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Shop Talk - Things We Waste Time On After Work

August 2014

Like most guys I know, I'm not a shopper. Shopping for clothes, shoes, and even food irritates me because I know I could be using the time doing other things—like getting my C10 running. Yet I can spend hours scouring eBay and Craigslist looking for stuff I don't even need but might be cool to install in the truck. Lately, I've been shopping for transmissions.

After seeing how well our Blue Collar 454 ran on pump gas, I have an unshakeable desire to drop it in the truck, but I don't want to use the stock SM420 four-speed behind that engine. Though they are tough as nails, there are a few problems with this transmission. First, it was designed to work behind a 283-inch engine that didn't make more than 200 hp. It relies on very steep First- and Second-gear ratios to get the truck moving from a stop (First gear is only usable when the truck is fully loaded). After that, the ratios are spaced so a 50 percent drop in engine speed occurs with each gear change. For example, you have to run the engine to 4,000 rpm to get it to drop to 2,000 rpm after each upshift.

The other problem is the monster throw between each gear. It's hilarious at first to drive because the 4-foot-tall shift handle feels tractor-trailer cool, but the shift into Third is actually longer than my arm reaches. I've gotten very proficient at shifting the thing, but the slow shift action and long gates make the truck very slow to drive in stop-and-go traffic, and I don't like constantly being passed by little economy cars.

Replacing this trans with a newer one having closer ratios will make for better driveability, because the engine stays in the powerband with each shift, and an overdrive allows for effortless 75 mph (or more) highway cruising. Though I'd love to bolt up a T56 to our 454, that option may be out of my price range, so I've been looking at used options online.

The New Venture 4500 was used in '93 and '94 Chevy, GMC, and Dodge pickups. I see several for sale on eBay, but the ratios aren't much better than my Muncie. The TR3550 is the predecessor to Tremec's current TKO 500/600 offerings, so it should be able to take some abuse. It has a Ford-style mounting flange, but Quick Time Performance makes adaptor bellhousings to put it behind a big-block/Gen I small-block or an LS engine. The ZF transmissions came behind 6.0L and Duramax engines in later-model Silverado 2500 and 3500 pickups, so it fits what we are planning to do with the truck. I've listed the T56 and Richmond transmissions as reference; it's rare to find either one used, and if so, they command top dollar. We're liking the ZF because we've seen dudes banging gears on dragstrips in 1,200hp diesel trucks on YouTube. It weighs a ton, but it can also handle tons of power, and our C10 has big power in it's future.

Let me know what you think. Would you like to see an in-depth rebuild of a TR3550 transmission? How about an article on performance manual transmissions in general? It's been a while since we ran one, and engines keep making more and more power.

Transmission 1st gear 2nd 3rd 4th 5th 6th
SM420 (Stock) 7.0:1 3.6 1.7 1.00
Tremec TR3550 3.27 1.98 1.34 1.00 0.82/0.68
NV4500 6.34 3.44 1.71 1.00 0.73
ZF S6-650 5.79 3.330 2.10 1.31 1.00 0.72
Tremec T-56 2.97 2.10 1.46 1.00 0.74 0.50
Richmond 6-speed 3.28 2.14 1.57 1.21 1.00 0.76

- John McGann

CarCraft@CarCraft.com
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El Segundo, CA 90245

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