To4b80 Turbo questions

It's been 45 years, but I'm pretty sure the D-21 and D-19 used the SAME turbo, which was a Thompson brand which later became a Rajay. I always thought that was interesting, but that D-262 couldn't stand much boost and the bigger size was just what it took to keep boost relatively low.

TO4B80's came with 2 different exhaust housings. The D19,190,200 all used the .69 A/R housing. The 7020 and some combines and industrial (gen sets) used the .58 A/R housing for about 2#'s more boost or the same boost at lower RPM.   The TO4 B90's were used on the 426 engines up to the 8000 series. They used 2 housings as well. Some combines, industrials, used the smaller .8 A/R  but most had the .96 A/R housing.  The smaller A/R housings forced more air to the turbine and spun it faster for more boost. The larger A/R's allowed some gases to escape around the turbine. The A/R # is usually stamped in the exhaust housing inside or on the radius. (some of the later China, perhaps, castings have no stampings)  

Edited by tbran - 01 Feb 2025 at 9:10am