What Powertrain for My 73 Mustang Convertible?

[73StangJK]

Years ago I started on a 351w fuel injection project for my 73 Mustang. I've got a lot of parts for it and lack maybe another $700 to complete it. The Stang has been sitting a couple years (we had another baby) and now I am trying to decide what to do with it. I think I want to come up with something more modern than the 351w and its maybe 13mpg at best lol

There is the ecoboost engine and I think I can easily fit one in the Stang. Probably I would go with the 2.0L.
https://www.drivingline.com/articles/go-home-50-5-ford-project-cars-ripe-for-a-23l-ecoboost-swap/
There are now e-crate motors from ford and others that I could also try to figure out.
https://www.thedrive.com/news/42974...rate-motor-costs-3900-and-you-can-buy-one-now

 

[73StangJK]

I'm searching for more information now on the 2.0l ecoboost engine. I wonder how different it is from the 2.3l. I think either, from just a quick look around, will fit within my 73's shock towers. https://www.rallyanarchy.com/phorum/read.php?5,106139

 

[71ProjectJunk]

You can get decent gas mileage from a 351W if you get a good 6 speed transmission, and don't go crazy on the rear end gearing or camshaft. I bet you could get 20 MPG+ with EFI, a 6 speed trans, 3.25 gears, and a cam with about 215 degrees of duration at .050 or less. Some good heads with smallish ports and a good dual plane intake. Need to keep the velocity up on the intake side. Some good headers and a good dual exhaust should complete the package. Remember that a 1987-1993 5.0 Mustang GT got 22 mpg on the highway and 15 MPG on the city, 17 MPG combined with a 5 speed. The 351W is a little bigger engine so the fuel economy will suffer a bit, but it should still be close. You need to calculate how much you will need to spend to get a new engine and transmission plus all the fabrication VS how much better gas mileage you will get. Also how much you will actually drive the car. Most of these cars are weekend drivers and are lucky to do 1000 miles a year now. I know mine don't get close to 1000 miles a year.

 

[giantpune]

Who said a 351w is 13mpg at best? I'm running a 351w+C4 with a bunch of bolt-on performance parts and getting 17-18 mpg if I can keep my foot out of it. I picked up a 72 chevelle last year with a 350, 4 barrel carb and a loppy cam in it. Drove it home on the highway, 6hr, and averaged 17mpg.

We updated the chevelle to a 700R4 to get an extra cruising gear and better gas mileage. I'm saving and planning for an overdrive transmission for the 351w mustang.

 

[TommyK]

If you are that close on the 351W you should finish it so you can get the car running and driving. You can always sell it when you are ready to upgrade to something more modern if that is your desire. IMO you can afford to spend a lot of money on gas for what an eco-bust swap or electric conversion would cost.

 

[jpaz]

An eco boost or an eclectic crate engine? What? Are you kidding me? Lol theses cars aren’t meant to get great gas mileage. They are meant to have fun!

 

[machphil]

If you want simplicity, do yourself a favor and get a 5.0, the old 302 found in the '71-'73, and upgrade with the factory H.O. roller cam and the MAF fuel injection using the long intake of the '89 style 5.0. I had that engine in my '89 Mustang GT and I was hitting 25 mpg on the highway with the five speed. I understand the desire to get the 2.0 Ecoboost for mileage. My mom has one in her '19 Escape and it is very peppy. She is averaging 24 mpg. How much work do you really want to put into the change?

 

[73StangJK]

An eco boost or an eclectic crate engine? What? Are you kidding me? Lol theses cars aren’t meant to get great gas mileage. They are meant to have fun!

My goal with my Stang was always to drive it a lot. And I have driven it a lot over the years, something like 200,000 miles.

I remembered a mistake I maybe made years ago which is switching to 3.73 rear end gears. I will need to drive a bit on the highway if I want to Autocross with my brother. Maybe I find my old gears and swap them back in? I want to keep my Tremec 3550 but of course I could sell and swap it out for something different if I did go Ecoboost.

I think Electric is not there yet. Once the F150 lightning is in the junkyards that will be a different story though.

The fastest way to deal with the need for EFI on the stang is to go with one of those throttle body injection systems. I do have an electric fuel pump and have plumbed a return line on the stang. It's unused currently. They didn't make an in tank pump for our body style when I was doing all that so I just added an external along the frame.

I have been reading a lot and measuring and pondering.

Thank you for all the suggestions and advice!

 

[71ProjectJunk]

The best way IMHO to do a 351W to get good mileage and power would be to find an engine out of one of the F150 lightnings that came with the 351W that had the GT40 tubular intake manifold with EFI and use that complete EFI setup out of that truck including the EEC-IV computer, distributor and wiring harness. The issue there is that it will probably not be cheap, but the factory Ford EFI that came in the late 80's early 90's was very reliable, and very efficient at producing a lots of torque, with good power, and excellent fuel economy. A MAF conversion, and you can pretty much modify the engine to your hearts desire. The trick here is an intake with long runners, like the OEM Ford one, to get good mileage. Trick Flow still makes the 351W complete EFI intakes and I think Edelbrock and Speedmaster may also still offer them.

 

[droptop73]

It's the complete package that will improve drivability, performance and economy. I am getting 20ish MPG with my carbureted 351C 2v with a T-5 and 3.50 gears. In my case gains could be made by going to an 8.8" rear as it has much less friction than a 9". EFI would likely help some. Reducing rotating mass with an aluminum driveshaft would help. Eliminating the engine driven fan and going to electric is worth a bit.
My car is also driven a bunch in the summer and part of the driving experience is an easier hit on the wallet. I guess what I'm saying, mileage can be had with the 351W just using a different approach.

 

[machphil]

An eco boost or an eclectic crate engine? What? Are you kidding me? Lol theses cars aren’t meant to get great gas mileage. They are meant to have fun!

So you admit you've never driven and Ecoboost? The 2018 3.5 Ecoboost has the same output as the '71 429 Super Cobra Jet. That same Ecoboost will get 21 mpg in an F150 weighing close to 5000 lbs. I challenge you to find a 429 SCJ getting better than 14 mpg tops. I don't think my '73 351 CJ ever got better than 12. I did have a '71 Galaxie 500 with a 429 2bbl that got 17 mpg but it also had a 2.75 gear and it wasn't a "fun" machine, but just a comfortable mode of transportation. The Mustangs were a product designed to fit a nitch and reflect status. In today's petroleum market having fun means being able to afford a perceived symbol of status and speed, while not robbing your kids of their inheritance every time you pull into the station and visit that one armed bandit.

I see a lot of people having fun in their current Dodge Chargers and Challengers with their modern Hemi. The 3.5 Ecoboost in an F150 will perform as good as, or better than a hemi in a Ram. The Ecoboost in a 3500# Mustang will provide the same ear to ear grin. I would drive a 3.5 Ecoboost in one of my Mach 1's. But if someone gave me a new Ford GT with the 3.5 Ecoboost(the only engine offered in that vehicle), I would jump on it in a heartbeat.

 

[jpaz]

Whatever floats your boat I guess, but I could care less what kind of gas mileage I get out of my 351c.
Good luck with your project!

 

[Hemikiller]

The returns need to justify the investment, both in money and time. If your primary goal is fuel mileage, the 351W will certainly fit that need if set up correctly. Since you're only $700 away from the goal, then IMO, carry on to it's completion.

 

[71ProjectJunk]

So you admit you've never driven and Ecoboost? The 2018 3.5 Ecoboost has the same output as the '71 429 Super Cobra Jet. That same Ecoboost will get 21 mpg in an F150 weighing close to 5000 lbs. I challenge you to find a 429 SCJ getting better than 14 mpg tops. I don't think my '73 351 CJ ever got better than 12. I did have a '71 Galaxie 500 with a 429 2bbl that got 17 mpg but it also had a 2.75 gear and it wasn't a "fun" machine, but just a comfortable mode of transportation. The Mustangs were a product designed to fit a nitch and reflect status. In today's petroleum market having fun means being able to afford a perceived symbol of status and speed, while not robbing your kids of their inheritance every time you pull into the station and visit that one armed bandit.

I see a lot of people having fun in their current Dodge Chargers and Challengers with their modern Hemi. The 3.5 Ecoboost in an F150 will perform as good as, or better than a hemi in a Ram. The Ecoboost in a 3500# Mustang will provide the same ear to ear grin. I would drive a 3.5 Ecoboost in one of my Mach 1's. But if someone gave me a new Ford GT with the 3.5 Ecoboost(the only engine offered in that vehicle), I would jump on it in a heartbeat.

A new Ecoboost Mustang will run 13.7's at 102 MPH and get over 30MPG on the highway. It is as fast as a Boss 351 and will be 3 times as fuel efficient. You get Boss 351 Performance with 1965 Beetle 1200cc 36 HP fuel economy. It is hard to beat in a performance to fuel economy comparison, except with an all electric drivetrain. What you do loose is the sound and feel of a V8, you end up completely changing the character of the car. The car no longer sounds or behaves like a muscle car should, it will certainly look the part, but it just will not act the part. It will certainly be muscle car era fast, but it just will do it with a completely different feel. Some people need to weigh that into the equation, as the character of the car, the being able to relive the past matters. The sounds, the feel, and the smells matter. To others, especially the resto mod crowd, it is probably irrelevant, as what they are looking for is the look of the car, with the feel and performance of a modern car.

 

[Lazarus]

I make it a point not to tell other people what to do with their car and their vision, but I will say that people can make some illogical (or, at least incomplete) decisions around fuel. Not every engine swap is equal in terms of an investment, so if contemplating potential fuel economy one also has to consider the cost of all the retrofiting, dialing-in, and maintenance (as well aftermarket support) of the potential swap. I suspect it will take a lot of miles and gas to overcome the difference in cost of install between a 351 and an Ecoboost. Most people end up driving these classics less than they planned (for various reasons), and even if they do drive a lot a drivetrain out of its native habitat tends to not have its usual expected lifespan. So people have to be careful not to overstate the fuel cost they are trying to avoid. But that said, it does sound like you tend to put some real miles on, so as long as the total life of the engine would get you the return on investment, it may be worth it for you.

I personally am a big fan of limiting complexity, even if that means some sacrifice in fuel economy. I am really impressed by the modern engines and can’t argue with the ecoboost performance. But generally the more dialed-in an engine is to so finely balance the performance/efficiency tradeoff the more complicated it will be to get it to work in another application. Also, cutting-edge efficiency technology usually sacrifices some durability here and there.

If I had an engine that was almost done, I’d finish it and put in a 5 speed, but I am not the bravest cat out there in terms of putting in modern drivetrains. I know how frustrated I can get when de-bugging a retrofit (it’s a real momentum-killer for me in a restomod project; other guys seem to just keep pushing through). Coyotes even scare me off; the farthest I’d go at present would be to put a modern pushrod engine, like a Godzilla or an LS (I know, sacrilege or whatever) in the car with a good manual overdrive and be happy with that on gas... but you have to do what will give you the most SMILES per hour brother.

 

[73StangJK]

The returns need to justify the investment, both in money and time. If your primary goal is fuel mileage, the 351W will certainly fit that need if set up correctly. Since you're only $700 away from the goal, then IMO, carry on to it's completion.

I was thinking about this last night. I do have almost all the parts I need. There will need to be a lot of tinkering and cursing and testing and tuning to get it to run. I was following Mesozoic's build and I like the lower intake, fuel injectors, and computer programmer. I could go with one of the MegaSquirt's instead of the stock computer. I do not know if that would be better though. I've not followed the MegaSquirt's development at all over the last 5 years. https://7173mustangs.com/threads/71-with-408w-cdan4-eec-v-retrofit.14444/

 

[mrgmhale]

I have found I can get up to 17 MpG with a 351W if it is tuned properly, the vacuum advance diaphragm is not leaking or ruptured, the power valve in the carb is not leaking, and I keep my foot out of the throttle WOT position. Another consideration is the rear axle ratio, of course. If you are running 3.0:1 or steeper gears it is easier to get decent MPG readings. But once you go to 3.5:1 or lower it is a bit harder. In our 73 Mach 1, with its transplanted, Street/Strip built 351W, C4 auto tranny, and 3.51 TractionLok rear axle gear set I would usually get closer to 1 MPH, whereas the tamer 73 Mustang Convertible it able t hit 17 MPG easily. At least that is where things were until last Spring.

What changed? We swapped an AOD into the 73 Mach 1, and reduced our engine RPM at 60 NPH from 2,850 to about 1,875 or so. That will help with the MPG, while preserving the spry lower speed performance with the 3.5:1 rear axle ratio. For the record, the only reason I care about MPG is for driving range, to make certain I can find non-ethanol gasoline along the way without getting the gas tank level down to desperate fumes. The AOD was a great move for us. There were plenty of nay-sayers who warned me of the difficulties I could expect. It was not an easy project, but it wasn't hard either. If anyone would like our vendor list, parts list, and YouTube video links just email me at [email protected]. I am happy to share our AOD experience.

 

[71Shelby]

I make it a point not to tell other people what to do with their car and their vision, but I will say that people can make some illogical (or, at least incomplete) decisions around fuel. Not every engine swap is equal in terms of an investment, so if contemplating potential fuel economy one also has to consider the cost of all the retrofiting, dialing-in, and maintenance (as well aftermarket support) of the potential swap. I suspect it will take a lot of miles and gas to overcome the difference in cost of install between a 351 and an Ecoboost. Most people end up driving these classics less than they planned (for various reasons), and even if they do drive a lot a drivetrain out of its native habitat tends to not have its usual expected lifespan. So people have to be careful not to overstate the fuel cost they are trying to avoid. But that said, it does sound like you tend to put some real miles on, so as long as the total life of the engine would get you the return on investment, it may be worth it for you.

I personally am a big fan of limiting complexity, even if that means some sacrifice in fuel economy. I am really impressed by the modern engines and can’t argue with the ecoboost performance. But generally the more dialed-in an engine is to so finely balance the performance/efficiency tradeoff the more complicated it will be to get it to work in another application. Also, cutting-edge efficiency technology usually sacrifices some durability here and there.

If I had an engine that was almost done, I’d finish it and put in a 5 speed, but I am not the bravest cat out there in terms of putting in modern drivetrains. I know how frustrated I can get when de-bugging a retrofit (it’s a real momentum-killer for me in a restomod project; other guys seem to just keep pushing through). Coyotes even scare me off; the farthest I’d go at present would be to put a modern pushrod engine, like a Godzilla or an LS (I know, sacrilege or whatever) in the car with a good manual overdrive and be happy with that on gas... but you have to do what will give you the most SMILES per hour brother.

Lazarus,

I appreciate and concur with your philosophy. These incredible cars are meant to bring joy in whatever form their caretaker envisions.

Off the subject, your convertible is stunning! Looks to be a beautiful restoration and I would love to see more images of what you have created. I am in the middle of a restoration/modification of a '73 convertible and appreciate seeing other finely crafted cars for inspiration. Enjoy!

 

[DAverkamp]

My goal with my Stang was always to drive it a lot. And I have driven it a lot over the years, something like 200,000 miles.

I remembered a mistake I maybe made years ago which is switching to 3.73 rear end gears. I will need to drive a bit on the highway if I want to Autocross with my brother. Maybe I find my old gears and swap them back in? I want to keep my Tremec 3550 but of course I could sell and swap it out for something different if I did go Ecoboost.

I think Electric is not there yet. Once the F150 lightning is in the junkyards that will be a different story though.

The fastest way to deal with the need for EFI on the stang is to go with one of those throttle body injection systems. I do have an electric fuel pump and have plumbed a return line on the stang. It's unused currently. They didn't make an in tank pump for our body style when I was doing all that so I just added an external along the frame.

I have been reading a lot and measuring and pondering.

Thank you for all the suggestions and advice!

Keep us in the loop on your project. A lot of neat suggestions and to add to the appropriate comment, IMO of "smiles per hour", I don't like to hold her at 120 too long because shes 50 yrs old, and I also don't care about the price at the pump because "smiles per gallon" to me is priceless. I hope my son feels the same when my tank is empty and he gets the sexy old lady!

 

[Stanglover]

Late to the party again, but reading this, I just had to add my thoughts.
To start, I try to always say, "your car, your way", but to be honest, if I saw a 71-73 Mustang at a show with anything less than a Coyote engine swap, I'd be disappointed. A 2 ltr Ecoboost would just look wrong. I mean there is this huge engine bay (until you shoe-horn a Coyote in there), with a relatively tiny motor dropped in. Yeah not for me!
Here in Canada, well Ontario, I'll currently be paying $7.60 Cdn for 3.8 liters or 1 US gallon of premium gas. With the milage I get from my 351C 4V M code, it will work out to be about 50 cents per mile. Yes it chokes me up to pay that much, but I really don't care. The car is a blast to drive and I can get between 12-16 mph /US gallon, 15-20 imperial.
So I'll spend an extra 200 bucks on gas for the summer's fun, still beats all the agro of an engine swap, just to save 50 cents.
If it came to needing to get better mileage, better gearing would be my go to approach, like a 6 speed manual. I already have 3.25:1 rear gears.