I’m setting up a Eldbrock 7525 manifold with 2 thunder series 500 cfm carburetors. My question is about vacuum lines. The brake booster will be attached to the back of the primary carb. The vacuum advance will be run from the primary carb, driver side port the to the distributor. This is the rear carb in this case. The pvc will run from the front carburetor middle port to the valve cover. My question is what port do I use for the transmission? There is no much room between the primary and secondary carburetor. Not sure what port on the front carb is appropriate. Any help is greatly appreciated.
The p***enger side vacuum port should be manifold vacuum on both carburetors, that is what you need for transmission.
Run the carbs 1-1 and you won't have any issues on which carb to put whatever hose on, plus the engine will be happier since it'll be getting better fuel distribution.
Nice construction! IMO, manifold vacuum for the trans, venturi vacuum for the ignition, brake booster and PVC large manifold vacuum. I like progressive linkage and have run it for 7 years with no problems. If you’re planning on having and using the car, an investment in a unisyn will be handy when setting idle no matter how you choose to run them. Summit sells them and I attach it to a Moroso carb cover to set 4 barrels.
Try running your carbs 1:1 , you may find it to be far more responsive . It should not affect your fuel mileage .
Everything can be attached to full manifold vacuum . venturi vac could be used on vac advance depending on cam , idle settings ,distributor curve .
Manifold vacuum ports on Edelbrock carburetors are always exposed to manifold vacuum, even if it is a secondary carburetor, with closed throttle blades.
For power brakes this is the best choice. The vacuum ports on most carbs aren't all that big, you need a fair amount of volume to operate the brake booster. I don't recall ever seeing the OEMs using a carb fitting for brakes, they always seemed to use a direct-to-the-manifold connection.
You can split with T or Y fittings to service more than one point without losing any vacuum signal strength. (Within reason. No 100-foot fat hoses which can cause a vacuum delay.) But for safety reasons, you shouldn't "T" into the brake booster hose to avoid any extra places leaking or pulling apart. Your life may depend on the booster hose....... the rest not so much.
The front-center port on an Edelbrock is a 3/8" hose barb, to manifold vacuum. The rear-center port is 1/4"NPT, to manifold vacuum. This is commonly plugged at the time of delivery. The 7525 has manifold vacuum port.
Thank you I have Lokar linkage that could be set up either way progressive or static. I will consider it.
I will have to look at the manifold again. I ***umed all the open ports were for sending units. I have the electric fan next to the thermostat housing the oil pressure is into the block on the back of the motor and the water temp is on a port in the back by the distributor.
If you look in the fire wall reflection you can see the water temp, oil pressure and brake booster pick up on the back of the crab. Is the blocked off port next to the oil pressure sending unit a vacuum port? thanks again for all the great support.
My understanding is this set up likes a lot of timing. I’m using a ready to run distributor blue springs in place. It’s a comp cams xe284. Pretty fat cam. 86 small chamber corvette aluminum heads. The motor cam out of a 1970 chevelle that did and LS swap. He was running 12:50’s pretty consistently but as always wanted more so I bought a running motor with all forged internals 30 over 4 bolt main all arp hardware that is more than enough for the 32.
One of my beefs with the aftermarket carbs is while the hose barb sizes are correct, the internal p***ages in the baseplates can be both convoluted and sometimes small. Just like a cylinder head, small crooked ports = less air flow, not a good thing where a brake booster is concerned IMO. I dunno, maybe I'm being too **** about it but I don't like it. My other beef is the carb aftermarket has seemingly decided that putting all those hose connections sprouting out everywhere is somehow helpful. I'll single Edelbrock out here in particular, their hose barb location choices seem perverse, especially for a Ford.
To me that looks like another port to the water jacket. A vacuum port would be in the intake runner. If you were to add a vacuum port for the power brakes, it would be in the intake runner, immediately behind the rear carb.
Your setup looks VERY nice, however, if it were me, I'd have the temp gauge sensor in the opening near the thermostat housing. That is where coolant is the hottest, as it leaves the engine and heads to the radiator. The fan switch sensor can go just about anywhere there is an open port to the coolant. Do your cylinder heads have a plug between the spark plugs (1 & 3 on the left or 6 & 8 on the right side) that could accommodate the fan switch?
The 2 plugs in the back of the intake manifold are for lines that you plumb to a thermostat housing for coolant flow. Remember these manifolds were built for racing and we street them; they may not be necessary for what you are doing. The fitting in the center rear of the carb is fine for a vacuum brake booster. With the carb off I have carefully enlarged the p***ages with drills and die grinders, they are split and take vacuum from both sides as these are dual plane manifolds. Each cylinder head will have the accommodation for a temp gauge just like the stock engine has. It looks as if you want your engine as simple and sanitary as possible but something’s just need to be there.
There is no need to go through antics to enlarge ports for vacuum. Neither the vacuum modulator for the transmission, nor the power brake booster require any sort of flow. That is not how they work. The only thing that both of those appliances require to function is a line pressure lower than atmospheric, preferably made so by engine operation.
I’ll take a look at the block. Funny the directions from spall said to put the sensor close to the thermostat. I can alway move them around.
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