1971 Chevrolet Nova - Transmission Conversion - TH350

Swapping a quick-shifting three-speed automatic trans in place of SuperNova’s wheezing two-speed along with a high-stall converter and a ratchet shifter dramatically improved upon last month’s dismal dragstrip outing—we knocked nearly 2.5 seconds off the ET and gained a whopping 16 mph in the quarter! The resulting 13.50 at 112 mph illustrates just how traction limited the car is with a pegleg rearend and radials, but it does good burnouts.
Swapping a quick-shifting three-speed automatic trans in place of SuperNova’s wheez
Converting any Powerglide-equipped GM car to a TH350 (foreground) is a breeze, because the three-speed trans shares the same overall length and mounting dimensions as the Glide (rear), making it a no-brainer bolt-in using the same crossmember and driveshaft.
Converting any Powerglide-equipped GM car to a TH350 (foreground) is a breeze, because the

The Powerglide converter (right) is not interchangeable with the TH350’s (left), in this case a B&M Holeshot 3000, which is rated at 3,000-stall with a mild street engine. It should stall a bit higher than that with our torquey 383. Read What's Up With Stall for more information about converters.
The Powerglide converter (right) is not interchangeable with the TH350’s (left), in t
We’re fans of the stock look, but speed-shifting with a column-mounted stalk is a dicey proposition due to the incredible ease of accidentally shifting into Neutral or even Reverse. We opted for a B&M Pro Ratchet racing shifter, which despite the name, is very user-friendly on the street. The reverse lockout is NHRA-legal, and gears can be quickly selected with a quick fore-or-aft bump of the stick.
We’re fans of the stock look, but speed-shifting with a column-mounted stalk is a dic

The preassembled shifter mechanism mounts to the floorpan with four bolts. We’re keeping the Nova’s bench seat for now, so we had to mount the mechanism slightly farther forward that we would have liked, but it’s still within a comfortable arm’s reach.
The preassembled shifter mechanism mounts to the floorpan with four bolts. We’re keep
To avoid pulling up the rubber floor mat, we drilled the four mounting holes from above then cut the access hole for the shifter cable (arrow) from below with a 11/2-inch hole-saw.
To avoid pulling up the rubber floor mat, we drilled the four mounting holes from above th

The Pro Ratchet shifter has provisions for both a Neutral safety switch and backup lights through two micro-switches (arrow) mounted to the side of the mechanism. They’re wired into the respective circuits on the column.
The Pro Ratchet shifter has provisions for both a Neutral safety switch and backup lights
Next to not being able to push-start a car with a dead battery, the most aggravating feature of life with an automatic transmission is dealing with leaky cooler lines, but at least our new reproduction lines from Inline Tube give us a head start on any problems. The prebent mild steel lines went in with a minimum amount of fussing.
Next to not being able to push-start a car with a dead battery, the most aggravating featu

The open headers were bugging the neighbors, so we took the Nova to an exhaust shop and had a quick 3-inch system built using Dynomax Ultra Flo mufflers.
The open headers were bugging the neighbors, so we took the Nova to an exhaust shop and ha
Project SuperNova, Part I: Meet Supernova, Car Craft’s Newest Project Car
Project SuperNova, Part II: Swapping In A Small-Block Chevy Engine
Project SuperNova, Part I: Meet Supernova, Car Craft ’s Newest Project Car Proj

OK, so maybe on second thought, running a stock Powerglide and converter behind a 540hp engine last time wasnt such a good idea. Call it an experiment, but all we proved during our SuperNova project cars maiden voyage down the quarter-mile was that blowing up the converter and not being able to shift the car leads to really bad track performance. A 15.80 at 95 mph wasnt exactly what we were hoping our 71 Chevy Nova would run after we swapped in the thumping 383 small-block, but we fortunately already had a better transmission, converter, and shifter ready and waiting, and the stock Glide was cast off in the driveway virtually as soon as we got home from the track. Swapping in the rebuilt Turbo 350 with a B&M Holeshot 3,000-stall converter and Pro Ratchet shifter took about a full days work, and the results were well worth the effort.

We trucked a junkyard TH350 core to a local transmission shop and had it rebuilt using a B&M TransKit, which incorporates heavy-duty clutches, new seals and gaskets, and provisions to convert the valvebody to manual/automatic operation. This feature allows you to select your own shift points by shifting the transmission manually through the gears, or to simply slap it in D and let it shift itself.

Bolting the TH350 in place of the Powerglide is so straightforward it barely merits description other than to say its a direct bolt-in. If you intend to keep the stock column shifter, there are kits available from resto companies like Year One and Classic Industries to convert the shift selector to three-speed operation, but if you use a floor-mount shifter like we did, theres nothing to worry about. The crossmember, trans mount, and driveshaft can all be reused with no modifications. You may have to tweak the cooler lines slightly, but we needed new ones anyway, so we got the proper TH350 parts from Inline Tube.

At the track, driveability and performance improved dramatically (see Dragstrip Results sidebar), with the high-stall converter and three forward gears keeping the engine in the sweet spot of its powerband, but the car still has a horrendous traction problem with the 3.08-geared pegleg rearend and radial tires. On one pass, we smoked one rear tire for 1,200 feet! We also didnt have a tach to monitor shift points, so this outing is far from the cars full potential, but were getting there

SOURCES
B&M Performance Products 8-18/-882-6422 bmracing.com	Inline Tube 33783 Groesbeck Fraser MI 48026 810-294-4093
BFGoodrich Tires 877-788-8899 www.bfgoodrichtires.com	Wheel Vintiques 5-59/-251-6957 wheelvintiques.com