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Discussion Starter · #1 ·
Hey guys, pondering at what gears I'm going to go with. I'll be putting a trac loc or Detroit in also. I know what gears i would go with in a 3k car but can't decide when it comes to this hefty beast. I won't be doing much highway driving. I've thought of 3.55s to 4:30s. I want to eventually swap to a 5 speed from this cruiseomatic. Post up what gears you run and how you like them. Thanks
 

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I don't do a lot of highway driving either, but when I do, 3:50 (with automatic and 14" tires) is the limit for me. (If I had a 3:1 rear end lying around, I just might try it.)

Also, being a convertible, my car's noise levels are already higher at highway speeds. Might be different in a hardtop.
 

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Discussion Starter · #3 · (Edited)
I now have 3.00 gears and it's just pathetic. The short stroke 390 just needs more gear. I have to hold 1st gear to about 3500 and nail it and shift at 5k to get excitement. If I had 35 spline axles, I would love to try the 3rd member from my ex race car with 5.00 gears!
 

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I just pulled my chunk and found a spool with 3.5 gears, it was not bad cruising around town and I found myself asking the same questions that you are....

My first thought was to go with a 4.11 but a lot of people are telling me that a 3.50 will be more than enough, that I should just stick with that, even that a 3.89 will be pushing it, especially since I have a C6.

I will be following this post closely because I am very interested, but for now I think I will stick with the 3.5 unless someone can convince me otherwise ;-)
 

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I am running 3:50 rear, 31 spline axles, tru-trac diff, With 255 60/15 tires. I like the combo for short drives and around town, The 63.5 432cu inch, with C6 is very responsive. I am turning 3200 rpm at 70 mph. I would not go any lower gearing for street use.
 

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I'm glad you asked the question here,....I'm getting ready to build a stroker for my 63 and look forward to reading the input from other members.

I'm happy now with the 352c.i. 3:1 for cruising down the road for now, but I dunno if that gear'll work with a 445c.i. stroker. Maybe.
 

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I know one big thing to consider is when you are at the track, especially if you are building a stout motor..

You don't want to be hitting your redline before the traps in top gear......
 

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My Comet has 457 gears with Tremic T5 .64 overdrive 2800 rpm at 70mph with 28" tire. Galaxie has 370 gear with t-10 no overdrive 3100 rpm at 70 mph 15' wheels but not sure of tire diameter their not small tires though. I'd go 325 gear in the Galaxie if it wasn't for the close ratio 4 speed, maybe a 355 ? The 370 would be just great if it had a wide ratio Mustang T-5 with .74 overdrive.
 

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Discussion Starter · #9 ·
You don't want to be hitting your redline before the traps in top gear......

Not always true. As long as the engine is still accelerating, not valve floating, basically not falling on its face, its what you want.

Extreme case/example is my 406" Windsor engine. Made peak power at 8300 on the dyno. Went thru the traps at 9200. You always want to shift past peak hp also, so when the shift happens you are back in a sweet spot and not to far back.
 

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Obviously there are a lot of things to consider here ... how built is the motor, how tall are the tires relative to stock, how much freeway time will it see, etc.

Based upon what information you have provided (limited freeway, and the 3.0 isn't getting the job done), I would be tempted to look at a 3.73 gear. It should keep you in your power band with mild acceleration or WOT so you don't get that engine braking feeling when you upshift.

If you are serious about moving up to a 5-speed (.68 OD final drive ratio) you could pretty easily go with a 4.11 gear to keep your RPMs up. Go much larger and I think streetability of your ride is going to start becomeing an issue unless you really plan on only running from light to light.

If this has been tubbed, or you're running some huge tires already in the back, you could run a bit steeper with your gear to accomplish your goal, in my opinion.

Good luck with it!

Paul
Howell, MI

1969 R-Code, 4-Speed, Drag-Pack Cobra Fastback Project
1967 Mercury Commuter Wagon w/mild 429

My Car Restoration Projects
 

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Not always true. As long as the engine is still accelerating, not valve floating, basically not falling on its face, its what you want.
Yes, true indeed, just make sure you know the limits of your car is all. You don't want to be setting your rev limiter and them bouncing off of it is all I mean.
 

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My 67 Ranchero started life w/ 3 on the tree, then C4 and now AOD. The car weighs 3700#. I have played with 3.0, 3.25 and now 3.55 there are 235-60x15 tires installed that are 26” diameter. I think 3.70 to 3.89 will be fine as long as you are running an OD trans.
 

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Just put 3.70 gears in the 69, it did wake it up. We also went to a 28" tall tire at the same time. it seems to be running about 3000 RPM on the hiway.
 

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I just swapped out my 4.11s for a set of 3.50s.

Went from a 26" tire to a 29" tire too. Hoping to be hitting about 2500 at 60mph on the highway. Haven't had it out on the street yet though.

The 4.11s are for sale too ;)

Richmond gear set with less than 3K miles on them, very clean.
 

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Gear swaps are always a compromise between how much rpm you can tolerate on the highway and how much acceleration you want on the track or in town....It sounds like you are no stranger to rpm and since you are going to be swapping in an overdrive trans I would go with a 3.70-4:11..We swapped a T5 into my brothers 67 mustang and with 4:11s it cruises in 5th exactly the same as it did with the stock 3:1 gears
 

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Lot of good advice has been given above. My '64 Gal is a 460 with stock 3.00 open 28 spline. I bought an axle to axle truck rear end at a swap meet, $175. 3.50 gears 31 spline traclok, the lash felt good, I thought perfect?!! Had it checked, pinion gear shot, had to have new gears. My rear end guy said he was out of 3.50's so he had to order a set but had 3.70's in stock, since I plan on a few 1/8 mile trips I said ohhh yeh. Was going to get the housing shortened and buy new axles so I just had him rebuild the traclok while me was at it, then I'd be sure. Have a set of 4.30 tracloc out of the '68 Mustang CJ I had when I was younger. 3.70's 4.30's, all set.
Weht to the swap meet the next year, found a set of 3.25's traclok was rebuilt $300, absolutely!!! Wow 3.25, 3.70, 4.30, now I'm really set.
I quess the reason I'm telling you all this is that since the Ford rear end is so easy to change that you might consider say 3.25's AND 4.11's, one for street, one for an occasional day at the strip. A couple of hours and you could have them changed. I think 4.30's may be a little much for your engine and 14" tires. When I had the 4.30's in my 428 CJ Mustang they were singing on the street even with the MT 28 x 10 x 15 'cheater' slicks that I ran all the time. I'd go through the traps right at 6000 rpm.
Just some food for thought.
Good Luck.:)
 

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Discussion Starter · #19 ·
Thanks, yes I've thought about multiple centers. FYI I'm running a 275/60-15 so it's a 28" tall tire.

I might be getting a parts car for a 4 speed conversion, it has a 3.50 rear in it also!
 

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This is all just simple math. If you start with a stock 14" rim and standard tire, and your rear axle ratio is 3.0, your effective final drive ratio is 3.0:1.

If you want more gear, say a 3.50 gear for example, and nothing else is changed, your final drive ratio is 3.50:1. The effect this has is if you used to cruise at 2,500 RPMs at 70MPH you would now be at a little over 2,900 RPM. Go to 4.11 gears and it would be 3,425 RPM (4.11 x 2,500)/3=3425.

Now add in overdrive with a final ratio of .68 and you now cruise at 2,329 RPM in overdrive (3425 x .68). Finally, if you decide to go from a 26" tire to a 28" tire, your cruising RPM is reduced down to 2008 RPM (2329 x ((26x26)/(28x28)). This is because your tire acts like a gear: a bigger gear = lower RPM, a smaller gear = higher RPM.

So, in effect, running a 4.11 gear set with taller tires and overdrive has a net reduction in operating RPM while in overdrive of roughly 20%. That's why a big ol' scary 4.11 gear set is so streetable with overdrive. And if the trans is an automatic with overdrive, but without a locking converter it may be mandatory to swap in a short gear set or you could find yourself burning out torque converters.

Too much gear reduction from overdrive without a locking converter can mean the converter never fully couples. The trans fluid will churn and build monstrous heat and the converter eventually fails.

There are probably a couple dozen calculators out on the web that can help you with figuring out your ideal gear ratio with a given set of parameters. It's a good place to start when if you are thinking about making a change to the driveline because you will probably eventually want you speedo to read correctly, too.

Good luck!
Paul

1969 R-Code, 4-Speed, Drag-Pack Cobra Fastback Project
1967 Mercury Commuter Wagon w/mild 429

My Car Restoration Projects
 
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