Ryan,
I'd pick the 3.50 (or a 3.70 if one is available).
At cruise you can't really tell the difference between 2300 and 2700 RPM.
Not your ear - maybe your gas gauge can....
I've got a 72 with a big block, THM-400. Ran 3.07 in it for a long time, now
have 3.73. Big difference in initial acceleration, hardly noticeable at
cruise. MPG never was any good anyway.
Economics aside, you won't hurt an engine to cruise at 3500 or 4000 RPM. My
1970 C-50 has a two speed rear end and the high ratio is something like
6.83. Of course it uses 38 inch tires, but if you run 65 it tachs about
3500. Seems to go on all day like that. That said, I picked up a Brownie
manual overdrive to cut that RPM by 20%. Cut the RPM to 3200 and boost the
cruise speed to 70. With a nice set of pipes its just music.
By the way, one of my projects is a 56. Am planning to leave the original
rear end in it (if it turns out to be in working order) and use a 56 vintage
3 speed with overdrive. Probably will get a 350 as I have a couple lying
around.
What did you use for front motor mounts? I'll have the bell housing with the
mounts on it, so a wide stance on the front isn't required. Can the front of
a 350 be drilled for the old front mounts?
Gwyn Reedy
Brandon, Florida
mailto:mgr@mgrcorp.com
> -----Original Message-----
> From: owner-oletrucks@autox.team.net
> [mailto:owner-oletrucks@autox.team.net]On Behalf Of BORDER,RYAN
> (HP-FtCollins,ex1)
> Sent: Friday, December 15, 2000 3:49 PM
> To: 'oletrucks@autox.team.net'
> Subject: [oletrucks] Gear Ratio wisdom sought
>
>
> In brief, I need to select the gear ratio for my rear axle, and
> am hoping to
> tap some of your collective wisdom.
>
> 55 Task Force
> Mildly tweaked 350cid (Headers, Manifold, Cam, etc.)
> TH-350 3spd tranny, 1:1 3rd gear
> Building for 30.9" Diameter rear tires
>
> Churning my calculator, I've come up with a magic number of 761.5: to
> convert a Gear Ratio to 70mph engine rpm's. For instance, 3.50
> gears should
> give me (3.5*761.5) 2665rpm at 70mph.
>
> Now, I just need to figure out what I'd like my highway cruising
> rpm to be,
> and I'll be ready to buy a ring and pinion.
>
> One one hand, a low gear ratio would definitely be a benefit at cruising
> speed.
> On the other hand, the truck will see a lot more in-town use than highway
> use, and just for grins, it would be nice to have a little snap off the
> line.
>
> Yeah, I know, in the perfect world I'd change to a 4-speed
> overdrive tranny
> and have the best of both worlds ;-). Then again, I could also
> put a blown
> big-block in it... in either case, if I one day decide to persue either of
> those options, I'll probably be able to spend $100 on a new ring
> and pinion
> gear to match. So, for now, I'm focusing on how to optimize for what I
> have.
>
> Given my setup, what would you guys recommend as a good compromise? Some
> possible alternatives:
>
> ratio 70mph
> 2.50 1900rpm What my rear end has in it now
> 3.00 2280rpm
> 3.25 2475rpm
> 3.50 2665rpm Common F-150 ratio
> 4.11 3129rpm Conventional street/strip gears
>
> What would you do??
>
> Ryan.
> oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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