88 2.5 Trans Swap to 5-speed (Page 1/1) 88FormulaDuke APR 27, 12:25 AM Greetings all! I’m recently getting back into Fiero ownership after several years. All my previous 3 fieros have been V6 manual trans, one 4-sp, and two 5-sp. My new car is a an 88 2.5 auto trans. I want to swap this to a 5 speed, partly as its more fun to drive, and partly for better fuel economy with the “economy” gear ratio trans. I’ve got most of the parts to perform this swap, but I’m still in search of the proper transmission. Anyone know how to identify this “economy” transmission? olejoedad APR 27, 08:08 AM The 88 Dukes used the Isuzu five speed. The Isuzu was also used in the 85-87 Duke Fieros. Any of those transmissions would be a good choice. The 84 Dukes had the option of an MY8 four speed, which was geared for economy, with a 3.06/1 differential. Most of the 84 manual trans cars had a 4:10/1 differential in the four speed, the 'performance'gearing. You certainly don't want that one Place an ad in the Mall and see what pops up. fierofool APR 27, 11:15 AM You may not be happy with the Economy Trans. I've driven one, and being only a 4-speed, it's like jumping from 3rd to 5th in a 5-speed. Some traffic situations can be too fast for 3rd but too slow for 4th with the Economy Trans. Revs are either too high, or too low.