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Torque Converter Upgrade: Installation and Testing

Our initial inclination was to open up the parts catalog and order an off the shelf torque converter. But after hearing some horror stories about such converters not performing well and even falling apart, we decided to get some recommendations. We noticed a few cars at our local track with Emerald Torque Converters decals, and considering they were local (Walnut Creek, CA) we decided to give them a call.

Emerald asked us details about our car, gearing, and engine, and based on our responses they suggested a 2800 stall non-lockup converter. The cool thing about Emerald is that their converters are built to the customers specific requirements, they don't try to fit you with a generic converter.

We spent a morning at Emerald's shop installing the converter, and the following weekend we took the car out to the strip.

Our initial impressions could be summed up with a huge grin on our face. A stock 5.0 engine is torquey as it is...throw in a converter and you may as well buy stock in Goodyear. The stock 225-60-15 tires are simply ill suited for the immediate torque shock. With the stock converter the torque builds gradually and max torque doesn't hit the tires until the car is in motion. With the new converter, stabbing the throttle just halfway results in tire spin. It took a few stoplights to teach ourselves to leave softly.

Other than the feeling we've added 50 more lb.ft. of torque to the motor, the converter has no major side effects in terms of driveability. Because this converter does not lockup there is about 200-300 rpm worth of slippage in drive and overdrive. With the stock converter the engine at 65 mph would turn at approximately 2200 rpm, we're now noticing it turns closer to 2500 rpm. While you'd expect some loss in fuel economy due to the increased rpm, our mileage in fact has remained exactly the same. We figure this is because we're not having to downshift from OD to D as often in order to accelerate and pass. The non-lockup converter reacts so fast in overdrive that there is very little need to downshift at freeway speeds.

One of the side effects of a higher stall converter is dampening of the shifts. With the stock converter and a TransGo shift kit we could bark the tires during 1-2 and 2-3 upshifts. With the new converter the transmission still shifts fast, but the shifts are softer than grandmas Cadillac.

We contacted TransGo to see if there was a valve body modification which would bring back some of the hard shifting we were used to. They recommended we upgrade the 1-2 valve with the "blue" spring (included in their shift kit). So we dropped the pan and valve body and swapped the green spring for the blue one. This resulted in bringing back the 1-2 bark at wide open throttle. We also installed a transmission fluid cooler, since the higher stall and slippage generate more heat in the transmission, which can also lead to soft shifts. If we really wanted hard shifts in all gears, the only other solution would be to rebuild the transmission with specific modifications to the fluid passages. We'll live with it for now.


Upgrade the 1-2 valve with the "blue" spring in the TransGo shift kit to firm up the 1-2 shift.	High stall converters generate heat, which is the enemy of automatic transmissions. Install a fluid cooler!

We took the car out to Sacramento Raceway to get some objective results from the converter upgrade. Unfortunately the weather conditions were worse that when we had baselined the car with the stock converter. Temps were in the high 90's, humidity was high, and barometric pressure was low (mid 29's) - about the worst conditions for racing.

Nevertheless the car gained a tenth over its best ET (13.84@97.5 versus 13.94@99.7) with the stock converter. We were down 2mph, but so were most of the other cars. We figure in better conditions there is at least another tenth in the converter. Keep in mind, this is launching easy on street tires, with 60 ft. times in the 2.0 range. With slicks and a full throttle launch a couple more tenths off the ET can be expected.
(see timeslip log for Project '88)

We took the '88 LX to Sacramento Raceway to test out the new converter. The car ran 13.84, a tenth faster than with the stock converter, in very hot weather and on stock radials. There is at least another tenth or two with cooler air and slicks.

Making Torque

Gary Mladinich is the brains behind Emerald Converters. We spent a couple hours with Gary discussing what makes Emerald Converters far superior to any of the off the shelf brands. Gary spends a considerable amount of time upfront ensuring the converter matches the customers stall speed requirements. The size, number, and pitch of the vanes in the turbine, impeller, and stator are major factors in determining the characteristics of a stall converter. Two converters which are rated at the same stall speed may feel and react completely different based on how they are constructed.

Gary pointed out also how the internals of many aftermarket converters are no stronger than stock. While they may achieve the stall speed, the internals are not meant to handle the power and the converter is prone to fail.

Building a powerful converter means having the right components and cores on hand. Gary explained that the typical 9" and 9.5" (245mm) converters are based on cores from GM front wheel drive 4T60 transmissions. They are preferred because they come in eight different impeller vane angles, and are also a good physical size for obtaining higher stall speeds.


The vanes of stock and many off the shelf converters are simply slip-fit into place. Fluid under high centrifugal force causes the vanes to flex or bend, resulting in a loss torque transfer, and eventual breakage or bending. Furnace brazing (top right) is a popular feature on many converters, but the vanes can still be flexed easily.
		Emerald converters feature tig welded vanes on both the impeller and turbine for the ultimate in strength and resistance to flex. For high power applications Emerald offer a double bladed turbine upgrade.

		Precisely machining clearances within the converter can make the difference between a poorly reacting converter and one that snaps you back in your seat at the slightest tip of the throttle.


Other strengthening features include a hardened steel impeller hub, billet front cover, anti ballooning flange (shown), and hardened stator sprague and race.		A sprague eliminator is also available for all-out race cars requiring constant torque multiplication.


The converter halves are precision welded using a robotic welder.		The finished converter is checked for leaks and balanced, then shot with the trademark Emerald green paint.