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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Rear Drivelines, Drive Axles and Gearing => Topic started by: TxFiddler on June 09, 2010, 06:55:51 pm
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In my stock 80 LWB C10 350 3spd auto th350, the stock rear end is a 2.73 ratio. I plan on later in the year to either rebuild the stock 350 or get a replacement with at least 350hp. I have been told that I will need to replace the gears in the rear end. What are the drawbacks of keeping the stock gears and going with a more powerful motor? Also, suggested ratios are welcomed. The truck is my daily driver, about 12 miles 1 way with only some occasional highway driving. It's also a 2wd. Thanks.
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Unfortunately, most things you do to increase the power potential for an engine decrease low end torque. Things like adding a bigger cam make great higher RPM horsepower but it will come at the expense of low end torque. Combine that with 2.73 gears and you will have a slug off the line.
Changing the gears would be the best mod you could do. And it's relatively cheap. ;)
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Josh454, I realize that about the hp and torque. I am just looking at giving the 30 yr old original 350 a break. Still runs like a champ but I want something with just a little more "ooh and ahh" factor. Not looking to build a drag truck by no means. If I do go with more power, what is a good ratio to run?
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It doesnt seem to be too hard to get 350 hp out of a small block. Id focus mainly on building an engine for low end torque based on what your describing for your use, and I believe the hp will be close to what you want. Horsepower is more of a higher rpm thing, and torque is what gets you moving anyway, horsepower just keeps you there, and unless youre trying to run 100mph+ for long periods of time, you"ll be just fine with a good torque motor. My 85 K10 is running 3:07 gears ( if I remember right, i forget) with 35s and runs down the highway just fine with a stock crate 350. Takes off fine, and maintains speed just as good. Granted, it wont pull the line on a Camaro, but moves the big truck well. If youre still running the original motor, even a fresh stock rebuild will show improvement, so with a few mods, you'd be happy. If youre gonna race it, or do the occasional burnout, regear it, if your just driving and enjoying it, dont worry about the gears,especially not with a th350 tranny. If it was an overdrive trans, that may be different.
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If you do allot of highway driving I would leave the 2:73s in there. I bet you get pretty decent mileage with them. I had an 84 K10, 2:73s, SM465 trans, Had a 283 in it, then a 305. It was a bit sluggish on take off, but I got 23 / 24 MPG on the highway. About 16 / 18 around town if I drove it normal. I had to use low gear high range to plow allot with it, but it did plow very well. I figured the high gears kept it from spinning as easy. Also seeing as how you don't have an over drive they will keep the Rs down.
On the other hand gears are a fairly inexpensive upgrade to breath new life into even the old truck / motor. 3:42s are a pretty good gear for a combo of driving applications. much lower than that you will be spinning the motor faster all the time without a 4th gear.
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A set of vortec heads, which are cheap ($500 a set), and RPM intake, and a set of 3.42 gears of something around in there will give you the feel you want with decent gas mileage still.
Shawn
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If you are going to keep the 2.73 gears, keep your cam no bigger than about 210 @ .050 depending on what heads, compression, intake etc, you are going to run it's probably going to net something closer to 280-310. I just don't think you would be happy with 1 HP per CI and a 2.73.
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I had a 2.76 ratio with a pretty mild 350 in my truck. I only have 28" tall tires though but even though 2500 RPM at 70 MPH was nice, it was doggy. Then I upgraded my heads and cam but kept the same ratio. I was disappointed with my power upgrade but no wonder with that gear ratio. Then I found a 70's-era 12 bolt with a 3.40 ratio and put that rear end. Much better! 2700 at 60 now on the highway but that's okay. Finding a 3.40 ratio stock 12 bolt to swap with the 12 bolt you have now might not be too hard and it's much easier to swap rear ends for a novice mechanic than to swap gears, IMO.