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2001 Subaru Outback, EJ253
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Discussion Starter · #1 ·
I'm not sure which transmission I have in my 2001 Subaru Outback. But I'm looking to figure out how gear rations in a transmission affect top speed, a gears top speed and gas mileage, and which gear ratios it is, final drive or the highest gear ratio.

Also looking to figure out how the number system works, is the higher the number the higher the speed and the lower the number the faster the excelleration?

Thanks for any info.
 

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GF OBS-T, GM RS EJ20, SF EJ20
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I think your top speed is limited to 110mph @ which point you will hit the limiter I banged into the limiter a few times - feels like the engine blew....
This is easy to get around, I did...

You have to look @ the gear ratio + the final drive to figure out what the the ratio is for each gear.
Doing this I learned that the overall ratios of a JDM 4.111 tranny were shorter thant the overall ratios of a JDM 4.444 tranny.

There are a few tranny charts floating around that have alot of info based on the tranny code of your car (sticker on the top drivers side of the trans bellhousing).
 

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2001 Subaru Outback, EJ253
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Discussion Starter · #3 ·
Well I know for a fact that I've never hit a speed limiter on my 01 Outback, I've always hit the max or just over 120 MPH, that's the max speed on the speedo, so either mine doesn't have one, it's been disabled or it's fried.

Anyways, here are the specs for my transmission on one of the charts:

TY754VCBCA
1ST 3.454
2ND 2.062
3RD 1.448
4TH 1.088
5TH 0.871
Final 3.900

Looks like this is a close ratio geared transmission, even closer in some aspects than the RA gearset is. So say I went and changed to a 5 speed STi gearset sold by Rallispec, with these gear ratios:

STI Ratios
1ST 3.166
2ND 1.882
3RD 1.296
4TH 0.972
5TH 0.738

Would my top speed increase?

I'm just looking at this from a knowledge stand point, I'm not actually looking at buying one quite yet.
 

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2001 Subaru Outback, EJ253
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Discussion Starter · #4 ·
Another thing that is confusing to me, is the gearing and the top speed, I was checking out the MFactory gearing calculator, and according to that, with my gearing and tire size, I should be able to make a top speed of 149 MPH. What gives?
 

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2005 Subaru Impreza RS 5MT
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Another thing that is confusing to me, is the gearing and the top speed, I was checking out the MFactory gearing calculator, and according to that, with my gearing and tire size, I should be able to make a top speed of 149 MPH. What gives?
1. If you've moved from stock tires to a larger size, you're speedo is incorrect.

2. With your stock redline, gearing, tire size etc etc if might be theoretically possible to hit 149 mph, but the engine has to generate enough power to overcome aerodynamic drag to reach that speed. Your engine doesn't produce the required amount of power, which grows exponentially at a rate casts a mighty shadow over the rate at which your speed increases. You would need to reduce your drag and gain a more than a hundred horespower to hit those kind of speeds.

*edit*
You must have more drag than me; we have the same motors (and I believe the same transmissions) but my '05 RS hit a solid 130 mph. But to hit 140 on a flat area, I would need ~200 ponies, and to hit 150 mph i would need close to 300, if not more.
 

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Discussion Starter · #7 ·
I kinda get it but I fail to see why my engines output and the drag coefficient of my car would limit my speed, I thought that my gearing would be responsible for that.

Does that mean that engine as it is, might be taking to long to go faster so my drive train is going up in revs faster? To me that just doesn't sound possible. How does this work?

On a second note my top speed is around 123 MPH on a good day, maybe more if I had more stretch of road.
 

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Red 2007 BMW Z4 M-Coupe
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The reason your car has a top speed less than what your gearing says you could be at is drag. Your car simply doesn't have enough power to overcome drag.

Drag is the force that pushes against an object as it moves through a gas/liquid... Example: Stick your hand out of the window while going down the freeway (as if you were giving someone a "hi-5").. Notice you have to put some effort to keep your hand still as the wind pushes against it. So we've established that it takes effort to move your hand through the air.

Its the same for your car. It has alot more air to push out of the way, so it takes much more effort to push through the air. So much force is involved that typically it is aerodynamics that will limit most car's speeds as opposed to gearing. If you want to compare other car's aerodynamics, the proper terminology is "coefficient of drag", or a 'Cd'. My old Rx-7 had a Cd of about .26, which by the way is really aerodynamic, and off the top of my head, I'd estimate the Cd of a '98 2.5RS to be about .35ish. Which is about the aerodynamics of a brick in comparison. :)

Another way to increase top speed is to reduce the Cd of your car. Some ways are more effective than others. Under body covers help a fair amount, removing the side mirrors help. Rims that do not have spokes (think flat discs) help, as partially covering/blocking the front grill. Tires that are more narrow will also help a great deal, as well as removing mud flaps. And believe it or not, lowering your car will help as well.
 

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Discussion Starter · #9 ·
The reason your car has a top speed less than what your gearing says you could be at is drag. Your car simply doesn't have enough power to overcome drag.

Drag is the force that pushes against an object as it moves through a gas/liquid... Example: Stick your hand out of the window while going down the freeway (as if you were giving someone a "hi-5").. Notice you have to put some effort to keep your hand still as the wind pushes against it. So we've established that it takes effort to move your hand through the air.

Its the same for your car. It has alot more air to push out of the way, so it takes much more effort to push through the air. So much force is involved that typically it is aerodynamics that will limit most car's speeds as opposed to gearing. If you want to compare other car's aerodynamics, the proper terminology is "coefficient of drag", or a 'Cd'. My old Rx-7 had a Cd of about .26, which by the way is really aerodynamic, and off the top of my head, I'd estimate the Cd of a '98 2.5RS to be about .35ish. Which is about the aerodynamics of a brick in comparison. :)

Another way to increase top speed is to reduce the Cd of your car. Some ways are more effective than others. Under body covers help a fair amount, removing the side mirrors help. Rims that do not have spokes (think flat discs) help, as partially covering/blocking the front grill. Tires that are more narrow will also help a great deal, as well as removing mud flaps. And believe it or not, lowering your car will help as well.
Thanks for the explanation, that explains a lot of why I'm not making over the max I have right now, looks like a good idea to invest in aerodynamics then.
 

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It would help your top end, and it will help with your fuel economy as well. Don't believe that aerodynamics only helps when going faster than 80mph... It makes a tangible difference at virtually any speed. Just don't buy into the aftermarket body kits that have flares, and vents and the sort. Typically the more vents/flares, and extra junk makes the aerodynamics worse. Search around www.gassavers.org in the aerodynamics section of the forum for some inspiration. Typically they have a good understanding about aerodynamics.
 

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MY99 GF4 EJ227 JDM 6spd
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The Outback tranny was chosen to be the way it is because IMO with these in mind; TOWING on the hiway. The gearing of the OUTBACK is the same 1-4 as with all the '96+ NA-trannies. However the 5th gear of the Outback was shorten IMO so towing on the hiway would be easier since the Outback is such a heavy vehicle. Only the OUTBACKS have this shorter 5th gear compared to the rest of the trannies. s

The 2.5L motor Subarus seem to have be equipped with the 4.111FD. Some other models that don't have a heavy weight on them and are of a lower trim of the newer years have a 3.900FD.

If you where to gather many gear ratios and Final Drives from all the Subarus, you'll have an idea of how they work and which is ideal for what. Ratios also affect power delivery if they make the next gear change stay in the power band or not.

Here's the JDM STi 6spd (i know the ratios by heart)
3.636
2.375
1.761
1.346
1.062
0.842
3.900FD
 
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