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With a dump-type Fuel Pressure Regulator installed, which of the two (yellow boxed) vacuum ports going to the Regulator would work best?
Thanks in advance,
Steve
Neither one of those. The port you have circled on the left is not a vacuum port - it's a vent port going into the air cleaner base area of the carb. The port you have circled on the right is a ported vacuum port - not manifold vacuum. The only manifold vacuum port on that carb is the one located under the float bowl in the throttle plate where the choke pulloff is hooked up. A dump-type regulator uses manifold vacuum/pressure and is usually used on a supercharged application to increase fuel pressure under boost. I don't see a supercharger on your engine, so I'm not sure why you are hooking up the manifold pressure sensor to the pressure regulator. The regulator port would normally be capped off on a normally aspirated engine.
Dump-type regulator on a normally aspirated engine - the vacuum nipple on the rear of the regulator is capped off to maintain steady/constant fuel pressure on the non-supercharged application (the only reason for capping it is just to keep dirt out of it - you can leave it open and uncapped and the regulator will work perfectly - just set the pressure you want and leave it):
Here is the same dump-type reg installed on a blow-through supercharged Corvette. On a blow-through supercharger, the sensor line on the regulator is hooked up to the bonnet over the carb so that the fuel pressure to the carb can overcome the supercharger pressure - you can see the hose coming off the regulator and going into the base of the supercharger bonnet. This would be the same as using the port on the left on your carb if you had a blow-through system installed. With no supercharger, the line from the regulator would always sense atmospheric pressure, so the regulator port is simply capped off:
Neither one of those. The port you have circled on the left is not a vacuum port - it's a vent port going into the air cleaner base area of the carb. The port you have circled on the right is a ported vacuum port - not manifold vacuum. The only manifold vacuum port on that carb is the one located under the float bowl in the throttle plate where the choke pulloff is hooked up. A dump-type regulator uses manifold vacuum/pressure and is usually used on a supercharged application to increase fuel pressure under boost. I don't see a supercharger on your engine, so I'm not sure why you are hooking up the manifold pressure sensor to the pressure regulator. The regulator port would normally be capped off on a normally aspirated engine.
Dump-type regulator on a normally aspirated engine - the vacuum nipple on the rear of the regulator is capped off to maintain steady/constant fuel pressure on the non-supercharged application (the only reason for capping it is just to keep dirt out of it - you can leave it open and uncapped and the regulator will work perfectly - just set the pressure you want and leave it):
Here is the same dump-type reg installed on a blow-through supercharged Corvette. On a blow-through supercharger, the sensor line on the regulator is hooked up to the bonnet over the carb so that the fuel pressure to the carb can overcome the supercharger pressure - you can see the hose coming off the regulator and going into the base of the supercharger bonnet. This would be the same as using the port on the left on your carb if you had a blow-through system installed. With no supercharger, the line from the regulator would always sense atmospheric pressure, so the regulator port is simply capped off:
Lars
Very enlightening Lars. Thank you very much. You explained it well.
Appreciate your time and your pictures, all to help me get it.
01-13-2018, 01:45 PM
Which Vac Port Works Best?
