Thread: What is K-factor "R115" on 4T65E TC?

Trannyman will probably have to answer that as I have no idea.

I know this is an old thread, but I'm rebuilding a transmission to use in my Regal which lists the "R115" K-Factor. Anyone ever figure out an answer?

Unfortunately these numbers are pretty useless to the real world and unless you know someone that works at Hydramatic with correct info, but even the stall ratings are way off on the supercharged cars so its not a big deal to worry about. They rate the stall speeds around 1700 rpm and they really stall close to 3K rpm on an M90 car! These converters were also used in some of the bigger-bodied cars such as the Bonneville and used with the NA L36 engine and would stall closer to the actual rating

I'm not worried about the actual stall speed, I'm just trying to get a handle on how the different stock converters compare to each other. If R115 is really just 115, it's going to stall lower than a 133, which will stall lower than a 155, right?

I dont have a converter book handy now, but here is the breakdown of how the 258mm converters stall from lowest to highest and you can compare this with the K-factor ratings.

LOWEST stall rpm

"JSFM"
"JTFM"
"JZFM"
"JXFM"

HIGHEST stall rpm


JSFM converters where used with most NA Bonnies and larger cars as well as a lot of Buick and larger bodied cars with the L67. The JTFM is the converter that came with most W-body L67 cars from 97-02/03 . Around the 02/04 time frame most of the L67 and L32 cars started coming with the JZFM converters. The 3.5L dohc engine equipped cars such as the Oldsmobile lineup used the JXFM. Keep in mind the stall ratings again are different depending on which engine they are matched to, so a JSFM matched with an L67 may stall higher than than the JXFM with an NA engine. The K-factor info is not given on all converters either and I have even seen a few OE converters from GM that dont even have a code at all on the converter just a part number so that throws more of a mess into the pot!

hmm, the converters listed as "R115" K-Factor are listed as JZFM. That should put it right between the 155-K JTFM and the 163-K JXFM. Very odd, but also very useful. I realize that the engine will change everything as far as actual stall speed, but having a basis to compare one to another is all I need, not actual stall speed. Thanks a lot, Dave!