Early 70's Cadillacs and fuel efficiency.

I've been thinking I'd like a Cadillac. Specifically from the early 70's. 

Part of me thinks it'll be a part time use car and to just deal with the fuel usage. The other part of me thinks that fuel usage is obscene and would like to double it. 

So leaving costs out and knowing that I will never see an ROI in fuel costs, and leaving out the amount of work involved. Only looking at the end results does the hive think I would get better mpgs going with a full in megasquirt, Port injected and timing control build on the 472 or swap the entire drivetrain out for an LS and modern over drive with lockup converter? 

LS and modern transmission will probably get you the best fuel economy. A 472 wasn't designed with efficiency in mind. Just power. 

With gas at sub $2.00 a gallon, I'd give it a fresh tune up and drive it. The Q -Jet wasn't a bad carb for fuel efficiency as long as you kept the secondaries closed. 

The 472 wasn't even designed with power in mind.  Just smoothness.  Any power it made was purely accidental.

As for economy, even after 1973... who cared?  You had a Cadillac.  You could afford it.  Or at least, you wanted the image that you were rich enough that you could afford it.

Nowadays you can buy a 2 liter turbo Cadillac that makes twice the power, weighs half as much, and gets four times the fuel economy, and doesn't drive like an old truck that is both drunk and stoned.  But our priorities are different today.

Gas was more like .40 to .80 per gallon in the 70’s btw.

I don’t think they’re as bad as people think.  I used to do 21 highway with my 78 deville with the 425.  

In reply to ebonyandivory :

With inflation, $0.40 in 74 is the same as $2.16 now  and $0.80 is $4.32 in modern money. So gas may actually be cheaper now (relative to other costs) than it was in the 70s.

Is 1976 early enough in the '70s because this would be my Cadillac inspiration.  

Swapping in an overdrive transmission that works without electronic control might be the easy button to improve fuel economy somewhat.

STM317 said:

In reply to ebonyandivory :

With inflation, $0.40 in 74 is the same as $2.16 now  and $0.80 is $4.32 in modern money. So gas may actually be cheaper now (relative to other costs) than it was in the 70s.

Exactly. People don’t usually consider these things. It makes a huge difference when you factor in inflation.

(80 cents in 1975 is $3.80 now)

I'm not concerned about the cost of fuel. It's the idea. 9-11 average mpgs is what I'm seeing with 13-14 highway cruise. 

So this is just an opinion- based on a lot of observations, but still, just an opinion...

The worst of the worst thing of that early Caddy is the trans- limited gears, and a lot of slip.   Yes, in theory, you could get into a sweet spot were mileage was good at a given speed.  But as a whole system, it's a huge weak point, and where most of the losses happen.  The modern engine probably has 6 gears and will lock up quickly and often.

The next worse thing, to me, is the control system- fuel was a semi controlled leak, and spark was sort of advanced with MAP- but it was far, far, far from optimum.  Getting a more consistent fuel delivery will help a ton, and if you can come up with a way to advance the spark in an appropriate way- you will pick up a huge amount of thermal and chemical efficiency.  

And that sounds like the MS addition will be a huge thing- and relatively speaking, it will.  HOWEVER- if you do the LS swap, GM has already done a huge amount of work for you- finding the most efficient spark, and controlling the fuel really well.

IMHO, if you want the best of the best fuel economy- find a smaller LS to put in- one where the power output isn't 5x that of the original engine (LOL....).  While the 472 will have a lot of torque, the modern LS with a modern trans will be more than capable of making up for that with a better system.  

I'm not familiar enough with the GM turbos, but knowing ours, and how they are ended up being controlled, well....  The v8 will fit really well....

(the fact that gas is so cheap right now is kind of mind blowing.  It's like $.40 a gallon back in the day.  I got my DL in 1982, and I don't remember what gas cost back then, but I'm pretty sure it was more than $0.75, which is what it would be adjusted to for today's prices)

Modern engine and trans will almost certainly net you better MPG, and probably more power to boot.

I am assuming “fuel efficiency” is actually about money. 

Regardless of what engine you use, you will be putting it in a 5000 lb vehicle. You are not gonna get 30 mpg. 

Lets assume 20. That’s only 9 mpg more than the average you are expecting.  If fuel remained at $2 per gallon, you will be saving about $0.08 per mile.

If the swap cost you $5000, you will have to drive 60,000 miles before you break even. 

Is the idea that important?

I had a '72 CDV.  472.  In general, it got 8 MPG.  Now, if you were on the highway and really, really careful and didn't go over 55, you could get maybe 14.  If you hot footed it around town, look for 6.  My aunt had a 75 CDV, which I think was the 500 by then, and it got about 6 or so.

ignoring build costs, as you've stated, I've always thought doing something like a Duramax swap would be the sweet spot in capturing the spirit of the animal.  Those old boats were all about effortless torque.  A newer diesel would give you the potential to tune for upwards of 1,000 ft. lbs. without getting crazy to tug that 2 ton+ boat anchor around with ease, and with the right gearing and the modern trans could probably knock down 20+ mpg hwy all day long.  New crew cab 3/4 ton diesel trucks are 7,000+lbs., so swapping into a 70's Caddy would be a significantly lighter load!   

No doubt an LS would be the easier button, and would make plenty adequate power, but that seems too easy.  

SVreX said:

I am assuming “fuel efficiency” is actually about money. 

Regardless of what engine you use, you will be putting it in a 5000 lb vehicle. You are not gonna get 30 mpg. 

Lets assume 20. That’s only 9 mpg more than the average you are expecting.  If fuel remained at $2 per gallon, you will be saving about $0.08 per mile.

If the swap cost you $5000, you will have to drive 60,000 miles before you break even. 

Is the idea that important?

It's not about money. It's the fact that 9 mpgs is obscene for cruising around Texas. It's just extremely wasteful. And if a modern drivetrain swap could double that then yes it's worth it. Even at 10K. Hell if they was an electric swap that had a range of 300 ish miles or so I would have no problems going that route.

I'd like a Coupe DeVille but they started putting pillars behind the windows in 74 I think so I'd be looking at a 71-73.

You guys suck, the biggest reason to own a big caddy is so you can swing your cubic inches around.

xflowgolf said:

ignoring build costs, as you've stated, I've always thought doing something like a Duramax swap would be the sweet spot in capturing the spirit of the animal.  Those old boats were all about effortless torque.  A newer diesel would give you the potential to tune for upwards of 1,000 ft. lbs. without getting crazy to tug that 2 ton+ boat anchor around with ease, and with the right gearing and the modern trans could probably knock down 20+ mpg hwy all day long.  New crew cab 3/4 ton diesel trucks are 7,000+lbs., so swapping into a 70's Caddy would be a significantly lighter load!   

No doubt an LS would be the easier button, and would make plenty adequate power, but that seems too easy.  

 

I've thought of that too. 

Theoretically, the modern drivetrain will easily net you far better MPGs than modding the original engine. Practically, as SVreX said it would take a very long time to pay off. And short of a pickup, an American land barge is the worst thing you could start with in terms of Cd.

Nick Comstock said:

SVreX said:

I am assuming “fuel efficiency” is actually about money. 

Regardless of what engine you use, you will be putting it in a 5000 lb vehicle. You are not gonna get 30 mpg. 

Lets assume 20. That’s only 9 mpg more than the average you are expecting.  If fuel remained at $2 per gallon, you will be saving about $0.08 per mile.

If the swap cost you $5000, you will have to drive 60,000 miles before you break even. 

Is the idea that important?

It's not about money. It's the fact that 9 mpgs is obscene for cruising around Texas. It's just extremely wasteful. And if a modern drivetrain swap could double that then yes it's worth it. Even at 10K. Hell if they was an electric swap that had a range of 300 ish miles or so I would have no problems going that route.

I'd like a Coupe DeVille but they started putting pillars behind the windows in 74 I think so I'd be looking at a 71-73.

It's this statement that makes me think the first person or business that can make an affordable (sub $25k) hybrid swap will print money.

One of those either/or/both systems, fuel, or electric, or both. 

I just picture in my head for body on frame vehicles being able to call a company, say you have X track width and Y Length, a few weeks later, you get a call to come get your frame that's setup with a motor, harness, and whatever doodads, then just drop the body on. 

I'm sure it could never be that simple, but it's nice to think about. 

GameboyRMH said:

Theoretically, the modern drivetrain will easily net you far better MPGs than modding the original engine. Practically, as SVreX said it would take a very long time to pay off. And short of a pickup, an American land barge is the worst thing you could start with in terms of Cd.

That very much depends on where you get the swap, and how much it takes to change it.

When you see complete LS powertrains being used in the challenge, then it's easy to conclude that at a bare minimum, you can do the swap for less than $2k.  Realistically, I'm sure the min swap price is under $1000.  And at that point, the payoff distance isn't that far.  Especially when the Caddy is likely getting under 10 mpg in it's current trim.

Patrick said:

I don’t think they’re as bad as people think.  I used to do 21 highway with my 78 deville with the 425.  

I think your DeVille is an outlier.  My '76 Olds Cutlass ( a "personal-sized" little coupe, BTW ) managed no better than 17 highway, 12 city with the 350 Olds.

alfadriver said:

GameboyRMH said:

Theoretically, the modern drivetrain will easily net you far better MPGs than modding the original engine. Practically, as SVreX said it would take a very long time to pay off. And short of a pickup, an American land barge is the worst thing you could start with in terms of Cd.

That very much depends on where you get the swap, and how much it takes to change it.

When you see complete LS powertrains being used in the challenge, then it's easy to conclude that at a bare minimum, you can do the swap for less than $2k.  Realistically, I'm sure the min swap price is under $1000.  And at that point, the payoff distance isn't that far.  Especially when the Caddy is likely getting under 10 mpg in it's current trim.

It can be done for cheap "on Challenge budget".  There are a good number of expenses that can be ignored for Challenge budgets, like tools or software.  I could make the PCM work for "free" but Average Joe is going to have to buy HPT or pay someone to make the PCM standalone-friendly.  I could make a driveshaft that works well enough for a couple drags runs and an autocross, Average Joe is going to have to spend $400-500 to have one made.  Etc.

Personally, I'd do what I could to tweak the ignition timing and the carburetor.  Q-Jets are awesome for atomization, and there's a lot to be said for a heated intake manifold as far as making sure the fuel stays atomized.  No you are never going to get "new car" fuel economy, when you figure that it has about the weight and aerodynamics (worse cd, better frontal area) of a modern truck or fullsize SUV.  They don't get 30mpg and you won't get that from an old Caddy no matter what is powering it.  But you can get a hell of a lot better than 9.  I was able to squeak 24mpg from an early 70s Thunderbird with nothing more than playing with ignition timing and making sure the Autolite 4300 (Ford-ified Q-jet) was working correctly.

Old Caddys are all about effortless torque.   Whatever engine you swap (or dont' swap)  ignore HP figures, it's torque you want.   A diesel wouldn't be a bad option, as those old gas behemoths ran out of steam above 4K anyways.   As Rolls used to say.....it's about Waftability.   Effortless cruising--- that's an old Caddy's raison d' etre!  

BTW my 71 Eldo with the 500 cid mill got about 8mpg in town, maybe 12 on the hwy.   There was no incline it wouldn't climb though! 

In reply to Knurled. :

If you are just doing a simple swap, is there a requirement to get HP tuners if the base calibration is good enough?  Heck, a 5000lb van powertrain into a 5000lb caddy would work pretty well, I would think.

The driveshaft, that would be something....

I'm not familiar enough with LS swaps, but it sure seems KISS would be a good way to go.

But my point is that it's not a $5000 swap.  $2000 with a $500 donor may be more realistic for this audience.

edit- now that I'm thinking about it- it's interesting to see people suggesting to NOT do an LS swap.  How odd.