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Regular
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Location: Apple Valley, CA | My recently aquire 59 Dodge Sierra was originally a 361 car and currently has no motor. I can find 440's all day out of motor homes, but honestly I am trying to get some decent fuel economy in this vehicle. Naturally I would jump to the 440 but honestly a 383 or 400 would probably be better, maybe even a 361?
Obviously I'm not expecting great fuel economy numbers, just trying to figure out if a 361/383 would get much better fuel economy over a 440 |
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Expert 5K+
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Location: So. Cal | Five things kill fuel economy: 1. Friction 2. Change in momentum 3. Poor burn of fuel 4. Heat loss 5. Poor pump efficiency
With that in mind, the only thing you can do to affect #2 is to reduce the weight of the car and the weight of the rotating assembly (like inside the motor, trans, & axles). You can do that to some degree with aluminum trans & motor parts, but you are limited to move it much more than that. Light aluminum rods & titanium valves really make a nice difference here because of them being a big part of the rotating assembly and aren't as prone to failure on the street as some people think they are. Number 3 can be optimized by going to fuel injection and electronic ignition and #5 can be optimized with new head, intake & header designs. But the big savings you are probably looking for is in the combination of numbers 1 and 4. A large 440 motor has drawbacks in terms of it's weight (#2) and heat generation (#4). Big displacements generate a lot more excess heat that is wasted to your cooling system if the power it offers is not needed. So in general, to reduce fuel consumption you want:
1. Relatively long stroke with small bore motor - This creates a strong, low end torque curve that allows you to gear the car way up for better fuel economy. And the smaller displacement doesn't waste as much heat. But if you don't gear it up, you will not realize this benefit as much. Long strokes increase friction though so there is a tradeoff here. Probably best not to go over square: bore diameter=stroke.
2. High gears - This will dramatically lower the motor speeds which will reduce friction of the fastest turning part in your car - the motor parts.
3. More efficient automatic trans or just run a manual trans. - A lockup converter trans will improve your mileage & efficiency.
4. Narrow, hard rubber tires - reduces road contact friction, but also don't handle or perform as well.
5. Better aerodynamics - Not much you can do here without ruining the looks of your car. But you can drive slower to make up for the aerodynamics of a brick on wheels.
As a practical example, my 70 Satellite wagon with stock 318/904 auto got around 15mpg and had poor performance. I converted to electronic ignition (#3), a 4bbl intake (#5 & #2 for aluminum), Dakota dual exhaust (#5), 700R4 overdrive with lockup converter (#1 & #4) with 3.23 gears to put the motor at a good performing part of the torque curve for its output. This resulted in 20mpg with a nice improvement in performance. A big improvement from where it started for such a big car. This combination was mostly limited by the available low end torque from the internally stock 318. It didn't have enough torque to raise the gear ratio up to 2.76 with overdrive. But if you could increase the low end torque further, this could potentially give you an even better result. The modern roller cam was designed to do this very thing - to increase low end torque by increasing the ramp rate. So installing one of these cams can help you out there too.
Edited by Powerflite 2017-06-20 6:15 PM
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Regular
Posts: 50
Location: Apple Valley, CA | Correct, I agree with your statements exactly. I figure that whatever b or rb motor I run I will run some aluminum heads rpm intake and vacuum secondary 4 barrel carb. More than likely I will go with a TBI unit like Fitech although from my experiences adding retrofit efi units to cars with finely tuned carbs (Wideband O2 sensors and track time/dyno time) did not net much of an improvement in fuel economy, but did generally produce a much smoother driving machine.
I would like to think that a 383 with the aforementioned modifications and a cam (Flat or Hydraulic roller) could reasonably get 15 mpg as an over all and maybe 17 on the highway. |
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Expert 5K+
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Location: So. Cal | Probably, but you could also probably get better fuel efficiency with a 361 as it has a smaller bore and the same stroke. Even better would be a 350 stroker. That would give you the power of a 383, small overall displacement, but more low end torque that would allow you to gear up more. The 383 has a relatively large bore and short stroke. Kindof the opposite of what you are looking for in terms of fuel mileage.
Aluminum heads reduce weight and improve pumping efficiency (because of the newer design), which is good, but actually increase heat loss to the coolant, which is bad. However, they also allow you to increase the compression ratio by 1 point, which improves efficiency. The increase in compression counter-balances the increased heat loss so the overall benefit is still positive.
Edited by Powerflite 2017-06-20 6:29 PM
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Regular
Posts: 50
Location: Apple Valley, CA | Makes sense, food for thought though, one could probaby get 383 pistons with smaller ring's (modern low tension rings) off the shelf and not a custom piston. Have you ever put a beam torque wrench on a 440 or other big motor and measured the torque needed to rate it with the heads off? Some staGering numbers. |
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Veteran
Posts: 145
| For what it's worth, my 300J Chrysler with the 413 ram induction will get a consistant 14 mpg at 60-65 mph with 3:23 gears. The car has a manual trans, 235-75r15 tires, and weighs just under 4,100 lbs. There's no reason a 361 or 383 shouldn't better that by 3-5 mpg. |
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Expert
Posts: 3887
Location: Northen Virginia | My stock 413 get 7 in city and 12 in highway..auto trans and slow driving.
The Edelbrock carb is adjusted lean for economy, but I could not get better than that.
Edited by hemidenis 2017-06-20 11:09 PM
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Expert
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Location: Kansas City, KS | hemidenis - 2017-06-20 10:06 PM
My stock 413 get 7 in city and 12 in highway..auto trans and slow driving.
The Edelbrock carb is adjusted lean for economy, but I could not get better than that.
I've been daily driving stock 383's/413's/440's for the past 27 years and that's the exact same mileage I've gotten with all of them. |
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Location: Parts Unknown | I have run just about all of the B and RB engines. I am something
of a miser, when it comes to fuel economy, where most guys want go-
fast, with no concern for fuel economy.
It has been my experience that the 383 is the proverbial "just right"
balance of displacement, bore, and stroke to move a car like my 58 or
60 DeSotos around. The 440 simply moves too much air to be able to
lean out to numbers approaching what the 383 can do, and built right,
a 383 can deliver stout go-fast and still push your pig down the road
in the mid-20's for mileage with the right gearing.
This is how I would work it:
Find yourself an M-code 383. Pick up a pair of 906 heads with matching
pushrods. Find some early 6-bolt valve covers and do a little cosmetic
work to remove welded on brackets to make them look like the older 4-
bolt jobs.
I have kept my original AFB's, but will likely experiment with fuel injection
when I get back on my DeSoto.
I dropped compression to 8:1 and used a cam recommended by my
motorhead friends that I can no longer remember the specs on. Out back,
I stacked the gears to 2.76
The idea is to have the power in the engine to overcome the high gears
at low speed, but a really high top end, where the engine can just lope
along at 1200 rpm and happily deliver great fuel economy. When I redo
the DeSoto, it will get a modern 5-speed manual, with the gears set up
as a 4-speed/overdrive 5th gear. I figure this will possibly kick me over
30mpg with a 2.5 ton car. Not bad at all.
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Board Moderator & Exner Expert 10K+
Posts: 13045
Location: Southern Sweden - Sturkö island | My Chrysler '60 with a 383, all original, never opened consumes 1,6 liters for 10 kilometers, average driving, accumulated over the years. I drive as fast as the speed limits allow with some extra margine that allow me to keep my licence :).
I think that that would be like 14,7 mpg |
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Expert 5K+
Posts: 9654
Location: So. Cal | Doctor DeSoto - 2017-06-20 10:32 PM
I dropped compression to 8:1 and used a cam recommended by my
motorhead friends that I can no longer remember the specs on. Out back,
I stacked the gears to 2.76
The idea is to have the power in the engine to overcome the high gears
at low speed, but a really high top end, where the engine can just lope
along at 1200 rpm and happily deliver great fuel economy. When I redo
the DeSoto, it will get a modern 5-speed manual, with the gears set up
as a 4-speed/overdrive 5th gear. I figure this will possibly kick me over
30mpg with a 2.5 ton car. Not bad at all.
What was the purpose of running a crappy compression ratio? Cars in the '70's only did that so they could then bog the motor with a lot of exhaust to get slightly better air quality. Notice that no new car runs less than 9:1, and they would run higher if they could eliminate some of the smog devices. In general, run the highest compression that you can get away with and still have good performance with your required ignition timing setting. Also, you are going to need a lot more changes than what you list to get up to 30mpg. Take a look at the mpg of a newer car of the same weight & motor size and compare what it can achieve to make a guess for what you will be able to do. You're only advantage over the newer car is that you don't have as many accessories to run, but in every other respect (and there are many), you will be at a disadvantage. The name of the game in efficiency is to get a lot of low torque out of a *small* motor. Your 383 is just too big to compete at that level and doesn't have enough stroke to make the amount of low end torque that would be required to lope at 1200 rpm. Just trying to put a little reality to your dream.
Edited by Powerflite 2017-06-21 3:31 AM
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Expert
Posts: 3887
Location: Northen Virginia | 30 miles per gallon is the consumption of 1.8L fuel injected daily car that weight less than 1/2 of a of a C body. and it is aerodynamically 100 times more efficient...
I doubt that can be done.. Back in 1957 the Imperial did an average of 20 MPG/ 4500 lb monster with a 392.
Case in point, the Jeep Cherokee is a Up to 21 city / 30 highway with a similar weight of a c body of 4,514 lbs, but with the advantage of been aerodynamically superior.
Edited by hemidenis 2017-06-23 2:42 PM
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 2017-Jeep-Cherokee-Trailhawk-front-three-quarter-06.jpg (85KB - 86 downloads)
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Board Moderator & Exner Expert 10K+
Posts: 13045
Location: Southern Sweden - Sturkö island | Check that the odometer is true as the first step in milage. Mine is off by 9 %. Once you know this, further calculations will be accurate. |
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Expert 5K+
Posts: 9654
Location: So. Cal | I just use google maps to calculate distance. You can create any complicated route you want on there. That way I don't rely on any other form of measure or guess. But I do have to average over a couple of tanks of gasoline in order to determine exactly how much fuel I am using. |
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Fuel economy of a b or rb powered vehicle.
