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Author Topic: Tire Diameter - Rear Gear - Transmisson to MPH  (Read 545 times)

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Offline Benton2840

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Tire Diameter - Rear Gear - Transmisson to MPH
« on: March 14, 2019, 09:55:51 PM »
On one of my bored days I played a little Excel spread sheet what if's.  Its based on a Ford 6r80 automatic, 3.40 rear gearset and various tire diameters. Based on RPM what would the speed in each gear be.


In the spread sheet a person can change any value ( gear - tire - ratio's - rpm) and instantly see the results.


I'd post the Excel File if it allowed.

Offline cossiepinto

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #1 on: April 08, 2019, 01:45:35 PM »
This little gem is invaluable when calculating gear ratio/tire diameter/speed at "X" rpms/etc.  I had one made by Autolite back in the day, but must have given it away at some point.  I had put Stewart-Warner gauges in my '70 Boss 302 years ago and had dispensed with the speedometer.  Centered on the dash was a tach, so I needed to calculate speeds at given rpms so I could avoid getting tickets.  Never did I ever get a ticket for speeding by mistake.  Take a look at this thing.  It's small, portable, requires no batteries, etc.  Come to think of it, I probably gave the calculator to the buyer when I sold the car.

https://www.markwilliams.com/cal.html

There are others out there, too.  This one is $3.00.  A great little tool.

Offline Wittsend

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #2 on: April 11, 2019, 11:05:04 AM »
I'll add that it is nice to see someone who grasps the fact the the TIRE DIAMETER and the REAR AXLE RATIO go hand in hand regarding the final drive output. Changing the tire size is the same as changing the rear ratio and visa versa.

What I wish there was a Standard for (forgive me this is probably the 101st time I've mentioned it) something like engine RPM's per 100 feet, or mile or whatever.  That way one could factor the tire size, the rear axle ratio, engine torque in relation to RPM etc.. This could be judged against a color coded chart that illustrated a sweet spot and the range of "acceptable." Perhaps one of the computer dyno programs does that already???

This way the person with a 2.79 rear ratio and 16" tires might understand why their car bogs and the person with a 4.56 rear ratio and 13" tires is screaming down the highway at 4,500 RPM. The cart would illustrate how far from the sweet spot they are.

Offline redcaddy

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #3 on: April 20, 2019, 11:56:39 AM »
Yep, My '72 Pro Street Pinto barn find is set up with a Ford 9 inch, 4 link, Detroit locker, 15 X 15 x 34 rear tires. Dropping in a 500 CuIn Caddy torque monster, TH-400
thinking about a 2:39 or shorter gear to lower the wheel stands. Any comments?

Thanks, Paul
If it turns $$$$$ into smoke and noise, I'm there

Offline Reeves1

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #4 on: April 24, 2019, 06:04:05 AM »
Yep, My '72 Pro Street Pinto barn find is set up with a Ford 9 inch, 4 link, Detroit locker, 15 X 15 x 34 rear tires. Dropping in a 500 CuIn Caddy torque monster, TH-400
thinking about a 2:39 or shorter gear to lower the wheel stands. Any comments?

Thanks, Paul

Combo is over 700 lbs with add ons you'll be well over 800 lbs......added to the front end !

Offline Wittsend

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #5 on: April 24, 2019, 12:39:15 PM »
Combo is over 700 lbs with add ons you'll be well over 800 lbs......added to the front end !

I was thinking similarly. That is a LOT of weight hanging out in the front. I'd think the tires would break loose before the front end lifted. I never heard of going to 2.39 gears just to prevent wheel standing.

 My experience with my Datsun 510 was that with 3.90 gears and 215-50-13" tires the RPM's came up so fast (I was shifting into 3rd gear before crossing an intersection) there was hardly a perception of torque.  It was very similar to starting off on a 10 speed bike in 1st gear going down hill. When I went to 3.36 gears the torque actually became noticeable because it was being effective. Basically what I'm saying is gear ratio is torque multiplication but you can actually lessen the effect of the torque (because RPM's spool up too fast) to lift the front end by going to something like a 5.13 or numerically higher ratio. Every situation is different so this is an example not hard facts.

Obviously there is a "sweet spot" based on a cars weight the tire/gearing and the engine torque characteristic s. That sweet spot is where one would most likely achieve wheelstanding. But, I doubt with 800 pounds up front the greater issue won't be tire spin at the rear then lifting at the front.

2.39 gears would make more sense if the goal was to get any kind of gas mileage out of the huge motor. But, even that said, my Studebaker (350 Chevy, 700R4, 3.07 rear gears, 225-60-16 tire) is at something near 1,600 RPM at 65 MPH. Gearing like 2.39 would probably drop the RPM's to about 1,200 RPM at 65 MPH, not much above an idle. If this is truly a Pro Street car 2.39 gears are counter intuitive to that purpose of a car designed to go a 1/4 mile as quick as possible.

The bottom line is that using gear ratios to prevent wheelstanding rather than proper chassis management is not a good approach.

Offline pinto_one

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #6 on: April 24, 2019, 03:53:21 PM »
My comment would have to agree with Wittsend and Reeves1 , carrying almost or better than a half ton on the pinto front end will not have to worry about wheel standing it ,  a 500ci caddy engine along with trans is taking up a huge space in the engine compartment , plus that engine has not been made in years and performance parts may be hard to find , unless you have the engine and want to do somthing with it , me I would use a 3.5 ecoboost engine out of a f 150 or a wrecked raptor , that less than 300 lb engine might make more tourqe than the caddy engine and can make over 500 hp stock with a good tune , with that light weight you may (will) have to have wheelie bars installed , but it just an idea for you to check out , as for me I would have to win the lottery for my pinto build ,,  (buying a new Tesla P100D and put the drivetrain in my pinto wagon , 9 second 1/4 times with 4wd )   
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline redcaddy

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #7 on: April 25, 2019, 11:07:13 AM »
wHOOOOOO WEEEEEEE. although I'm impressed with all the replys, Every body take a breath and I'll fill in a few facts.
My "new to me" Pinto is a full on, tube frame pro stocker, built in the mid 70's. It's a close clone of the one Glidden campaigned in '72 - '73 (his was ladder bar rear, mine is 4 bar, with an upgraded halo, funny car cage) Mustang II front with aeroquip hat's and calipers. Worked over upper and lower "A" arms and adj. coil over shocks.

My intent is to pro street this old war horse and drive it 'till one of us can't do it any more.


The Cad motor I have in hand is the one I built to drop in a 225" W/B rear engine dragster, (1987 Richard Earl top alcohol car, dumbed down for fast brackets. (My home track was NHRA and ran a wide open bracket operation) First season, ran 10.00 flat in fast footbrake. moved up to super pro, without a box or throttle stop, thumped the suspended chassis guy's, and door cars, eating their injected 502's hangin' around the 9.90,s deadly consistent. An average night's work was  10.101, 10.103, 10.102, 10.100, 10.102, get paid.

The 472/500 Cad engine was designed by the same guy that drew the 455 Olds motor. the 500 Cad was much lighter, about 40 lbs, than a SBC in stock trim, and could be built to double the displacement, easily

Most engine dyno's can't accurately measure the horsepower because of the massive torque at low RPM. This one showed over 500 lbft of torque @1400 RPM. The torque curve is straight from 1100 RPM to valve float at around 5100 RPM. It really pulls much like a diesel. After all, this engine was built to drag a 7000 Lb around, smartly,quietly and smoothly. Published HP numbers were barely over 250 and the insurance companies and smog junk kept them from ever reaching their potential on the street and they were gone from the option list by 1976.

A lot of 502 and 572 BBC guys like to brag about big torque, mine, mildly built, will double the numbers they brag about.

I use the TH-400 because it was designed to stand up to the torque, (like the TH425 transaxle)

By the third season, I built a TH350, to gain back almost 60 lbs and a ton of parasitic loss horsepower. I rather enjoy blowing past a door car, running 130 MPH in the lights, at 165, with the 2.39 gears.

The weakest link in the big Cad, is the valve train. Anything much over 4900 RPM's they start breaking things, although newer, tougher parts exist, they are a bit pricey and not really necessary for the track, or the street.

I think the Pinto and the Bad Cad are gonna be a good match, I only posted to point out what gear selection can add or detract from performance.

I joined this board to get help finding body parts and, maybe to make a few meets for burnout's and such. I didn't mean to steal the thunder from some very impressive unibody cars.

Right now I'm searching for a one piece 'glass front end, Pinto or Bobcat. Any leads?

Thanks for your time,
Paul

 







 
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Offline Wittsend

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #8 on: April 25, 2019, 01:59:43 PM »
I think some of us here were taken by surprise that such a physically large engine..., and heavy..., compared to a sub 500 pound SBF would be of consideration in a diminutive Pinto. As it is there is often debate here as to the practicality of a lighter weight SBF - VS - an even lighter Turbo 2.3. A high torque, low numerical gearing car is certainly a different concept for racing, but if you enjoy the challenge so be it. As to a one piece front end..., maybe someone has a lead??? Most of the dialogue here is to keep stock Pinto's on the road with a small few SBF V-8 and Turbo 2.3 people also.  When done I think many are curious to see pictures. Certainly it is going to be unique.


For clarity of understanding regarding what was said:


"The 472/500 Cad engine was designed by the same guy that drew the 455 Olds motor. the 500 Cad was much lighter, about 40 lbs, than a SBC in stock trim, and could be built to double the displacement, easily"


What I'm not understanding is how the Cadillac engine comes out 40 pounds light than a "SBC" (small block Chevy). The listed weight for the Cadillac is 625 pounds. The SBC is listed at 575 pounds. So, somewhere 90 pounds has to come off the Cadillac engine to get it 40 pounds lighter that a SBC. I realize you use the term  "SBC in stock trim" but to be fair if say..., the intake on the Cadillac was changed to aluminum then the weight comparison should be with a SBC having a likewise alteration. These are obviously "Published" numbers but light or heavy likely properly divided by engine. Also see the attachment of a Cadillac engine in Dyno trim weighting in at 777 pounds. Reeves1 estimate between 700-800 pounds seems accurate.


The SBC engine came stock in size up to 400 CID. To get a the Cadillac engine to double that would mean 800 CID. The largest Cadillac engine displacement modification I could find was 541 CID and that was with a significant overbore (.075) and an offset ground 1/4" stoker crank. There was the mid 50's 265 SBC and double that is 530 CID but again a fair comparison would to the full spectrum of SBC offerings (including the 400 SBC).




Offline redcaddy

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #9 on: April 25, 2019, 05:48:34 PM »
Hi,
I have no desire to wee in the wind, or split hairs. It does indeed take olds pistons, custom rods and a welded  offset ground crank, along with a .120 pass with a boring bar, to get 769 CuIn. but it has been done, many times, There has even been big stroker's built for LSR cars, successfully.

Just pulling the cast iron intake manifold puts the caddy within reach of the SBC weight.

I know you guys are trying to keep the Pinto alive, more power to ya. I fell in love with the Pinto/Vega size rigs when I discovered that light weight and gobs of torque makes for a fun ride. Bob Glidden proved the concept.

Again, not trying to stir the pot or pic nits. For a long time, I thought the big Caddy's were only useful in pick up tow rigs. (and they still are) In a HP to Weight ratio numbers crunching battle the cad's look a bit weak against the SBF/SBC kids. However, horsepower is a calculation, Torque does the work. Lift the wheel speed numbers, with short gears, and fun things start to happen. The whole is MUCH more than the sum of the parts.

When my RED embarrassed too many door cars in the bracket wars, the whiners protested me out of foot brake, as a "center steer" car, (They could put the driver in the center of a Malibu, to see the tree better, but I didn't have a left seat to sit in, so I wasn't allowed to play) I just went on to own local super pro and index classes. They tried to protest me out of super pro because I wasn't running a box and throttle stop...(My RED, trailer, tow rig  and spares is on Craig's list, looking for a new home.)

I can see I've pissed in my corn flakes on this board, SO, I'll pick up my tool box and move along. The parts I need for my street toy are out there...

I wish all you guys the best of luck in your endeavors, C-ya

Paul
If it turns $$$$$ into smoke and noise, I'm there

Offline Wittsend

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Re: Tire Diameter - Rear Gear - Transmisson to MPH
« Reply #10 on: April 25, 2019, 11:08:55 PM »

I can see I've pissed in my corn flakes on this board, SO, I'll pick up my tool box and move along. The parts I need for my street toy are out there...


No, I would say not (referring to the bold). It is just when someone presents a radical idea it takes time to grasp everything involved. I went back through the posts and it did not appear anyone spoke derogatorily. Befuddled - yes. But it is a learning process and things needed to be understood. We were asked if we had comments and 2.39 gears to prevent wheelstanding was an emphasis. That is something I had never had proposed before.


 I myself invested well over an hour before my last post searching the internet and enlightening myself on the Cadillac engines displacement and weight. I did so for the purpose of understanding its aspects and potential.  When your Cadillac powered Pinto is done I'd actually appreciate seeing the end results. It was never my intention to tell you you couldn't do it, rather it was that it seemed to have significant weight/fitment issues to overcome.


And with that, I wish you the best in your endeavor.