I’ve been out of this for a long time and finally decided I want to get the olds running. It’s a 55 with a 324. I’m rebuilding the 324 and I’ve decided to use an Edelbrock OL396 3x2 intake that came in the trunk when I bought it. This car originally had one 2 barrel Rochester 2gc. One issue is that these intakes have the 3 bolt Stromberg/holley bolt pattern and I intend to run 3 small base rochesters (4 bolt) on this engine. About a decade ago I had bought a set of baseplate adapters that were made out of machined aluminum. I have never been happy with how they look… too billet-y. Recently browsing online, I found out that offenhauser makes a cast aluminum adapter (#5159). I put some on an order with Charlie Price but he does not keep these anymore and the order shipped without them. I opted to order the knock offs from speedway. After receiving them, I remembered an issue I had with the first set of adapters. The*****erfly ports on the intake are much larger (1.36 inches) than normal 3 bolt bases- they are roughly the same size that my Rochester needs. The adapters were naturally much smaller, so I took them to my then work and had them opened up on a CNC machine so that the base was the same size as the top (no taper in the throat). This effectively unshrouded the orifices on the intake. If course, the new adapters are also much smaller on the base than the orifices in the intake. I can open them up, but some preliminary measuring indicates I can’t take them all the way due to insufficient wall thickness of the casting. I’m thinking that I’m probably stuck with the ugly adapters, but the cast ones look a lot better on the intake. How much shrouding is unacceptable? Or maybe is there a way to make the ugly adapters less so? This will be street driven pretty much exclusively, maybe 1 pass on strip for a (slow) time slip. It will have a warmed over cam grind from Ross, and the heads (#8) have been cut for bigger valves, throats, and a little bowl blending. I have attached pictures because words are hard.
Looking at the last two pictures, I can see where the spacer is blocking the intake ports, IS this what you are talking about? If so, and you don't have the wall thickness needed to open them up, can you blend the intake ports towards the centers, in other words, make the intake fit the spacers. It won't be ideal, as adapters never are, but it will be better than having the flat intake surface impede the air flow. I would probably just make spacers out of 1/2" aluminum with two holes each that match the Rochesters, there's no need for that tall of an adaptor Using spacers with matching holes will keep the velocity higher, and the throttle response snappier. With open spacers, you will loose some of the benefits of your dual plain intake.
If I understand correctly, the adapter throats are smaller than the intake ports. This shouldn't be a problem. The intake is only going to pull what the throat and carb allow. True, it's not a smooth tapered expansion from adapter to intake, but it's basically a built-in shear plate, and you wont have any reversion, lol. If the adapters were actually bigger than the intake, then you could get some funky turbulence that might impede flow, but that's a different story. I'd run the better-looking ones, even if they are smaller. If you want to maximize the flow, I'd suggest reclaiming some throat area by thinning and blending the center divider in the intake. Sure it may relegate the intake to only be used by your specific set up, but who were you planning on loaning that intake to, anyway... -rick
For a engine that's not going to be really high performance or drag racing use I don't see any issue with the adapters being slightly smaller than the intake ports. It should work well and not be a problem. Much better than if it was larger than the intake ports.
Yes, the last two pictures are of the cast aluminum adapters that somewhat block the ports. The picture right before them is the machined adapter. The fabbed adapter that you mention making is basically what these are; however it takes two machine plates per adapter because the bolt holes would interfere with each other. The front two holes of the 3 hole mount are about half a bolt hole off alignment from the 4 bolt pattern… so first plate mounts to the intake, has four threaded holes for the second plate, which screws to the first and has 4 threaded holes for carb studs. Hopefully this makes sense. I am a little hesitant to modify a vintage car part to accommodate a 2 bit adapter, but I will keep that in mind. As you can see from the second picture, the ugly adapters are slightly larger than the ports in the intake. I didn’t think this would be a problem, but am I mistaken?
I have done things like this , I think a little diffrent out side box,, If the pad on intake has room ( witch it should , take 1/2 -1.00 plate Custom drill 4 -6 holes threw plate into intake , tap intake 10/32 or 1/4 , Conter sink aliens,, The Bores you can eather drill straght down , or a slight angle tapper 10-20deg ? To to match intake Bore s Or leave the shelf , just depends on how much time you want to make custom part The the 1/4 (paper ) Is your new custom bolt pattern bolt & other 2 optional Bolt size 10-32 or 1/4 1 plate / adapter per carb instead of two adapters per Carb
Update: I bought a 1 3/8 carbide hole cutter that fit perfectly in the bores of the billet adapters. I screwed one of those to the small end base of the cast adapters, and used them as a cutting guide. I slowly used the carbide cutter to enlarge the throat of the cast adapters… I figured if I ruined one trying this I would just buy another… long story short, it worked way better than it should have. I just have a bit of work inside with sandpaper left to maybe smooth things out, but even that probably isn’t necessary.
The other thing you might try is to bead blast the "ugly" ones with a course grit to give it a rough as cast look. I have done that before with some success.
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