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By sundance241 - 17 Years Ago
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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 !!!!
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By speedpro56 - 17 Years Ago
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Is the speedo correct and what size tires are on the back?
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By charliemccraney - 17 Years Ago
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If the speedo's reading correctly, 2500 @ 70 aint bad.
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By kidcourier - 17 Years Ago
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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
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By Ted - 17 Years Ago
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sundance241 (12/27/2008)
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 a little , but not to bad ...Talk to me .............Sam................... 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”
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By Ted - 17 Years Ago
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Brian_B (12/28/2008)
Can somone figure what I am actually turning at say 55 for me? or 65? The tires are 205/70/15s. (I know...small tires, but they were nearly new michelins, cheap, I was broke, and running on slicks..soo) 1:1 3rd gear 3.73 rear gears Using the above listed formulas, at 55mph….2621 rpms. At 65 mph….3098 rpms.
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By sundance241 - 17 Years Ago
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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
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By Pete 55Tbird - 17 Years Ago
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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.
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By sundance241 - 17 Years Ago
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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
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By BFOOTER03 - 17 Years Ago
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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
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By Pete 55Tbird - 17 Years Ago
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About your 700r4 transmission torque converter lock-up. The car it came out of had some means of "talking" to the torque converter and "telling it" to lock and unlock. Computer and/or a speed sensing unit that sent the signal. Since your 1956 is not equipped with this device a simple on/off switch is put in. You "tell" it to lock/unlock via this switch. Google 700R4 switch for more info. Or ask the place you bought the transmission. Pete
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By sundance241 - 17 Years Ago
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Thsnks Pete and all, Will check the switch out.! .....Sam
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By pegleg - 17 Years Ago
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Sam, Find a road with mileage signs. At 60 you will cover one mile in one minute. To be sure, try to cover three or four miles at a steady 60 indicated. If you time yourself and it takes longer than a minute your speedo is slow. Tell me the times you get and I'll tell you what the error is.
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By Tom Compton - 17 Years Ago
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GPS unit will tell the MPH very accurately.
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By HT32BSX115 - 16 Years Ago
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Another way to do it for any tire, any rear axle and transmission... (that you can measure yourself) is as follows.
20168 divided by the (rear) tire dia[inches] 20168/dia=tire RPM @ 60mph
Once you know the rear tire rpm, you can multiply by the rear axle ratio to get ENGINE RPM at 60 mph.
If you have an OD transmission, then you also have to multiply by the OD ratio (0.71 for my E4OD for example) to get the rpm (at 60mph) ..............Direct drive is a multiplication of exactly 1.0 btw.
This is completely based on the rolling radius of the tire so it's not perfectly exact because the rolling radius of any tire is dependent on the pressure, load, etc.
For our purposes it's going to be "close enough" to predict what the engine rpm will be at 60 mph. (5280 ft/min)
By the way, if you have a lot of "squish" in your rear tire, it'll even be more accurate to measure the actual radius of the tire from the (center of the) axle to the ground if you do it that way then simply use 10084/radius=rear wheel rpm@60
I have 9.00-20 tires on my F-600. I measured them at 40" diameter. I have a 5.83:1 2 speed rear axle.
20168/40= 504 rear wheel RPM @60mph.
With the 5.83:1 axle, 5.83 x 504 = 2940rpm and in OD, 2940 x 0.71 = approx 2100 RPM
Happy New Year everyone!
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By sundance241 - 16 Years Ago
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Well , i finally crowled under the vic today to check out the switch.....Its wired up . I couldnt remember , but i think its wired to the on position on the ignition switch..............When driving i can feel it shift , so ireckon its working ok .................a big thanks for all the help , had me worried for a while , been a couple of years ago when we rewired the whole car and a didnt remember if we had wired the switch or not ......been working on other projects since , and sometimes they sort of blend ............!!.....................Sam.................West Central Florida
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By GregDove - 16 Years Ago
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There is a great article on this subject in the Rod & Custom magazine Feb. 2009 issue ... Hitting the Sweet Spot ... Calculating the optimum performance combination for your drive train .... it covers the tires, transmission and rearend ... it is not one thing but the combination of all of them. Great read ..... Greg
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By LON - 13 Years Ago
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Try this one .Add all the info you can .Then push the button .It works out everything . http://www.f-body.org/gears/ Lon
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