"New", same old ratio ?
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Senior User
Joined: May 2009
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From: Chicago
"New", same old ratio ?
Ok, I have read just about every ratio thread on this forum and not just in this section but I am going to ask this anyway. I have a 3.7 in my '58 f100 with a 292 in front of a original 3 speed. I was thinking of chaning the gearing so that I could cruise around a little easier and every once in a while get her going like 60-65 mph without sounding like the engine is going to explode. I found a 3.0 pumpkin to swap in but I am afraid that I will not be able to haul lumber or drywall when need be (very rare but does happen). Will I be like a semi trying to get off the line with the 3.0 or have people done this and felt like it was fine? Any and all weigh in please.
Regards,
Cbass
Regards,
Cbass
Cargo Master
Joined: Feb 2008
Posts: 2,795
Likes: 129
From: Windermere Valley,B.C. Ca
I think the 3.0 ratio would be ok, if my unreliable memory can be trusted I think I used it with a 302 automatic, it was no dragster but nice highway cruiser. Worst case, you will have to change it. 
Post Fiend
Joined: May 2008
Posts: 7,641
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From: Poway, Ca.
In order to figure out speeds and RPMs for different ratios, we need to have your back tire diameter or roll out distance.
Here are two excellent calculators - one of which that was just recently posted by another member that should answer your question
All non overdrive transmission outputs are direct drive 1:1. 3.0 would be ok, but recently Ross commented that the 3.5 is what most guys are using if it's available for your rear end in back of the flatheads (@ 86 Net HP).
Here are the links:
http://www.onlineconversion.com/bigger_tires.htm (scroll down)
http://www.et-studios.com/motorsports/gears/gears.html
Basically if (and that's a big "if") you are running 16" wheels with a tire diameter of 28 inches, you will be at 65 mph at about 2350 rmp with the 3.0 - that's a little low but ok. For hauling it may cause a little grief. I guess it also depends on your first and second gear ratios and HP.
With a 3.25 rear, you would be at 2500 rpm at 65.
With your 3.7 it says your rpm at 65 is about 2885 - that's pretty high.
On my truck, I have 15 inch wheels, a 2.8 rear and cruise at 70 mph at 2500 rpm. I have no problems with 750 pounds in the back - can even excellerate going up hills (gas gauge drops quickly) but then again, my 390 PI @ 395hp isn't a 292
Here are two excellent calculators - one of which that was just recently posted by another member that should answer your question
All non overdrive transmission outputs are direct drive 1:1. 3.0 would be ok, but recently Ross commented that the 3.5 is what most guys are using if it's available for your rear end in back of the flatheads (@ 86 Net HP).
Here are the links:
http://www.onlineconversion.com/bigger_tires.htm (scroll down)
http://www.et-studios.com/motorsports/gears/gears.html
Basically if (and that's a big "if") you are running 16" wheels with a tire diameter of 28 inches, you will be at 65 mph at about 2350 rmp with the 3.0 - that's a little low but ok. For hauling it may cause a little grief. I guess it also depends on your first and second gear ratios and HP.
With a 3.25 rear, you would be at 2500 rpm at 65.
With your 3.7 it says your rpm at 65 is about 2885 - that's pretty high.
On my truck, I have 15 inch wheels, a 2.8 rear and cruise at 70 mph at 2500 rpm. I have no problems with 750 pounds in the back - can even excellerate going up hills (gas gauge drops quickly) but then again, my 390 PI @ 395hp isn't a 292
Senior User
Joined: Dec 2008
Posts: 104
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From: Central Florida
Back in the day, I tried several combinations with my '56 (292/3 speed) including 2.78, 3.0, 3.25, 3.5 and the original. I found the 3.5 to be the best compromise using the stock wheels/tires. Highway speeds were achievable and I could still pull a trailer and haul stuff. The 292 is powerful enough to deal with a 3.0 but I had to put a heavy duty clutch in to handle pulling the sailboat (1700 lbs) out of the lake. The 2.78 car rearend that was in it when I got it offered 20 mpg on the highway but it wasn't worth the trade off in power (or the awful install job the PO did on it). Pick your poison, but I recommend 3.25 - 3.5 if you are sticking with original tire size and still need versatility.
Side note--I now have a 239 flathead in a '49 that I'm leaving the stock rearend in and would not consider anything below (higher than) a 3.5. Your motor puts out about 167 hp, mine 90-100 hp on a good day and, as Julie implied, that makes a big difference.
Also--my '56 had 15" wheels and your '58 might as well so make sure you know your tire diameter before plugging it into the calculators!
Hope this helps.
Ryan
Side note--I now have a 239 flathead in a '49 that I'm leaving the stock rearend in and would not consider anything below (higher than) a 3.5. Your motor puts out about 167 hp, mine 90-100 hp on a good day and, as Julie implied, that makes a big difference.
Also--my '56 had 15" wheels and your '58 might as well so make sure you know your tire diameter before plugging it into the calculators!
Hope this helps.
Ryan
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Senior User
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From: Chicago
I will definatly not be pulling a sailboat (my wife doesnt like boats
) and I will only be putting lumber in it and probably smaller loads 500-700 lbs. I think that the 3.0 will work for me and my needs. Thanks for the help guys.
Cbass
) and I will only be putting lumber in it and probably smaller loads 500-700 lbs. I think that the 3.0 will work for me and my needs. Thanks for the help guys.Cbass
Cargo Master
Joined: Jun 2001
Posts: 2,571
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From: Oxford, Indiana
mclaughlinrp is right on the money as far as I'm concerned. I still think you'd be better off with a 3.25, but a 3.00 will probably work OK. Another consideration is transmission type. A manual transmission tends to need a little more gear than an automatic. The torque multiplication that happens in the converter on an automatic can make a higher gear like the 3.00 a little easier for your engine to cope with. With a stick, all you can do to get it moving with a load is slip the hail out of the clutch.
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Senior User
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From: Chicago
I am running a 3 speed manual (original), I would love to go with a 3.25 because I think that it would be ideal but there is none with in 200 miles of my house. I am in no rush to do this but also dont want to wait on something that isnt going to happen. I have the opportunity to get the 3.0 and thought that it might work out fine, plus even that ratio is hard to find.
On this same topic, when I finally do change the ratio I beleive I read that I have to do something to get the speedometer to work correctly, right?
On this same topic, when I finally do change the ratio I beleive I read that I have to do something to get the speedometer to work correctly, right?
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Senior User
Joined: May 2009
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From: Chicago
I had not thought of that mostly because it sounds expensive and I really like the three on the tree. If I did something like that would I be able to keep the three on the tree setup? Would I have to get a new/modify old drive shaft? How hard is it to change over(changing 3rd member is fairly easy)? How hard is to find and what is the expensive of a 3spd overdrive tranny?
Thanks
Cbass
Thanks
Cbass
Post Fiend
Joined: May 2008
Posts: 7,641
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From: Poway, Ca.
You would still have the column shift. Only difference would be a few electrical ccomponents. I think it should be a direct bolt in/swap. Length should be the same but I'm not exactly sure about the transmission mount location. 58 trucks did come with optional overdrive transmissions.
I had an OD transmission behind my 289 on my 55 and it worked great!
I had an OD transmission behind my 289 on my 55 and it worked great!
Senior User
Joined: Aug 2008
Posts: 277
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From: Sacramento, California
Yeah, I have one that was behind a Y-block (272-312) complete with the solenoids and it appears to be rebuilt so it should fit right in! I'm only asking $75 for it. Now the only problem is getting it to you as shipping would be very expensive plus my labor to crate it up and ship it. Let me know, maybe we can work something out. Anybody going from Commiefornia to Chicago?
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From: Chicago
Flatheadjohn, would love to work something out and that price is amazing but like you said to ship it to me would triple the price. I dont know anybody coming this way, just had friends move that way but that doesnt help any.
let me know if you can think of anything because I would take that at that price in a second.
Cbass
let me know if you can think of anything because I would take that at that price in a second.
Cbass
Fleet Owner
Joined: Jul 2004
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From: NM
There's more to installing a B-W O/D, like kickdown switch, relays, etc. and it requires changes to the ignition wiring. Unless you are clever at electrical work, it will be a challenge to wire one in. Finding all the pieces could be a challenge, too.