ISSUE 61 AND 62 FUEL ECONOMY (STUPID) FOLLOW-UP: THERE IS NO MAGIC BULLET
by John Martin
TDR Writer
Well, the editor has done it again! While having lunch with a mutual Friend, Robert discovered that another engineer and I hold the Shell Mileage Marathon fuel economy world record. Robert immediately called and asked for some ideas you readers might use to improve
fuel economy.
Before I start, let me mention some experiences which qualify me to write about fuel economy. I worked eight years for Shell Research and Development. After I quit drag racing (funny cars), several friends got me involved in the unlimited class of the Shell Mileage Marathon. Ben Visser and I still hold the record we established in 1973 (376.59 mpg).
I then went to work for an independent test laboratory in San Antonio, Texas. Among other things we conducted thousands of fuel economy tests, both in the lab and on the road.
After leaving Texas, I entered two motorcycle fuel economy contests and won both of them. I obtained 145mpg on a Harley-Davidson FLT (second place was 85 mpg) at the Aspencade in Ruidoso, New Mexico. I got 245mpg on a Suzuki 250 at the Aspencade East in Glens Falls, NY (second place was 125mpg). My daily driver used to be a small block Chevy Monza, which, in 1976, got 27.3mpg.
Okay, now my chest is sore from all the pounding. Robert sent me a copy of TDR 61 and 62 and asked for my comments about what had been written to date about fuel economy. First, Kevin Cameron (whom I’ve read for years), Robert, and others have given you some good, solid information. I’ll try to build further on their foundation.
“There is No Magic Bullet”
Practically every magazine out there contains ads for products which will improve fuel economy by 10% or more. These ads are usually next to the male size enhancement ads. In all of my years of fuel economy testing, I’ve never seen a single device which legally yields more than a 2-3% improvement in fuel economy. As many of the TDR’s writers have aptly pointed out, you then need to compare what the device costs to your actual tested fuel economy improvement to see if you will really save any money in the long run. Often the break-even point is 8-10 years at best.
Let me give you a good example. Synthetic engine and driveline oils are inherently more slippery than mineral oil products. NASCAR and NHRA racers all use synthetic oils because they want maximum horsepower regardless of cost. Large truck fleet operators use synthetic oils in their differentials and transmissions because they see positive fuel economy benefits, and these oils don’t have to be changed frequently. Fleet operators don’t, however, use synthetic engine oils, because they cost three to four times as much as mineral oils, and they must be changed frequently. The economics just aren’t there!
The most productive way to improve fuel economy is to perform many small improvements in several areas. It’s a ton of work, but the results are well worth it. And don’t just consider the engine; look carefully at the entire vehicle and how you drive it. As has been preached in the TDR, driver differences are often larger than any mechanical improvement you can make.
Efficiency and Exhaust Emissions
Regulators, particularly those in over-populated areas, focus on NOx emissions reductions to reduce smog. Any good engine designer will tell you an efficient engine produces the highest NOX levels. For years scientists have searched for efficient NOX absorbers so engines can be operated efficiently, and the NOx can simply be removed from the exhaust stream. So far it hasn’t happened.
NOX levels are a direct measure of peak combustion temperature. Retarded timing (either retarded ignition timing in gasoline engines or retarded injection timing in Diesels) is the most frequently used NOX reduction method. Exhaust gas recirculation (EGR) is also used to reduce NOX by effectively decreasing the oxygen level in the combustion chamber. In both cases, fuel economy suffers. The only bright spot on the horizon is the advent of selective catalytic reduction (SCR) in diesels with diesel particulate filters (DPFs). Fuel economy is improved, but don’t forget to factor in the cost of the urea catalyst and the urea additives.
So, how do engine computer re-programmers work? Most of them simply advance the timing, which improves both power and fuel economy. Exhaust emissions are, of course, increased. Again you should do a little math to compare the cost of the module (about $400) to your potential fuel savings over the life of your vehicle. Issues 61 and 62 beat this horse to death. Don’t you hate this math?
So, What Can Be Done to Improve Fuel Economy?
Fuel economy of the average vehicle is determined by engine and driveline efficiency, aerodynamics, and rolling resistance. Let’s examine each factor to search for areas of improvement in your fuel economy.
You’ve already selected the most efficient power plant, since diesels are more fuel efficient than gas burners. (See the sidebar article “Why a Diesel” reprinted from Issue 55 at the conclusion of my text.) Engines are also most fuel efficient when operated as slowly (minimum RPM) and as hot as possible. Try to keep your RPM at or below the torque peak whenever possible. To help with this, try to run the tallest tire and rear axle ratio possible to minimize RPMs. We ran the Mileage Marathon vehicle at 1500 RPM or less. We also ran coolant temperatures at 300º F on straight glycol.
Since some horsepower is required to pump engine oil, both NASCAR and NHRA Pro Stock racers run very thin (low viscosity) oils. You might try using an SAE 10W30 oil instead of your more typical SAE 15W40 oil. Be sure to run light synthetic oils in your differentials and transmissions.
Harness the Power of the Air
I have a friend whose very aerodynamic 1953 Studebaker runs 241mph at Bonneville with only 750hp. Your pickup truck isn’t very aerodynamic. Stand back and look at your vehicle from a distance. Visualize how the air might flow over, around, and under it. The ideal
shape, of course, is a raindrop with the blunt end forward.
Try to eliminate those items which disrupt air flow such as sun visors, large mud flaps, large mirrors, and bug deflectors. The pickup bed also spoils air flow. What about utilizing a small camper shell (one which doesn’t protrude out from the sides of the cab)? It would be nice if this camper shell tapered and had rounded corners at the rear to smooth air flow as it leaves the vehicle. Single rear wheels offer much less drag (and less rolling resistance) than duals.
Also look at Bonneville racers for aerodynamic clues. Bonneville racers run their vehicles as low as possible because the air flow under a vehicle is worse than the air flow over it. Also notice how low the front spoilers are on NASCAR and NHRA vehicles. I would try to run my pickup very low and utilize some type of front air dam to minimize air flow under the vehicle. You could also run a belly pan, but I don’t think the economics would make sense unless you built it yourself.
Don’t forget that aerodynamic drag increases drastically with speed. Aero drag is responsible for about 33% of total fuel usage at 55mph and over 50% of fuel usage at 80mph. We ran the Mileage Marathon vehicle at an average speed of 5mph. I can’t believe a guy who has paid as many speeding tickets as I have is saying this, but try to slow down as much as possible.
So What Exactly Is Rolling Resistance?
Rolling resistance of a vehicle consists of several factors, the most important of which are tires, wheel drag, and wheel alignment.
For maximum fuel economy, inflate your tires as high as you can safely to minimize deflection, thus decreasing rolling resistance. Look at the maximum inflation pressure listed on your tires’ sidewalls, and add 10%. I routinely run 50psi in my Durango tires (max inflation pressure 45psi) without problems. Don’t worry about blowouts. Most blowouts are caused by heat buildup due to underinflation or damaged tire casings. You can air your tires up even further, but you may cause uneven tire wear.
Believe it or not, straight rib, old, worn tires are the most fuel efficient. Those bold block tread patterns and new tires with deep tread pattern often squirm around no matter what the inflation pressure is. You want zero deflection, if possible. Tires get harder the older they are and the closer the tread gets to being worn out. We routinely shaved all the tread off our Mileage Marathon tires, but we didn’t have to run in the rain, and you can’t hydroplane at 5mph.
Check to make sure your brakes and wheel bearings aren’t causing excessive drag. Older disc brakes seem particularly bad about seizing up on their sliding mounts, which creates excessive drag. Make sure your brake calipers are free to move around on their mounts. Wheel bearing should be adjusted so there is just an infinitesimal amount of free play. Use thinner wheel bearing grease if possible.
Wheel alignment is super critical. You want absolutely no side scuff, which increases rolling resistance. Start by checking the wheelbase on both sides of your truck — you might get a surprise! Check the rear end first to make sure the rear axle is not bent and is mounted straight in the chassis.
Make sure the vehicle is pointed exactly straight ahead, and set the front end alignment with the normal load (including the driver) in the vehicle. For maximum fuel mileage, shoot for 0 camber, even caster, and 0 toe-in with the vehicle being pushed forward on its wheels.
We checked the Mileage Marathon vehicle by pushing it across two thin metal plates with grease between them under one of the front wheels. If the plates moved at all sideways, we knew we had side scuff. You’ll go crazy aligning a front end this precisely, but you will enjoy the end result. We could push our 2020-pound Mileage Marathon vehicle with one finger!
I hope I’ve stimulated your thinking about how to improve the fuel economy of your vehicle. If we’re ever going to break the strangle hold of oil dependancy we must all become more energy efficient. It means quite an adjustment for most of us, but I’ll bet we can do it.
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