85lebaront2 Posted March 19 Share Posted March 19 Bill, what are "umbrella boosters"? I've never heard of those. I don't have a picture of one handy, but the bottom of the booster venturii has what looks like a miniature hoop skirt on it to increase the vacuum signal. So instead of two 390 cfm 2 barrels back to back, you have a 345 cfm primary side and a 390 cfm secondary side. Main venturii size is still the same. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted March 19 Author Share Posted March 19 I don't have a picture of one handy, but the bottom of the booster venturii has what looks like a miniature hoop skirt on it to increase the vacuum signal. So instead of two 390 cfm 2 barrels back to back, you have a 345 cfm primary side and a 390 cfm secondary side. Main venturii size is still the same. That makes sense as a smaller venturi provides better vacuum signal and therefore (usually) better throttle response. They just achieved the same goal a different way. I've had to explain to people many times that bigger carb does not equal more fuel. An 850 double pumper on a mostly stock 302 in an F-150 is not a good idea. I know someone who did that and it ran like garbage. Link to comment Share on other sites More sharing options...
mat in tn Posted March 20 Share Posted March 20 That makes sense as a smaller venturi provides better vacuum signal and therefore (usually) better throttle response. They just achieved the same goal a different way. I've had to explain to people many times that bigger carb does not equal more fuel. An 850 double pumper on a mostly stock 302 in an F-150 is not a good idea. I know someone who did that and it ran like garbage. too many don't know what a carburetor does. it feeds the air with fuel vapor. and in doing this, it allows the engine to run as it can. it does NOT make the engine do anything. if the engine cannot provide enough cfm velocity for the Venturi, then it will not get the fuel. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 20 Share Posted March 20 too many don't know what a carburetor does. it feeds the air with fuel vapor. and in doing this, it allows the engine to run as it can. it does NOT make the engine do anything. if the engine cannot provide enough cfm velocity for the Venturi, then it will not get the fuel. Mat, we had a parts store that once sold an Offenhauser 360 intake, a Holley 850 cfm carburetor and an Accel distributor to a young USAF enlisted man with a 1957 Chevy 283 with a Powerglide. When it didn't run worth a crap they sent him to my shop (we were the Holley authorized warranty center). When we told the kid is was a totally impossible combination to get to work, the store that sold it (part of a group of loosely affiliated stores with one extremely rich partner in common) called and was extremely angry with us for telling him the truth instead of covering for them. Link to comment Share on other sites More sharing options...
mat in tn Posted March 20 Share Posted March 20 Mat, we had a parts store that once sold an Offenhauser 360 intake, a Holley 850 cfm carburetor and an Accel distributor to a young USAF enlisted man with a 1957 Chevy 283 with a Powerglide. When it didn't run worth a crap they sent him to my shop (we were the Holley authorized warranty center). When we told the kid is was a totally impossible combination to get to work, the store that sold it (part of a group of loosely affiliated stores with one extremely rich partner in common) called and was extremely angry with us for telling him the truth instead of covering for them. but 850 cant be too big . the 283 came with dual quads right:nabble_laughing-25-x-25_orig: Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 20 Share Posted March 20 but 850 cant be too big . the 283 came with dual quads right:nabble_laughing-25-x-25_orig: Not with a Powerglide. Link to comment Share on other sites More sharing options...
mat in tn Posted March 20 Share Posted March 20 Not with a Powerglide. when I was a kid, I went through my learning curve like all the others. even had an 1850 with a machine screw with nut in the secondary slot. haha. don't do it! a good friend built great chevys and built a beautiful 55 two door post and put a 454 w a Doug Nash five. we went out on a "run" and stopped for what they now call a test hit. launched like a boss until he forced open the secondaries and then it fell on its @&&. he then said that he needed to adjust the track screw and I was stunned. he was my father's age and built award winning cars and even this 19 yr. old kid had learned that doesn't work. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 20 Share Posted March 20 when I was a kid, I went through my learning curve like all the others. even had an 1850 with a machine screw with nut in the secondary slot. haha. don't do it! a good friend built great chevys and built a beautiful 55 two door post and put a 454 w a Doug Nash five. we went out on a "run" and stopped for what they now call a test hit. launched like a boss until he forced open the secondaries and then it fell on its @&&. he then said that he needed to adjust the track screw and I was stunned. he was my father's age and built award winning cars and even this 19 yr. old kid had learned that doesn't work. Let's see, at 19 I went in the Marine reserves to avoid being drafted into the Army (this was in 1965). When I returned from my 6 months active duty, dad gave me a choice, find a car or take over the payments on the 1964 Falcon he had bought while I was at PI. I ended up with the Falcon, a 260 V8, 3 speed fully synchro with factory AC. It didn't stay stock long, first change was a BW T10 and the needed floor tunnel and shifter. Then Jahns 10.5:1 pistons, Lunati hydraulic cam, Hedman Headers and dual exhausts, later i built a C4 for it. Then an Offenhauser 360 intake and a Rochester Quadrajet for a 1966 Buick Riviera. Later I bought a Ford performance tri-power kit from Beach Ford in VB VA. I finally ended up getting rid of it after I bought a 1966 GT350. Link to comment Share on other sites More sharing options...
mat in tn Posted March 20 Share Posted March 20 Let's see, at 19 I went in the Marine reserves to avoid being drafted into the Army (this was in 1965). When I returned from my 6 months active duty, dad gave me a choice, find a car or take over the payments on the 1964 Falcon he had bought while I was at PI. I ended up with the Falcon, a 260 V8, 3 speed fully synchro with factory AC. It didn't stay stock long, first change was a BW T10 and the needed floor tunnel and shifter. Then Jahns 10.5:1 pistons, Lunati hydraulic cam, Hedman Headers and dual exhausts, later i built a C4 for it. Then an Offenhauser 360 intake and a Rochester Quadrajet for a 1966 Buick Riviera. Later I bought a Ford performance tri-power kit from Beach Ford in VB VA. I finally ended up getting rid of it after I bought a 1966 GT350. I wasn't even born yet! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 20 Share Posted March 20 One of the best carbs I found for a lot of applications was a Holley 4609 Ford PN C9AF-9510-U. It is a 735 CFM carburetor, essentially a 3310 (780 CFM) with umbrella primary boosters. Originally for the 1969 428 CJ engines. We had scored a batch of them as in 1970 they were only on Mustangs and were a new number hand choke version. I put them on a number of different cars, including my dad's 1971 Lincoln Mark III in place of the Autolite 4300. Better throttle response and fuel economy. This is what my truck is wearing ATM Link to comment Share on other sites More sharing options...
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