Final Drive: 4.56 vs. 4.88
 

I've ordered all the extras needed to make the swap (seals, bearings) but have yet to order a ring and pinion due to not knowing which would fit my needs better.

I use the car as my DD, work commute is around 5 miles to/from. The closest freeway is the DC beltway an hour and a half north of me. My goals are to have a noticeable increase in acceleration without sacrificing the driving experience. We usually take my wifes car on longer trips during holidays but I do enjoy the 5+ hour drive to WV occasionally.

What are the top speed limitations to each?
Does 4.88 make it basically torture to drive 80mph for hours on end?
Which would be the better choice?

What transmission do you have?

You can calculate top speeds per gear here: http://www.apexgarage.com/tech/gear_ratios.shtml

manual transmission.

4.10 to 4.56 is pretty much 11%
So if you are at 3k rpm at a given speed, 4.56 would be about 3,300rpm. Maybe that will help you imagine what rpm you would be at with a higher final drive.
4.88 is is about 18% Let me know if you find out the rpms at 80mph for all the different final drives. I am too lazy to check right now.

I went for 4.67 Mfactory on my DD M/T. It's perfect. Easier to drive than before due to the extra torque and comfortable cruising at higher speeds.

I don't think Weir sells a 4.67, or I would be very tempted to take that route myself!

Final Drive: 4.56 vs. 4.88
 

No it's an Mfactory one. I'm in the uk.

It also depends on other mods. You won't need the 4.88 if you've got header exhaust etc for a DD I would say.

4.56 is very streetable and daily driveable, 4.88 is a bit more aggressive and maybe a little rough on a +5hr drive.

Your at around 113 MPH when topping 5th gear.

crusing speeds in 6th gear at 70-75mph is around 4K rpm.

I drove to Toronto from Northern VA without any complaints. My Girlfriend was happily asleep. it all depends on the drivers needs and how loud the exhaust can be because the RPM will be higher most of the time.

Use this handy little calculator to get a more precise idea of the final ratio at the wheels with tire size.

https://tiresize.com/gear-ratio-calculator/

MFactory has a really good gear ratio calculator with a line graph for each gear:
http://calc.teammfactory.com/index.php

Here is a 4.56 vs 4.88 with 245/40/17 tires and stock 86 gears:
4.56vs4.88

I guess my next question would be this:

Looking at the MFactory gearing calculator, I will have to be in 5th gear to hit 100mph. With 4.88 gears how will 5th feel? Like 4th currently?

For NA i recommend 4.72 or 4.88 , personally prefer 4.88 from weir

You will have actually less acceleration when you hit 100mph in 5th gear. Reason is that 5th gear is 17% slower comparing to 4th gear. You gain a bit with the shorter drive ratio, but not so much. Overall, you lose in this range of speed.


This is the common thing that most people don't get it. With a shorter drive ratio (e.g. 4.56, 4.88 etc.) you are actually slower in the higher range of speeds and faster in the lower range of speeds. There isn't such a magic that will give you the "missing" engine power. By changing the drive ratios, you are just shifting your available power band in another area.

The OPs car is his DD so I doubt he will be hitting 100 mph on a regular basis.

When selecting 5th you are well into the power band and the acceleration does not feel as though it looses momentum. It may do on a stop watch but in real life it doesn't.

Actually there are even more factors - in the end lower rear end gearing will make the car feel more responsive and accelerate harder in a given gear. But you'll have to shift sooner - compared to a stock geared car, the stock geared car will still be accelerating, while the re-geared car has to shift to a higher gear ratio. You're right - there's no free lunch. One of the main advantages to lower rear gears in drag racing is it takes less time to get the car moving and in its power band. Once in it's power band (assuming the gear spacing is correct), the differences will be less than you think. Caveat: on a track, if you change the rear ratios it might allow you to take full advantage of a straight stretch if the ratios are right... or it could prove a disadvantage if it forces you run out of RPM's at the end of a straight. Overall performance aside, for street driving, the added responsiveness and feel of acceleration in a given gear will make the car much more fun to drive!

Yes this can be an argument. Personally, I am in Germany and we drive differently here. Even small tracks go with 100 mph ..

You lucky lucky person. 😄

I hit 100mph pretty regularly on some of the roads to/from my work because there are no homes, no residents, and nothing around to harm from speeding. So the tldr; is that 5th will be slower than stock but 1-4 will likely be quicker?

Final Drive: 4.56 vs. 4.88
 

No way 5th is slower.

I did a test run before exhaust and FD fit (otherwise stock)

2nd @30mph then through the gears to 90mph.

Totally stock 13sec
FD and exhaust 11sec

No ecu tune.

I think that answers your question.

Increasing fd ratio by 10% make you feel it response 10% better but overal acceleration from zero to 130miles will not increase over 5%

I realize that sometimes our cars feel kinda lazy to move around 2800 rpms and the engine feels kind of breathless(torqueless). How does the 4.67 combat that?

Basically by multiplying the torque that the engine puts out.

The breathless feeling has gone from my car now. I thought the same as you. I notice the difference more in 3rd and 4th gear where it just keeps pulling.

No matter what gear I'm in I always feel like there is enough power to pull away.

I liken it more to my friends 350z now but with a few more revs.

Wow, so it feels about as torque-y as a 350Z in FEEL right? I remember when I first drove a Z the torque won me over in a big way more than the car overall.

As a owner of a auto tranny with a 4.67, and a former owner of a manual. The biggest mistake Subaru and Toyota did was not to put the right gear ratio in this car. With the 4.67, this car rocks!! With the manual I could only wish to get to 135. But in the auto with gears, I can touch 135 with easy, offen. And the way it goes though the gears is just fantastic. This should be the first mod to the car.

Your statement doesn't make sense. Auto tranny has bigger power losses and a much smaller top speed (130 mph vs. 140 mph of the manual tranny). You cannot get an improvement on top speed by changing the final drive to a shorter ratio. This is a well know fact valid for ages. Did you buy the car second hand? Your car should also have some other mods.

What he means is he can reach the that speed easier due to the increased acceleration. For example he doesn't run out of road or hit traffic.

Gears are an overrated mod. If you want more torque to the drive wheels at a given speed, go to a lower transmission gear, i.e. delay upshifting. People have the idea that lower (numerically higher) gearing improves acceleration everywhere. It doesn't. You are forced to upshift sooner and put yourself in a taller transmission gear, and at that point you are accelerating slower vs. stock gearing in lower trans gear.

Nonsense.

4.1 to 4.67 up shift is 300 revs sooner which equates to around 4 mph it's not a factor.

It took 2 whole seconds off my 30 - 90 mph time.

Yes that's true. But if you could measure 90 - 130 mph time (before and after change), you would see that now you are 2 whole seconds slower. So, you just have a shift of your power band to the lower speeds. That's the whole idea.

I don't blame this kind of modification. In fact it gives very good results if you're doing auto-x or tracking in small tracks. It also gives a better feeling and response in driving within town. :thumbsup:


Personally, I have a 3.727 FD and on high speeds the car is very very strong. I was running lately side by side with a bmw 535d (313PS, 630Nm) and bmw couldn't get away. Reason is that my car was pulling using 4th and 5th gear instead of using 6th gear.


So it depends the application ...

In a nutshell, lower gears will benefit you from lower rpm starts, especially on cars like ours with the torque dip. What rpm did you start your 30-90 run? Lower fd gearing will get you into the power band (through the torque dip) faster, which is a tangible benefit for street driven cars over higher geared cars. To zdans point, what rpm did you end at when you hit 90mph? If near redline, then your gearing was optimized for a run to 90 mph. But you'd lose that advantage as you up shift and a higher geared car stays in a lower gear. It's why we rate cars with hp (rpm dependent) rather than just torque.


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MT Has perfect gearbox ratio but AT are so long in 3 and 4 and 5.
the acceleration after FD swap depends on speed range.
for example acceleration in 0-176km/h in AT 4.88 is 5% better than AT 4.1 but acceleration from 0-200km/h in AT 4.88 is equal to AT 4.1

average result in all speed range give you maximum gain of 5% after FD swap even if you use 40% higher FD ratio.
you can imagine it with considering the FD 4.88 goes sooner to next gear and acceleration drop after shifting to next gear . stock FD 4.1 has better acceleration before shifting to next gear but after shifting to next gear the FD 4.88 will give better acceleration.

Not sure of the rpm but it was started in 2nd gear

I still have to disagree on this. As I gather you don't have one fitted. Maybe you have experience of driving one but will not of done a specific test.

If we were to run the test till the OEM geared car had to change then 4.67 FD car will surge past.

The argument is flawed

At the end of the day no one bought this car to do drag runs because it's slow.
It's all about the cornering and general handling.

For real everyday fast road driving FD is a great option and will cover ground better than an OEM one.

Actually there is no argument, it is physics. When I get some spare time I will illustrate here backed by mathematics.


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I'll look forward to be educated 😂

My point was that by changing the rear end gear ratio It will get to 135 a whole lot faster than the stock car would.

4000 rpm @ 30 mph 2nd gear to 6700 @ 90 4th.

Put together a quick spreadsheet - the number are all hypothetical and simplified, assuming torque curve is completely flat from 0 to redline. Left has a final drive of "4", right has a final drive of "4.5", significantly greater than the left. Notice the distances and the delta at the far right. The lower geared car surges forward, but shifts up and the higher geared car passes it - they continue to swap positions the whole way. In real life, a lower FD would have some advantages, particularly moving the car through the torque dip into the upper power band in 1st gear, but results will diminish after that. Your scenario was ideal in that you ended at near redline. If you timed yourself to 110 or 120 you'd find a stock geared car would probably cut the time advantage you saw to very little. The 'oscillation' back and forth regarding which car is in the lead is magnified in higher gears. Also keep in mind, lower gears amplify effects such as shift times, rotational inertia, and frictional losses - albeit these differences aren't that huge considering the gear ratio changes we're really talking about.

https://drive.google.com/open?id=0Bw...UZhdWxHaWFleEE