My signature...
I'll include my signature with this.
Bill said that if I were to tow anything heavy (which I have done and still plan to do), I would need to have around 230 hp to sufficiently run the 91% converter. An 89% TC would probably require less hp. They are both considered "low stall" converters and are WORLDS better than stock.
I can't see your signature, so I'm not sure what hp you're putting out now. If you're stock 215 hp, you could advance your timming to around 15. 5 and do some internal pump mods to increase your hp a bit and you probably wouldn't have to buy any other upgrades.
I was running stock 160 hp and couldn't reach the 230 sufficiently with internal mods... so I went for broke and upgraded my Delivery Valves, Injectors, Exhaust, and Intake Filter.
91% will pull your engine down (sounds and feels great) a little more when idling than the 89%. 91% + a heavy load AND not enough HP, you could stall the engine. 89% has less of a tendency to stumble at launch or stall the engine than the 91% but won't take high HP and very heavy loads quite as well as the 91. There's the trade off. Note: I have virtually no stumble with my set up.
I wanted something that would tow hard, but didn't want any stumble at launch. 91% for towing vs 89% for less chance of stumble... . humm???? I debated this heavily for several weeks.
Called Bill. He said that given my anticipated HP with the upgrades AND my intended towing, that he wouldn't sell me the 89%. It needed to be a 91% to perform and last as needed for what I would be using it for. He did however, soften the setting somewhat so that it would respond a little more like the 89%, but still have the tighter fluid coupling of the 91%. I'm actually glad I have the tighter converter and more power transfer to the ground.
I'm not sure what adj's he did to "soften" the 91 a little (definition was probably over my head). I also had him include the 2nd gear band strut and an additional setting in case I ever added an engine break. I also had him narrow the shift points from 3rd to 4th so that there isn't such a long jump between them. I'm EXTREMELY happy with the way it shifts up and down and either empty or when towing. All aspects are MUCH more enhanced over stock. I can actually feel it downshifting and holding back when slowing down - something that was almost non-existent when stock.
If your not towing much, you might be happier with the 89. I'm very happy with my 91 - both towing and empty. Sucker lays it down!!!
PM me if more ? Glad to help. Send me your phone number and I'll call you.
- Ben