This is something I have yet to figure out, hear all the time, and will be dealing with very soon. From a physics point of view, it would seem that the larger the gear, i.e 4.10 as opposed to 2.73, would always make more acceleration, just obviously a lower top end. Everyone says the stock TPI stops making good power at 4500rpm, and that 3.42s are the best rear. Why? Is it because you must shift at a lower speed, and thus lose acceleration throught the tranny gears. Please xplain. The reason I ask is because I'm finally ready to install my six speed into my 305 TBI. I plan on a 383 TBI with the Holley 670cfm TBI and want to plan around that. Any ideas? Thank you

 

Let's say you had 4.10s. By the time you're in 3rd gear and your car is wound up to it's powerband (like say 4500), most likely, you're not near the end of the run yet. So for the rest of the run, you're not making any more power. You get faster acceleration, but slower mph. If you had the numerically lower gears, you'd hit the end of the 1/4 right at the top of the powerband, so you're making power the whole run. Slightly slower acceleration, but overall, more efficient (you're not wasting any of the distance running in an RPM range that makes no power).

 

Ever ride a 10 speed bike? Ever take off in first gear? Very quickly you are pedaling so fast your feet fly off of the pedals but it isn't really getting you anywhere. If you however use a higher gear, but not too high (like 10th) you can take off well and still pull strong. RPM does not equal power. If that were the case every little toyota tercel should kick any big blocks but since they rev higher but that isn't the case. There is a certain RPM range, or power band, that the engine is happiest at. My old carbed 305 in an '86 Firebird would flatten out at @4000 RPM. Even though it would WOT upshift at 4500, I probably would have accelerated better if I changed it to @4000. On the other end, your car may not do much under 1000 RPM but by let's say, 18-1900 it may start to really pull strong. That is the beginning of the power band. This is where the right stall converter and rear end gears make all the difference. It is not an either/or choice as many seem to think. The stall gets you to the beginning of the power band and the right rear (and tranny for that matter) keeps you in the RPM range your engine likes.