Gear ratio/RPM
Comments
-
Rob the formula is MPH X gear ratio X 336 divided by tire diameter: 70 MPH x 4.56 x 336 divided by 28 = 3830.4 RPM. Have fun playing around with the figures to get the combination you desire. If you have over drive then multiply the RPM (3830.4) by .72 which is the over drive ratio for the 47 hudson I do not know if the later hudsons had the same o/d ratio. I hope this helps you. Lee O'Dell0
-
Rob, as you can see I plug in the wrong MPH. 60 mph x 4.56 gear ratio x 336 divided by 28 = 3283.2 x .72 = 2363.9 RPM. It apears that your tires are slightly less than 28 inches but close. Have a good day. Lee0
-
The Borg Warner overdrives used by Hudson all had a 30% reduction.0
-
Thanks, I found that formula on the internet and have been playing around with it. I want to change the rear end ratio so I am debating something between a 3.42 and a 3.73. With the 4.56 I am reaching for OD by 40 mph. 60 ain't that fast on the freeway by todays standards. You need to run between 70 and 80 or get run over. IMHO even with the OD that is just twisting a torker like the 308 to fast for long periods of time, not to mention wasting gas, which I am sure you have all noticed isn't cheap. At 80MPH I am turning 3100 rpm. Whew that's a lot for a 4 1/2 inch stroke for any long period of time.0
-
I have overdrive with standard ratio 4.1:1 on my Jet, and it is a really good combination. Turns around 2000 r.p.m. @ 60 m.p.h., which is the speed limit here. I also had this on a '50 Pacemaker, but it was bit tall for the short stroke 232. But for a Hornet, with the bigger diameter tyres, and 4.1 with o/d would give you around 1,920 @ 60 m.p.h. The 308 would handle a higher ratio, but performance would be down, and I would advise against too much use of the kick-down facility, as the input shaft of the transmisison is a weak point - I have sen them starting to corkscrew.
Geoff.0 -
Thank you Geoff. I really appreciate all the tech people in the HET CLUB for their invaluable information and their time to help the members. I want to learn as much as I can about Hudsons. I've only been a HET member for about 5 years and look up to members with Hudson experience. And I don't want to give anyone erroneous information. I have never been able to find in print what the Hudson O/D really is. In my 47 owners manual it does not say, but the manual has 4.56 in O/D is 3.28 and 4.11 is 2.96. So I multiplied 4.56 by 30% (.70) and it came out to 3.192 but at 28% (.72) 4.56 came out to 3.28 which matches the owners manual. And the 4.11 came out to 2.9592 (2.96). I was a GearVendors dealer for 22 years and their unit is also a 28% reduction unit which happens to be a perfect midway gear split between 1st and 2nd gears. If I gave erroneous information I apologize. My 47 Hudson PU also has 4.56 gear but it does not have O/D, so overdrive is one of my options as well as maybe changing rear gear ratio. However, it is not running yet so that come first. Now here goes with a 30% gear reduction. 60 MPH x 4.56 x 336 divided by 28 = 3283.2 x .70 = 2298.240
-
I quote from the 1952 Mechnaical Procedures manual - "In overdrive the engine revolves 30% slower than in direct gear at the same car speed". I know that Borg-Warner only supplied one basic unit, that was adapted to various makes of cars by altering the input and output shafts. The innards are all identical. When I rebuilt my Jet overdrive I used various parts that I located all round the country from Austin Westminster, Mark 1 Ford Zephyr, Studebaker, Wolseley 6-110, and Nash. ( I live in New Zealand). So if you are looking for parts, spread your net wider than just Hudson.
Geoff.0 -
Rob, I went though the same rear axle change that you are doing.
I have a 1949 super six with 262 & overdrive . It was screaming to keep up with interstate traffic - I think the rear end was 4:11 ratio.
I installed a rear end from a 1954 hornet parts car with automatic transmission . If I remember correctly I think the ratio is 3:56.?
I had to change the speedometer ratio with a "gearbox" to get the speedometer to read correctly.
I like it. Takes a while to wind out - but at highway speeds, 65 - 70 it run smooth . My car is a little low on power at 75+ mph. If hills or head wind - But your 308 should do well if you choose that ratio.
In city traffic I usually use 2nd & 2nd overdrive for up to 40 MPH.
Hope that helps you.
Kerry0 -
Geoff thanks for the information. I learned something new. I was aware that most O/D's were 30%. It's good to know so many car makers used the same parts that are inner changeable. I like the quote in the 1952 Mechanical Procedure Manual. That encouraged me to look in my 1947 Mechanical Procedures Manual. I somehow overlooked the overdrive reduction. The quote in the 1947 Mechanical Procredures Manual is "In overdrive the engine revolves 28% slower than in direct gear at the same car speed". It would be interesting to know when the change occured if it did. If it did happen, when did the change occure. Did it happen when the step down was made or is the 1947 Manual in error and all overdrives are really 30%. It's not all that important to me one way or the other but I am interested to know if there is a difference. Thanks again for your helpful information Geoiff I appreciate it. I'm still learning. Rob stic with Geoff and 30%. Lee0
-
One of my favorite online gear calculators is at this link:
http://www.f-body.org/gears/
I've used that online program alot over the years. Where to design your "cruise" speed has alot to do with where you'll be driving the most. I've had the pleasure to drive around alot with both a tachometer and a vacuum guage hooked to our '49 w/308 just to watch some of the engine's behavior on the road. The 308 seems to really love cruising somewhere in the 1900-2600 rpm range and will do so all the live long day. It will cruise in that rpm range happily and with good torque and throttle response with about any carb setup readily available, as long as you have it tuned reasonably well.
Having said that, we drive the majority of the time locally on two lane roads and usually drive to nearby shows on the same kinds of roads. Speed limit of 55, we want to cruise somewhere between 50-65 mph. A non-OD 3 speed, 3.07 rear ratio, and a 235/15 tire nail us right in the range we wanted to be, and so far is working out really great for our kind of travel. Somewhere in the low-mid 20's for gas mileage with plenty of hill climbing power without a downshift for the terrain we have.
With the existing combo, we're turning 2000 rpms at 54 mph and 70 mph at 2600 rpms. I realize that if we start spending more time on the interstate, we'll need to plan on a cruise speed of 70-80 mph in the 2000-2200 range. That resulting combo would be a 3.42 rear ratio with an OD transmission running 235/15 tires. In OD 70mph@2000 rpm and 80mph@2300rpm. You have to realize your acceleration will be slower due to the increased load, but a 10 mph change with 300 rpm is pretty easy for Hudson torque-monster engines.
The gear calculator I posted is good for also looking at the speeds/rpms for all your gears so you can see where you need to shift up and what speed/rpm you need to downshift at to keep from jerking your car around.
I want to echo one of Geof's warnings, be wary of your transmission's input shaft. Particularly single lever transmissions. As the gearing gets taller, it puts even more strain on the input shaft and clutch. One would think the cork clutch would save your input shaft, it won't if its worth its salt. Wherever your driveline weakness is, going taller in the gears will point it out quickly to you if you jerk it around without consideration.
Mark0 -
I was figuring on 30% as that is what I have read and I also have one in my 55 F-100. I am not concerned with the power problem as I just rebuilt the motor and I did several modifications that gave it considerably more power than stock. Also my OD is operated by a toggle switch so I control when to have it on or off. The frustrating thing right now with the 4.56 is I am always switching it on and off around town anywhere above 40. With a taller rear end, I can just leave the toggle off unless I get on the freeway and cruise for a while.0
-
Found an interesting fact in the Borg-Warner OD manual. It mentions the R-10 unit was for lighter, smaller-engined cars, while the R-11 went into heavier cars with bigger engines. Then a note says the R-10s were 30% reduction, while the R-11s were 28%. That explains why we've heard both numbers. Now the question ... which unit went into the Hudsons, pre and post-stepdown?0
-
With the existing combo, we're turning 2000 rpms at 54 mph and 70 mph at 2600 rpms. I realize that if we start spending more time on the interstate, we'll need to plan on a cruise speed of 70-80 mph in the 2000-2200 range. That resulting combo would be a 3.42 rear ratio with an OD transmission running 235/15 tires. In OD 70mph@2000 rpm and 80mph@2300rpm. You have to realize your acceleration will be slower due to the increased load, but a 10 mph change with 300 rpm is pretty easy for Hudson torque-monster engines.
Mark,
What is the aspect ratio or tire diameter for the P235's you're running? What width rims are you using. Thanks, Walt-LA0 -
Walt-LA wrote:
What is the aspect ratio or tire diameter for the P235's you're running? What width rims are you using. Thanks, Walt-LA
I couldn't tell you the exact diameter, the program/website I listed has a diameter in it if you know your tire size. We're running 235/70 15's (program says its 27.952"diameter) on a Hudson 5" rim. They are a bit bulbous at the bead/rim, but seat square and look good.
The Super Wasp has the wider 5.5" Hudson rims, so the 235's look much better on them.
We've checked the rpm against the mph while passing those automated radar billboards that show how fast you are going and if you deserve a ticket, and they've been accurate to the mph chart I printed off the website with our setup.0 -
I'm pretty sure the big six Hudsons only had the R-10 unit. The R-11 unit was used on T-90 and T-85 Borg Warner 3 speeds.
For example, by bigger engines they mean such as the Ford FE 390. The T-85 w/R-11 OD was available on a 325hp 390CID Ford as late as '72. Since the Hudson only ever had the T-86 from '52 onward, I doubt we have anything but the R-10.
I researched the dickens out of OD type transmissions hoping to find something a bit stouter for the Hudson. The T-85 w/R-11 was what I had settled on, but haven't found one to figure out how to adapt it or if I can.0 -
If you want a go cruiser, try 2.72, they are in some corvette rearend and jeep cj rearends, a friend of my uses that ratio alot in his Hudsons0
-
I'm running the Dana axle with 2.73 gears in my '51 Hornet with OD, and very happy with that combo. 3.58 was just a little too tall for moderate hills. Amazing what performance difference there is between that and the 3.73.0
-
I would have 5,166 RPM in my '37 Terraplane w/OD, at 150 mph.
Doable.0
This discussion has been closed.
Categories
- 36.9K All Categories
- 102 Hudson 1916 - 1929
- 16 Upcoming Events
- 90 Essex Super 6
- 28.5K HUDSON
- 554 "How To" - Skills, mechanical and other wise
- 992 Street Rods
- 150 American Motors
- 172 The Flathead Forum
- 49 Manuals, etc,.
- 73 Hudson 8
- 43 FORUM - Instructions and Tips on using the forum
- 2.8K CLASSIFIEDS
- 597 Vehicles
- 2.1K Parts & Pieces
- 77 Literature & Memorabilia
- Hudson 1916 - 1929 Yahoo Groups Archived Photos