Dual Carb?

killamaniac · 07-07-2009, 06:06 PM

Is a dual Carb set up worth it? I was looking at the Edelbrock RPM Air Gap dual quad intake manifold with 2 thunder AVS 500 CFM carbs. What would the performance be like compared to say a single 750 carb set up? How bad would the gas mileage be compared to a single carb? I'm making a monstrous DD, so gas mileage is not my biggest concern, but its there... I'd like to keep it above 10 MPG.

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67mustang302 · 07-07-2009, 11:20 PM

Pointless. In 99% of cases a single 4bbl will outperform a dual 4bbl. It was one of those ideas that seemed like a good idea at the time in the 60's, but really wasn't. They have their places, which is tunnel ram type stuff in all out drag setups, but even for a monster street engine a single 4 will work better, and the mileage will be a lot better.

JD1969 · 07-08-2009, 12:51 AM

If all you want to do is impress rednecks at a cruise night or car show go for it, otherwise stick with a quality single 4 barrel.

killamaniac · 07-08-2009, 01:55 AM

alright thanks for the info, Im new to the carb set ups, I was planning a supercharged EFI system but it was just going to be too expensive so I decided to go carb with my rebuild. Just for info, are there any carb positive displacement blowers around for the SBF anymore? It could be in the future, when I can afford it, and I figure it would easier then going EFI again. I don't like centrifugals, they just seem like a poser turbo, haha. Kidding, but I would like the lower torque and wider powerband

also for the carb, as a nasty street machine, what kind do i want? an electric choke or a double pumper mechanic or what? I heard something about custom Demon carbs from holley but they aren't on their site. I figure a 700-750 CFM is what i was looking for, is that right? I know you probably get this question a lot but my searches are coming up short. Its late here so I might just be failing. Thanks guys

67mustang302 · 07-08-2009, 02:03 PM

For a roots you can pretty much run any carb on top, it functions the same as n/a, but will need to be a bit bigger and probably need a bigger accelerator pump to account for the carb being farther away from the cylinders. Centrifugals can run more boost pressure because of the way they work, they won't produce as much low end power(which can be good in helping to maintain traction) but will make more top end power, especially when compared to a roots since modern centri units are far, FAR more efficient that a roots, and they get less heat soak.

Mechanical secondary with an electric choke, but if you do centri then you need a blow through carb, and most of them have no choke. Size needed depends on the setup, but I like Quick Fuel myself. Pro Systems also makes really good carbs.

killamaniac · 07-08-2009, 02:15 PM

ok, well Since its a street car I'd rather have the low end. Did twin screw blowers ever make it to carb'd engines? also, what are your thoughts on 4bbl throttle bodys? I was reading a Mustang5.0 magazine article where they used this http://www.holley.com/950-24S.asp on the 174 weiand blower. They claim better fuel efficiency and throttle response. Is it worth it? I would have to tune it and its speed density, but better mileage for a DD would be kinda nice, along with the claimed throttle response, but its not the end of the world if it isnt what they claim. also, thanks for helping me learn with all my topics on here, 67mustang, I appreciate it!

67mustang302 · 07-08-2009, 02:24 PM

The only screw setups I've seen for carb are for GM engines, and they're few and far between. Those TBI setups aren't really any better than a good carb, and throttle response and mileage will be determined by the carb and how it's tuned, and mileage to a great degree by how you drive. If you want a good EFI setup you could look into FAST's EZ-EFI, which is great if you're staying under 600hp.

killamaniac · 07-08-2009, 03:57 PM

oh that EZ-EFI looks awesome, but I don't think the 53 injectors would feed a supercharger would it? I am going to get a good 4bbl right now, and then when I get the supercharger Ill see how it does with the carb, and work from there. Thanks again, 67

67mustang302 · 07-08-2009, 05:25 PM

The EZ-EFI is good up to about 600hp, regardless of how you get there. Since blower setups usually run on the richer side though, the brake specific fuel consumption is a bit higher, so with a blower it might not make as much power, maybe 550-575 and it'd be maxed out.

If you're looking for a good carb, I'm running a 650 mechanical Quick Fuel, and am very happy with it. Extremely high adjustability in every part of the carburetor, and their customer service is excellent. They sell a whole mess of differeing carbs, annular boosters or down leg, vacuum or mechanical, small, large etc etc.