Slant 6 MPG Upgrades?

[chinze57]

I'm soon to have my grenaded /6 back, and starting a new higher paying job so I'll have some disposable income. Being that I have my Dart to daily, and want to continue doing so, I want to maximize my actual mpg. With the modifications made to my setup, I was getting 20 mpg average, predominantly highway driving. That included removing the A/C compressor, switching to headers and aluminum intake for weight reduction, as well as an aluminum radiator. If I could have fit an electric radiator fan between the engine and the radiator, I would have liked to do it but couldn't find one thin enough.

It looks like the next big step is going to be EFI, specifically per-port fuel injection. I cannot find a straight answer on this forum or slantsix.org about this topic, and believe me I've been searching. For simplicity and to work with parts I own, I'm thinking about sending my aussiespeed intake to gill welding and having them add injector bungs and a fuel rail. I know I'll need to add pump(s) to my fuel lines, but beyond that- what parts do I need to start budgeting for and what's reliable? This is where my research has started to fall apart.
- What throttle bodies are available to replace a carburetor, but will allow me to place injectors at the end of each runner on the manifold?
- What ECU works well with a /6 and is reliable?
- Which injectors work best for the /6 and what other sensors do I need to get my hands on?
- What upgrades need to be made to my ignition? Should I switch to an electronic ignition system, if so, do any ECU's do both EFI and ignition?

Beyond that change, I want to also add on a GV overdrive system. I know it's not as low of an RPM drop as the factory overdrive units, but the 904 is the only auto trans that works with the pushbuttons, and that's a feature I want to keep. At the end of the day, lower RPMs translates to less fuel consumed, so any savings there is higher MPG which is the priority. I have no intention of racing my car, I want to reliably daily drive it for as long as I can, and I'd like to keep fuel costs lower, even if that means a higher up front cost.

Any knowledge or tips are appreciated.

 

[halifaxhops]

I can help on the ignition side.


Your curve probably needs to be changed to maximize the MPG. As far as I know there are no specific ECU's That go just for the Fitech. Now you can lock out the distributor and have the Fitech control the curve I believe, that is with the electronic ignition. When you go looking for a electronic set up, keep away from the new Mopar kits, they are made overseas and the orange ECU's have a very bad reputation for failing, that is a whole new thread, and the cure is really fast in them also.

 

[teringer]

What are you trying to do get 40miles per gallon ,oh wait they did that in 76
L

 

[George Jets]

2.76 rear end gears for mileage.

People that do gas mileage competitions say the rear end gearing is the biggest factor to start with. (on the rear wheel drive cars)

Good chance you have 3.23 rear gear ratio on that early push button shift A Body.

What's the car, what size engine?

170 cubic inch slant 6 was the original engine in the '67 Dart I had with 3.23 rear gears and 3 on the tree.

____________

It gets to the point when you lean them out so far there is not enough Power left to keep up with today's traffic at 70 mph + out on the freeways.

 

[George Jets]

The old saying goes:

"You will get such good milage, that you will have to stop and let out some gas once in a while."

Lol . .

 

[66fs]

Skip all that, mill the head for compression, use the factory 2 barrel carb and intake, as well as 2.76 rear unless you have a manual O/D. Get a vacuum gauge and run it at the highest vacuum at a given speed. Maybe a cam and double roller timing set. Put the A/C back on.

 

[diymirage]

what are you willing to invest?

lest say you go from averaging 20 to 25
and lets say you driver 25 miles to work

now, you are putting 250 miles per week on the dart, thats 14000 miles per year
at 20 MPG that is 700 gallons
at 25 MPG that is 560 gallons

so you'd be saving 140 gallons per year
lets say it runs about 3.50 a gallon, thats $490.00

that $490 would be what we call "return on investment"

what does aussie speed want for their services ? one years of savings?
a new pump and lines, thats another year
add a fitech, and sparker, another two years

see where im going with this?


im not trying to rain on your parade, but if it were me, id spend that disposable income on fuel...or boost
boost might be the best way to go to increase your MPGs aswell

 

[dano]

What MPG are you shooting for? Have you looked into what the slant guys are getting with the Sniper EFI?

When you compare a modern engine to the slant there are several technologies that allow higher efficiency (MPG's) and power over the slant 6. Higher static compression, control over dynamic compression, EGR or exhaust re-breathing systems, more efficient chamber design, multiple valves, better flowing intake & exhaust ports, Spark plug location and reach better intake tracts and exhaust systems all help.

If anything ditch the 904 with GV and get a T5 manual from a 87-93 5.0 Mustang. Reducing rotating mass off the engine is a win to a point.

 

[67Dart273]

One of the huge fights you have, which people don't take into account is FUEL. Alcohol --izz--eeed fuel --you need more of it, and the more alky content, the more fuel you need.

Frankly, I doubt the money you will spend on MPFI vs TBI will be worth the trouble. Find a 1 or 2BBL TBI setup and run it

You for sure want to run a setup that allows the EFI to control spark advance

Pick an EFI that has a companion display so you can see what is going on. One key to better mileage, other than a light foot and lowered cruise speed, is high advance numbers at low throttle settings

 

[volaredon]

I was gonna say something about being "worth it" what you're looking to spend for what you get out of it in return... The more you have to pay to "have" done for you the less worth it this becomes. The more you can do yourself or with the help of a buddy for beer money, sort of thing the more feasible it becomes.

And your statement about lower rpms = more mpg doesn't always hold true either. There comes a point where you are lugging an engine. When I had my wrangler with it's 4.0 inline 6 and 5 speed (all stock) with 3.07 gears and 235/75-15, it didn't like being run in 5th below about 60 unless I was rolling downhill. Which was worse with the 31/10.50-15s I had in it for a while.

 

[RustyRatRod]

Sell your intake. Gill Welding can help you out with any of the engine related items. Call them. David and Bryce are fine fellas.

 

[chinze57]

Good chance you have 3.23 rear gear ratio on that early push button shift A Body.

What's the car, what size engine?

It gets to the point when you lean them out so far there is not enough Power left to keep up with today's traffic at 70 mph + out on the freeways.

Yes, currently 3.23. With overdrive of .78 final drive ratio, my effective rear end will be effectively 2.5 without sacrificing torque for acceleration. Once I get up to a nice cruising speed it'll drop down the RPMs, making up for fuel inefficiency in the city.

The car is a 64 dart with a freshly rebuilt and mildly modified 225. Milled slightly, ported, and a mild cam. The car can accelerate no issue and maintain speeds of 70+ without being all out. I've cut, by my estimate, a little over 100lbs in switching to more modern components in the engine bay, and less mass to move is less fuel spent accelerating. Realistically I've cut about all the weight I can while keeping the car comfortable, I'll probably relocate my battery to the trunk to make the back-to-front balance better.

Parasitic loss is what I'm worried about. The direct mounted fan is (relatively) heavy and induces, by most estimates, a 10-15hp loss. On a stock 225 that makes 145hp that's around a 10% loss in efficiency, which translates to less of the energy from the fuel being used to propel the car forward. I'm just having trouble finding a thin enough electric fan to mount direct to the radiator.

One of the huge fights you have, which people don't take into account is FUEL. Alcohol --izz--eeed fuel --you need more of it, and the more alky content, the more fuel you need.

I have ready access to no ethanol fuel here in the south, same price as premium/high octane where I am, around $4.

what are you willing to invest?

lest say you go from averaging 20 to 25
and lets say you driver 25 miles to work

now, you are putting 250 miles per week on the dart, thats 14000 miles per year
at 20 MPG that is 700 gallons
at 25 MPG that is 560 gallons

so you'd be saving 140 gallons per year
lets say it runs about 3.50 a gallon, thats $490.00

that $490 would be what we call "return on investment"

what does aussie speed want for their services ? one years of savings?
a new pump and lines, thats another year
add a fitech, and sparker, another two years


im not trying to rain on your parade, but if it were me, id spend that disposable income on fuel...or boost
boost might be the best way to go to increase your MPGs aswell

I'm looking at $4-5k including the GVOD, which itself is roughly $3k.
You make a great point about ROI based on a commute of 25 miles. At that point it would take me almost a decade to "pay back" what I spend. However, I do a good number of road trips. Whether that's Athens or Alabama or down to the beach, and that's where a lot of the miles add up. That can be anywhere from 1500 to 2000 miles a year, plus miscellaneous driving around town. Lets say all told thats 16500 miles.
At an average of 19 miles a gallon (have moved to the city since I last drove the Dart, still do a lot of highway miles, but an increasing number of city miles as well) that translates to ~869 gallons of fuel a year.
At an average of 25 miles a gallon (a low, but believable estimate of what I want to achieve) that's 660 gallons/year.

That's become a savings of 200 gallons/year which at current prices is about $800 saved per year, let's say I spend $4500, I make my money back in just over 5 and a half years instead of almost a decade.

But that's aside the point - I'm in my early 20's and this car is 60. It's been nothing but fun for me, and I vastly prefer driving it to any modern car. I want to drive it until it's at least 100 years old if I can, so long-term, a few thousand dollars up front should be well worth it, even if it doesn't pay off in the immediate future.

What MPG are you shooting for? Have you looked into what the slant guys are getting with the Sniper EFI?

When you compare a modern engine to the slant there are several technologies that allow higher efficiency (MPG's) and power over the slant 6. Higher static compression, control over dynamic compression, EGR or exhaust re-breathing systems, more efficient chamber design, multiple valves, better flowing intake & exhaust ports, Spark plug location and reach better intake tracts and exhaust systems all help.

If anything ditch the 904 with GV and get a T5 manual from a 87-93 5.0 Mustang. Reducing rotating mass off the engine is a win to a point.

I'm shooting for high 20's MPG as a mix of highway/city with probably 80%+ of my driving being on the highway. If I could hit 27 I'd be plenty happy.

I wish I could ditch the 904 and switch to a small standard trans with OD built in. I like the push buttons too much to get rid of, and am willing to suck up the loss in efficiency there to keep them. I also know that the vast majority of my cost is going to come from trying to make up for that loss with an OD unit for the 904. I didn't buy this car cause I like my wallet I guess, lol.

Sell your intake. Gill Welding can help you out with any of the engine related items. Call them. David and Bryce are fine fellas.

For a hair over $500 they'll modify one to accept injectors and send it back with a fuel rail as well. I really oughta call them and see what system they know plays well with the /6 since they've been messing around with fuel injection on it for a while.

I was gonna say something about being "worth it" what you're looking to spend for what you get out of it in return... The more you have to pay to "have" done for you the less worth it this becomes. The more you can do yourself or with the help of a buddy for beer money, sort of thing the more feasible it becomes.

And your statement about lower rpms = more mpg doesn't always hold true either. There comes a point where you are lugging an engine. When I had my wrangler with it's 4.0 inline 6 and 5 speed (all stock) with 3.07 gears and 235/75-15, it didn't like being run in 5th below about 60 unless I was rolling downhill. Which was worse with the 31/10.50-15s I had in it for a while.

I like electronics. Once I get a feel for what's required of the build and can get high-quality components, I can do the EFI install myself and set it up. A lot of the good ones are self-tuning so once I get some basic target data, it'll attempt to achieve that.
The issue I have with a lot of the electronics made for our older cars is that they're low quality. It seems like a company found a good product, took a picture of it, and then recreated it without any testing or verification that it works.

On your second point, absolutely. Too low of RPM won't be efficient for the engine. With my current tires/trans/rear end, I go around 3200 (I believe, been a minute since I did the calculation) RPM at 75mph. I'd be dropping to around 2500 for the same with OD. A carburetor that's outputting an ideal A:F while city cruising isn't necessarily outputting the ideal ratio while highway cruising, and vice versa. A system that can adjust itself as it drives can create a close to ideal mix at every RPM, which means it can be happier when it drops into overdrive, as well as while its driving around the city.

 

[Killer6]

I'm soon to have my grenaded /6 back, and starting a new higher paying job so I'll have some disposable income. Being that I have my Dart to daily, and want to continue doing so, I want to maximize my actual mpg. With the modifications made to my setup, I was getting 20 mpg average, predominantly highway driving. That included removing the A/C compressor, switching to headers and aluminum intake for weight reduction, as well as an aluminum radiator. If I could have fit an electric radiator fan between the engine and the radiator, I would have liked to do it but couldn't find one thin enough.

It looks like the next big step is going to be EFI, specifically per-port fuel injection. I cannot find a straight answer on this forum or slantsix.org about this topic, and believe me I've been searching. For simplicity and to work with parts I own, I'm thinking about sending my aussiespeed intake to gill welding and having them add injector bungs and a fuel rail. I know I'll need to add pump(s) to my fuel lines, but beyond that- what parts do I need to start budgeting for and what's reliable? This is where my research has started to fall apart.
- What throttle bodies are available to replace a carburetor, but will allow me to place injectors at the end of each runner on the manifold?
- What ECU works well with a /6 and is reliable?
- Which injectors work best for the /6 and what other sensors do I need to get my hands on?
- What upgrades need to be made to my ignition? Should I switch to an electronic ignition system, if so, do any ECU's do both EFI and ignition?

Beyond that change, I want to also add on a GV overdrive system. I know it's not as low of an RPM drop as the factory overdrive units, but the 904 is the only auto trans that works with the pushbuttons, and that's a feature I want to keep. At the end of the day, lower RPMs translates to less fuel consumed, so any savings there is higher MPG which is the priority. I have no intention of racing my car, I want to reliably daily drive it for as long as I can, and I'd like to keep fuel costs lower, even if that means a higher up front cost.

Any knowledge or tips are appreciated.

Fill in the blanks;
1) static CR
2) camshaft specs
3) current rear axle ratio
4) tire size/OD
5) which Aussiespeed intake/carb
6) what model/year car(I know You've been here, but My memory ain't THAT good!)

 

[Killer6]

OK, You filled half of that in already, lol.

 

[RustyRatRod]

I get the modify thing. But......oh nevermind. Do it the hard way. What the heck do I care?

 

[chinze57]

I get the modify thing. But......oh nevermind. Do it the hard way. What the heck do I care?

I'll call them before I commit to anything, thanks for the advice

 

[chinze57]

OK, You filled half of that in already, lol.

I like to make a thorough response instead of piece meal, just makes it easier if someone comes and looks at this thread in the future. Hell it makes it easier if I need to come back to this thread too

Fill in the blanks;
1) static CR
2) camshaft specs
3) current rear axle ratio
4) tire size/OD
5) which Aussiespeed intake/carb
6) what model/year car(I know You've been here, but My memory ain't THAT good!)

I'll need to pull my logs and get those numbers for 1 and 2.
3) 3.23
4) It should be 205/70R15 which is 26.3"
5) Cannot remember, QFT 450 carb
6) 1964 Dodge Dart 270

 

[chinze57]

I get the modify thing. But......oh nevermind. Do it the hard way. What the heck do I care?

Actually now that I'm thinking about it, you're right.
If I keep my current intake/carb setup on the car I can continue using it while I assemble the parts I need and make the conversion. Once I know it works and works well, I can sell my intake and maybe my carb and recoup some of the cost.

 

[MopaR&D]

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.

 

[volaredon]

K I S S principle convert to either the Mopar ecu or HEI, plop on a super six, tune/tweak it out and call it good. I am so sick of electronics, and falling behind ever "current" ways, having to spend the $$ to keep my scanner updated for my daily work, there is much to be appreciated with being able to make changes with a timing light, distributor wrench, vacuum gauge and screwdriver vs flashing a computer, and such. They proved in the 70s that you could get great mileage from these engines, with none of Today's complicated BS,
I had a B body with a V8 that would get mid 20s if I drove it right, in the mid to late 80s... I have a different B body currently that does the same. A lot of today's vehicles with all the extra (unnecessary) electronics still don't.

 

[autopar3000]

Some thoughts, as others may have mentioned and some of which you've noted:

- With the cost of aftermarket EFI and all the mods you will have to make, it will take you a loooong time to pay it back in fuel savings. If you're doing it largely for the fun of working on the car, then I can support that 100%.
- You will get better fuel economy with a later slant that has the cast crank. The cast cranks are something like 15 lbs lighter, which is a huge difference in rotating mass.
- Highly recommended you figure out that electric fan situation. On my old warmed up 318 getting rid of the fixed fan was worth around 1.5 mpg on the highway (at 70+ MPH). I had a 3.23 gear with a 26" tire, so about the same RPMs you're looking at.
- Look for a 2.76 rear gear. Will be the biggest bang for the buck fuel savings, and with a 7¼ rear you should be able to get the gears super cheap (or even free) from someone here.
- Don't discount the value of synthetic oil and differential fluid. Trans fluid probably helps too, but I'm not sure if it's a lot.

 

[chinze57]

Some thoughts, as others may have mentioned and some of which you've noted:

- With the cost of aftermarket EFI and all the mods you will have to make, it will take you a loooong time to pay it back in fuel savings. If you're doing it largely for the fun of working on the car, then I can support that 100%.
- You will get better fuel economy with a later slant that has the cast crank. The cast cranks are something like 15 lbs lighter, which is a huge difference in rotating mass.
- Highly recommended you figure out that electric fan situation. On my old warmed up 318 getting rid of the fixed fan was worth around 1.5 mpg on the highway (at 70+ MPH). I had a 3.23 gear with a 26" tire, so about the same RPMs you're looking at.
- Look for a 2.76 rear gear. Will be the biggest bang for the buck fuel savings, and with a 7¼ rear you should be able to get the gears super cheap (or even free) from someone here.
- Don't discount the value of synthetic oil and differential fluid. Trans fluid probably helps too, but I'm not sure if it's a lot.

- I'm not so concerned about how long it takes me to make back what I spent. I like working on my car, and want it to run the best it can. I'll make back the money in a few years at least, but I'll have had fun making the change and figuring it out.
- I didn't know that about the cast cranks. I was under the impression they were garbage but yeah that's a good amount of weight reduction.
- If I were using a stock radiator or even one close to stock it wouldn't be an issue fitting on the electric fan. I went with an aluminum rad, and it's significantly thicker, meaning there's barely any room between the front of the engine and the back of the rad. There's enough room to fit a direct fan, but the electrics I can find are too thick in just the wrong places, or just totally unreliable if they do fit. It's the top of my list.
- Yeah before I dump $3k into an overdrive, I'll look at swapping to 2.76, it may be exactly what I'm looking for. If not, I can always go back and spend that money later.

 

[volaredon]

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.

 

[volaredon]

I went the opposite way, because of what I had. But mine is in a truck. I wasn't worried about going from cast crank to forged and heavier because once rolling it's easier to keep it rolling...

 

[Projectile Dart]

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...