MTFCA Forum

Anyone ever encounter a higher ratio T than 3:1? I found an period ad (1920)for a T with Rajo and 2.5:1 diff.

I’d like to find a 2.5 or taller.

Thanks for any info or ideas how to make a higher ratio diff.

Rob

You might consider a Watford auxiliary transmission. I am wondering what kind of power plant do you have.

Thanks Art. We have one of the six Ford “special” racing engines built and raced between 1910 and 1912. Ours is the 2nd largest at 298 cu in. Currently we have a 3:1 diff, but that’s geared too low for the hp/torque of this motor. When Ford raced with these motors in hill climbs, they used 1.5:1 and 2:1 diff. I don’t know what was used on tracks and road races, but I imagine they diffs were as tall.

At 3:1, we run much too high rpm, and these motors rev up like a Chebby small block.
Thanks,
Rob

This a short clip on our gravel road. There’s no reason to run the high rpm we run at 60-70 mph with this motor. In this video we just go to 50 mph because the gravel is loose:

https://www.dropbox.com/s/mjlxi62rxc4it ... r.MOV?dl=0

it might work in a speedster, but I don't think it would be practical in a stock Model T. I have a 3:1 in one of my T's and need to use Ruckstell to start out from a start on the slightest grade. It runs great on level or slight downhill. Also when going up a 6% grade, I can go up at about 30 mph, but the stock T's go up about 22 mph so I have to go to Ruckstell because of the slower T's ahead of me. We had a national tour and at least one car came out from the flatlands and after the first day, parked it and rode with someone else. I think they had a 3:1 but it was a heavy Towncar.
Norm

Rob I have an odd 2:75 to 1 in a 1930's 3/4 scale sprint car project. The only one I have ever seen.

Hank

Hank,
Is it a T diff? I’m curious, did they have to add to the pumpkin to accommodate a large pinion? I have this photo of the large (389 ci at that time) Ford special at the 1911 Algonquin hill climb.l. The diff is extremely wide, and the racing program said Ford was running a 1.5:1 diff.

Probably the same thing Hank Lee has in his project. A good friend fifty years ago had a 13/36 original set made by Ruckstell.He had it in his speedster with a Rajo and Ruckstell and loved it!
I have only seen a very few others since then, so they are quite rare. I would imagine some sets must still be around in private stashes. I would hope someone having a set they have not been using would make the sacrifice and sell one at a decent price?
As I understand it, the 13 tooth pinion gear is the same as the more common Ruckstell 13/40 set. So you should grab a good one of those if one comes along. The 36 tooth ring gear is configured to run against that regular 13 tooth pinion somehow. I never got to see the set my friend had in his car. The original Ruckstell gears are sometimes overly hardened, and tend to be brittle. I would NOT suggest matching an era Ruckstell ring with a new replacement pinion!


Rob! You aren't posting here enough lately! People are beginning to forget what a fantastic and special car you have!

Rob,

This fits in a conventional Model T rear end housing. The car has 12" tires on it, 13" removed from the width (6 1/2" from each side). Pictures and plans are in The Complete Ray Kun's Auto Racing Book. Should have taken pictures years back when we replaced the bad housings. For the like of me, cannot remember exactly the gear counts but came out to those ratios.

Hank

Rob, The 2 :1 and 2.5 :1 rear axle ratios were used in Model T racers on the high banked board tracks where speeds were high on the smooth track. They were also marketed to Model T speedster builders in the 1920's for use on flat area roads. If you can't find a set for your racer you could try to find a overdrive type Moore that would mount at the Model T rear end with the 3 :1 gears, which would give you something around 2.5 : 1 in overdrive, plus you would have a netural for tow starts, if you have rear wheel brakes. The Moore was made in the late teens, one of the frist aux trans for a T but a little late for your car of 1911.

Rob, probably Martin Gear, or another specialty shop could make a set, for not too astronomical a cost. Please keep the antique information coming. Thank you, Dave in Bellingham, WA

Hi Rob, I'll try to not get too long winded with this. Old #4 has a final gear ratio of 1.7 to 1, so I'm familiar with ratios like that. Knowing H. Fords thought process on those race cars, my guess is that they had a larger rear axle housing in order to get the strength for the inner workings for durability. I've seen a few sets of the higher ratio Ruckstell gears and a close friend Tim Stangland (we used to tour a lot together) ran a set (still is, 40 some years later, although he moved to Washington years ago thus ending our touring together), I believe 13/35 or 36 in his speedster. His only concern, and mine, would be breaking the ring gear. As you know, with 3 to 1 gears the ring gear is recessed on the back side. The recess is deeper on the higher ratio gear therefore weakening the strength of the gear. Tim was always concerned about, on acceleration breaking the gear. If you're thinking mostly track time, and careful on acceleration the high Ruckstell gears would probable be okay with a stock housing, that is....if you can find a set to purchase. Just my 2 cents worth.

Ed aka #4

I must be missing something. As old man Ferrari use to say, rpm is free. So the cheapest way to get more power is more revs. With 30” wheels a 3:1 ratio will give 30mph at 1000rpm. That’s 90 mph at 3000 rpm. The eight or sixteen valve overhead engine will easily rev to 3000rpm, one I worked on peaked out on a dyno at just shy of 5000rpm. At a 3:1 thats 130moh. I’m not sure any road going T has ever travelled at that speed. Indeed on the eight valve engine I worked, we changed from 3.25:1 to standard 3.63:1 for better road performance.
Now 2.5;1 is about 38mph per 1000rpm and 2.1:1 is about 42moh. That’s 125 mph at 3000rpm. Who’s kidding who.
Now if you drop to smaller wheels and wider tires, these calculations will need revision. The fastest Model T at Bonneville was timed at 214mph using slicks, turbo charged T block with five mains at 5000rpm and a custom rear axle at 2:1.
So I have trouble understanding why anyone would need a ratio less than 3:1 when using antique wheel sizes for a road car.

Thanks for the replies.

Tony, I recently separated the flywheel from the output shaft on our Ford Special racer. This isn't a Ford Model T motor, but one of six specially built and raced Ford motors built between 1910 (probably begun in 1909) and 1912. Our motor began as a 298 cu in four cylinder. The motors had auxiliary exhaust ports (ports at the top of the piston in the downstroke position) with a slide that can be opened and closed with the right foot while driving. When open, the motor breaths (and runs) much better, but the carb must be richened as the slide (ports) are opened.

For whatever reason, this motor accelerates extremely quickly (reminds me of a small block Chebby, of which I had a few in my younger days). The flywheel (I'll add a pic or two below) is nothing link a T, but a large, smooth 65 lbs. pure flywheel. Ignition was provided by a dual spark Bosch magneto, and the engine has two plugs per cylinder.

The flywheel left the company of the output shaft when I was driving about 60 mph, still breaking in the motor. I suspect the four bolts, threaded into the flywheel, and two index pins may have had some "slop" that we had not detected, and when she let go, that was the end of that. Now the racer sits forlornly at Dean Yoders shop, waiting for another performance T motor builder from Oklahoma to pick up the motor and line everything back up.

Meanwhile, there are a few things I know about these racers. They were extremely fast, and performed well on one mile tracks, in road races and hill climbs. In 1911, FMC was the 5th winningest automaker in U.S. racing, due to the success of the special racers. Another Ford Special, sent to France, came in first in it's class and 2nd overall in what was considered one of Europes two most prestigious hill climbs, Mont Ventoux. That racer also placed 2nd in both a one Km sprint and 1/2 km hill climb, preliminary events to the Grand Prix. Unfortunately, while practicing for the Grand Prix, the racer was wrecked, killing the mechanician. Reports are that the racer was traveling 75 - 80 mph at the time.

To place things in context, the largest of the special racers (now at THF, off display) has a 410 cubic in. motor, and was officially timed at 109 mph on ice in 1912, mimicking Henry Ford's world record in 1904 on ice driving 999.

The Ford specials won hill climbs in both 1911 and 1912 (setting the record on both hills at Alongquin in 1912). We know due to published racer specifications that the Ford racers ran 1.5:1 diff ratios in 1911, and Ford reported that due to tire slippage on the hairpin curves (both hills had at least one hairpin curve, and used "flying starts" to begin the hill climb) they (Ford) wen to 2:1 ratios for 1912, and mopped up, defeating well known makes such as Mercer, Benz, etc. etc.

I would like to drive this racer on the road (highways) at 50 - 65 mph. The motor is far and away strong enough, and there seems to be no reason to run this motor at high rpm ro do this.

I'll add photos below. Meanwhile, the "crowning jewel" in my opinion is the fact that at the Michigan State Fairground track outside Detroit in 1911, the largest of the Ford Special racers secured a timed race agains the Blitzen Benz, as well as a Hotchkiss racer (both 200 hp). The Blitzen Benz, with Robert Burman driving, at the time held world records for a) fastest mile in the world, 141 mph (a record that stood until 1919), fastest one mile circular track record, fastest five mile and twenty mile dirt track records.

The timed event was from a standing start (the world records were all flying start), and the Ford Special beat both the Blitzen Benz and Hotchkiss. The Ford mile, at 50 seconds, was an average of 72 mph.

Another colorized photo from the Ford Times. This is one of the two racers sent to New Orleans for the Mardi Gras races held in February 1911. Again, notice the large pumpkin (with opening to get a large pinion gear into the diff housing):


Older photo of the flywheel. This was taken before I acquired this project, and the motor was together. In hindsight it looks to me like the flywheel may have already been damaged:

A little more "into the weeds."

A Model T with 30 inch tires, 3.63:1 diff ratio should be turning about 1400 rpm at 35 mph:

Our racer has 32 inch tires (Ford drawings specified 32 inch wire wheels for this motor, although photos with what appear to be 30 in wood wheels were also used). With our 3:1 diff ratio and 32 in wheels, the racer should travel about 45 mph at the same 1400 plus rpm:

With a 2.26:1 ratio, the racer would travel 60 mph at the same 1423 rpm:

I hope we can all see this special car at the Greenfield Village Old Car Festival in the future. It will really bring some attention!

Ed,
I had planned to have it there this year. However......

It’s incredibly loud and quick. I was hoping for a good pass in review moment. Hopefully next year.