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Discussion Starter · #1 ·
I'm just about done planning for my first engine build, and so far, thanks to the help of many fellow members here (especially TI), I have most of the parts that I will need picked out. Now I need to figure out which gears would be best for my particular application. It's an 86 chevy pickup. 1/2 ton 4x4. It will be a daily driver, but it definitely needs to have some snot! I'd like decent acceleration but I need to be able to tow the occasional project home as well, so I need some kind of a balance there. Towing is the least important of the two.
Here's the setup so far:
350 block. 0.030" over. 9.012" deck height
L31 Vortec w/ Z28 Valve Springs (0.525" max lift)
1.5:1 Ratio Stamped Steel GM Rocker Arms
Edelbrock Vortec Performer RPM Air Gap Intake
Summit Hypereutectic Flat Top Pistons
COMP Cams Xtreme Energy Cam and Lifter Kit (includes timing set)
-- Hydraulic Flat Tappet
-- 268/280 Dur
-- .477/.480 Lift
Hedman Hedders - Street Headers 1 5/8" tube, 3/8" Flange, 3" Collector
Holley 4160 750cfm Electric Choke Carb
 

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First gear in the 700R4 is 3.06:1, so I don't see any problem with initial acceleration with most any final drive gear and 31" tires. Second gear is a different story. It's ratio drops to 1.63, so there will be a tremendous rpm drop on the 1-2 gear change. Third gear is 1.0 and fourth gear is 0.7.

Multiply the rear gear ratio by .7 to get your final drive ratio. For instance, with the 4.10 that va4cqd advised, it would work out to 2.87:1. On the other end, multiplying the rear gear by the first gear ratio of 3.06 would work out to 12.54:1 and should allow climbing trees or pulling stumps. Not that it would be a bad thing. :D

Most everyone will settle on a 3.73 rear gear with a 700R4 and 27" to 28" tires, but with the 31's, he may be real close to right with the 4.10 rear gear.

4.10 gear @70mph =2200 rpm's
3.73 gear @70mph =2000 rpm's

I might use the 4.10 gear for improved passing on the freeway and because 2200 cruise rpm's on the freeway would be acceptable to me, but not because I would need more gear in first gear. :eek:

The cam I chose for the build is spec'd by Comp as the largest cam to use with a stock converter and so should work ok. If you want a little more umph on acceleration and less roll against the brakes at a stop sign, you might use a little more converter.
 

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If I were going to change it at all, I might be inclined to go a little tighter, 1800-2000, with a unit such as the Hughes part# GM22LTow. It's specifically designed for 4x4 trucks. Here's the blurb on it....
"Tow Master 1800-2000
Our severe duty performance converter used in many late model trucks, crew cabs, 4x4's and motor homes will increase bottom end pulling power without sacrificing top end efficiency or lock-up. Mileage is increased by as much as 1-2 miles per gallon. Recommended for slightly modified engines."

I'm recommending Hughes because I have known Jim Hughes for over 20 years and I know him to be a man of the highest personal and business integrity. He'll stand behind his work.

Now, I'm definitely not the know-all, see-all when it comes to torque converters, but Jim and the boys are. If I were you, I'd call 'em up and get a professional recommendation. A converter is a pretty good chunk of change to spend if I'm wrong. Tech Line: 1-800-274-RACE
 

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Discussion Starter · #9 ·
Found someone that has a B&M 2500 Stall Converter. he claims there's only 2500 miles on it. assuming he's asking a reasonable price for it, would it be a good option for the setup?

Also, one of you says 4.10, one says 4.88.
Pros and Cons of each???
 

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4.88 well give it more power around town compared to a 4.11. But, 2600 rpms at 70 mph is a little busy by todays standards. If you don't plan to make long trips down the highway (over 30 miles) then it will not be a big issue.

My truck runs 2600 rpm at 70 with a 3.08 gear, 28 inch rubber, and th400 and it seems it needs more overdrive to me. nice at 60 but starts to get busy at 70 and 75. 80 seems like a big waste of rpms (3000 rpms). But I have a small cam (206/212 at 0.050') and it makes the engine seem like it doesn't like rpms. bigger cams make the engine rev easier.

4.11's will still run fairly strong around town. but will really shine going down the highway with a 700r (2200 rpms at 70).

Maybe split the difference and go with a 4.56. (2430 rpms at 70 mph) with a 14:1 first gear ratio (really like a 12.6:1 due to the 31 inch rubber).
 
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