Change gear ratio


The old and reliable.

Pile of Parts
Pile of Parts

Posts: 28

Joined: Sun Sep 17, 2017 7:13 pm

Post Thu Jul 09, 2020 2:07 pm

Change gear ratio

I have a 1949 KB-5. It is "happy" at 35 mph. I can make it go 45 but it is quite loud and the engine is starting to turn faster than I would like. What is the most efficient way to make it "like" 50 mph? 2 speed rear end? A different transmission? Different ring and pinion? Whole different rear end? I don't want to go fast but I do want to go without turning such a high rpm.

Thanks!

Golden Jubilee
Golden Jubilee

Posts: 8370

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Thu Jul 09, 2020 2:28 pm

Re: Change gear ratio

You need to know what rpm the engine is turning. This can be done with some simple math using the tire diameter and the ratio of the differential. Another way is to use a tachometer. If the high rpm is within the OEM specifications, you will be OK>
Finding 71 year old differential or parts that are good enough to use may be impossible. I think it is safe to say, the best ratio for that old truck may not allow you to go much faster.
The simples way to get a more favorable down the road is a Gear Vendors over/under drive. I have been using GV for decades. It is not necessary to buy an adapter that matches the GV to the transmission, GV offer a divorced OD option. https://www.gearvendors.com/index.html
GV are about about $2500. You can expect to spent this much to upgrade what you have, if you can find the parts. Google for a used GV-OD.
I had a GV in my R120. My 1940 Ford has the pictured GV-OD behind a Ford C4 automatic..
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I would rather have tools I do not need than to need tools I do not have
“Never argue with stupid people, they will drag you down to their level and then beat you with experience.
Mark Twain

Pile of Parts
Pile of Parts

Posts: 28

Joined: Sun Sep 17, 2017 7:13 pm

Post Thu Jul 09, 2020 2:37 pm

Re: Change gear ratio

Thanks for the input. I don't think the engine is over speeding but it is very loud and it feels like it is resisting more speed. I can drive it all day long at 35 and not have any issues but 45 or 50 feels like it is more than it's designed for.

Golden Jubilee
Golden Jubilee

Posts: 8370

Joined: Thu Dec 27, 2012 12:45 pm

Location: Canada's left Coast

Post Thu Jul 09, 2020 5:00 pm

Re: Change gear ratio

A lot of the the "engine" noise you hear is from the fan. Those fans can be even louder if there is no fan shroud. The shroud, while making the fan less noisy, can improve the efficiency of the fan by several times.
Those old flathead engines were very quiet. Most of the valve train noise was muffled inside the engine. Later push-rod engines had a rattle that was not fully contained by the valve cover.
You could experiment with removing the fan for a short drive so you can hear the engine only. The fasteners should be installed to hold the water-pump pulley in place. You might be surprised and how much noise if missing.
A motor driven fan needs to have the fan exposed, at the back of the shroud between 25% to 40%. Those fans act like an airplane propeller first. Second, air has mass and the fan will be more efficient if it can "fling" some the air out radially. A shroud that is too long will be almost a bad as no shroud.
Just an important side note.
A bent fan blade should never be reused. The blades of blade may have been stressed and cracked when it was bent. I know of a person who was killed when he was nearly decapitated when a fan blade became detached and hit him just under his chin. Our farm neighbour had a straightened fan blade come off and launch through the hood of his pickup. Louvers are nice, but this is not a good way to make one.
Fan blades coming apart were common in the 1950s. The Tri-5 Chevy V8 were known for shedding the fan blades when persons discovered a few more rpm could win the race.
I would rather have tools I do not need than to need tools I do not have
“Never argue with stupid people, they will drag you down to their level and then beat you with experience.
Mark Twain

Pile of Parts
Pile of Parts

Posts: 28

Joined: Sun Sep 17, 2017 7:13 pm

Post Thu Jul 09, 2020 6:25 pm

Re: Change gear ratio

Thanks again. I never knew that about fan blades.

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