building a long distance touring car

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str12-340

str12-340

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I'm building a 1970 Dart specifically to use for long distance touring, like taking 101 down the coast to Rt66 across to Chicago then hitting the Nats and Chryslers at Carlisle and then doing it in reverse the next year. I'm trying to figure out the best small block to use in front of a 4 speed overdrive automatic. I'd like to get some decent gas mileage (20-24?) but don't want it to be a dog either (the low 1st gear in the trans will help). So throw out your thoughts, please! I've considered everything from a crate 408 to a 273 power pack style motor.
 
My stock build 273-2/auto did great on my recent trip to Oregon, 2255 mile round trip. Overall average 17+ MPG
I engine builder thinks he can get better out of it, I did get 20+ on a couple tanks.


Alan
 
Doing it on the cheap and easy, ether the 5.2 is a good route, fuel injected or not. The real key here is to be easy on cam timing. IMO, a stock camshaft is the key to any mileage. The second part to it would be tire size coupled with the final drive ratio & where it cruises at rpm wise.

Krooser suggested a Q-jet, which I’m not familiar with but I am with a TQ which is of course a spread bore. The small primary version is a good idea. IDK if Rochester’s have different primary versions. If you can find/rebuild a good TQ, that would be a good candidate, but a spread bore is a cool idea. Otherwise a 600 cfm carb will do ether engine well.

I did a RPM carbureted 5.9 swap with headers/2-1-2 exhaust, a 727 & 3.55’s on 245/60/15’s.
I did get the mileage you seek.
 
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Awesome idea! Some day when I retire I want to do the same.

If you are wanting fuel economy then the smaller V8 is better. Go 318 with a 2bbl.

Remember they are just big air compressors. The larger the holes the more fuel and air you need to work. The smaller engine the smaller need to feed.

Figure out how much power you actually need to move that car and the weight load. Run AC or pull a trailer. Not sure what if any. Are you alone or 800lbs of people?
Even a little steel crank 273 Ci engine with a small 4bbl will do well if not all HP-ed out.
A good dual exhaust and good tires for rolling not drag racing. Gearing around 3-1 dependent on tire height.
Ok- off soap box. Lol!
 
I few years back I took my 340 Duster on a 2700 mile round trip from Fla. to N.Y. state. it was running 12.80's at the time., 4 spd car. The only thing I did was swap in a 3.23 gear. The dang thing got 18 mpg. My newer Chevy pickup with OD and FI cant hit that number. The old stuff can work.
 
The key to low fuel consumption is to keep the revs down...
so build an engine not too big (5.2L), with decent compression to make it efficient,
fuel injection (maybe tuneable) and a low rear gearset.
 
If you have a decent budget for swap parts, a 5.7L Hemi would be a good option. Either with a 518 4speed or 5 speed Hemi, the NAG1
(car) or 545RFE(ram).
It's practically a drop-in and its modern drivability and efficiency is more challenging to duplicate with a carbed small block.
 
I consistently got 18-19 mpg at 65 mph from a 351C, torque and mileage cam, 10.3 compression, 600 CFM Holley specifically made for better mileage, headers, 3 speed non-overdrive, 3.08 rear gear. A 318 like that would be my idea here.
  • The higher compression raises combustion efficiency; something in the 9.5 if fine IMHO.
  • Headers clears out the chambers better after each cycle to get a hotter, more effiecient burn.
  • Cam ought to be a 114 LSA, intake duration below 200@.050", modest cam advance, as much lift as you can get.
  • Small primary carb like suggested. I used a List 6619 Holley, which was just a variant on their standard 1850 vacuum secondary 4 bbl designed in the 70's for better fuel economy by making the primary cruise circuits leaner.
  • The OD trans you have with locking TC ought to give you another 3-5 mpg.
  • Use a performance intake, like an RPM Performer. Anything that helps cylinder filling at lower RPM's will boost torque at the lower RPM's.
  • I would not hesitate to use better-than-stock aftermarket heads for the same reason.
  • HEI ignition
  • Add an AFR gauge and tune your light cruise ratio for 15-16 if carburated.
  • Rear gear ratio in the high 2's.
The 5.2L fuel injected Magnum is also an excellent suggestion IMHO, with some headers.
 
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I have a 71 dart, bone stock 5.2 magnum, with a Chinese air gap knockoff intake, thermoquad, Doug's headers, 904 trans and a 3:23 rear, it gets about 22 mpg on the highway, and cruises effortlessly
 
I drove a 67 cuda 383 pretty much stock cam, TQ 2:94 rear, 4 speed from Ca to Mo 70 mph and averaged 18 mpg. I would also consider 3"23 gears and A833 OD and any good small block with stockish cam and good TQ.
 
Weight, aerodynamics, topography and weather can all affect your mileage outcome beyond the combo. I like the 318/5.2 mag idea. Cheap, easy to come by, enough stroke to make torque but small bore to help fight detonation and keep fuel stratified, roller cam, lower friction rings, etc. 5.7 Hemi would be cool too but how much do you want to spend on this? Slant with a turbo would be fun too.... Swap that 4 speed od for a World Class T5 and 2.92:1 gears.
 
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str12-340 said:
I'm building a 1970 Dart specifically to use for long distance touring, like taking 101 down the coast to Rt66 across to Chicago then hitting the Nats and Chryslers at Carlisle and then doing it in reverse the next year. I'm trying to figure out the best small block to use in front of a 4 speed overdrive automatic. I'd like to get some decent gas mileage (20-24?) but don't want it to be a dog either (the low 1st gear in the trans will help). So throw out your thoughts, please! I've considered everything from a crate 408 to a 273 power pack style motor.
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Since my Dart goes on long trips on occasion I'll throw my combo out there.
Stock bottom end 5.9 with a 214/224-.512 lift cam on a 110 lobe center.
Edelbrock 600 cfm on an aluminum dual plane intake.
1-5/8 long tube headers
Thermostat controlled electric fan
42RH OD trans with a stage 2 shift kit
HEI ignition and vacuum advance used.
273 gears currently
25 mpg at 80mph on the hiway running high 14's/low 15's AFR at 2,100 RPM's
 
I have a '68 convertible Barracuda. It gets 17 mpg at 70 mph with the top down, and the A/C blasting. It gets a bit better with the top up. I guess it would hit 20 mpg if I could put up with going slower on road trips, but with a Valentine 1 on the job.....why suffer.

I run a 408 inch 5.9 Magnum stroker with massaged Eddie heads, 10.2 to 1 compression and a lopey .575 lift hydraulic roller spec'd by Dave Hughes.

That spins a 3.91 sure grip through a Stage 2 200R4 from Extreme Automatics via a 3800 stall lock-up converter from Precision of New Hampton. The lock-up is like having 5th gear.

It out runs stock tire'd Hellcats in the quarter, because it gets out of the hole very hard street or strip. It's dead reliable, a daily driver and put's virtually everyone right in shock when they try to run against it, except 4WD Nissan GTR's etc.

It's the unusual combination of the EFI and the awesome trans, the nearly perfectly matched torque converter and the Nitto Drag Radials. Oh yeah, the properly adjusted slapper bars are painted black, so I don't have to hear how they don't work on Mopars as much after I beat them.

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My ‘18 Ram Express did a best of 24 on a recent east coast trip. To bad around here there not cheap and easy to obtain.
 
Thanks for all the input! Some really great ideas for me to process (and some really cool cars to appreciate). Keep your ideas coming as I have 9-12 months to make up my mind while finishing the body, suspension and interior.
 
What is the budget and/or desire besides mileage?
 
Using an old car for road trips isn't about mileage, it is about the cool factor. You want mileage buy a Prius.


Alan
 
str12-340 said:
I'm building a 1970 Dart specifically to use for long distance touring, like taking 101 down the coast to Rt66 across to Chicago then hitting the Nats and Chryslers at Carlisle and then doing it in reverse the next year. I'm trying to figure out the best small block to use in front of a 4 speed overdrive automatic. I'd like to get some decent gas mileage (20-24?) but don't want it to be a dog either (the low 1st gear in the trans will help). So throw out your thoughts, please! I've considered everything from a crate 408 to a 273 power pack style motor.
Click to expand...
Did the same with my 68 Barracuda. I went with a 73 360 with a 340 resto 4spd cam, and 727. I used M body spindles and brakes in the front, with RMS upper arms. Have an 8 1/4 with 3.21s in the back with 11 inch drums. Put A/C and cruise control on it plus a nice stereo. Finished it in 07 and have close to 35k miles on it. If I set the cruise at 65-67, I get between 19 and 20 mpgs. Also put fuel injection on it three years ago.
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I would go 318/5.2... EQ heads with really good valve job and cleaned up ports/bowls. The closed chambers should bring compression up and have a good quench. Get a custom cam ground by good cam guy. Fuel Injection and a Daytona systems ignition..small tube headers..
Then get the FI and ignition curves set to a Gnats *** !

3.23s out back and I think you could see mid 20s mpg.
 
With the O/D, 3.91 gears and a hot 273 with 71 340 TQ and intake, my 64 Cuda would get mid 20's. Never a hiccup, and would easily cruise at 100 mph all day long. Lots of ways to get there though. TQ or Q-Jet makes mpg easier and cheaper.
 
Lets use this trip as an example (Seattle-Los Angeles-Chicago-Seattle)
5300 miles at 15 AVERAGE MPG and $3.75 per gallon you are at $1325 in gas
5300 miles at 20 AVERAGE MPG and $3.75 per gallon you are at $994 in gas
a difference of $331

On my recent trip (2255 miles) I had tanks from 15 MPG to 20 MPG with an overall average of 17.5 MPG and I'm pretty easy on the throttle.

So the question is how much is mileage worth? Spend $1000 in improvements for mileage would take 15-20,000 miles to pay for itself. Spend more, take even longer.


Alan
 
If he needs to build an engine for the car anyway he mught as well have some fun maxing out the performance... mpg in this case.
If it were just cost renting an Econobox would be the way to go.
 
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