Proper Gear Ratios on a Turbo rally car?

[UP2MTNS]

So here's a topic I know nothing about, so I just want to start the thread and let people smarter than me discuss.

If you want a contex, use mine....2004 WRX, soon to have a Blouch TD0620g, APS TMIC, GrimmSpeed PnPnC everything, PE850CC injectors, Koyo Race radiator, Crucial 160 degree thermostat, lighweight crank pully....I think that's about it for power mods. STOCK tranny...but will put in an ACT street clutch as well.

ok....the 20g w/tmic is normally a torque monster,....quick spool up, decent top end. BUT....stick a 34mm restrictor plate in there, and that changes things. My tuner said to keep the 20g even with the plate, so I'm fine there (I think).....but eventually I'll want to upgrade to some PPG helical gears.

Discuss.

[I Like It Sideways]

The gearing will depend on the tune. Choose gear ratios that will keep your engine in a good torque range.
As for actual ratios... I dont really know.
Bleh not much help that is haha.

[L and E Fab.com]

I run the stright cut PPG gears with the 4.44 final drive.

There is not really that many choices on the PPG gears.

Seems like final drive is the best way to control the gearing.

[409industries]

I dont know much about gear ratios, but are there really that many options with PPG gears on a subaru?

I will keep an eye on this thread because i too would like to learn something.

[UP2MTNS]

I need to do some research on 'final drive' ratios and options.

If someone would like to start with telling me what the hell 'final drive' is/means...that would be a start. (like I said, I know very litte about gears/transmissions)

[MBasile]

for what I understand is that there is the ratio of the gear that the individual gears turn which is the "final drive gear" I'm assuming because it goes out of teh tranny to turn the wheels. You add this ratio plus the ratio of whatever gear you are in to get the "total ratio" but what that ratio tells you I have no clue. If you want to come down to Monterey you're welcome to check out my RA gears. I'm also getting closer to being willing to sell my automatic tranny parts, which includes a 4.44 final drive rear diff

[UP2MTNS]

from www.tpub.com
FINAL DRIVE
A final drive is that part of a power transmission system between the drive shaft and the differential. Its function is to change the direction of the power transmitted by the drive shaft through 90 degrees to the driving axles. At the same time. it provides a fixed reduction between the speed of the drive shaft and the axle driving the wheels.

The reduction or gear ratio of the final drive is determined by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. In passenger vehicles, this speed reduction varies from about 3: 1 to 5: 1. In trucks it varies from about 5: 1 to 11: 1. To calculate rear axle ratio, count the number of teeth on each gear. Then divide the number of pinion teeth into the number of ring gear teeth. For example, if the pinion gear has 10 teeth and the ring gear has 30 (30 divided by 10), the rear axle ratio would be 3: 1. Manufacturers install a rear axle ratio that provides a compromise between performance and economy. The average passenger car ratio is 3.50: 1.

The higher axle ratio, 4.11: 1 for instance, would increase acceleration and pulling power but would decrease fuel economy. The engine would have to run at a higher rpm to maintain an equal cruising speed.

The lower axle ratio. 3: 1, would reduce acceleration and pulling power but would increase fuel mileage. The engine would run at a lower rpm while maintaining the same speed.



a 2004 wrx (and most WRX's) except the 2006 and 2007 have 3.9:1 final drives. so going to a 4.44 drive does just what the first example states.....adds acceleration and torque at the expense of fuel economy.....you have to keep higher rpms to stay at the same speed.

assuming your 1st through 5th gear ratio's stay the same, I think this is the answer. with a 34mm restrictor, anything much above 6000rpms will not be as nearly as effective....and you want your power band to start as close to 3000rpms as possible.

but does this mean it literally shifts your power band? If you were to run dynos on before/after, would you simply see your torque/hp graph shift to the left? Or is it not that simple?

[UP2MTNS]

for what I understand is that there is the ratio of the gear that the individual gears turn which is the "final drive gear" I'm assuming because it goes out of teh tranny to turn the wheels. You add this ratio plus the ratio of whatever gear you are in to get the "total ratio" but what that ratio tells you I have no clue. If you want to come down to Monterey you're welcome to check out my RA gears. I'm also getting closer to being willing to sell my automatic tranny parts, which includes a 4.44 final drive rear diff

I think you have to convert both front and rear diffs to the same final drive, but that might be for 4x4's....and not full time awd cars. I've been told the R180 is the rear diff to get...stronger. not sure about the 'final drive' on it though.

so you upgraded from 2002 gears to the 2003 RA gears?

from wikipedia:

Rev. C (2003)
There are few changes from Rev. B.(2002) The gears are changed to RA-width gears (1 mm increase in size) to increase durability of the transmission

[Flyby]

from what i understand and have learned... with my swap was i lost hp feeling but gained tourge "feeling" like a mother humper i went from 02 trans to 04 jdm spec c sti trans with 4.44 and i have the vf34 my tourge starts at about 2800 and pulls hard till about 5500 but im also runing a hybrid 2.5

[Flyby]

o and i cruise 70 at 4000 rpm in 6th....

[UP2MTNS]

from what i understand and have learned... with my swap was i lost hp feeling but gained tourge "feeling" like a mother humper i went from 02 trans to 04 jdm spec c sti trans with 4.44 and i have the vf34 my tourge starts at about 2800 and pulls hard till about 5500 but im also runing a hybrid 2.5

got any pulls on a dyno you can post up?

so I was thinking about this more last night cause I couldn't sleep. I don't think going to a 4.44 drive will 'shift' your power band left. the power generated by a turbo motor is dependant on the turbo...which is dependant on the RPMS. so any gearing won't change that. It should, however, RAISE your torque band (see above example) at the expense of HP.

hp is robbed by the 34mm restrictor anyway, so who cares. now if you didn't have that, I assume ported heads, new valves and cams would help restore the HP at the higher rpms....then you could run 8 or 9000rpms at redline depending on your setup.


...I still feel like I'm 'missing' something.....

[Flyby]

nope no pulls im to broke for awd dino session but i talked to a kid with sim mods and raced and pretty close to same speed he said hes puttin 330 awhp so ima assume about 310 awhp and 325 awtq these are assumtions

[MBasile]

for what I understand is that there is the ratio of the gear that the individual gears turn which is the "final drive gear" I'm assuming because it goes out of teh tranny to turn the wheels. You add this ratio plus the ratio of whatever gear you are in to get the "total ratio" but what that ratio tells you I have no clue. If you want to come down to Monterey you're welcome to check out my RA gears. I'm also getting closer to being willing to sell my automatic tranny parts, which includes a 4.44 final drive rear diff

I think you have to convert both front and rear diffs to the same final drive, but that might be for 4x4's....and not full time awd cars. I've been told the R180 is the rear diff to get...stronger. not sure about the 'final drive' on it though.

so you upgraded from 2002 gears to the 2003 RA gears?

from wikipedia:

Rev. C (2003)
There are few changes from Rev. B.(2002) The gears are changed to RA-width gears (1 mm increase in size) to increase durability of the transmission



I went from a 2002 automatic to RA gears. The wikipedia article says "RA width" not RA ratios.

Talk to the guys at LIC Motorsports in Novato, they can help you with all the technical info

[RS22b]

great topic! i will be back later to read and then add in my .02

[Azewaldo]

As far as I know (which is about as far as I can toss a transmission :roll: )...

Changing the final drive from 3.9 to 4.11 would just quicken your shifting a little bit (about 5%). You'd go through the gears a little faster, but it wouldn't change your power band, or where you shift in the power band. To narrow your power band you'd have to change the individual gear ratios, like swapping in an STI 6MT.

Also, your (theoretical) top speed wound be reduced. Think of it this way: whatever speed you travel at 3,900 RPM now, it would take 4,110 RPM to achieve the same speed.

By the way, you can play with gear ratios virtually by jumping into Gran Turismo, or Forza. Both have Subarus, however GT3 & 4 have rally modes as well.

[MetalNeverDies]

o and i cruise 70 at 4000 rpm in 6th....

well ya.... rally drivers try to keep it close to redline. and of course with short gearing your gonna be at high rpms with my car stock im at 3k to 3500 at freeway speeds.

[noisycricket]

As far as I know (which is about as far as I can toss a transmission :roll: )...

Changing the final drive from 3.9 to 4.11 would just quicken your shifting a little bit (about 5%). You'd go through the gears a little faster, but it wouldn't change your power band, or where you shift in the power band. To narrow your power band you'd have to change the individual gear ratios, like swapping in an STI 6MT.

Yes that's true.

However, there's something to be said for making a "torque hole" happen at a lower speed. Lower final drive helps even if you keep the crappy gear spreads.

Also, your (theoretical) top speed wound be reduced. Think of it this way: whatever speed you travel at 3,900 RPM now, it would take 4,110 RPM to achieve the same speed.

Only if you can redline in top gear, which most cars don't.

One of my cars was a total riot. Wish I could pull the video clip from the camcorder. It wasn't a Subaru, but it was pulling near-Subaru-redline just to get down the highway...

[UP2MTNS]

As far as I know (which is about as far as I can toss a transmission :roll: )...

Changing the final drive from 3.9 to 4.11 would just quicken your shifting a little bit (about 5%). You'd go through the gears a little faster, but it wouldn't change your power band, or where you shift in the power band. To narrow your power band you'd have to change the individual gear ratios, like swapping in an STI 6MT.

Yes that's true.

However, there's something to be said for making a "torque hole" happen at a lower speed. Lower final drive helps even if you keep the crappy gear spreads.One of my cars was a total riot. Wish I could pull the video clip from the camcorder. It wasn't a Subaru, but it was pulling near-Subaru-redline just to get down the highway...

well, if you change the gearing, at any point, its going to either make more or less power (or torque, or whatever)....the question is how much/how little/and when. you may still have a 'torque hole' because individual gears aren't overlapping properly, but power transfer is still happening somwhere. <----so that's what this thread is about/what I'm asking here......if there's a 'best practice' rally gear set ratio for anycar/subaru/whatever, I would love to know what it is. What do Block and pastrana use? anyone? anyone? bueller?

[noisycricket]

"best practice" rally gear set seems to be redline in top gear is the fastest expected speed for that rally, 1st gear redlines out at about 40-45mph, and the remaining gears in between.

Top speed for rally cars seems to be about 90mph-120mph. Picture having six gears to play with all before 90mph, with a slightly taller First than you have now :D :D

If you must have a "torque hole", make it happen at as low a speed as you can live with. Would your car accelerate better off-boost at 30mph or at 25mph?