores of the holley better...would be fun and interesting to see which approach the 300 likes
Is this what your intake looks like? If so, can you lay a Holley gasket on it to see where it is too small? Also, can you show both a Holley and a standard gasket on both sides to show how much it needs to move? First off, I'd say you need to fill in those heat crossover passages that pass in front of the intake. Fill them with plugs or pour molten aluminum into them. After that, you'd be able to take a Rochester to Holley adapter and get it to work with very little effort.
Mine looks like this (see pic). I don't have them on hand, everything is stored for the winter but it'll be warmer soon. I will need to plug the holes in the heads {65 engine}, but intake is fine. As for the taper down, I think the venturi effect is less effective after the throttle plates, it will just create a bit of turbulence. Ill be using the adapter knuckle busted has shown as the bolt pattern is different. You can also see in the image the gaskets are different
That adapter that Greg shows above is all you need. If you have to ream out the primaries a little bit you'll be alright. When it is hogged out to two ovals you would open up the water jacket.
The restriction is the shallow plenum side of the Manifold. What you want to do is get a 4 hole spacer, it needs to be atleast 1/2" tall , in fact if you can fit a 1 inch and still have air cleaner to hood clearance and hook up the throttle the better. What you then want to do is open the top of the Intake between the front and rear throttle bores on that shallow side and then do the same to the spacer that you get. This mod will help tremendously in evening up the flow difference between the shallow and deep side plenum. Running a Holley is fine as long as it's not a DP. Also a Carb of over 600 cfm will on serve to reduce drivability. A 600 cfm Carb can make 400 hp and for sure your 300 ain't doing that!
Hey guys, just think about this a minute OK? It doesn't have to be anything fancy. All you need is a smooth transition from the Holley throttle plate bore to the intake and you can do that with a die grinder. The transition doesn't need to go deeper down the throat than maybe 1/4" and you certainly aren't going to hit the water jacket that close to the top. If you had access to a mill that could cut the taper that would be great but hard to find. It really isn't much metal you would be removing. You only need to do two things, eliminate any chance of the throttle plates hitting (unlikely anyway) and smooth the step. It should run OK even if you did nothing, just have extra turbulence there which will cut down full throttle power some but likely improve fuel mixing. The bigger issue is matching up the bolt pattern. For that you may have to add some metal. Jim
Thanks guys. I will be running a spacer for sure wth a taper. Here is the thread I'm thinking of. https://www.v8buick.com/index.php?threads/aluminum-intake-on-iron-block.221582/ The pics show the water passage is extremely close. Looks like it's a no go, or Atleast very very very close. I'm not willing to mess with it only to learn I've ruined the intake. Better to air on the side of caution.
I'm trying to pick a spacer but getting lost in the options. I didn't realize a square bore flanges came in so many variants. What's the different between Rochester 4GC LARGE and Rochester 4GC SMALL? Is this the same bore and bolt pattern as a Carter afb? Im considering the trans dapt 2064. Or speedway motors 1351935b.
I modified mine to be the same as a small Holley (1 9/16" bores), with no break-through. However, all of the gaskets and phenolic spacers that I have found are made for bigger Holley (1 11/16" bores), so I am still going to have a slight stepdown lip as mixture enters the intake manifold. I believe that it is going to break through if I go to 1 11/16" bores.
You may have got lucky, the pics with 2 oval holes the water jacket is between the bores. Maybe chamfer edges? A guide to building the lil guy. The Mighty 300 | Page 22 | V8buick.com
