Lock Up Torque Converter ?
Le Mans Master
Joined: Apr 2005
Posts: 6,349
Likes: 419
From: Seattle Area WA
This is probably way over simplified, but it does just what it implies. At speed it locks up to transfer as much power to the rear wheels without frictional losses due to internal slippage.
Here is a cut and paste:
Lock up stock style converters. These are usually 12" converters that have a lock up clutch in them. Modified versions can have a stall speed of 2600-2800 rpm, depending on the construction. The lockup clutch is engaged under light throttle situations (cruise), which allows for greater efficiency, less heat generation and slightly better mpg. When racing, you can lock the clutch under WOT with a switch or with a race chip. This practice will gain about a tenth in the 1/4, but will eventually wear out the clutch.
Non-lockup converters. Available in various diameters. The most popular version of these is a 9" converter that stalls in the 3000-3200 range. There is no lockup clutch, so at cruise there is some slippage (200-300 rpm usually). They work very well on big cam/turbo combos. You trade off some heat generation (from the slippage) and efficiency losses, for the responsiveness gained. You need to make more HP to gain enough advantage in staying in the "sweet spot" of the RPM/torque/HP band to overcome the slippage losses and reduced efficiency.
9" and 9.5" lockup converters. These are hybrids that try to combine the best of both worlds. They allow for the higher stall and responsiveness. However, due to the smaller size, there isn't as much clutch surface available, so if they are locked up under WOT you can burn up clutches fairly quickly. Newer 9.5" converters are built with more clutch area to counteract this, while still allowing 3200-3500 brake stall.
The non-lockup style converters have more "slippage" by design. A properly operating clutch converter will have less slippage (even unlocked, due to its lower stall speed). Going to a higher stall converter is usually necessitated by the owner also installing a bigger turbo and/or camshaft. Therefore, before you buy a new converter, discuss your combination with the potential vendor to decide which converter is best for you.
Here is a cut and paste:
Lock up stock style converters. These are usually 12" converters that have a lock up clutch in them. Modified versions can have a stall speed of 2600-2800 rpm, depending on the construction. The lockup clutch is engaged under light throttle situations (cruise), which allows for greater efficiency, less heat generation and slightly better mpg. When racing, you can lock the clutch under WOT with a switch or with a race chip. This practice will gain about a tenth in the 1/4, but will eventually wear out the clutch.
Non-lockup converters. Available in various diameters. The most popular version of these is a 9" converter that stalls in the 3000-3200 range. There is no lockup clutch, so at cruise there is some slippage (200-300 rpm usually). They work very well on big cam/turbo combos. You trade off some heat generation (from the slippage) and efficiency losses, for the responsiveness gained. You need to make more HP to gain enough advantage in staying in the "sweet spot" of the RPM/torque/HP band to overcome the slippage losses and reduced efficiency.
9" and 9.5" lockup converters. These are hybrids that try to combine the best of both worlds. They allow for the higher stall and responsiveness. However, due to the smaller size, there isn't as much clutch surface available, so if they are locked up under WOT you can burn up clutches fairly quickly. Newer 9.5" converters are built with more clutch area to counteract this, while still allowing 3200-3500 brake stall.
The non-lockup style converters have more "slippage" by design. A properly operating clutch converter will have less slippage (even unlocked, due to its lower stall speed). Going to a higher stall converter is usually necessitated by the owner also installing a bigger turbo and/or camshaft. Therefore, before you buy a new converter, discuss your combination with the potential vendor to decide which converter is best for you.
Last edited by Scott Marzahl; Jan 11, 2008 at 05:25 PM. Reason: added info
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Saying it a different way, the torque converter is a "fluid" coupling of the engine and transmission gears. With any fluid, there are slippage losses, because it is not a solid mating of engine and tranny (like a std. trans. clutch). The lockup clutch performs that purpose...it mechanically connects the engine to the mainshaft in the transmission, so there are NO slippage losses. Better mileage, lower operating temps, etc. are the benefits. The LU clutch is activated electrically, when the relative speeds between the engine and trans are close to the same; when the relative speeds are much different, the trans stays in convertor mode so you don't get jerky shifts.
