That is a good point about the wind resistance.  Trying different diameter tires will probably be best to find the sweet spot.


Lawrenceville, GA

Howdy all I'm in the same boat as everyone else I guess....(well maybe its a BARGE!!)



I have a final axle ratio of 5.83:1 and the transmission OD will be 0.71 (E4OD) but I have approx 40" tires!





I am figuring approx 2050 rpm at 60 mph in top gear.. (TC locked) ......... I think that'll be a perfect Y-Block RPM for an empty, flat road cruise.



I'll probably have to tweak the throttle position sensor to drop out of locked TC/OD at the "right" throttle position though...







Regards,














-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1955 F-600/272/E4OD// Disclaimer: No animals were injured while test driving my F-600 except the ones I ran over intentionally!

---------------------
This post was created using OpenSuSE Linux x64 and Firefox

Charlie - Just remember the aero resistance is based on the speed squared - slowing down 10 mph makes a big diff in req'd torque/horsepower (fuel consumption). The headwind or tailwind can really get in there and cause some mischief if you are trying to figure this out while driving.

 
 Steve Metzger       Tucson, Arizona

Thank you.  Good point, so then I will make a mark and put a pointer on the tire as well.

Well, I got some more data on the way back.  For the first tank of gas I did not use overdrive.  I got 13.33mpg.  I was trying to keep it at 3500rpm, doing about 80 keeping up with traffic.

For the second tank I did use overdrive and tried to keep it around 2200rpm which was also about 80.  I got 14.28mpg.

I forgot to mark mileage and gallons used for the rest of the trip.

A friend suggested that I get on the interstate, use 4th gear and drive at 2000rpm, check mileage, then 2500rpm, check mileage, then 3000rpm and so on and so forth, to find the most efficient rpm.  Then I know where my cruising rpm will have to be.  It sounds logical to me.  What do y'all think?

Lawrenceville, GA

Charlie,

I like your idea, and I agree with the math.  Perhaps the most gratifying is that it is creative and possibly an original thought.  Keep in mind that for every one degree error in one rotation of the tire, it will effect the drive shaft rotation approximately 4 degrees.

Good luck..........................

Charlie Burns Laton, Ca (South of Fresno)



BurnsRacing981@gmail.com

It is an Edelbrock carb.  If it is the cause, it seems almost like I'll need two tunes.  The cruise and power modes are tuned well for city driving.  Timing hasn't been optimized, though.  I'm not going to get too caught up on the carb.  I plan to get rid of it this year, anyway.

I was actually thinking about taking a piece of masking tape, marking it every 10 degrees for the circumference of the driveshaft, using a magnet to hold a pointer and use that to figure out the ratio.  That way I can translate the number of degrees of rotation into the precise number of turns it made for one turn of the wheel.  For instance, the difference between 3.70 and 3.89 is 68.4 degrees.  That will be easy to distinguish with 10 degree graduations.

Lawrenceville, GA

Charlie.  Don’t recall which carb you are running but that in itself can be a big player when dealing with fuel economy issues.  On some carb models, I find it necessary to enlarge the PVCR (power valve channel restriction) while decreasing the primary jet size.  This allows the same amount of fuel at full throttle but permits the engine to use less fuel under cruise situations.  With a leaner fuel mixture, the engine will prefer an increase in ignition timing though.  And while on the subject of ignition timing, this is also another area worth exploring as the Y’s do tend to like more timing at cruise than is normally being supplied.

 

Fuel quality from station to station also varies.  I find it increasingly difficult as time goes on to maintain a consistency in fuel mileage even when getting the fuel at the same station.  As an additional note, gasoline with an actual 10% added ethanol will get a reduced mileage over pure gasoline (no ethanol) but without testing each load of fuel beforehand, it’s difficult to know exactly what is going into the fuel tank.  I sometimes wonder if the ethanol itself stays adequately mixed in the gasoline or if some separation takes place over time in the storage tanks which in turn changes the amounts getting to a vehicles fuel tank.

 

As far as rear end gearing changes go, it’s typically the most cost effective change that can be made when working with the mechanicals.  If a ready to go additional third member is already set up, then the actual third member change in the vehicle only takes an hour.

Lorena, Texas (South of Waco)

Charlie,

Sorry, here comes the math teacher.

Using the one tire rotation method is a good one.  It does require you to estimate the last rotation of the drive shaft, but would probably get you close enough to determine if you have one of the standard ratios.

If you are anyone reading would like to be exactly sure, it would take two people and perhaps 10 minutes.  Turn the tire 100 times and the number of drive shaft turns would be the exact numbers in the ring and pinion ratio.  So, 350 drive shaft turns would be a 3.50 ratio.  If 100 seems to many, turn the tire 50 times and multiply the drive shaft turns by 2 (25 tire turns, multiply by 4, 10 turns, multiply by 10).

This is the method I use in selecting the closest ratio transmission possible for the tiny-Y.  I put vice grips on the input and output shafts and turn the input shaft 100 times in each gear while my wife (crew chief) counts the number of tail shaft turns. (Using math is too tough!)

By the way, when you get around to doing the math with different tire diameters, don't forget the overdrive in calculating the final drive ratio.  It will require you to know the exact ratio in the overdrive.  I put together an Excell program to calculate speed with given rpm, rear ratios, and tire diameters.  I would do the math on it for you, but it is specific for a 1:1 drive through the trans. 

I am changing to a T-5 myself this winter.  If 4th gear is not 1:1, I will have to change my little program and then I can do the math for you.  If the transmission ID tag is still on the trans I have a reference chart to tell you the exact overdrive ratio.

Hope this helps.....................

Charlie Burns Laton, Ca (South of Fresno)



BurnsRacing981@gmail.com

I'll do that.  Just have to wait for a relatively warm day.


Lawrenceville, GA

Tip..

check rear end gear ratio by lifting the rear end

mark the a rear tire/wheel  and drive shaft

rotate the tire/wheel one full turn

and count the rotation turns  of the drive shaft

cheers