This is a super common performance upgrade on the 300, done by dozens here (including myself). It would also completely eliminate the EGR.
MPG depends a lot on how well you tune it. Holleys aren't exactly a bolt on and go, as I'm learning right now, but once dialed in correctly can give some great MPG. Tuned correctly, some get better MPG than with the original 1bbl (but it takes some work.)
I don't believe I've heard of the Holley 390 being used on any stock vehicles. It's always possible to find one someone put on a vehicle, but you'd be just stabbing in the dark and hoping every time you went to a junk yard. Your best bet would be EBay. If you're going to get a used one anyway, get one that you can know the history of, pick your price, and then rebuild it. They're SUPER easy to rebuild, I just did mine.
I've seen them go for $50 (in need of rebuild) so keep your eyes open. The intakes can be purchased used as well. Just be sure to avoid any with any broken ear tabs.
Some pics of my install with that setup. Keep in mine that the two projects were done some time apart, so some of the EFI manifold install includes parts and applications for the 1bbl that were later removed.
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
An Edelbrock 500 cfm is used quite often and are probably not as fussy to tune. Poster fmc400 just did a conversion a while back with the Edelbrock and posted some pics.
Whatever carb you go with there will be tinkering/tuning since there was never a factory option for this type of upgrade/modification.
Do as AB suggested to save yourself some money. Shop eBay Motors and Craig's List.
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1983 F150 300 I6, Comp Cam 260h and lifter kit, Port/Polished head, Offy DP Manifold, Holley 4160/1848-1 465 cfm, EFI Exhaust manifolds, Walker Y Pipe to 3-Way Cat, generic Turbo Muffler, Recurved DSII, Mallory HyFire 6a & ACCEL Super Stock Coil, Taylor Spiro Pro Wires, EFI plugs.
The general consensus is that, since there was never a 4bbl, or even a 2bbl, designed with the 300 in mind, nothing is exactly a bolt on and go. However, some work better than others.
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
I'd just say that Clifford parts are usually a bit more costly than Offy parts.
Also, Craig's list doesn't charge fees for the people selling, so it might me cheaper, and also, if you're buying from someone semi-local, you won't have to pay shipping charges. On ebay, the shipping charges are usually about 15--20 bucks for a carb.
Those are some nice deals on the carbs. The Holleys are all pretty modular, so it depends mostly on what CFM they are, since you often can't tell just by looking at them (I'm sure there are some that can though. ) The other two would mostly be trial and error, but they would work. If they're not very tuneable, you might just be stuck with where they are as far as performance goes. However, for $10 and $20 for a rebuild kit, it might just be worth a shot.
4bbls off of a 302/351 work too. Several people use them here, since they're really simple and easy.
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4bbl Holley 390 w/ Offenhauser DP intake. 4 speed Manual w/OD. K&N air filter, EFI manifolds, 2.5" exhaust.
3.00 rear end and 2000 RPMs @ 80mph!
QuadraJets are fine with small block calibration. The small primaries make for good, economical running. The secondaries have to be adjusted to restrict their opening so as not to get a horrendous bog when mashing the gas.
The Hollys are probably bigger than needed...I would guess they are at least 600 cfm. They can be tuned to run but mpg may suffer. Best keep the carb size to 500 cfm max unless using a spread bore. An AFB or Edelbrock in the 400-500 cfm range would probably work well. The 400 cfm AFB is hard to come by though and are usually priced rather high. 500 cfm Edelbrock Performers are common.
Using carbs that were never a stock option on these engines may require a considerable amount of tuning/tinkering.
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1983 F150 300 I6, Comp Cam 260h and lifter kit, Port/Polished head, Offy DP Manifold, Holley 4160/1848-1 465 cfm, EFI Exhaust manifolds, Walker Y Pipe to 3-Way Cat, generic Turbo Muffler, Recurved DSII, Mallory HyFire 6a & ACCEL Super Stock Coil, Taylor Spiro Pro Wires, EFI plugs.
Of course be aware of your intake manifold; is it set up for a square bore (all four holes are the same size), or is there just one large retangular opening. It it has just one opening, then the spreadbore carbs could work.
However, those spreadbore barbs are made for larger engines, and dump a lot of gas when the secondaries open. Like Harte3 said, it will require 'tuning' and restricting the secondaries quite a bit to avoid a huge bog when they open.
I would do a little research. Read about the different carbs. Contact people on the forum who have what you like, and ask how they like them. Learn to recognize certain types so if you're at the swap meet or boneyard and you spot one, you know what it is. Check/ask about stripped fittings, cracked housings and/or carb body. Think about milage too.
I didn't want to toot my own horn, but what the heck: another carb you might want to think about is the autolite 4100. I chose one for my 300. You can read about them on Ponycarburetors.com. Also, if you go to classicinlines.com, you can watch videos of dyno tests using different carbs on inline 6's. The 4100's are one of the easiest to work on in the world. Kits are still available.
I went on ebay just now, and the 390's are a bit expensive
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) The other two would mostly be trial and error, but they would work. If they're not very tuneable, you might just be stuck with where they are as far as performance goes. However, for $10 and $20 for a rebuild kit, it might just be worth a shot.
