Vacuum or mechanical secondaries best?
Thread Starter
Burning Brakes
Joined: Aug 2001
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From: Bay City MI.
Vacuum or mechanical secondaries best?
Which one is best for all around street driving, vacuum or mechanical secondary carb? I currently have a Holley 780 vacuum secondary style, but would like to go bigger, 850DP. Some say that the mechanical dumps too much fuel when you hit the gas? Thanks for info.
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From: Forked River NJ
Re: Vacuum or mechanical secondaries best? (467-Ratman)
I would say with your engine and gears an 850 DP would be OK. Just be prepared for an empty tank a lot quicker. A 780 is a good street carb but I think a little small for your motor. My LT1 had a 780 vacuum from the factory with only 350 cubes. Properly tuned they dump the correct amount of gas when applied.
[Modified by Gordonm, 5:26 PM 7/30/2002]
[Modified by Gordonm, 5:26 PM 7/30/2002]
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From: Sierra Foothills CA
Re: Vacuum or mechanical secondaries best? (Gordonm)
[QUOTE]I would say with your engine and gears an 850 DP would be OK. Just be prepared for an empty tank a lot quicker. A 780 is a good street carb but I think a little small for your motor. My LT1 had a 780 vacuum from the factory with only 350 cubes. Properly tuned they dump the correct amount of gas when applied.
I agree...or you could check w/ Demon to see what they like for you. Although it was a few years back when they were still known as Barry Grant, they steered me right- refer to my sig. I dropped .35 in the 1/4 mile swapping from a well tuned 780 to the carb I got from them.
I agree...or you could check w/ Demon to see what they like for you. Although it was a few years back when they were still known as Barry Grant, they steered me right- refer to my sig. I dropped .35 in the 1/4 mile swapping from a well tuned 780 to the carb I got from them.
Drifting
Joined: Mar 2001
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Re: Vacuum or mechanical secondaries best? (Gordonm)
I've always thought mechanical secondaries for a manual tranny and vacuum secondaries for an automatic. I'm not sure if thats old school thinking with the technology out there today or not. The smaller carb will give you better throttle response, the bigger one will probably make some more HP I believe.
Scott
Scott
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Re: Vacuum or mechanical secondaries best? (467-Ratman)
This ALWAYS gets emotional, but here's mine....
You need a Double pumper. I'd use a HP series Holley. The annular version will help low end throttle response usually with a big cam. They get a little rich at high rpm, but that can be tuned out with bleeds IF you go that high and it's a problem.
The ONLY reason the typical DP gets worse mileage is that it feels so good and you mash into it more! There is no reason it can't match a vacuum sec. carb for mileage.
Kind of like a lady at work with a GT Mustang. She HAD to have some flowmasters. I got them for her and then took her to muffler shop to get them installed. Later she said mileage was worse. I then followed her back to work one day. She was constantly ******* it listening to the pipes. After the new wore off a few months later mileage was better than ever!
Jim
You need a Double pumper. I'd use a HP series Holley. The annular version will help low end throttle response usually with a big cam. They get a little rich at high rpm, but that can be tuned out with bleeds IF you go that high and it's a problem.
The ONLY reason the typical DP gets worse mileage is that it feels so good and you mash into it more! There is no reason it can't match a vacuum sec. carb for mileage.
Kind of like a lady at work with a GT Mustang. She HAD to have some flowmasters. I got them for her and then took her to muffler shop to get them installed. Later she said mileage was worse. I then followed her back to work one day. She was constantly ******* it listening to the pipes. After the new wore off a few months later mileage was better than ever!
Jim
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From: Sierra Foothills CA
Re: Vacuum or mechanical secondaries best? (Scott78)
[QUOTE]I've always thought mechanical secondaries for a manual tranny and vacuum secondaries for an automatic. I'm not sure if thats old school thinking with the technology out there today or not.
That had been the conventional wisdom in my experience. However, when I talked to Barry Grant techs about what would be best for my application(TH400 auto) they said that my car would love the carb that I ended up buying. It's a 750 DP that's heavily modded(flows up to 1140 cfm if the motor can pull that much) & I couldn't be happier w/ it. Your point about current technology probably accounts for this.
That had been the conventional wisdom in my experience. However, when I talked to Barry Grant techs about what would be best for my application(TH400 auto) they said that my car would love the carb that I ended up buying. It's a 750 DP that's heavily modded(flows up to 1140 cfm if the motor can pull that much) & I couldn't be happier w/ it. Your point about current technology probably accounts for this.
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From: central FL, near the beach.
Re: Vacuum or mechanical secondaries best? (467-Ratman)
i love my DP's, but with a stick they can jar the driveline when shifting fast and flooring it. (spinning tires). While it is fun, i think it might actually accelerate faster(or at least attract less cops) with a smoother vacuum carb.
So i say try them both and see what you like.
So i say try them both and see what you like.
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