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Originally Posted by aaron ford
I saw a previous post that OBS trucks are limited to 65HP tunes. What determines this limit? Oil? Injectors? EGT's?
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The "limit" on power output for the 95-97 trucks comes from the comparatively lower fuel injector output capability versus the 99-03 trucks. So you are right when you suspect the injectors for this limit. EGT? Hardly. With a 3" downpipe, it's REALLY hard to get above 1200 degrees even with a fairly radical tune.
You have a great start with your truck as far as modifications go. Especially with the 17 degree HPOP which opens up a larger arena for larger injectors down the line.
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Originally Posted by aaron ford
Also what are the differences between FS, DD, Perf and Tow? I have read that throttle tip in and shift points are changed, but which would way to go in hilly terrain? Low speeds on the hilly twisty one lane to work?
I also tow 7K a few times a year through Appalachia.
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Fuel Sipper's only real obvious trait is that it alters the amount of injection on throttle tip in. It's a great-running tune but runs like stock with less throttle input at 1/2 throttle or less....especially when the engine isn't up to operating temperature. However, it will improve economy as long as you don't drag race from light to light with it....it almost HAS to. More transparent are the injection "timing" and the injection control pressure in the cruise rpm/load ranges.
Daily Driver tunes are designed to take the mundane out of every day usage. Your accelerator pedal is responsive, your power goes up, the shifts aren't quite as mushy, etc. Your truck becomes more fun to drive to work (and face it, we all need help with putting "fun" in work).
Performance? Firm, later shifts, early torque converter lockup under load, and lots of power to put to the ground.
On hilly terrain, I'd recommend towing tunes....even while empty. These trucks shift VERY early under light-load conditions. The problem is that unless your programs are designed to shift a little later than stock, you will be in and out of certain gears at certain speeds. Fuel Sipper and some Daily Driver tunes don't change the shift speeds much (if at all) so hilly terrain may not be the best usage of these programs.