Maximizing MPG in a 1973 Ford 200 Inline 6-Cyl for a 65 Mustang

[Charlie Cheap]

TL;DR Summary

Basics of cam profiles for torque at RPM's likely seen on the street.

I am building a 1973 Ford 200" inline 6-cylinder, for my 65 Mustang. Because I drive it cross country to Rod Runs (car shows) I am looking for the best MPG not max HP.

The block will be .030"over, with .040" off the head to get the bigger cc chambers back close to the 51cc chambers in the 65 head. The later head has 62cc chambers. I'll take .010" off the block which has .019" deck height to further raise compression due to the 6.5cc dish of the pistons. The pistons are either 13cc, 6.5cc or flat-top. I am shooting for about 9 to 1 static and 8 to 1 dynamic for today's ethanol 89 octane gas.

This is a road-runner car built for long stretches of 500 to 700 miles a day, with the Air Conditioner running, the radio playing my recorded music while the wife reads her book. We have done this for decades in much older Street Rods (32 Ford 5-window/40 Ford coupe-both 289 V8 power), so this is not new to us.

The carb is a 2100 Autolite 2-barrel with annular atomization with the cast-to-head 1-bbl intake machined to fit a 2-bbl directly on the intake. The ignition is home-built with Pertronix trigger, 36 degrees total advance, BWD Select parts, MSD low resistance (1 ohm) ignition resistor, ACCEL coil (42Kv Max, 1.4 ohm primary, 100-1 windings), Wire Wound resistance plug wires, and Autolite platinum plugs set at .040"gap.

The exhaust has been modified eliminating several bends and replacing the restrictive muffler with a 24" straight-thru glass-pack. Timing is 12 degrees with vacuum disconnected. All the info I find on-line is for MORE POWER and torque is seldom mentioned.

Unless I am barking up the wrong tree, Torque should relate to MPG better than HP, if it is made at cruising RPM's. Cam specs are listed as 256 duration, 366 lift, 28 overlap, 112-108 separation for my present choice hydraulic cam. I get 24.5 in this situation now with the 65 bored .060, and that is not recommended but was necessary due to #6 broken ring...and why a new-er motor.

Is my Torque thinking correct? Are there cam profiles one should look for to get more torque, and what role do lift, overlap, lobe separation, duration play in relation to Torque? I am talking on-the-street driving. Obviously I am dumb in this area, though I have built many engines, 95% being stock or minor modification. THANKS in advance.

 

[Ranger Mike]

what size read end gear are you running?
automatic trans or stick? if stick what is the 1st gear?

 

[Charlie Cheap]

Mike, the tranny is a C4 with 2.46, 1.46, 1 to 1 ratios...I think. The rearend is 2.83-1 turning 26.3" radials. If my thinking is correct, best torque in the 1,500 to 3,000 RPM range should give very good MPG. However, I am often wrong assuming way too much as fact when it is not.

 

[Ranger Mike]

unless you special order a ring and pinion like 2.73, your set up is best
tires are maxed out as your tires are tallest you can stuff under the wheel wells without using the blue wrench
the only other options are to rig up timing advance kit to increase spark lead when at cruising speed
go to aero to cut drag
put car on a diet to loose weight
put over drive tranny in it.

 

[JBA]

I can't speak from an experienced engine builders perspective; but, from my driving experience in a series of smaller emplacement engine powered vehicles, it appears that setting the maximum torque just a bit above your anticipated cruise speed will give you good gas mileage and still a bit of a boost for accelerating for passing etc. when you hit the max torque point. As to selecting the recommended rpm for the torque for cruising, that is going to depend upon the maximum efficiency point of your combined intake and exhaust systems. All of that said, you still require an adequate amount of rpm to provide the horsepower needed for your preferred cruising speed range. As to the specific type of cam, if high performance driving is not a concern then selecting the cam with a wide max torque curve profile is probably a good choice.

 

[Charlie Cheap]

My gears/tires work well now and I am looking at an A4LD overdrive. Thanks Mike & jBA for your answers. I will probably go with a mild cam with not much overlap and only a little more lift. Stock valves work fine as velocity is a good helper in chamber mixing...and I am never going to run out of fuel/air with this engine. With 25 MPG on the highway not using the AC, I am in a good place now. If I can adapt the overdrive things will get even better. My real concern was using Torque numbers as a good MPG reference...or am I wrong there? Thanks again.

 

[JBA]

To paraphrase the initial part of my above response, "from my experience I believe you are correct.
With regard to overdrive, keep in mind that it will only help if it does not reduce your engine speed below the rpm, i.e. torque, top efficiency range. This is taken into consideration in automobiles that come originally equipped with overdrive. Either way, it will still reduce engine wear at cruising speeds. I had a Porsche 924 that in 5th gear overdrive would give 30 mpg at 75 mph, but 35 mpg at 85 mph.

 

[Charlie Cheap]

I think my chosen cam is okay for my purpose...without an overdrive. If I can fit the A4LD I will probably go down one size in rear tires. Right now I am torn between doing a complete rebuild of the 65 Mustang or put my $$ into my 67 Sunbeam Alpine with a Ford 2.3 and overdrive, and it has a removable hardtop. At 76 years I must narrow down my building work. The 65 Mustang may go up for sale this winter with the extra 73 motor and C4 thrown in because the 65 still runs good. In fact the wife and I are scheduled to go to Mississippi and Louisiana October in it for a show, and I am making a list of work done to the 65...just in case a buyer is there. In a previous post I have a pix of it in front of my house and the LH-6 can be seen on the hood. It stands for Long Haul 6-cylinder.

 

[JBA]

Sounds like you have two excellent choices for a project, I started my acquaintance with sports cars with a 1959 Triumph TR-3A with an Laycock de Normanville electric overdrive and a removable hardtop as well; and, I always liked the Alpine's design, particularly the Alpine Tiger with the V8 engine, which I assume you were referring to as your Alpine alternative to the 65 Mustang. Hard choice.
PS I applaud your six cylinder inline engine selection, there is no smoother running engine configuration than an inline 6 engine.

 

[Charlie Cheap]

jBA, I have had 2 Sunbeams for over 30 years on the back burner, and now that I am totally retired with a backyard shop, it is time to build one from two. The 2.3 is built and the A4LD overdrive is built, I have all the body parts...so no excuse. I do my own body, paint, electrical, engine, and chassis work so all I need is time. At 76 I hope I have time to enjoy it...if I get it done. I feel fine but a guy at Church younger than me, dropped dead last week. Reality can jump up and slap us in the face sometimes. You are right about the inline 6. Smooth design.