Slant 6 MPG Upgrades?

[chinze57]

On the fan, I'd just put a clutched, thermal mechanical fan on /and call it good. More efficient than a solid drive fan, but the electric fan takes more electric power to run which is more load in the charging system. If the alternator has to work harder it in turn takes more power to run as well.

Argonne National Laboratory did a few studies on engine lubrication and efficiency, which is fascinating, but they also provide valubale data on all of the various power losses in operating a vehicle.
2006 2014
They're a rabbit hole in and of themselves, but the highlight is that they estimate .5% each of the total energy from the fuel is expended on the alternator and the cooling fan. So yes, more load on the alternator does equate to more energy being spent, but at the end of the day you save more energy by switching away from a belt driven fan. Alternators are fairly efficient, not as efficient as the power supply on your computer, but not as inefficient as running a fan off the crank while driving at 60 mph, inducing extra drag.

Now, is it worth it? Not necessarily. The main benefit to electric fans is better cooling at low speeds and idle. A clutched fan is better than direct drive in that you're not fighting wind resistance at high speed, which increases parasitic loss.

Just to be the devils advocate here, I see everyone discussing directly modifying the /6 (with good reason) but as I am sure you are familiar with the "Feather" duster and similar a bodies of the mid-70s, much of the gained economy came from weight reduction. I see that you are already on the way with the lighter weight engine components but the same way you can cut drag times to make your car faster at the strip with more power, you can have the same effect with less weight. That applies to mpg as well, the less weight you have to move around, the less power it takes to move it. Have you considered any type of fiberglass components? At bare minimum bumpers and maybe even fenders, hood, trunk lid?
Just a thought...

I've thought about it some, but at this point I'm not sure how worthwhile that is. I'm trying to strike a balance between removing unnecessary weight and comfort. A decades old underdash A/C system is just heavy and inefficient and barely functioning, getting rid of it doesn't hurt me at all. If I swapped any single component, it would be the dashboard and out of fiberglass/carbon fiber and then painted to match. It's unnecessary weight being made of steel.

How much do you want to keep running a slant-6? The 225 is inherently inefficient by design with the super-long stroke and heavy rotating assembly. If I was to ever intentionally own a slant it would be the 170 variant. I think that would be the best bang-for-buck move in search for MPG and keeping the car 6-cylinder. Could just swap over the upgrade parts you already have. The slant wasn't intended to go over 170 cubes, when Chrysler management asked to make a bigger version the engineers wanted to increase the bore but the Valiant designers were fixated on the length dimension of the engine bay so the only option was to increase the stroke.

IMO you'd be way ahead swapping in a stock 5.2L Magnum V8 with the factory multi-port EFI. Only potential issues would be needing a different intake manifold to clear the hood. Mounting options aren't tough to come by, either conversion mounts with current K-member or find a V8 one. You could use factory 273/318 A-body exhaust manifolds which nobody wants and are dirt cheap and could easily find a V8 904 transmission to bolt in place of your current one. Even with the current gearing you would easily surpass 20 MPG average in such a small and light car and you'd easily double the HP as a bonus. I had a 1988 Chrysler Fifth Avenue that averaged 20 MPG and that is a much heavier car with a roller-cam 318 and 904 trans with lower 1st and 2nd gear ratios. My average MPG didn't even change after I swapped to 3.07 gearing (they never came with overdrive), 4-bbl carb and intake and 2 1/4" dual exhaust off the factory manifolds as well as ditching the spark-control computer for conventional distributor and used MSD box I got for free from a friend.

I like the /6 at the end of the day. It's a fun engine, and its the heart and soul of my Dart. I started with a 170, but when I went to rebuild, a previous owner had bored it way too far over and it just wasn't going to be feasible to rebuild without expensive testing to make sure the block was fully intact. It was cheap and easy to get a 225 that had never been touched and bore it and modify. If I could have stuck with my 170 I would have.

 

[mpgmike]

May I suggest MPGenie Program | Ecoceptor for fuel efficiency ideas. Lots of topics, different approaches, maybe a few things will resonate.

 

[my68barracuda]

I run a Mega Squirt 3 Pro ecu in my mpfi slant six. It has been in use since 2016 and has been reliable. The intake is a Clifford 4 bbl unit that I drilled the NOS bosses to accept the fuel injectors. The injectors that I use are Ford 460 units. There are on line FI sizing calculators that can help you pick injectors.
For the Throttle Body I used a GM Vortec unit from a 4.3L v6 motor. I made an adapter from phenolic canvas to fit the TB to the intake.
The fuel tank and pump came from Tanks Inc. I made the delivery and return fuel lines.
I use a locked lean burn distributor with a MSD 6 box running through the MS3 Pro to control the ignition.
It runs well. I originally set this motor up for drag racing but have recently returned the car to street use and have done autocross with it.
An AEM O2 gauge provides the feedback.
A dual electric fan from a Ford Contour fits fine between the radiator and the water pump. There is a posting here on FABO that goes through the wiring.
I am a fan for FI for racing and performance, but I have my doubts that MPFI will provide sufficient fuel economy gains over a well tuned carb to overcome the added expense. But if you want to go that way, go for it.
Mega Squirt has a great online support forum and many users.
If I can prove any additional info to you on my install feel free to message me.
Some other engine / body ideas to consider that can affect fuel economy.
*work with the machine shop to get modern clearances on the rod and crank journals so you can run 0 or 5 weight synthetic motor oil.
*install a windage tray
*use modern pistons with thin low tension piston rings
*the thinner rods on slant six cast crank motors will have less rod bearing friction.
*raise the static compression to 8.5
*install a front air dam and limit - clean up the air flow through the front grill area. On my 68 Barracuda I ducted the grill so that the only air that goes through the grill go through the radiator.
*re consider the AC, driving with the windows down at highway speeds hurts fuel economy.

 

[chinze57]

I run a Mega Squirt 3 Pro ecu in my mpfi slant six. It has been in use since 2016 and has been reliable. The intake is a Clifford 4 bbl unit that I drilled the NOS bosses to accept the fuel injectors. The injectors that I use are Ford 460 units. There are on line FI sizing calculators that can help you pick injectors.
For the Throttle Body I used a GM Vortec unit from a 4.3L v6 motor. I made an adapter from phenolic canvas to fit the TB to the intake.
The fuel tank and pump came from Tanks Inc. I made the delivery and return fuel lines.
I use a locked lean burn distributor with a MSD 6 box running through the MS3 Pro to control the ignition.
It runs well. I originally set this motor up for drag racing but have recently returned the car to street use and have done autocross with it.
An AEM O2 gauge provides the feedback.
A dual electric fan from a Ford Contour fits fine between the radiator and the water pump. There is a posting here on FABO that goes through the wiring.
I am a fan for FI for racing and performance, but I have my doubts that MPFI will provide sufficient fuel economy gains over a well tuned carb to overcome the added expense. But if you want to go that way, go for it.
Mega Squirt has a great online support forum and many users.
If I can prove any additional info to you on my install feel free to message me.
Some other engine / body ideas to consider that can affect fuel economy.
*work with the machine shop to get modern clearances on the rod and crank journals so you can run 0 or 5 weight synthetic motor oil.
*install a windage tray
*use modern pistons with thin low tension piston rings
*the thinner rods on slant six cast crank motors will have less rod bearing friction.
*raise the static compression to 8.5
*install a front air dam and limit - clean up the air flow through the front grill area. On my 68 Barracuda I ducted the grill so that the only air that goes through the grill go through the radiator.
*re consider the AC, driving with the windows down at highway speeds hurts fuel economy.

I had a 70s kneeknocker in there. Between that and the york compressor from the same time, it was just dead weight. Eventually I'll swap over to a unit that replaces the factory heater box and does it all. Modern compressors are lighter, and the heater box replacements are the same weight or less than the factory components. I think VintageAir recently released a new generation and dropped the price of the previous one, so I may go that route.

Front airdam is on the list, the front end gets a bit light around 70. There's a post I've got saved where someone fit a 90s ranger airdam and I'm thinking about that since it's like a $30 install all told.

 

[my68barracuda]

I put a Classic Auto Air system on the 68 Barracuda. Works well.
Modem compressor, all new under dash heater box….

 

[AJ/FormS]

For fuel-economy, the best things that you can do are;
>If the engine is coming apart; Plenty of Cylinder pressure, like 155psi, or more.
>Additionally;
>reduced cruise-rpm, together with adequate Cruise timing.
>Then the tune, including; coolant temp, inlet air temp. and
>Finally, is driving style.
>a manual trans is worth about 10% or an easy 2mpg.
> an overdrive is best served with adequate ignition timing. Without timing, it will likely be a disappointment.
> I've had good results with a SuperSix 2-bbl intake. The small primaries do a good job.
> high-altitude will kill your potential.
--------------------------------
IMO,
a GVod may be a disappointment. It is all too easy to get your rpm so low that you cannot, with the factory type distributor, give the engine the timing it wants.... so you may lose more than you gain. Furthermore the buy-in is so large, that it will take many years to break-even.
Last time I checked, I heard that a GVod was over $3000, plus install; and I don't think it will fit in your early tunnel, so extra cost there, plus I think you will have to convert your B&T mainshaft to slip-yoke style, plus a driveshaft = lots of money, for about 28% rpm reduction, and then add in the matching rear gears.
Say you spend $4500. That will buy you an awful lot of gas.......
Say you drive that baby 10,000 miles a year, and the new combo is worth 3 mpg in the long run, going from 20 to 23mpg. That would represent a savings of 65 gallons a year; say $390. Then 4500/390=11.5 years to break-even. See what I mean?

IMO, a good cruise rpm to target is no less than 2200. Any less and you will need a stand-alone programmable timing computer...... like a Lean-burn, lol.
With 2.45s, you would get about 2250@3% slip.
To get that with a GVod and 24.5" tires would take 2.45/.78= 3.14s, rounds to 3.23s or 2.94s.
The problem with 2.45s is that take off will be a tad sluggish. You can mitigate that some by slamming the A999 gears into your A904 pb case. This will get your starter gear back up about 12%, making those 2.45s feel like 2.74s.
Of course the GVod would solve that, with the aforementioned 3.14 gears.
The thing is:
Your combo might have a potential to get 24 mpg when yur done, in point-to-point traveling; but every time you have to accelerate up to speed, there goes a half-pint, because of those 2.45 gears. So that's like 2 or more gallons per tankful, bringing your average down to something like 22mpg. So then you might as well run 2.76s...... whereas with 3.23s you would burn less getting up to speed but more in point to point.
So really, what you need is a higher stall ..... but that pb 904 is gonna be the handicap.
If it was me, and because I have the skills, and parts laying around, I would stuff the A999 guts into her, with a custom LU hi-stall, with 27" tires and 2.76s, for 65=2230. But I don't like that old-style VB so I would get me a post 71VB and convert it to a pb, if I just really had to keep it..... but more likely I would just throw a console shifter on her; which would allow me to run the A999 as is.
Of course the GVod would skip all this too, but with a crazy price tag.
Here's something else;
slowing down 10% is said to gain you 5% in fuel economy, so cruising at 60 should be worth 1 mpg, over cruising at 65. On a 1hour trip, that costs you ~5 minutes, and you saved about .6 qt of gas......... On every tankful, you'll save about a .7 gallon , over 10,000 miles you'll save 24 gallons say $144 bucks a year@$6 per gallon ..... just by slowing down by 5mph.
And finally; jumping your cylinder pressure up to 150/155 from the typical 130/135, is gonna restore your engine's bottom end .....to the point that you can run 2.76s no problem, with your pb904; and so 65=2535@3% slip with 24.5s .....That, IMO, is a daymn fine low-buck compromise.
To compliment that, install the SS intake and 2bbl, and install a free-flow exhaust system.
As to EFI, IDK. IMO again, the change is not worth the buy-in.
BTW
>If you have to cut the tunnel for the GVod anyway, then, IMO, you might as well install a Chevy 4-speed auto, assuming you can get an adapter. They are fairly compact. I know/I know, you want to keep the pb,
>a well engineered 273, in terms of fuel-economy, can easily match your 225, while pulling 2.45 rear gears, for 65=2250@3% slip, which is just about perfect.

 

[Charrlie_S]

You can mitigate that some by slamming the A999 gears into your A904 pb case.

The low first gear ratio of the 999 will not work in the PB case. The splines in the gear train are different then the splines on the output shaft. You would have to use the late output shaft, also. But that creates the problem of compatibility of the new output shaft with the rear punp, and the tailshaft housing bearing/seal.
Plus, if you did use the 999 gear train then a new converter would be required, as the input splines are different, also. But then that would mean a "custom" converter, as the pilot hole in the end of the crank is too small for a standard converter with the correct splines.
I like the PB trans, but if I were looking for the best bang for the buck on fuel economy. I would, in addition to normal engine rebuild procedures.
1) up the CR by milling the head and/or decking the block.
2) 2 or 4 bbl intake manifold (price decides which)
3) I haven't tried any of these myself, but my choice would be, either a Weber progressive 2 bbl, or possibly a spread bore 4 bbl (Q-jet, thermoquad) FI is an option but not cheap, and not TBI (use port FI)
4) Stock exhaust manifold (maybe open up the outlet), and a free flowing single exhaust (2 1/4 - 2 1/2 inch).
5) Of course fine tuning the advance curve, and fuel mixture ( this would depend on what the engine/car likes)
6) While the engine is out I would either open up the torque converter pocket in the crank or use a 68 or later crank, then
7) you can install a later 998/999 style trans with the LU converter
8) remove the 300 lb tool box from the trunk

 

[MadScientistMat]

My experience with TBI vs port injection is that the jump in drivability and mileage between TBI and port injection is about the same size as the jump from a carb to TBI. While this may not be cost effective if the goal is to save money, if the goal is to optimize the slant six to see how far you can push it, I'd call up Gill Welding for a multiport manifold. As for an ECU - I'm kind of partial to the MegaSquirt III line, but if you want other options, the Holley Terminator designs would be a solid choice. I'd steer clear of designs that simplify things too much, the ones that advertise "no laptop" as if that is a good thing.

 

[chinze57]

The low first gear ratio of the 999 will not work in the PB case. The splines in the gear train are different then the splines on the output shaft. You would have to use the late output shaft, also. But that creates the problem of compatibility of the new output shaft with the rear punp, and the tailshaft housing bearing/seal.
Plus, if you did use the 999 gear train then a new converter would be required, as the input splines are different, also. But then that would mean a "custom" converter, as the pilot hole in the end of the crank is too small for a standard converter with the correct splines.
I like the PB trans, but if I were looking for the best bang for the buck on fuel economy. I would, in addition to normal engine rebuild procedures.
1) up the CR by milling the head and/or decking the block.
2) 2 or 4 bbl intake manifold (price decides which)
3) I haven't tried any of these myself, but my choice would be, either a Weber progressive 2 bbl, or possibly a spread bore 4 bbl (Q-jet, thermoquad) FI is an option but not cheap, and not TBI (use port FI)
4) Stock exhaust manifold (maybe open up the outlet), and a free flowing single exhaust (2 1/4 - 2 1/2 inch).
5) Of course fine tuning the advance curve, and fuel mixture ( this would depend on what the engine/car likes)
6) While the engine is out I would either open up the torque converter pocket in the crank or use a 68 or later crank, then
7) you can install a later 998/999 style trans with the LU converter
8) remove the 300 lb tool box from the trunk

Hey, the toolbox is only 50lbs lol.
I’m running a 4 bbl qft jetted down to match the 225 better and headers with pretty free flowing exhaust.
The trans issue is something I’ve considered. I have a second 64 dart I’ve been using for parts and it’s a manual, so I have the 4 speed trans and pedals if I decide to change at some point. If the push-buttons hadn’t existed for only two years on the dart I’d be more open to replacing it with something, but it’s one of the only original things left on my car.
I’m sure there’s a way to make a later transmission with lock up work, but as of yet I don’t know what that would be. For the time being, changing the rear end from 3.23 is probably the thing to do for lowered cruising rpm.

As far as timing goes, ditching the distributor is the best way to get exactly the timing I want out of the engine. Those ECUs can give any degree of advance you want when you give them a cam and crank sensor.