Thread: For Don Shilady

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Jerry that is an interesting observation. As far as I know the torque convertor stall is 1600 rpm. While I was looking up LT1 and related Camaros from '92-'97 I noticed that the auto transmission cars had 3.23 or 2.73 rear ratios with four speed trans and 3.42 with the six speed trans. While those Z28 cars got 22-24 mpg on the road none of them had a rear ratio as low as my 3.55 Maverick rear. It is possibly ironic that I changed what was a 2.7 Maverick rear to 3.55! I am a victum of my own frozen memories of only Ford ratios of 4.11, 3.78 and 3.54 which were available for the old banjo rear ends, although I think there were some 3.2?? ratio rears used by lakes streamliners. I thought I was being conservative keeping the ratio near the old Ford high ratio of 3.54. Jerry's comment suggests consideration of my torque converter stall speed and a new "experiment" of watching the Tach with acceleration in low or second gear and potentially some more experimental "fun" but at this point I think it is a blessing to keep the rpm low for good mpg as long as the 700R4 is not slipping. As far as I know the stall speed of my converter is 1600 rpm. So I will try to accelerate with the trans restricted to low gear and again restricted to second gear after the first shift.
For Rodger, my wife is not eager to ride in the car anyway but does seem to like the look of it. It is not easy to remove the fenders because I have the Bebops all-in-one fenders attached to the floor panel. At this point I now understand that my 3.55 rear is a bit low for good economy so another "scientific experiment" leading to more "fun" is to run some mpg tests using 87 octane instead of the 89 I have been using and if 87 is OK then maybe I can achieve some economy financially with lower cost fuel. I have run the car on 50-50 87-89 without any pinging but the C. R. is about 9:1 so that leads to another "fun experiment". By the way Rodger, what mpg do you get with that 347 Ford?

Don Shillady
Retired Scientist/teen rodder

Don,
A couple of comments. First, that's too bad about the fenders being integrated with the floor, but I was not really serious about changing your body configuration back & forth. It is what it is, right? Second, you want to be cautious about dropping your rear gear ratio too much unless you know the characteristics of your specific engine's torque curve. If you drop it down too the point where you're backed down on your curve too far you're going to actually lose efficiency - have to give it more fuel to maintain speed as opposed to cruising easy. And before you go there, saying "..my engine is essentially a _____ (fill in the blank), so my torque curve is ______ (fill in the blank)" is NOT going to cut it. Each engine combo is different, and a small change in the cam timing can have big impacts on your torque. Third, you know that you can find your stall speed by dropping into gear, locking the brakes and depressing the accelerator, right? It'll go up to stall speed and stop increasing rpm at your true stall speed. Just remember to let off the gas before you get off the brake, or you'll learn how well it'll launch!!

Originally Posted by Don Shillady

By the way Roger, what mpg do you get with that 347 Ford?
Don Shillady
Retired Scientist/teen rodder

My mpg is all over the map, probably depending on how much I play more than anything else. On the way to Des Moines we made an un-planned stop after only 75 miles of highway cruising between 75 and 80mph, everyone topped off and I got 21mpg, much to my surprise, but the next time we stopped it was down to 16. Short trips into town and back, with a couple of attitude adjustment cruises of fifty to sixty miles thrown in I'll get 12 to 13 mpg over a tank full, and I'm running 10.3CR so it's 91 octane for me, ethanol free whenever I can. I don't really sweat the mileage, but consider it more an input into my fuel map tuning than anything else. I'd really like to get my air/fuel ratio indicator mounted in the dash, hardwired into the ECU with the wide band O2 input, but haven't gone there yet.

One of the things you might consider is running a vacuum gauge where you can watch it while you cruise. If your carb is tuned right, the vacuum reading will tell you more about efficiency than about anything else. Have you pulled a plug or two after one of your "economy runs" to see how your mixture looks by electrode color?