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Old 07-05-2016, 05:16 PM
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The Summit Carbs seem to be fuel efficent guys that swapped from a standard Holley or Edelbrock have gained 2-3 MPG on several forums.

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Old 07-05-2016, 06:17 PM
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It depends on the tuner as well as the vehicle itself along with the build and there foot that can make all the difference on gaining fuel mileage. I always believed the myth that the double pumper would use more gas then a vacuum secondary and yes it does if you keep kicking in the secondary side of things but just cruising and a few romps here and there it can do exactly the same. I have cracked 20 mpg on both my holley 600 vacuum secondary and 650 double pumper with changing idle feed restrictors and also basic jetting. The summit carb does have one advantage over the other holley style carbs as I do believe you can change out the boosters and there would be a true way of gaining over 2 to 3 mpg or even more depending on the build as booster design can have a great effect on things.

I will have to do some research on them summit carbs and get in a little deeper and see just how they did get the extra mileage. I would get one of those is fuel mileage is the main concern and you want every ounce you can get and such I bet they would do just as good as an edelbrock afb style carb. I don't know too much about the thermoquad style but have seen photos and stuff and know the street demon is just an update of that carb but I have read mixed reviews on them though. I like traditional style holley carbs first over anything else since its easy to get parts and really easy to tune each circuit. I did not know on the summit ones you could change out the idle feed restrictors and that can make a big difference on fuel mileage as well by changing them out to different sizes.
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Old 07-05-2016, 11:02 PM
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The easiest carb to radically change the tune that I ever worked with is Zenith carburetors. It's a shame that most of the carbs they make are single throat carbs. They do make some 2 and 3 throat carbs for the import market.
I worked with carbs for industrial engines and the single barrel Zenith, even back in the early 70's had removable jets for idle and high speed air bleeds, idle and main jets and adjustable power jets. I adapted one to my 62 Falcon to see what kind of fuel mileage I could get. On a 550 mile trip I got 41 mpg. There was a cost for that kind of mileage - it had almost no power. I ended up putting a different kind of tune on it and setting the governor to 70 mph as a poor mans cruise control. I had full power right up to 70 mph and then it would cruise (with my foot on the floor). When it came to a hill the power came back and it would climb the hill at 70 mph.
The Falcon had a 200 inch engine swapped in and a C4 three speed transmission out of a E-150 extended van. I just changed the bolt-on bell housing and converter ti match the small six and away I went. I didn't even have to change the driveline because the C4 and Ford-O-Matic two speed were the same length. I converted and old three speed manual shifter to control the C4 and it was a fun car. That C4 was one of the test beds we used to make changes to for performance. We made a lot of mistakes but we ended up with a really strong performer that was as at home behind that little six as was behind a 600 hp blown 351 Cleveland. I have two almost identical in my two 302 powered 73 Mavericks. (daily drivers)
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