I recently purchased a 40 Ford with a 400 sbc, had sat for many years, used new fuel, plugs and started up and runs fine (No smoke, no knocks) Question, I would like this to be a driver with good MPG, thoughts on what to do to this stock 2 barrel truck eng (code CSA) to achieve my goal ? ( I don't want to change the firewall to install a LS) Thanks
the fact it's a 2v carb will help fuel economy, slightly retarding the ignition timing will help too, but I wouldn't expect more than 20 or so at highest. gearing affects fuel mileage more than anything, an overdrive trans can help greatly as well. Ls swaps are not permitted here as they are not "traditional" in nature.
Put an egg between your shoe and gas pedal. You will accomplish one of two things. You will either get good mileage or eat a lot of scrambled eggs but not both.
The stock 2 barrels for the 400 were pretty large because of what they had to do. A 600-650 4 barrel will have smaller Venturi’s and give better milage if you control your foot. A lower number power valve or stronger springs on plunger type carbs will help with milage. You could look to a Summit 4 barrel that starts at a 500 cfm with excellent drive ability. Smaller Venturi’s and annular discharge boosters are a plus offered on the Summit.
I ran a 400 in an OT Vette for several years. A properly set up Quadrajet runs really well if you stay out of the secondaries. Adding an o/d (700R4) made even more difference. But again, getting good mileage take self control.
Compression is your friend with respect to efficiency, as high as can be tolerated by the fuel you intend to use. You said it is stock, so probably around 8:1 compression ratio. Its heads will be open chamber 72-74 cc. Changing to heads with 64 to 67 cc chambers will give a significant bump in compression and with a well tuned carburetor and proper ignition timing would get a good increase in efficiency. A Quadrajet or vacuum secondary 650 Holley seems about right for your intended use. If you want to dig deeper into the engine, a cam change to go with the heads and intake changes, could get you some decent power with good economy. Be realistic when talking to a cam company regarding your intended use and expected rpm range and they will likely recommend a mild cam. All this is assuming that you want to make those kinds of changes.
Okay, for starters, the LS family is not welcome here....... and the 400 barely makes the cut only because it has a generic SBC look. But the 2-barrel on that many cubes is your clue that GM was trying to squeeze a few extra miles out of a gallon at that point in history. I'm not smart enough to speak on 'torque/efficiency/mpg from those days..... but I'm inclined to guess that it's going to be tough to squeeze more out of it.
And those steam holes get blocked with lime and sediment. You might want to closely monitor the temperature. Maybe pull the heads and check everything out.
A quadrajet on a performer style intake is going to be the best all around setup with that engine carb wise. Had that on the 400 in my 75 Chevy 1 ton 4 wheel drive crew cab and it did pretty good on mileage for a big old 4x4. Other than that a Fi unit that looks like a carb from 20 ft and a big honking air cleaner to cover it. I'm thinking that the two barrels were put on more for cost for fleet service than trying to get gas mileage. You could drop the price a few bucks with the two barrel and they were easier for fleet mechanics to work on. From there it is having it tuned right and having the right final gear ratio. If you have a Turbo 350 or 400 behind it that engine will handle a 2.7 or 3.0 rear end easy enough for highway use. I've lost track of the number of rods I have been around in the past 50 years that sucked out on the highway because the builder just flat believed that it wasn't a real hot rod without 4.11 or 4.56 gears. You don't need drag gears unless you spend every weekend at the drag strip.
As others have mentioned, DEPENDING ON ONE'S DRIVING HABITS, a four-barrel sized and calibrated for the combination, can provide better fuel economy than a two-barrel. And multiple carbs, again sized and calibrated for the application, can do even better. Jon
I had a 327 and switched from a 4 barrel to a 2 barrel around 1979 during a gas crunch. I did pick up a couple more MPGs out of it.
Install a vacuum gauge and keep that reading as high as possible at all times. You'll learn a lot about how to squeeze every MPG out of an engine.
X-2!! Advance is your friend in the chase for better mileage! Rear gear ratio??! (important) Overdrive tranny...... both will get you better mileage at the cost of less than blazing acceleration. Free flow exhaust........ weight reduction......quit hauling around a bunch of junk( many things and people qualify as junk.) Taller rear tires will in effect improve the rear gear ratio. Ya gotta figger THE COST of improved mileage vs just doing nothing and save the money! How old are ya... how much longer will you be able to drive?.... IF you're in your 70+s why worry about saving $$ on gas?? Enjoy the ride and..... the stupid cost of fuel is the price for that enjoyment!! (preaching to the choir here) Just my thoughts 6sally6
So, what kind of gas mileage are you getting right now? I would put an O2 sensor in the exhaust and monitor what it says, then consider "if" there is something that needs some fiddlin. Unless you are getting really poor gas mileage, probably not much change can be expected from throwing parts at it. Using a 5 speed or changing the rear gear ratio may help noticeably. Since you aren't interested in performance, I'd just drive it and enjoy it.........
learn something new everyday. don't believe i ever saw a small block 400 in a truck other then put in by someone, every time i saw a 400 emblem on the fender of a chevrolet or gmc truck it had a 402 big block in it.
Vac advance does not trump a full mechanical distributer that is properly curved. Vac advance will trump sloppy building and most of us are not tuners. As has been mentioned a compression bump even with the stock heads will help as well as a 4 bbl in place of the 2 if it is properly setup. I have a personal preference in carbs as does everyone else. For example my good friend Jon ( @carbking ) will prefer a Rochestor or a Carter. He is a wizard with them and set up is relatively easy for him. Tuned properly on an intake with a smaller plenum 600-625 cfm will more than feed a stockish 400 small block. All that said "lets build a small block" has more than been covered here in various threads. Easiest and cheapest is bolt a decent 4 bbl and intake on it, make sure the distributer is up to par and drive it. 400 were not known for fuel mileage but 16-18 MPG highway is attainable with about any small block that is not wore slap out.
I have an off topic C-10 with a lazy SBC 400 and 700R as a daily driver. 15 to 17 mpg on highway with 2.80-ish rear gears is average for it. It's equipped with aluminum intake, demon 625 carburetor, headers, 2.5 exhaust & high flowing mufflers. It also has the aerodynamics of a brick. Good luck and enjoy the torque.
Because those of us past 70+ on a fixed income have to do everything in our power to try to at least maintain some quality of life in the face of rapidly rising prices !
This winter I screwed together a 400 sbc for my old truck using Speedway Motors head gaskets part number 91010266, only .024 thick for $14.99 ea, along with 64cc heads, give it a compression ratio of about 9.5 This blocks deck height was about a .025 average, one magazine article had a 400 block with up to .060 on a rear piston so some may end up with less compression.
As stated QJet and good tune, timing, advance etc. Depends on yow far you wanna go. If the heads are stock, very lazy 70s smogger heads. A vortec head will greatly improve power across the whole range. But it's a head and intake swap. Might as well change the cam if you're that far into it.
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