Thread: For Don Shilady

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34-40 and others, Thanks for the suggestions. I did the chalk trick but only at 30 psi. It may be slightly on the high side but I want to favor mileage. Anyway you can see from the chalk pattern that the whole width of the tread is present. I also saw a suggestion on a Corvette web site to just use 5 psi less than the max rating. I also saw other suggestions ranging from 22 to 33 psi. Anyway the pattern looked good to me so I used 32 psi in the front tires and 30 psi in the rear tires and took the identical 63 mile trip as before including a stop at the same spot in a McDonald's parking lot and a quick lunch. This time I used only 3.889 gallons of fuel (WaWa 89 octane) so this run gave (63 miles/3.889 gallons) = 16.19954 mpg or about 16.2 mpg for an improvement of about 8.02%. Thus I will have to keep checking the tire pressure and 32psi front with 30 psi rear looks like about all I can do to optimize the mpg. Of course this little experiment was fun because I got to drive on rural roads but I did keep the speed roughly between 57-62 mph since I saw some traffic pull over tickets along the way. Again the Tach stayed under 2100 rpm the whole trip. On the previous run I hit 70 mph a few times but that is about the top speed with the top up due to vigorous flapping of the top at speed. I also recall seeing a wind-force curve versus speed somewhere and it is pretty steep after about 35 mph. When the Model A body was new most highways had a 35 mph limit so the flying brick aerodynamics was no problem then but when you get up to 60 mph the drag coefficient becomes important as Jerry noted. As far as the ride goes the choice is between "harsh" and "harsher" anyway although most of the trip was on smooth roads. However there is one pothole in Route 1 just north of Ashland that I forgot about and when I hit it again this time it almost took out some of my eye teeth! Well I did not even get to 17 mpg and 20 mpg seems impossible even with my 0.7 4th gear. I do note that the 1977 Z28 had a 3.42 rear gear compared to my 3.55 rear ratio. Thanks to several of you for suggestions as well as some unknown folks on Corvette chat rooms. I look at the Corvette comments because technically my engine is from a 1976 Corvette. The first picture is for 34-40 as to the new padded mount for the coil. I am not happy about all the wires which resulted when relays were added for my dual fan setup and the plug wires could be hidden better but you can see the edges of the black foam around the back of the coil and the mount is now flush with the firewall. The second picture shows the chalk pattern for 30 psi in the rear tires as Roger suggested. One good result is that I was toying with the idea of changing to smaller rear tires for better acceleration but obviously this experiment shows that I better stay with the 235/75r15 tires!

Don Shillady
Retired Scientist/teen rodder