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Discussion Starter #1 (Edited)
hey, i am new to carbarated engines and I was wondering about that adaptor plate and any mpg gains i'd see. the truck has a 350 engine and a edlebrock 550 4 barrel carbaretour and a holley intake. i think the intake is for a 2 barrel, but it could be 4 barrel. if i bought a 2 barrel carbaretour and this plate (if needed), what type of mpg gains would i see? its getting 12 now.
 

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I doubt you'd see any gain in MPGs with the 2 barrel, unless there's something drastically wrong with the 4bll you have now. If you look at the venturis & throttle plates in a 2 bll carb you'll see that they are larger than the primarys in most 4 bll carbs. (The exception would be some of the "square bore" 4 bll carbs.) This is because the 2bll is a compromise that has to cover the entire rpm/power range with just 2 venturis so they have to be larger than the primaries on most 4 blls. The 4 bll will get better mpg with the smaller venturis, as long as you can resist the temptation to give it full throttle & keep opening the secondaries. I would investigate your manifold & determine if it is a 2 bll mani with a 4 bll adapter plate, because this is a no win situation. There's no gain in MPG or power if this is the case, as this causes poor flow characteristics which hurts both mpg & power.
 

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Discussion Starter #3
ah okay that makes sense. so check out the intake manifold to find out which one it is. so lets just say it is a 2 bbl intake. so then putting a 2 bbl carb on it would give me the most horsepower and mpg gains?
 

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Yes, definitely see which manifold you have & go from there. If it's the 4 bll manifold, keep it & your 4 bll carb. The 550CFM carb you have now is just about right for the 350CID engine. No, you won't get better MPG or power with the 2 bll carb & manifold because of the reasons I stated above about the venturi sizes. The 4 bll with the smaller primaries, (better MPG) & the available secondaries when you need them (more power) makes the 4 bll with a 4 bll manifold the winner.
 

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Discussion Starter #5
4 barell intake it is! so looks like thats good. also, opinion on a quadrajet carb? the guy who i am buying it from said the edlebrock carb is not working anymore so he'll replace it and he might replace it w a quadrajet.
 

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Glad it's a 4 bll manifold, & yes Quadrajets are fine. A little more difficult to work on & tune than a Holley, but good carbs.
 
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