Originally posted by c55m8o
hold your opinion until you see it calculated out though (I'm tell'n ya, get CatTest2000 )... I'd say after seeing the runs, you shouldn't underestimate the impact such a drop-off in torque @ high RPM can have, and how that works against raising the rear-end gear ratio, too much. Hey, I was a =die-hard= advocate of converting my rear to 3.45:1 ; that is, was, but not with this engine's torque rolling off as it does @ high rpm .

yes, CarTest2000 also says 3.07 is pretty much the optimal rear. What I was saying was it also proves out that going longer (to 2.82:1) would be better with that engine then going to shorter gearing (to 3.45:1).

BTW, raising the gear ratio is not all upside ; there's trade-off there too, since the shift occurs a few mph sooner in each gear when you have shorter gears; (I hope I can explain this right) ... for the few mph difference between where it shifts with the shorter gears, compared to where it used to shift with the longer stock gears, acceleration is actually =lower= because you have less torque multiplication working for you, as you're in the next higher gear. Less "F", same "m", less "a". So that actually takes more time to get through that few mph range, then with the stock gears. Of course, for all the rest of the mph range in that gear, acceleration is quicker with the shorter gears. However it's important to realize there's some given back through the RPM range, so it's not all up-side.

This is also why I say going to shorter gears should be accompanied with a raise in the redline as well (which of course is easier said than [safely] done). [ Please read my analysis on this subject here ... ]

If this is done, there is no trade-off, as
a) you have more pull in each gear @ the tire's contact patch from the shorter gears...
b) since you have a higher redline, you can now pull longer (to a higher RPM) then you did before, and you will not have to shift out of the gear sooner because of the shorter gear.

I'm really not sure if this is clear enough. If you read my analysis on this, it should be clearer. Also, please read my reply to ironchefc43 just under the one I'm linking to, regarding the gains if you raise the redline to accompany the shorter gears.

Yes I agree threre is threshold , you cannot just pick random shorter gear. you have to calculated to determine which is optimal for.

then again what is optimal for all around is not the same for optimal performance.

Since optimal performance doesn't always conform to better MPG.




PS: I don't see why that thread contracdic with I am saying.
Especially going from 3.07 to 3.45 is not that extreme.
When you go much shorter gear you will most likely need to increase the read line since the sweep rpm spot shift higher now. So you want to be able to use the usable power through out the entire rpm in which now is higher (hence need to raise rpm limit).

Regardz,


Regardz,