need help with gear ratios, stock final gear ratio's not spaced out evenly - why? Options

[jimkelly]

for me - chevy v8 - stock 2nd is fine as a first gear, but it winds out fast, as does stock 3rd, as does stock 4th, and 5th is fine, but taller would get rev's down for highway cruise-ing ( 3000 rpm at 65 +- ) on 195x60x15 tires.

my question is why are stock final ratio's not spaced out evenly?

stock
3.091
1.889
1.261
0.926
0.710

3.091 x .61 = 1.889
1.889 x .66 = 1.261
1.261 x .68 = .926
0.926 x .77 = .710

evenly would be ...

3.091
2.496
1.901
1.306
0.710

for my v8, i am thinking of course to delete cantilevered first - thus i can use a beat up slider ; )
stock 2nd 1.889
?? 3rd - i need the right gear for inbetween stock 1.889 and 0.710
4th - use stock 5th ZD 0.710
5th - use flipped H 0.59 as an overdrive gear.

how the hell do i calculate the correct final gear ratio for my 3rd gear?

looks like an R (1.080) 25:27 - or - a flipped V 27:25 - is about right ??

jim

[r_towle]

consider changing the ring and pinion gear...
Carquip is who you need to call.

Rich

[Dr Evil]

There are a number of things. I need to calculate tom see, but a flipped v may work. Cheap too.

[jimkelly]

i have an H gear - so i only need to determine the best 3rd - to fall between F and ZD - so that i would have a 3 spd plus overdrive : )

or i could try to make a 4spd with the correct 3rd and 4th to fit between F and flipped H. but this is more money as i would likely have to buy 2 gear sets.

doc - i think a flipped V might be right - pls let me know what you think.

at some point - i will need two transes built this way.

thanks!

jim

[ArtechnikA]

my question is why are stock final ratio's not spaced out evenly?

The short answer is that the faster you go, the more air you're pushing.
You can deal with a big rpm drop 1->2 because you don't feel the effect of being so far below peak torque as much.

Anderson and Carroll Smith both spend a bit of time on this subject if you want more background than I am qualified to distill into a paragraph...

In a perfect world, the drop would be the same - from about 50 rpm over peak HP to peak torque. But at higher speeds, you can't afford to give away that much HP and continue accellerating.

And there are lots of other factors that may lead you to optimise one operating regime at the expense of matched rpm drops.

[Dr Evil]

Jim, I am crazy busy as usual so it will be a bit before I get to this.

To answer your question, the R/P is 7:31.

To figure out your speed v RPM:
Take ratio of gears --> multiply buy 31/7 -->multiply by the circumference of your tires (stock is 24" roughly, actual is at top of chart in your post) --> Multiply by RPM
(IMG:style_emoticons/default/smile.gif)

[Dr Evil]

A flipped V is an R. Easier to figure that way.

[messix]

lets just say you are building a 4sp gear box [2=1,3=2,4=3,5=4]

with the torque of the v8 you really don't want to "close ratio" the 1 to 2 shift because you will over power the tire pretty easily [you aren't fighting aero drag at all and all power will be hitting the tire hard], so a wider ratio from 1 to 2 is better to live with. from there the stock third will match shift rpm pretty good with a 4th gear flipped h/a gear set. this will make freeway driving nice and give you a good top end.

just make sure your clutch is up to holding the power.