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I have a 1960, 4 speed, 270hp, With a 411 posi-track rear end. I have a spare pumpkin that I would like to set up with Highway gears, so that when I am doing 60 mph I will be at about 2000 rpm. I don't know if I need a 3:70,3:55 or 3:36. Any body running a 270 hp,4 speed with one of these ratio?
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Re: How low can You go?
Andy - you'd need a 2.63 rear gear to get the revs down to 2000 with 6.70-15 or equivalent revs/mile (760) tires. I have a 3.08 in my SWC with SHP and CR four-speed. It runs to 75 MPH in first gear and turns 2340 revs at 60. It's like a five speed with no first gear. A 3.36 will yield about 2560 revs at 60 (760 x 3.36). With a 4.11 you're taching about 3120 at 60.
Duke -
Re: How low can You go?
Andy,
Assuming you have the "correct" 6.70X15 tires, and looking at it strictly from a mathmatical approach, I calculate you would need 2.73:1 to do what you want to do; 3.36:1 would result in 2465 rpm at 60 mph. I haven't a clue regarding what's possible in '60s, and/or what other problems it might cause you.
Chuck SangerhausenComment
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Re: How low can You go?
Duke,
Hee, Hee. It's a good thing ONE of us got promoted into management; The difference has to be in what we used for tire diameter. I used 27.50" from Coker's catalog.
Chuck SangerhausenComment
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So which one of use got "promoted", plus...
If you use the tire diameter to compute revs per mile it comes out too high because it's for a "rigid body" like a steel wheel. Pneumatic tires deform and typically have two to three percent less actual loaded revs per mile than the "rigid body" diameter yields. We got into this discussion about three months ago, and I got in trouble and drew a whole bunch of hoots from the Board when I started discussing a "regression analysis" on manufacturer's revs per mile data that I conducted several years ago. As a result I am consigned to be an engineer forever and will never be promoted into "management". Also, I had to round off to three significant digits, as I can only read my slide rule to that level of accuracy as opposed to the modern electronic calculators used by "managers" who can generate double precision calculations at their desk. The only way I can get double precision is to try to sneak a FORTRAN card deck into Data Processing at night.
BTW, Andy, if you want to get an idea of what a 3.08 would be like, try driving around without using first gear. With my 3.08, my first three gears are, overall, about the same as your top three.
DukeComment
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3.08 will gettcha around 2000 @ 60
That's what I run. And with a Doug Nash 5 speed I got the equivalent of a 4:56 in the first four gears!
The Rev.Comment
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Re: So which one of use got "promoted", plus...
I used to be an Engineer as well. Then the railroad went belly-up! Just as well cause I was having trouble with them new-fangled diesel locomotives!
The Rev.Comment
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Re: So which one of use got "promoted", plus...
FORTRAN? Gee Duke I didn't know you were THAT old!
The Rev.Comment
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Re: How low can You go?
All these mathematical determinations are GREAT! (and inaccurate). Anything less than a 3.08 will make your Vette feel like you're pushing a piece of wet rope! Even a 3:08 with a T-10 feels "wimpy"! The best STOCK combination I've ever had my foot into is a 3.70 with a 2.20 first. REAL good all-around comprimise.
By the way, if you go with a 3.08, the ideal T-10 will be a WIDE ratio version. This tranny will allow you to take advantage of the entire engine power band!
The Rev.Comment
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Actually, they could come out too low...
...depending upon how fast you spin your rear wheels. If you look at Top Fuelers you will see that their speed is overdriven not by another gear (they are direct drive) but by tire growth.
JPComment
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It's The Peter Principle- Promoted To Incompetence
Duke,
I figured by this time, BOTH OF US would have been promoted to management, AND ONE of us wuz' definitely better off THERE. What else can they do with old, seasoned (hard-headed) veterans except shove them up the ladder or lay them off.
Looks like it wuz' me; No fair using NDB regression theory; I missed that class.
Chuck SangerhausenComment
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Re: FORTRAN. Careful, I still write programs in...
FORTRAN, since it provides standard linkage convention for assembler I/O routines. In addition, my car ahas a 3.08 rear gear with CR transmission, and I think of it as a 3.36 (which my spare pumpkin has) and a WR 5 speed with no 4th gear. Muncie 4th acts like an overdrive 5th. Spin the tites in town, AND get good mileage on the road. - DaveComment
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No! No! - go close ratio with a 3.08
As I said above, the 3.08 with a CR has the low gear effect of 3.36 with WR, but the 4th gear feels like a reach to a 5th gear with overdrive - for highway driving. Also, if you want something in between, their is a gearset for four speeds that was not used by GM that has a 1st gear between CR and WR. - DaveComment
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The term ya wanna use is "How High Can I Go"?
The lower the numerical value, the higher the gear ratio, the higher the numerical value, the lower the gear ratio. Makes sense? No?
Example: 4:11=low gear, 3:08=high gearComment
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And Cheaper than a DN as well!
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