Yeah, one of these things is not like the others.

Does anyone run a mild/moderate B/RB stroker build with an OD? If so, how bad did the increase in cubes kill the mpg?

"Before" for me was a 318/auto in a Challenger. "After" is a 496, 10.2:1 CR Ed heads, 243 @ .050 cam and 5 speed with .82 5'th. 3.23 rear with 25.x" tires. It is fuel injected with decent "vacuum advance" dialed in.

It gets 14 MPG at 75-80 MPH measured on a long X country drive with the stroker. The combo could eaisly pull more OD (eg .74) for cruising and probably gain another MPG or so. Somewhat less cam would probably be worth some MPG also.

Overall, I am very happy that the OD and EFI gets is solidly in the double digits with a performance oriented setup.

The reason that I ask is that I'd love to have the added torque of a stroker but the purpose behind the Imperial is road tripping. With the 440/727/3.23 and a loaded weight of 5500+ lbs that beast was getting 13 mpg at steady highway speeds across flat land. Get into the mountains and I'm sure it'll drop into single digits.

At these low mpg numbers small differences add up.

in your case I would look into a 383 stroker. you don't need cylinder volume, just lots of stroke for tons of torque. keep the bore small, use higher compression, some aluminum heads. personally I wouldn't shy away from headers and a small 2.5" exhaust with good mufflers. and a small hydraulic roller cam, add some roller rockers. and your good.

if you really want to get into it, add so dry film lube to the piston skirts, keep your oil pressure on the lower side with a stock volume pump and limit it to 60 psi. roller timing chain

I don't know if a 727 is your best option here, might want to consider at least a gear vendors or a 518 conversion. i'd leave the 3.23 gears. and efi definitely efi.

Feets, that is an interesting concept. I doubt many build stroker big blocks to improve gas mileage, it might be hard to find someone that has done what your looking for.

Pure speculation, I suspect the stroker with an OD is going to fair a bit better then the 440, 727, 3:23 will, for mpg, if both were driven the same.
The added torque of the stroker to get the mass moving, and for a temporary pull on a hill to maintain the speed should be well offset by the reduction in rpm over the long haul. I don't believe the added cu in to feed will have that much impact given the weight of the Imperial, but I'd probably go for a smaller cu in stroker rather then a larger one.

I kind of picture it like what a 383 in that Imperial would do for mpg compared to the 440. The 440 likely would get better mileage over the smaller 383 because of the torque required to get the thing moving and keep it moving. Gene

There was a magazine article a few years back where a guy built a stroked BB in a C body wagon for long road trips. For the life of me I can't find the damn thing. It was a real interesting build.

What is your timeline? I'll have a mild 512 in my car with a 518 behind it come Spring.

A stroker is not for efficiency. It is for power. EFI and OD is for efficiency.

I have a 518 that needs to go in the Imp. It will get a FITech system too.

As for the long stroke making cheaper power, I think that's not quite right.

To get better mpg you need better engine efficiency. Heavier rotating mass is not the way to go. That being said, the B/RB platform is far from the model of efficiency. I'm not sure which way would make it more efficient with a given amount of fuel.

While I like the idea of a large engine working lightly more than a small engine working harder it comes down to balancing construction cost, performance, and operating cost.

I, too, plan on having this done before summer rolls around.

I think it might come down to cubic inches per mile. That's also proportional to gear ratio times engine CID, tire size staying constant.

The Fifth Avenue that my mother had had the "highway gears" 2.29 or so with the 998 auto transmission. With a 318 that car got reliable 24 mpg.

With a really heavy car a very accurate fuel map could make quite a difference in mpg. Running a carb with vacuum dipping below the power valve setting can destroy mileage. So EFI should be able to help. Also electronic spark advance could allow tailoring of the spark to match engine speed and load.

One thing I think of is that frictional losses in the engine increase as the square of or maybe a little less than the square of the engine speed. So building a larger engine and running it a lot slower may actually increase efficiency.

Build a lot of mechanical efficiency into the engine. Compression and mixture motion should be at top of the list. Keeping heat in the chamber should help. Keeping the engine dimensions as close to square as you can will also minimize surface area per volume. Lighter weight reciprocating components could show benefit.

There are other things to think about, this is a start.

R.

Actually I think a twin turbo 360 would suit you better, with all things optimized for either system.

I was getting 16.5 mpg with the 512 in my 69 Bee with a GV over drive and Fast 2.0 throttle body EFI. The best I could get with the carb was 9 mph. Im convinced the difference was the ability to program an efficient timing curve into the Fast 2.0. When I sold the car I was running 46 degrees of total timing at cruse speed.

I have a 68 Charger 512,a518 overdrive.3.54 gear, Holley carb,I have gotten 15 mpg @ 70 mph driving VERY easy.

CSK yes basically the same set up I had in the Bee. I think the reason my mpg was so bad with the carb was I had a quick fuel 1050 race carb with the dist locked at 34 degrees. In could tune the carb for 14.5 AFR but milage still sucked.

Lack of vacuum advance really kills light-throttle cruise mileage. Timing should be more like 48-50 degrees for that, instead of 34...

EFI lets you tune in a lean burn fuel and timing package for cruise efficiency. Does Fitech have that flexibility?

I'm thinking a cam long on lift, mild on duration with a wide LSA.

I don't know what possessed Edelbrock to build those heads with 59 Desoto combustion chambers but that is a big puzzle piece you're missing. If you had a fast burn Vortec type chamber you would pick up pumping loss efficiency from less required timing lead.

Kevin.

are you doing a long arm rather than an octopus now?

When I was running a 493 wedge in my Roadrunner I drastically improved my mileage after I installed a wide band O2 sensor. I initially installed the 02 sensor to help me better tune my six pack. When I switched back to a big 4bbl I discovered that I was running phat at cruise with the single carb - in the 12.5-9 :1 range. That's bad++ for a lot of reasons.

I realized that my old/obsolete Holley HP 950 metering blocks we're designed for WOT and simply did lean out very much at cruise (duh... it is a street/strip car). I tried changing the jets and the power valve and that didn't really help the mixture at cruise as much as I wanted. I successfully leaned out my cruise mixture ratio from mid 12s:1 to mid 13s:1 by using modern billet metering blocks from Quikfuel. My mileage increased dramatically. I've read somewhere (I think one of my Holley tuning books) that an AFR change of 1 point is roughly a 30% increase in fuel economy. Of course, you need to be careful and not lean it out too much and risk detonation.

I also have an overdrive and it didn't matter as long as I was phat, I was getting crappy mileage. My current big Hemi has 2x4bbls and I get decent (mid-teens) mileage with that too - as long as I don't get on it. I use the 02 sensor get the tune I want. I run one tune for the Summer and different one for the Fall and Spring when the air is better... and a different one when I race.

I do have vac advance & have spent many hours tuning with a wide band. adjustable IFR & adjustable air bleeds are your friend !!!!!

I don't know what I'm doing. That's what makes it fun.

After that much effort I'd go to EFI and let it tune itself.

👍

What I did.

Would an octopus with longer arms still be considered an octopus?