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O.K. I have a 37 Chevy truck. I bought it with a 327 engine, totally rebuilt. (4000k mi.) It gets 10 miles to the gallon. Has 4 barrel. I am thinking of installing a LS so I can get better gas mileage. Even tho I can afford gas, the low mileage bothers me. Anyone know how much gas mileage would improve if I installed Electronic ignition and EFI on 327? Thanks for any help. Daily driver.

A properly dialed in carburetor, and by that i mean using an AFR gauge to jet/meter it for your driving situation, can approach an EFI in terms of fuel efficiency. It won't likely match EFI because it isn't a closed-loop system but it can be very good. Same with Electronic ignition. When running right, the old systems worked extremely well - modern electronics brought better starting, reliability, less maintenance, and lower emissions for the most part.

In short, I don't think you will gain that much fuel economy by putting modern electronics on a vintage engine unless your current carb is out of whack and you don't want to tune it.

Thanks. Appreciate your info.😎

So will a LS give better milage.

I think it will because of the heads/flow design, but I have no experience with that swap to give an opinion

Beebs,

I have a 2001 5.3 LS in my 49 Chevy pickup and I calculated it once and best I can remember it gets about 16-18 mpg. I'm runing a 350 Turbo with 273 gears all setting on 18" wheels.

Hmm, it may be better to spend the money for gas than the expense to gain a few MPG.

What transmission are you running? Does it have overdrive? And do you know your rear end ration?

I have not checked my mileage recently but I'm running a hot 350 engine/4 barrel, with 700R4 tranny and a 2.73 rear end. I get 15 if I drive it with a somewhat light foot! It'll burn the tires but going down the road in overdrive she just purrs.

Find someone who understands your carburetor: $100.
Replacing the engine: $$$$$$$$$$$$$$$$$$$$

What is the rest of the truck like? Gear ratio, tire diameter, transmission type, torque converter, carburetor type, camshaft grind, all these are part of fuel mileage.
My '37 drops 3 or four miles per gallon if I drive over 65 miles per hour due to wind drag. 250 inline six, 3.08 gear, 28" tires, T350 with tight converter,
21 mpg@ 65 mph, even high at 55 mph.

Install a Quadrajet would be the first move along with HEI and a Air/Fuel ratio gauge.

On a good day, downhill with a tailwind, a brand new 327 in 1962 might get 12-14 MPG. My father was the best carburetor man in several states around Nashville Tennessee, and that's the best he could do with them. I doubt if 50 years or so of use will improve that figure by much, no matter how expert your carburetor rebuilder or tuner is. The saying back then was "A 327 can pass anything but a gas station!"
Jerry

WOW 10 mpg again WOW. In the past I owned a 70 1/2 Z/28 Camaro with a LT1 350, T400 trans, 4:11 gears, 11:1 comp, Holley 780. GM rated it at 360 hp & 380 tq but NHRA rated the HP at 425hp.

Now with all that said I could get as much as 16 mpg if I keep my foot out of it. Sounds like your 327 has some problems. Something isn't right with your combo of Carb/s, Heads and Intake not matching or working together. I have had many SBC motors 283,302,327,350 slightly built and still getting in the neighborhood of 16 mpg range.

Yeah what he says :~)

I'm with Alvin, I'd see what gear ratio you're running and go from there.

John

Whoa. 😎

Like the others here, there are just too many unknowns. how "Hot" is your cam, what size 4 barrel, what heads, what ignition? All that before we get to the drive train, what trans, what rear gear ratio?

A good tuner can improve on your overall performance but it will only go so far. Most times we want great performance and MPG's, it can be done but there may be a compromise along the way. Your overall build should match what your expectations are, Hotrod, Cruiser or Stock?

I have a 68' 327 (very modified) with a 4 speed and 3:08 gears, the 3:08's are my compromise.

10 MPG is too low. Something's amiss. Find it, fix it, then check your mileage.

Don't be like me when I was a kid: I swapped a whole new engine when my original just needed a tuneup.

A big part of mpg is related to total gear ratio. For that you need to know ring gear/pinion ratio, top gear ratio and last but just as important, tire diameter.

Example

IF, you're running a 3.73 rear end and 26" tall tires with a non-overdrive transmission and going 70 mph your 327 is turning 3,374 rpm. If that were the case, 10mpg sounds about right.

Add a .72 overdrive to the above scenario and you're looking at 2424 rpm when running 70mph. Not only would things quiet down, you'd likely see a major mpg improvement.

This might help.

Good Luck,

RonR

And we still don't know what carburetor you have...

Just a guess: no vacuum advance?

Thank you all for your input. Much appreciated. I am not a mechanic. So if anyone. Is interested my final thoughts are these. The 327 is for someone who likes speed. So someone else can put it to good use. I and having done a engine swap. I have seen some listings with low milage , ls' for around $700.00 including tranny and computer. I can hear them run before purchase. The front springs will be replaced, etc, for smoother ride. Like most of you , I have saved some loot. This is where it will go. Thanks again.

Wow. $700 with a tranny and ECM. You better buy em all. That setup worth 3 times that on this coast. And not talking low mileage either.....