As in our previous installment, one thing truly led to another. This time, it was our cam swap (hydraulic to solid street roller), which led us to this torque converter swap. We anticipated this would happen after the cam swap gave our 509 a smoother idle, more peak torque at a lower rpm, with gains in peak horsepower at a higher rpm. Unfortunately, the trusty Transmission Specialties 10-inch torque converter we've been using all along would be replaced for another unit with less stall speed to better match the 509's new power curve (more low rpm torque, higher rpm horsepower).
We could have removed the old converter and sent it back to the manufacturer so they could modify it according to our engine's power curve. Instead, we took it upon ourselves and picked a converter with a roughly 400-500 rpm less rated stall speed. The new TCI Ultimate Street Fighter converter we chose was rated to 1,200 hp (the previous converter was rated to 800 hp) should we decide to squirt it with giggle gas. With less slippage, the Nova's street drivability and the TH400's upshifts should feel much better. We found that when accelerating in Drive (third gear) and when stepping on the go-pedal there was too much noticeable slippage in street driving.
Dialing in the right converter is a trade-off between slippage and efficiency. Different stall speeds change the efficiency of a converter, so a lower stall torque converter will produce less slippage and more efficiency. The difference from a low stall to a high-stall converter is a give-and-take situation. Usually less stall means less of that slippage feel. When choosing a converter, its best to confer with a reputable manufacturer with every bit of information you have. This way it can build just the right converter with just the right stall speed to reduce that slippage feel when street driving, and get your car down the track in a hurry.
"Getting the right converter is one of the most important things you can do to increase performance in any application," noted Scott Miller of TCI.
After the converter swap was performed, a ride in the local south Jersey Pine Barrens confirmed what we anticipated—improved drivability with less slippage and crisper shifts. In Drive (1:1 ratio), the Nova felt much stronger (again, with less slippage) when punching it at highway speeds. Improved low- and medium-speed drivability was also evident in all types of driving situations in each gear. Our fresh, new converter felt so much better, we anticipated measurable gains on the dyno and at the track. Check out the captions to see how we made out.
1. This trusty converter performed admirably for us for over 1,000 miles and over 50 passes (quarter-mile and dyno pulls combined). While being reluctant to remove it, we were striving for less of that slipping feeling when driving around town and on the highway.
2. We ordered this TCI Ultimate Street Fighter 10-inch torque converter (PN 241004) rated for extreme street/strip applications. It features a heavy-duty front anti-ballooning plate for nitrous applications, and a lower stall (3,000-plus stall rated) configuration than the regular Ultimate Street Fighter (3,500-plus stall rated).
3. Side by side, both 10-inch converters have similar size and appearance, but internally have different stator designs, impellor pumps, and fin angles to achieve their rated stall speed. Our old unit (left) was rated up to 800 hp, while the new converter is rated up to 1,200 hp.
4. By tilting the new torque converter on roughly a 30-degree angle, we were able to fill it with two quarts of TCI Max Shift synthetic transmission fluid. Don't skimp and use el cheapo trans fluid. It's not formulated to handle the higher heat temps in a high performance environment. It's also a good idea to coat the snout of the converter with trans fluid right before installation to prevent tearing the front seal.
5. A few days after installation, we drove the SS509 Nova back to Atco Dragway. We used the same wheel/tire combination (15x11.5 Weld RTS with 28x14.50-15 M&H Racemaster Cheater Slicks and 15x4 Weld Draglites with 26x 4.5 Moroso DS-2 front skinnies) from our previous test session after the cam swap. Our best run on this day was 10.60 at 128.73, down slightly from when we tested last time (10.47 at 129.21. Weather conditions were much worse than they were in our previous test, swinging from 1,303 feet below sea level to 1,671 feet above. This 10.60 corrects to a 10.40 at 131.23 mph. Short times were consistent, with a string of (uncorrected) 1.52 to 1.54 60-foot times.
6. We replaced the aforementioned front Moroso skinnies and the M&H meats (all four are bias ply tires) with front 15x7 Weld RT-S sporting 215/70-15 BFG Redline Radials and 15x11 Center Line's mounted with 325/50-15 Nitto 555 Drag Radials. Despite the radial tires accounting for more rotational weight (46 pounds total), they offer less rolling resistance over the bias ply tires.
7. In the previous strip test, the radials showed us low e.t. On this bad-air day with temps rising and the barometer dropping, the radials came within 0.004 of the lighter bias-ply tires with an impressive 10.64 at 128.05 mph.
8. The different looks of our Nova. Here it's shown with the front 15x7 Weld RT-S and Coker BFG redline radials (215/70R15) and rear 15x11.5 Weld RT-S wearing M&H Racemaster 28x14.50 cheater slicks. Tune in to the October issue of Super Chevy. Our next installment will cover the author and Editor Jim Campisano driving the Nova from South Jersey to the SC home base in Tampa.
9. A close up of the Weld RTS/M&H cheater slick combo.
10. We love the look of the redlines on our Nova. Though you couldn't get them from the factory by 1972, we think the redlines accent our bright blue metallic paint well.