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Is it possible to build a big block for great performance and good economy?


Well-Known Member
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6:09 PM
Dec 24, 2013
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Surprise, Arizona
Can a big block be built to make good power and still have exceptional fuel economy? I am just wondering if it can be done? What would it take?
5 or 6 speed transmissions, efi, taller diff gears for starters. All very expensive and probably not cost effective. Basically all the things that give todays muscle cars great power and efficient gas milage.
You need 2 cars. A puddle jumper and a BAD ***! Average their mileage.
Maybe with the OD, EFI, and a puny cam. Highway gears.

250hp shot of nitrous.

You’ld still be lucky to get 18-20 mpg.

I like the “build a badass then get a cheap throwaway Hyundai” option.
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The transmission, and rear end choice will have a lot to do with the answer to your question.
If you have a modern automatic OD trans or a 5/6 speed manual, then you have more options
If you are running a 727, or 4 speed, and want ANY fuel economy, IMO a stock(ish) 383 is the way to go.

I have pumped up quite a bit of 383's and 440's and in my experience they preform GREAT, but they are not good on fuel.

The most fun combo for the street I ever had,(and got good MPG) was a 383, with all the regular go fast goodies: headers, good duel exhaust with X pipe and flowmasters, carb, intake, electronic ignition, aluminum WP and housing, and the stock cam, with 3.23 gears. I got 15+MPG and it would surprise most people.
It wasn't the fastest thing on the road, but it may have been the best on fuel. of my big blocks.
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Friend's 2019 Mustang GT has 465 hp and gets 31mpg with the 6 speed manual; the car is all stock. Big block from yesterday wont ever come close to that number no matter the tricks used on it, but in my opinion it isnt meant for that sort of performance...
15+ in the old B and C body cars with a 383-2 and a 2.70xx gear. May be with a overdrive now days you could squeak out almost 20 but not a lot of power to go along with it. 55 mph with cruise rpm in the 1800 rpm range.
Personally, I think a lot is possible but like anything it depends on your goals. If you are wanting to get 30 mph out of one, well I don't think that will happen, they are too inefficient. However, 20 mph is possible I think but it takes some work. with modern technology such as good heads (aluminum) EFI and a system to control spark and fuel along with the right trans and rear gears as well as tires.
The 383 in my Charger can get an honest 17 with 3.23 gears and EFI (set really lean).
We had a 66 Newport for years with a 383-2bbl it could get 18 pulling a small aluminum boat.
That engine was just one of those "good ones" from the factory it could really move that big car on the highway.
You said in your original post "go good" really depends on how good you want it to go.
In general from my experience you can achieve a reasonably substantial gain in HP and gain fuel efficiency but there is a point were the scale tips and HP goes up fuel efficiency goes down. You would also need to be an experienced engine builder and machinist.
This broad theory would apply to most older design American V8 motors.
What I would do:
Decent tune-able carburettor but not to big in the CFM and a good free flowing air cleaner. Vacuum secondary.
Low rise dual plane manifold. Edelbrock are hard to go past.
Good electronic tune-able ignition system.
Modern design heads - not to big in the port CC
Get the compression up a bit with as much squish in the combustion chamber as possible.
Modern cam with no more the 280 degrees advertised duration. I am a hydraulic roller guy.
Good headers with smaller primary tubes and a well designed quality mufflers/exhaust system.
Tune the engine to be as lean as possible at cruise RPM.
The amount of guys who spend 20 grand on an engine and think their next door neighbour is the best tuner in the universe blows my f****ing mind.
In short, I believe building a dedicated turbo engine (not for insane power) is the answer.
I'm running a mildly built 456 stroker with a 750 DP that gets around 19mpg on the freeway so yes it can be done. Originally I built it with a 727... fuel economy was horrible but as soon as I switched to a 6 speed my fuel economy skyrocketed. No better cure than slowing the motor down which also saves wear and tear.
I'm running a mildly built 456 stroker with a 750 DP that gets around 19mpg on the freeway so yes it can be done. Originally I built it with a 727... fuel economy was horrible but as soon as I switched to a 6 speed my fuel economy skyrocketed. No better cure than slowing the motor down which also saves wear and tear.
My findings as well. But my thinking is to keep the cam in a broad power range to deal with the extended low RPM.
510 cu. In. we got 23 on the highway w 3.23. The 440 before got 14. We checked the mpg often beause we couldn't hardly believe it.. Had a Mp 484 cam with 108 lsa. Most economical motor we ever had. Better then any 440s we had and even better the the 318's we ran. It was not slow, but not as fast as you would normally think of a 510. We drove it 2 the track (340 miles round trip) 60' were almost 2.3 with old hard radials and we ran 13.2 at 108 mph. Bracket racing it was fun being able to easily put a fender on the 12 second cars that had slicks. It had ported 452s stock valves, iron intake, crappy 1 3/4 hedmans and 11:1 compression. It more or less idled down the road hardly had to put your foot on the pedal. One way to get good mileage is to try running 11:1 on pump gas. You could not get on it... till we dumped 5 gal of av gas in. I think if we would've lowered the compression a point it still would've been a very economical motor.
The best our 850 thermoquad got was 21mpg, Our most economical carb was the race 850 dp of our 10 sec 70 cuda we averaged 23mpg on 120 mile trip...amazingly we did not change anything just moved it from one car to the other. But the holly double pumper was noticeably harder on gas at the track then the thermoquad.
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My 70rr with a 450hp 383, 4 spd, and 2.73 gear would idle at 60mph in 4th. Never checked mileage tho..
I’ve had big C bodies with 440s and 276 gears run 22/23 mpg with a thermoquad. 18/19 with 3.23s. My B bodies would run about the same, but being lighter they had more performance. Kim
whats funny is my charger with a lightly warmed over 321 geared 440/727 using a little 1406 gets better mileage than my daily shitbox 6 cylinder Taurus. *if I drive it like a regular person would*