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this site will give you some specifics
http://www.vcoa.org/700-900-faq/TransmissionAuto.html#TurboLockupTorqueConverterFunction
Lockup Torque Converter Function for Turbos?
[Inquiry] Can I install a locking torque converter in the non-locking transmission in my turbo car? Fuel economy is better with the AW70/71L units than with the AW70/71.
[Fitz Fitzgerald] A 700 series Volvo Turbo car would have come fitted with an AW-71 transmission (non-lockup). The 71 series are a bit stronger mechanically speaking, and there are some differences in the valve body to help it respond better to the torque and HP curves of a turbo engine. US market Turbos (and quite possibly the rest of the world too) never received L series automatic transmissions. The Turbocharger's response curve is directly dependant on the engine RPMs and if you had the lockup engaged, the engine RPMs are now directly coupled to the vehicle speed. Much of the extra torque and horsepower that a turbocharger can provide requires that the engine can rapidly climb the RPMs. Aisin Warner lockup trannies aren't well known for the ability to quickly disengage the Lockup TC, unless you drop down to 3rd gear in which case the response is almost instantanous.
To convert any AW70 equipped car to AW70L, you must swap both the transmission and the torque converter, since the valve body controls and additional converter clutch are different from the non-lockup versions. The torqure converter has the lockup clutch inside it, and the transmission has a special valve body and hydraulic actuactor that enables/disables the clutch. You can't just swap the valve body either, you need to swap the entire tranny. If you are looking to install an L series tranny in a turbo equipped car, they did make an AW-71L series tranny and it can be found many of the 940 non-turbo wagons. The US spec turbo cars only received the AW-71 during their entire production run. This should be "plug and play" but make sure your detent/kickdown cable is properly adjusted after installation. If you tighten this cable, the transmission will shift at higher RPMs, if you loosen the cable, it will shift at lower RPMs (this will effect every shift point, not just your 3-to-4 shift). Find the spot that's best for your driving habits.
[Inquiry:] My 1989 745T with AW71 has a lock up torque converter that is locking and unlocking too much. At some speeds and loads and boost levels, it constantly locks and unlocks until I either back off or speed up.
[Abe Crombie] A US market spec Volvo rear wheel drive turbo doesn't have a locking converter. If yours has a locking converter the ID plate on driver's side of gearbox will read 03-71L or possibly 03-70L if someone has changed it. The lockup control in either case is a function of it being in 4th gear and governor pressure reaching approx 50 psi. A lock/unlock at threshold of locking speed can be caused by a worn bushing in tailhousing allowing the gov. pressure to fluctuate. This can be checked by attaching a trans press. gauge and reading the gov. pressure at speeds around 45-55 mph to see if the pressure is stable as speed is brought that range gradually.
[Gene Stevens] The only AW71L gearboxes available in NA behind the B230F (not turbo) do NOT have the same valving or number of clutch plates as the turbo version. Same for the AW70/70L used before 1992. It is a light duty version and will not live long behind a turbo engine, regardless of the "71" designation. The reason a lockup converter was used with turbo in Europe, but not NA, is that the higher 120-140 kmh highway speed allowed the turbo to stay in boost range but US/Canada 80-90 kmh speed lowered engine (and turbo) speed too much for good performance. The theories of weak converter clutch as the reason are baloney.
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