Brazed Vs. Non-Brazed Bowls...
Brazed Vs. Non-Brazed Bowls
On non-brazed bowls (left), fins are pressed in and bent over and can work loose over time, making bad stuff happen really quick and usually really messy. The furnace-brazed bowl has outer fins that are TIG brazed after they have been bent to the desired angle. Brazing and TIG welding the fins as Phoenix does creates a much stronger assembly, and keeps fins from working loose or bending under extreme load and rpm.
According to Phoenix, this converter has a flash speed of up to 3,200 rpm, but drives like a much tighter converter. The idea is that we wouldn't even notice we had a high-stall converter until we nailed the throttle. It sounded perfect for us, but would it deliver the goods? We threw it in the trans, and hit the road for some road testing before our date with the chassis dyno. Ducato had warned us that if it was too tight, our relatively big-cammed small-block might want to stall at idle when placed into gear, but we had no problem keeping the 408 lit. That was a good sign. Next, we did some around-town driving, trying to see if the revs would still flash way up while pulling away from the light modestly. We quickly discovered that unless provoked, our new converter was very well mannered in traffic, a bonus considering our obnoxiously loud side-exit exhaust. Next, we accelerated hard on the highway on-ramp, pushing the engine toward redline and digging deep into the converter's meat. Even with Nitto Drag Radials, the posi rearend broke loose with ease, proving that the bigger converter still had the torque multiplication we'd need for dragstrip duty. On the freeway, with the converter locked up in Fourth, the high-strung small-block settled back into a deep freight train rumble. So far, the larger 258mm converter had performed as advertised.
Back on Westech's Superflow chassis dyno, we elected to do an unaltered baseline test, realizing that should there be a dramatic difference, we'd probably need to reconfigure some of the jetting to the carb. On the very first pull, the dyno registered 434.9 hp (5,900 rpm) for a gain of 69.3 hp. The bigger converter was clearly showing more efficiency, so Westech's Ernie Mena began a tuning loop using the facility's wide-band O2 monitoring equipment. With the converter's flash point occurring another 500 rpm lower, the engine was now demanding more fuel earlier, and after a few changes to the primary and secondary jetting (pulling fuel out of the secondaries and adding it to the primaries), and upping the size of the squirters, the Laguna's small-block pushed the pony count north to 441.9 hp (5,900 rpm) with 431.3 lb-ft of torque (4,800 rpm). The increase in output over the smaller, less-efficient converter was 76 hp and 23 lb-ft of torque. We were stunned.
These are two stators from...
These are two stators from the 9.5-inch 245mm GM converter series. This is the converter on which so many aftermarket converters are based in the over-2,800-rpm category. You can easily see the difference in fin angle and opening between the fins. All other components being equal in the converter, simply changing from one of these to the other can make a difference of several hundred rpm in stall speed. With the 245mm converter, there are dozens of possible stator and fin-angle combinations to produce stall speeds from 2,600 to over 4,500 rpm. The trick is to know which combination to use.
That's a lot of increase, but it remains to be seen if that translates into real performance at the dragstrip. It's really important to note that a chassis dyno is not the best tool for evaluating converter performance, simply because it treats all cars as if they weighed the same. (The dyno's inertial roller drum acts as a proxy for the mass of the car, and is usually much less.) We do not want to convey the idea that a larger converter is always going to be better. It may be for some cars, but it really is an individual thing. In our case, our initial chassis dyno numbers were so far off from our engine dyno numbers, that most likely any tightening would've shown an improvement at the wheels, and that's why we did it before hitting the track. Another point we want to make is that our Laguna is on the extremely heavy side at 3,900 pounds (and that's a conservative estimate). At race weight with driver, it's looking more like 4,100 pounds. Our looser, 245mm converter would be right at home in something like our 3,660-pound '68 Chevelle. Said another way, the same converter when put into two different cars with two different engines will behave in completely different ways.
We hope to get out to the dragstrip soon to see what the real result is. We think a realistic goal would be to go 12s with drag radials, and eventually low 12s with slicks. Once we fix a few things, we'll hit the track.
After we swapped from Phoenix's...
After we swapped from Phoenix's smaller 9.5-inch (245mm shell) converter to their 10.15-inch (258mm shell) converter, we took the Laguna back to Westech Performance for another session on the Superflow chassis dyno. Here, Westech's Ernie Mena makes an adjustment to the carb squirters. We found that the tighter converter turned on sooner, demanding more fuel at a lower rpm. For that, Mena added some jet to the primaries. The bigger squirters helped eliminate a dead spot when rolling into the throttle off idle.
How Not To Build A High-Stall...
How Not To Build A High-Stall Converter
Notice how the "builder" of this 298mm converter was going for "maximum" stall speed here. Unfortunately, in creating the highest stall speed, he also created a giant heat pump incapable of good hydraulic lockup, and wasting engine horsepower that would have never made it to the rear wheels. Note how the center fins have been bent over with a chisel and the outside fins are bent at the most negative fin angle possible. If the builder had selected a smaller cover and pump to begin with, the high stall could have been achieved without sacrificing the efficiency of the converter. These kinds of decisions are usually the result of someone who needs lots of stall, but has very little money to spend.
The dyno shows the huge improvement...
The dyno shows the huge improvement in torque converter efficiency, with the red traces showing the first converter, and the black traces showing the larger, tighter converter. Max torque with the first converter was 407.8 lb-ft (4,400 rpm), and max power was 365.6 hp (5,700 rpm). The tighter converter maxed out at 431.3 lb-ft (4,800) rpm, and 441.9 hp (5,900 rpm).