Gear Ratio Change

[CSG Mike]

Originally Posted by Lunatic

Yes I will be adding a tranny cooler, oil cooler, and with time wider tires, brakes, coil overs, and yes, some kind of forced induction.

Keep your stock final drive; you'll want taller gears when you're FI.

[SmsAlSuwaidi]

Originally Posted by CSG Mike

Keep your stock final drive; you'll want taller gears when you're FI.

preach that ! especially on high boost levels the stock gearing gets too short; I'm fed up with it so I'm slapping a 3.73 in this weekend

[Lunatic]

Originally Posted by CSG Mike

Keep your stock final drive; you'll want taller gears when you're FI.

Even with the automatic?

[CSG Mike]

Originally Posted by Lunatic

Even with the automatic?

Yes, especially with the automatic.

[Lunatic]

Now I'm confused. I took it to the track today and spent all day in 2nd and 3rd. There is only one place at the end of the straight where I would momently need 4th. Wouldn't I want it geared to be able to use all 6 gears?

[fatoni]

Originally Posted by Lunatic

Now I'm confused. I took it to the track today and spent all day in 2nd and 3rd. There is only one place at the end of the straight where I would momently need 4th. Wouldn't I want it geared to be able to use all 6 gears?

just go faster. thats usually the best way to fix that.

[gramicci101]

Originally Posted by Lunatic

Now I'm confused. I took it to the track today and spent all day in 2nd and 3rd. There is only one place at the end of the straight where I would momently need 4th. Wouldn't I want it geared to be able to use all 6 gears?

Why would you want to use all six gears if you didn't need to? That's just more shifting that needs to be done, which means more time that needs to be taken to shift, which means less time putting power to the ground.

And your gear usage was just for that track you were on. Say you get a final drive ratio that lets you use all six gears on that track. What happens when you go to a faster track and you're topped out in sixth gear on a straight while people go around you?

For an extreme example, consider an autocross course. The runs are around a minute long, very tight and windy, and you're usually in second and occasionally third gear. If you geared your car to use all six gears on that course, you would constantly be shifting up or down, which would make you a lot slower than the person staying in second the entire time, and potentially upset the car in a corner. Now compare that to the back straight in Le Mans, where you can genuinely max out sixth gear before you hit the end of the straight. If your car is geared for the autocross course, you're only going to be going about 60-80 mph while other cars are passing you doing 150+.

[7thgear]

Originally Posted by gramicci101

Why would you want to use all 6 gears if you didn't need to? That's just more shifting that needs to be done, which means more time that needs to be taken to shift, which means less time putting power to the ground.

more usable gears is always good, especially in cars with narrow powerbands


ideally you'd want your top gear to max out at the point on the track where your car can reach it's theoretical maximum speed (HP vs Aero) and no more. Having more gears means you get to stay in the peak area of your power band longer.

look at formula 1


your autocross example is also not totally correct, because with more gear choice you get to choose the best powerband for corner exit. Time spend shifting can easily be made up by having the car in it's powerband 100%. Instead, we often sacrifice power-out by staying in 2nd gear because dropping to 1st will yield too little time spent under the curve. By having more gears you can accommodate more corners.


i mean ideally you'd want an 8-9 gear auto DSG box.. then you'd never even know the car was shifting gears.. it would just always be in the best place.

the gears in our cars are made entirely for economy. Our 6th gear tops out at like 180mph or something, the car would never even reach those speeds on any race track without maybe some serious drafting.


check out the Cusco Final Drive thread to understand why.

[gramicci101]

Originally Posted by 7thgear

your autocross example is also not totally correct, because with more gear choice you get to choose the best powerband for corner exit. Time spend shifting can easily be made up by having the car in it's powerband 100%. Instead, we often sacrifice power-out by staying in 2nd gear because dropping to 1st will yield too little time spent under the curve. By having more gears you can accommodate more corners.


i mean ideally you'd want an 8-9 gear auto DSG box.. then you'd never even know the car was shifting gears.. it would just always be in the best place.

Except in an automatic it would be shifting constantly. You'd accelerate through a corner and it would drop a gear, then shift up a few seconds later, then drop again for the next corner, then back up, then up one more as you enter a small straight, then down two for the sharp corner at the end, etc... Plus autos shift in response to your actions, not in anticipation of your actions.

I would love a tightly geared sequential manual for autocross. You'd be able to set up for the next turn, not have the transmission react once you're in the turn. And you'd only have to worry about up or down, not fighting with shift gates. Or an aggressive CVT that would keep the car at 5.5K+ the whole time.

[7thgear]

Originally Posted by gramicci101

I agree, to a point. I would consider a narrow power band to be 1K RPM or less of usable power though, and our cars have more than that.

our powerband is roughly 1k... I'd even say 800rpm


here is random dynoplot I pulled off google





1st to 2nd gear the car drops 3500 rpm, that puts you roughly 20-25 horsepower below had the shift only dropped you 1500


ohh whats that, a turn coming up and you're not even back to your powerband while I'm already in it? and we need to brake a little? Guess who is going to power out of it faster?


if c-stock allowed a final drive change I'd be over that cusco unit like white on rice.


especially in autocross where you have no idea what kind of corners are going to be thrown at you, that extra shift in some long straight will be outweighted by being able to power out of the previous 4-5 turns with more power than the other guy.

[7thgear]

here is a "long" powerband car... a VW TDI


this is where your gearing barely matters, you'll pull at any place.

[gramicci101]

Originally Posted by 7thgear

our powerband is roughly 1k... I'd even say 800rpm


here is random dynoplot I pulled off google

I managed to kill my previous post; not sure how I did that.

I see at least 2K of usable power there; from ~5K to 7.4K rpm.

Originally Posted by 7thgear

if c-stock allowed a final drive change I'd be over that cusco unit like white on rice.

That's building a car to be competitive in a certain class under certain requirements though, which is not what OP was talking about.

[7thgear]

Originally Posted by gramicci101

I see at least 2K of usable power there; from ~5K to 7.4K rpm.

there is always power......


and it's all usable... even 1hp is usable power.




but the area under the curve between 6200 and 7200 is far greater than 5200 and 6200

[7thgear]

right now for slow speed autocrosses we have a choice, either stay in 2nd for whole track or drop to 1st for some corners. Both options SUCK because we either drop out of our powerband and lose 20-25% of our peak engine power or we drop into 1st to hang in it for split second (not to mention upsetting the car)


for fast speed autocross we have the same thing but only 3rd and 2nd


but if we had 4 gears for the same speed spans then we'd have better ability to mesh with the course.


so instead of hanging at 5000-6000 rpm coming out of a turn, bogging down, you'd hang in 6400-6500 and power right out with 20 more horsepower under your foot.