Chuck the Truck's 52 Chevy - Manifolds & Linkage
There seem to be two schools of thought on intake manifold heating; it is necessary for good driveability when cold or it is unnecessary and hampers power output. I decided to use it, since I plan on driving this truck year round and driveability is more important than ultimate power output. I am using water heating, but before I installed the manifolds, I thought to check for leaks. The welch plugs on the bottom of the Offy 3X1 intake leaked like a sieve. Even if I were using the stock exhaust heat, I'll bet it would have made a nice hissing sound. A little JB Weld fixed it. I made a plate of 1/2" aluminum, drilled & tapped mounting holes and 1/4 NPT for the plumbing. I used 3/8 steel tubing tee'd off the heater hose fittings on the water outlet and water pump. I thought about adding a shutoff so I could turn it off in warm weather. Didn't, for expedience, but may in the future.
Checking clearances. The cast iron headers are from The Stovebolt Engine Co. They are beautiful, thick castings. I am going to use a super-special high-tech coating process rather than VHT paint or ceramic. I thought about using stoveblack wax, but decided that once it's on the road no way in Hades am I going to do that every month. Shoot, I don't even wash my vehicles. Ceramic is too expensive, VHT won't last, so I am going to use RUST! That's why I bought cast iron - so I don't have to worry about them rusting out. You can see the original throttle link passing behind the rear header. No easy way from there up to the center carb, so I fabbed everything new from the pedal. Plenty of room by the column and clutch linkage (I don't know if the 250 block mounted pivot would clear - I'm using the 1952 linkage), but I had to relocate the clutch return spring.
The flanges were the same thickness so I didn't have to do any fitting as I have read that others have had to do. I did have to cut a couple ears on the Offy, as indicated in the instructions with the headers. I used the stock 250 hold downs.
This is my linkage setup. The center bellcrank is stock from the 250, the end bellcranks are from the Offy kit, as is the firewall mounted pivot. I don't know what that last piece was for, but I didn't need it elsewhere so I cut down to use a pivot block. I ordered ball joints from Midwest Controls and used straight rod and flat stock from the hardware store. Oh BTW, I didn't like the Offy linkage since it seemed flimsy and looked hokey. The end bellcranks I used, since the short arm/long arm allows the end carbs to "catch up" when using progressive linkage.
I used a piece of 3/8 rod (should have gone 1/2" to seal better on the felt) coming off the gas pedal. A 1/4" clevis pin, 1/4" flat stock, 3/8" rod, that mystery piece, and another piece of 1/4" flat stock got the linkage around the header. I spring loaded the cross shaft to eliminate side to side slop. I wanted plenty of expansion clearance since the mystery piece is aluminum and inches from the header. All the 1/4" linkage was made from solid rod that I only threaded as necessary. Allthread looks cheesy. The 1/4" link tying the front and rear carbs together has sliding pivot with a 2 set screws to lock it in position. This allows me to adjust when the secondaries come in. The short links are also adjustable.
I modified the stock bellcrank by adding a piece of 3/8 steel tubing as a pivot shaft. Slightly reamed, it rotates on the 5/16" mounting bolt. Swinging freely off the shaft is another link I made from 1/4" stock. It is held centered by 2 light springs. One of the set screws on the front/rear link pivot attaches it to the swinging link on the main bellcrank. This allows me to adjust when the secondaries come in: The "U" on the bellcrank contacts the swinging link, and adjusting the gap changes when the secondaries start to open.
The secondaries start opening at about 25% throttle opening on the primary. When it's running and I finally decide which carb will be the primary, I'll delete the extra choke plates. No, they aren't a matched set - I scrounged what I could. One came on the engine, which I rebuilt, one is a factory rebuild, the third is NOS. Ebay again. Once it's running, I can play with tuning and calibrating.
Air cleaners on the rear carb interfere with the fender brace. I can move the rod, or maybe fab a trick air cleaner. Yes, I'll remember the engine moves (most likely after I've built something).