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I have an opportunity to change the gear ratio on my 61 Galaxie. Currently I am running a 4.6 with 4R70W with 3:1 gears. Car drives good. I found a set of 3.5:1 gears for a reasonable amount. The issue for me to pull this off, is that I would have to get the ECM reprogrammed to work correctly with the lower gear ratio. The cost for reprogramming however is minimal.
I have never changed gears out before so I am just wondering if the performance gain is going to be worth the effort involved? I don't race the car, but it seems to me that for the cost and time involved in switching out gears, it might be worth a gain in performance. The question is...how much more performance or will it even be noticeable?
Last edited by dan_6776 (January 31, 2017 11:21 am)
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I don't know if that question can be answered, especially for a street car. My guess is it would be noticeably quicker off the line and the sound of the higher RPM's will add to the feeling of greater performance. You have an overdrive trans, so the change in highway RPM is not going to be substantial, maybe 200 and some RPM. You can calculate RPM's at various speeds and in various gears to see what difference there would be. I would consider going to 3.50:1 in my car, from 2.75:1, without overdrive, and your mod motor is a higher RPM engine anyway. You know, if you don't like it you can always go back, but for day to day use I think it would probably be more smiles than frowns.
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What was the ratio of the rear in the donor car? With OD the rears tend to be pretty steep and once you're in OD the RPMs drop off significantly. I'd think a 3.55 would be okay and as high as a 3.90 would be good too. My OT Nissan has a 4.10 "rear" in it. I have a 3.70 rear in my Ford with the 4-speed and am considering a 4.10 rear so I can pick the revs up a little around town. Use an online RPM/ speed calculator and calculate the differences at 30, 40, 50, 60 and 70 mph for a better idea. This is what I did and I wanted to see how close my speedometer was too.
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Not to hijack this thread, but Bobss396, what motor are you running in your Ford to want to go up to a 4.10?
I have a 351 Cleveland 4 speed in a 64 Galaxie, and am trying to decide what gear to replace my 3.25 with. I was thinking 3.89, but still wondering about a 4.10.
Thanks
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Here are some questions to think of as well as what 3.5s will do for you. How often are you on the freeway? Even with an OD trans, depending on your tire diameter 4.10s might be a little steep for you as tire diameter also plays a part in your effective gear ratio. Are you looking to be a quarter mile bruiser or just get a little more "umph" off the line? Is gas mileage a concern at all? 4.10s are one full revolution per driveshaft rev which is quite a bit, so even with your od trans that will net you quite a bit more revs at highways speeds. If you're running higher revs than a standard trans with a relatively high gear then the purpose of using an OD is kind of defeated unless you are quater-miling it and want lower gears for racing and a high enough gear to drive it on the freeway with your OD.
I would say that the 3.5s would work well with your combo, and 1/2 more revolution per driveshaft rev will net you a good bit more off the line (better acceleration). Your call will also pull a little better in top gear with less need for downshifting. 3.5s are a good compromise between performance and economy. Am using them on my '68 Cougar WITHOUT an overdrive and still have acceptable revs at highway speeds here in metro Atlanta where 75mph is considered slow. At least on my car, even with an overdrive, I wouldn't go any lower than 3.5, but that's my car. Your car is up to you.
It's all a matter of taste, but you can calculate your highway speed revs at the Summit Racing website with their gear ratio calculator, just be sure to be accurate on your top gear ratio.
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462HO wrote:
Not to hijack this thread, but Bobss396, what motor are you running in your Ford to want to go up to a 4.10?
I have a 351 Cleveland 4 speed in a 64 Galaxie, and am trying to decide what gear to replace my 3.25 with. I was thinking 3.89, but still wondering about a 4.10.
Thanks
I have a 355 SBC that is worth about 415 hp. 4-speed is a '64 Corvette M20 with a 2.56 1st gear. Tires are close to 29" tall (235-75-15). I plugged the numbers into a calculator for various ratios. I'd like to pick up the revs in high gear a little so it won't lug around town. I pick up another 200 RPMs at 40 mph, 275 at 60 and 325 at 70. Which is as fast as I usually drive it. The cam manufacturer was right that it likes more RPM.
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Thanks, Bob.
This 351 C cam comes in at 4000, so it definitely needs to rev and bucks at low rpm's. The roads there are very curvy and no anticipation of high speed, long distance driving. I am hoping that 3.89 is enough gear.
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Thanks, Bob.
This 351 C cam comes in at 4000, so it definitely needs to rev and bucks at low rpm's. The roads there are very curvy and no anticipation of high speed, long distance driving. I am hoping that 3.89 is enough gear.
You should see improvement with the 3.89 ratio. I figured I have a 3.70 by the chart I made up, car was supposed to come with a 3.56 rear. If it is in fact a 3.56, I'll go to a 3.89 and call it done.
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Thanks for the replies. I contacted Ron Francis Wiring about a software program change for swapping out to 3.5:1 gears. They indicated it may not be necessary because I may end up liking how the car responds with the gear change. If a program change is necessary, its no big deal for them.
So, I think I am going to go for it. The lower gear ratio should provide a little more snap off the line and with overdrive, a few extra RPM at highway speed will most likely not even be noticeable.
If I don't like the change, I can always get the computer program adjusted or put the old gears back in. I will post a follow up later in the spring.
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So I decided to go with 3.89 gears. I get my hands on them next week. I based my decision on the fact that most of my driving is in town and I want a little more snap off the line. My current set up: 61 galaxie, 4.6 engine, 4R70W, 3.0 gears with a 20" rear wheel spins at 1690 RPM at 60 MPH. Going to 3.89 will increase the RPM to 2300 RPM based on an online calculator. It's a little faster spinning than I would like, but the increase in performance where I would like it is the trade off.
Some information I discovered when doing research on 9" diffs before setting out to find gears:
Generally speaking...in the early 60's, the standard application seems to be that if you had a V8 car with automatic you most likely had 3.0 or similar gears. If you had a 6 cylinder standard car, you probably have a 3.5 or 3.89 ratio. If you had a 6 cylinder standard transmission truck, you probably had a 3.89 gear ratio. Again, not always gauranteed but seems to be the common application. By mid 60's, Ford went with the large bearing 28 spline axle and 31 spline axle shafts as the cars got bigger and heavier as well as engines started producing more power.
US built cars had the axle ratio stamped on the ID tag. If there is a number identifying the axle ratio you had a standard diff, where as a stamped letter identified a Traction Lock diff. My trips to the salvage pretty much confirmed all of this.
All cool stuff.
Last edited by dan_6776 (April 28, 2017 7:38 am)
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