I need some opinions.........1956 victoria...292...stock...with 700R4  Trans.........3.89 rear............On test drive today.....50 MPH..@  1800 RPMs.........60 MPH...@2100  Rpms.........70 MPH  ........2500  RPMs.....................Anybody  have any thoughts ?      Would like to bring RPMs  dowm alittle ,  but not to bad ...Talk to me .............Sam...................   West Central   Florida.......................ps....83 degrees here today !!!! 

56 victoria

Is the speedo correct and what size tires are on the back? 

-Gary Burnette-

If the speedo's reading correctly, 2500 @ 70 aint bad.


Lawrenceville, GA

How does the motor feel at 70@2500,running smooth or does it feel like it's really having to work(like taching out).I think it was said that the best RPM was between 1800-2200 RPM@70 MPH. Try running a taller tire and see what it's like 70@? if you like it you might drop to 3:70's and put you in that range,but is it worth the expense and labor to you for a 300 RPM drop? KID

Ditto on the comment on verifying the speedometer reading.  When performing the calculation for your combination, there are two unknowns:  the tire diameter and the amount of overdrive in the transmission when in final drive.  Knowing the tire diameter will allow the amount of overdrive to be mathmatically determined with the rest of the information you’ve provided.  If simply trying to bring down the rpms while maintaining the same speeds, then either a taller tire or a numerically smaller rear end gear will get you there.   My ’55 Customline runs at 2170 rpms at 70 mph with fuel mileage hovering in the 19mpg area.

Here’s a couple of relevant formulas:

RPM = (mph X gear ratio X 336 X final transmission ratio) / (tire diameter)

Tire Diameter = (mph X gear ratio X 336 X final transmission ratio) / (rpm)

 

And here’s the formula for calculating tire diameter using the metric designation on the side of the tire.

Tire diameter  = (section width X aspect ratio X 2 / 25.4) + rim size in inches

Example for 205/70R-15 tires.  205 is the section width, 70 is the aspect ratio, and 15 is the wheel size.

(205 X 70% X 2 / 25.4) + 15 =  26.3”

Lorena, Texas (South of Waco)

Using the above listed formulas, at 55mph….2621 rpms.  At 65 mph….3098 rpms.

Lorena, Texas (South of Waco)

Gary and all ,   by using Teds formula ,   tires p215 s =  26.85    tall  ..............I am running a 57 t-bird dist. with a the bird tac ,   so i think it must be right .......as per miles per hpur ,  i had a friend with a brand new pick up follow me ...we had walky talkys  for communication ,  so i believe its pretty close.......the speedo in my car is way off  ........i was not aware of  a 3.70 gear ratio..........That may be the way to go ...........anybody have one for sale ?   let me know!  e-mail me at ...sundance241@aol.com.......I have a pickup with the same trans ,   turns 2000 rpm at 70 mph  ,  but thats with a differant engine ..................Thanks for the imput..............Sam................................West Central   Florida

56 victoria

Hello: From your post I could not figure out what you are asking? Why do you want to lower the engine RPM? Is it gas mileage, engine wear, to get into the power band of your motor or something else. Do you know the stall speed of the torque converter in your transmission? Can you lock and unlock the converter with a switch? Expand your description.

Pete,    I have no idea what the stll speed is   !!   This is a stock 700R4 trans.   Shifts well at the right speeds...there is no switch  to lock the converter.   It may be me , but it seems to me the RPM s are alittle high ,  and wanted some opinions  from other  y-blockers...........Sam.......................West Central     Florida

56 victoria

You might search the net for rpm calculators and tire size calcuators.  Know they helped me.  Below are links to both.

http://wahiduddin.net/calc/calc_speed_rpm.htm

http://www.discounttiredirect.com/direct/brochure/info/tmpInfoTireMath.jsp

Warsaw, IN