^^^ Alright, makes sense.

Quick question though about gear ratio's. Say two exactly equal cars ran the same distance in the same amount of time, both with a final drive ratio of, say, 4.7. Now, Car A then changes only the final drive ratio to a 3.0. Car B changes only the final drive ratio to a 6.0. Which car would: run the same distance faster? Trap a higher speed? Have a higher overall top speed? Reach thier top speed quicker?

 

That's hard to say.

From a performance standpoint, gearing is selected to keep the engine in its most efficient operating range.

 

So, the final drive isnt exactly the deciding factor as to the top speed of a vehicle?

 

I'll let you reread my previous post and decide for yourself.

 

Ah, okay, I get. Gear ratio = efficiency, not neccessarily top speed.

 

Sort of... gearing lets you change your engine speed relative to your vehicle speed. Since the engine is efficient is a small range, that can help or hurt you.

To make the car quicker/faster, you want to select your gearing so that you can produce the most average horsepower (once you have traction).

 

Okay. . .so here's a rough question: say here's the setup. . .

N/A motor putting down 3xx hp and 2xx tq (all to the wheels)
Running flat surface, surface is normal highway-type material
Ambient air temp. is 85 F

Open throttle, complete traction all the way

Transmission is EP3. What would be the pros - cons of running a stock FDR of 4.7 as opposed to an aftermarket 6.03 ?

 

Beats me, you'd have to do the math.

 

If by math, you mean literally, then what equation? Would the one previously mentionted work?

 

It might not be trivial.

You'd have do what I said earlier: make a plot of thrust vs. vehicle speed and drag vs. vehicle speed. Drag can be plotted using the previous equation. For thrust, it'll be a little more complicated. You'd have to figure out the engine speed based on the vehicle speed for each gear and then use a dyno plot of your torque curve to figure out the thrust.

EDIT: You can get a rough idea of the horsepower you need using the previous equation. For "F", substitute Power/Velocity. Plug in your intended top speed, and solve for power. Make sure you check your units.

 

Alright, cool. Thanx guys

 

or until the transmission can no longer handle the power put out by the engine.

in regards to the 6.03 FD, keep in mind what i said earlier: higher ratio=faster acceleration and slower top speed. that means that the pinion needs to spin 6.03 times for the axle to spin once. so when comparing car a+b that are the same aside from car a having the 6.03, assuming it balanced well with the gears, from 0-take your pick of any number up to car a's top speed, car a would get there quicker. if on like a 5 mile strait away, car B would go flying by it because it will have a higher top speed.
honda put A LOT of work into gettings its gears right for the cars power-curve (what didnt they put a lot of work into getting the most out of these little I4s though?).
if you want to go changing things with the tranny to try to get a faster top speed, i'd suggest finding a car with a close tq/bhp curve that yours has and look at its gear ratios. i honestly have no clue what the equation would be to find what gear ratio is for you based off of hp,velocity, tq, etc. dig around, see what other people did, and see what worked i guess. some of the european companies have made pretty fast I4s (porsche, alfa romao), granted they have a much larger displacement (i think around 3L compared to hondas 1.6-2.0) but depending on what you have done to your car (i.e. boost) your power curve might sync up pretty closely to theirs.

forgot: keep in mind that if you just change your 5th gear there will be a pretty big drop off in RPMs and your engine might not make the needed power to accellerate. if your looking for a b series tranny thats already made, the 94+ LS (s80) tranny has a FD of 4.266 and a gear ratio in 5th of .714. i'm sure there is some very technical (and most likely very expensive) computer program out there that you can input your cars data and it can calculate your optimal gear set.

 

Aweswome. Great information. Thanx to everyone for thier input.

 

Check these out. Play around. MFactory is good stuff http://www.teammfactory.com/gearcalculator.php http://www.fatboyraceworks.com/gears/