Postby Workshop Help » 10 May 2008 02:16
Oh dear, I saw this coming a few months ago, gas mileage. This won't be pretty, but here goes. Provided one has tuned the engine to the peak of efficiency with regards to ignition and fuel mixture using a vacuum gauge or separately installed oxygen sensors with an exhaust gas analyzer, the one real key to increasing fuel mileage is in the gearing.
For those remaining cars with a four speed, a conversion to a rebuilt five speed can markedly increase your fuel mileage thru the advantage of the fifth gear being a .83/1 ratio overdrive from the fourth gear being a direct drive. The one fly in the ointment keeping this conversion from being a bolt-on is the four speed driveshaft must be lengthened by a competent driveshaft shop.
The full conversion using the factory 3.90/1 ratio rear end will diminish your fuel mileage from the four speeds 3.63/1 ratio. We are using this conversion in our TR7 retaining the 3.63/1 ratio rear end and are more than satisfied with it. We cannot imagine any legitiment need for the 3.90/1 ratio other than pulling a horse trailer or jerking fence posts out of their holes. As for the 1" increase in the rear brake shoes, we again are satisfied with the four speed rear ends brakes. But, for those wanting to have their cake and eat it too, the 1981 fuel injected TR7's had 3.45/1 ratio rear end with the larger brakes. If one can get this rear end along with the 1981 LT77 gearbox, the bonus is fifth gear will be a .74/1 ratio. Oh! Happy days! Your fuel mileage will go off the charts.
Refueling from an honest gas staion pump, we regularly record a mix bag driving rate of 33 mpg. An honest pump, this is becoming a more than significant problem. Driving in the same manner, at another station owned by 'Apu', we record 28 mpg. At the supermarket gas pumps, we record 29.5 mpg. Now, who's got the honest pump? Does the 33 mpg gas station have a defective regulator in his pumps that meters out too much, or is 'Apu' with his low posted price making up the difference by cheating the consumer with a 'set' regulator to give us a lower mpg recording?
Another issue is the presence of 10% ethanol in the gasoline and other elements such as oxidizers. The BTU capacity of the motor fuel is diminished and this adversely affects the power AND the fuel efficiency of our engines. As such, we are butting our heads against a wall.
Lousy fuel, cheating gas stations, the wrong gearing, out of tune engines, all conspire with the current insane oil and gas commodity markets to disrupt our lives. I may have to put some TR8 decals on the old Raleigh bicycle and avoid the use of gasoline all together.
Mildred Hargis
<font color="red"><b>My two 1980 Wedges...</b></font id="red">
