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Ok know it all....You put a 4.10 gear it to give it more bottom end ...and when you do that your going to lose top end...You cant gain both so you keep reading a speedo that is lying to you after you change the gearing..and keep thinking your running 160...lol
if drag was not a factor then yeah, you want the lowest numerical gear, however you have to keep in mind drag and what RPM IE power curve the engine is when it goes over 140 mph. when you get over 140 you will want the engine to be at its max power in the power band. that is why in some cases the higher numerical gears may run more top speed
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Ok know it all....You put a 4.10 gear it to give it more bottom end ...and when you do that your going to lose top end...You cant gain both so you keep reading a speedo that is lying to you after you change the gearing..and keep thinking your running 160...lol
<sigh> How many different ways do I have to say that the sims I posted the results of HAVEABSOLUTELY NOTHING TO DO WITH THE SPEEDOMETER? Or that the simple math that works for the first three gears does not necessarily do so in either of the other two?
It's purely an application of high-school physics with respect to acceleration. When the total drag equals the traction force, you stop accelerating. When you stop accelerating, YOU HAVE REACHED THE TOP SPEED FOR THAT CONFIGURATION.
Knowing that traction force comes from the engine torque CURVE, and that things like the OVERALL gearing and tire dimensions tell you where on the torque curve you're at and a few other necessary things means that you can solve for top speed if you're willing to do enough math. Or write a spreadsheet that does all the hard work for you.
Hints aren't going to be enough, I guess, so I'll tell you straight-out that I've been tinkering with this specific topic off and on since about 1969.
It really is possible to gain a little at both ends of the speed scale if conditions are right.
And if you stop and think about it a little, it does make some sense for an OE to gear a performance-oriented car with a 5-speed transmission such that top speed is reached in 4th gear, leaving 5th as the only overdriven (and power-limited) gear.
I would say that what's being referred to in the "top speed" issue are two different things; capability of the vehicle to reach a top speed vs. mechanical ability of the vehicle to reach a top speed without other factors, such as being strapped to free-spinning rollers while not actually moving. Capability may be increased due to the lower gearing (a.k.a. higher numerical gearing), this contributed by where the vehicle's power band is at versus speed traveled when at its final gear ratio in comparison and at its capable limit with the other factors such as gravity, friction, and aerodynamic drag in play. Mechanical ability would be lowered if the lower gearing, though given the vehicle could achieve its maximum rpm, such as if on rollers or if modifications were performed to lessen if no eliminate the outside factors (a.k.a. variables), as the final ratio would be less with a steeper gear (numerically higher) and in turn limit the highest achievable outcome. Higher gears (numerically lower), higher outright ability, though maybe not capable due to variables such as aerodynamic drag...as in our case. Lower gears (numerically higher), lower outright ability, though maybe more capable in achieving a maximum due to the utilization of the higher rpm for more power at the top. This is why you will see higher speeds out of the lower gearing because of mechanical advantage.
The main thing to remember, as I have learned, is that the lower the gear, the faster you will achieve speed. Think of starting in first gear; the vehicle with 2.73 gears will get to 35 mph a bit slower than the same car with 4.10s because there is more powerband being utilized at the lower end of the gear's range than the 2.73 gear-equipped vehicle; this, of course, dependant on where this hypothetical vehicle is making it power versus the rpm. If you want an example--and have friend willing to do it--find someone with a 4x4 vehicle and have them give an acceleration test in 4-High (offroad, of course) then 4-Low...there is a gearbox that will enable a lower ratio addition to the normal gearing and multiply the gear ratio greatly, thus acceleration will be faster, though you will wind the gears out faster, as well. Of course, this was meant for terrain grip, but you will get the idea. Hopefully this has helped in understanding...so neither of you were wrong, just hinting at two different equations, from what I understand here.
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Last edited by dragrace4fun80; 11-04-2009 at 10:19 AM.
Think of starting in first gear; the vehicle with 2.73 gears will get to 35 mph a bit slower than the same car with 4.10s because there is more powerband being utilized at the lower end of the gear's range than the 2.73 gear-equipped vehicle; this, of course, dependant on where this hypothetical vehicle is making it power versus the rpm.
There's a bigger factor than that in play. The 4.10 axle ratio provides (theoretically) 4.10 ÷ 2.73 -1.00 = 50.2% greater axle torque, which means that the traction force down at the pavement is also 50% greater. 50% greater traction force (assuming that you have enough grip) is huge.
I did say 'theoretically', and in actuality the improvement would be slightly less than 50% because you lose a little more torque in spinning up things like the crank, flywheel/clutch, tranny internals, and driveshaft (spinning them up faster to be consistent with the greater vehicle forward acceleration involves more torque that never makes it to the rear wheels).
Not on the street, but I've seen my v6 with 373's and auto in 4th gear at around 6k rpms top out at 145. I've not had it that high in 4th as it gets into 5th by then
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Mike - 2005 V6 Automatic, 300+ RWHP; 12.79 1/4
Vortech supercharger (SOLD); 180*T-stat; PLX Wideband O2, VEI digital gauges, SOS pillar pod; JBA 9MM wires; Mac LT headers, high flow cats; 8.8 w/3.73s, LPW girdle, alum driveshaft, 3000rpm TC; Steeda UCA, panhard bar, brace; CHE lca's & reloc brackets; Steeda Sport springs, Tokico DSpecs. .. "Sally" is getting "balls" ...forged V8 swap in progress
For me it has never really been about top speed, but how fast you can get to that speed. I have 4.10 gears, built 302 and 14 PSI of boost and my top speed is not much different than what a well tuned stock GT could run but I can walk down the 1/4 mile in very low 11's
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When in doubt..... Throttle it out!
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.. "Sally" is getting "balls" ...forged V8 swap in progress 
