Final Drive Ratio Help
 

You know that feeling you get when you're given a ton of options and can't choose between them? Yeah, that's where I'm at right now.

I'm trying to decide on a final drive ratio for a brz. It's driving me crazy, cause I can't go out there and test them individually... xD

So...can I get your opinions on what a good fdr might be for me?

My situation looks something like this: Manual transmission, daily driver, no plans for FI, the car will never see speeds over 80, infrequent interstate trips (30 mins to 2 hours), and not interested in 0-60 times. I'm trying to give the car a very clear sense of urgency. I want to make it feel like it's hauling buttocks without it actually hauling buttocks.

My options are as follows: 4.56, 4.67, 4.88

Stock 2017 brz has a 4.3 fdr, and based on a number of videos, people driving the updated model can feel the 4.3's difference over earlier models' 4.1. They basically said that the fdr woke the car up a little. It's a little more eager to push. With this in mind, 4.3 still seems to tall. So, looking at the other three options, the "pull feeling" of 4.56 should be twice that of 4.3; the "pull feeling" of 4.67 should be just under thrice that of 4.3; and 4.88 should be fourfold that of 4.3. Assuming my maths are correct, 4.88 seems best.

But, I've seen it mentioned a couple times (there are FAR more final drive posts for ATs, which makes sense, but still...) that fuel economy on highways becomes abysmal. If you think about it, traveling stock at 70 is 3k, and that yields 29mpg. With 4.88, 70 is at 3600. 3000/3600 = 0.83, 0.83 * 29 = 24. And 80 would be 22. So, I'd be placed right up there with V8s. Go 'Murica! This, in and of itself, isn't so bad, so long as there aren't any other powertrain-related downsides apart from natural wear.

I've also heard that the first gear becomes useless and that, in manual applications, it's really only used to tailor cars to specific tracks. How true is this?

In all, I obviously favor the 4.88 'cause of the mechanical torque gain. But, if it's too impractical for daily driving, there's also the 4.67. And if that's still too impractical, there's 4.56. What do you all think?

I went 4.56 in my daily driver... but if I had it to do over again I just may have gone 4.67. I wanted quiet so I used the Toyota set (same as Cusco) - helical cut and as far as I can tell no noticeable increase in gear noise over stock.

I mention this because I did not see noise listed as a concern for you. I like my 4.56 gears, a definite improvement, just perhaps a bit too mild.

I would be a little hesitant of 4.88 on a daily that saw lots of highway miles.

Tough choice, and the only way to know for sure is to drive them. As far as the freeway noise and gas milage goes, you can simulate that by just not shifting into the higher gears and running the approximate RPM of the final drives you are interested in on the freeway.

Good luck!

From your description of how you drive your car ........ I'd suggest you leave the FD alone ..... ;)


humfrz

4.56 or 4.67. 4.88 personally is a bit too impractical for a manual, but since you seem to be more interested in performance I'd say go with 4.67. Pair it with headers and a tune and you'll get pretty close to the feel of a 4.88 without the impracticality

BTW, fuel economy shouldn't take THAT much of a hit with different FD. Yes, more rpms per speed, but with less power/gas/pedal pushed needed due higher gearing. Mechanical losses increase (of engine and gearbox), but they are just part of all the forces engine power is used to counter when car is moving. For example air drag stays same.

Good morning, North America Peoples! Thanks for the replies :)


Yeah, noise isn't much of an issue. I'm pretty sure a revving engine and an aftermarket exhaust would drown it out... xD

Subjectivities aside, if 4.56 is only a bit mild, 4.67 might be my best bet.


Pfft! Where's the fun in that?! xD I wanna reduce top speed and gain low- and mid-level torque. I just wish someone had a use-guide for FDs, lol.


Oh yeah, uel headers and a tune are on the list. I want those rumblies, and the torque dip will be poofded, haha.


Yeah, those maths were just a general estimation. I didn't take into account all the other little factors. So, it would probably be more like 3-4 mpg.


So, it looks like 4.67 would work best for me. Coolbeans. Thanks again for your replies :)

To me "best" would be close ratio gear set (making 1st & 2nd gear longer, placing closer to 3rd). Or that + higher ratio FD. Unfortunately gear set costs much more then FD.

My car has a Weir Performance 4.56:1 final drive, OS Giken 1.5 LSD, ACE 4-2-1 Type-A 350 header, EcuTek Pro ECU with Delicious Tuning tune, and a Cosworth drop-in filter and the car is just about perfect. I wouldn't change a thing and the car is very strong - highly recommended!

For what it is worth...

I had to take an extended freeway drive today - San Diego to Santa Ana and back - round trip 172 miles - light traffic - sea level - low 70s temp - no wind - near perfect driving conditions.

I averaged about 75 MPH and was turning just shy of 3600 RPM.

Calculated mileage: 32.3 MPG with my 4.56 gears. No complaints from me! I rarely do extended freeway runs - my running average is about 25 MPG, so this was a pleasant surprise.

Pretty nice setup you have! It's pretty close to what I had in mind (updated FDR, UEL header, air intake, tune). So what would an extra 4% do to it, out of curiosity? Too much?


That's pretty damn impressive. I guess that means I suck at math, haha.

No, my gut feeling is that a 4.67:1 final drive would be just fine, although with the extra power from the header and tune I'm not sure it's necessary. Like I said, I think the 4.56:1 setup is just about perfect - there's a very noticeable mechanical advantage over the stock final drive (my car is a 2013, so it had a 4.10:1) without it being buzzy or ridiculously short.

I think that changing diff gearing is a hugely overrated mod. It's not like its going to magic you any more power/weight. Overall acceleration performance is going to be close to the same. There is more pull in each gear, but you have to upshift sooner. So there are some speeds where "gears" will give you greater acceleration, but at some speeds acceleration will be far worse due to having to be in the next taller transmission gear.

If it's not specifically 0-50mph you are interested in, I wouldn't bother. If you want to be speedier, just keep the revs up and shift later with the gears you have.

I think it can be overrated in terms of "bang for the buck" depending on what you pay for parts and labor... some people spend almost $1500 getting a spare carrier and tons of labor charges. Others get away with doing a lot of work themselves and only spend about $400. I came in about $750 and am mildly disappointed- would probably have been totally happy with 4.67 - I do not have a header/tune due to strict smog enforcement.

To be clear I really like the mod for daily driving with lots of time in the sub 50 mph range- I just think it is a bit expensive

P.S. I absolutely love the pull in 3rd gear on freeway cloverleafs- puts a smile on my face every morning

I have a 5.1 pair with cusco lsd type rs spec F , acceleration between 0-100 almost no different , the gain time don/t out run shifting time .


I think the advantage on track condition , is 100-180km acceleration, other benefit is more option to choose gear in corner cause even +1 higher gear have power .


When I run the 5.1 FD with stock diff. , it was having difficulty get back on throttle on corner exit and bump , it feel the lsd was too active cause lost of grip and control , it may be also cause by the Tein SRC being too stiff .But these are fix , once I got my cusco lsd type rs spec F install .


If you go 4.88 or higher , please consider the clutch type lsd .

Well, I'm not really looking to increase power, per se. Like I said before, I want to make it feel like it's faster without actually making it faster. I have absolutely no interest in moving faster. I like having to row through gears. I know. I'm weird. To each his own, I suppose, haha. Or her. 0_0

And yeah, shorter final drives concentrate torque to the first portion (the first half, if my maths are right) of a gear's travel through the RPM band. After that portion is run, it'll slouch off speed-wise, in comparison to longer final drives. It sounds like a decent compromise, for what I'm trying to achieve.


Holy guacamole, batman! 5.1?! I'm guessing you're running an AT, haha. I think I'm steering away from a 4.88, from what I've read here. 4.67 is increasingly sounding like the sweet-spot. With that said, you brought up something I hadn't thought of before--rearward capabilities. The stock axles/lsd would handle the increased mechanical torque, so long as I cap out at 4.67, right? :o

In his descibed case it looked not so much if 'can handle the load', but if 'have enough grip', no? IIRC clutch type diffs can improve traction on track above that of torsen's. Of course in return for more maintenance/noise.

If there is any advantage it should be in 0-100km/h (62mph) as both setups need to upshift twice. 100-180 km/h, or 62-111mph, with 5.1 gears you have to upshift to 4th almost immediately, whereas stock you don't have to until 84mph, but by then 5.1 has to upshift to 5th. At 106 mph, stock upshifts to 5th and 5.1 upshifts to 6th. Overall, more upshifts with 5.1 gears, and similar overall gearing from 67mph on up, my money goes with stock 4.1.

You don't have more options to choose gears in corner. Actually, fewer...

OP, if you want to know the effect of changing to 5.1 gears at just about any speed, just drop down a transmission gear. If you can't, then know that at that speed you'd most likely have to be in a higher transmission gear with 5.1.

I'll say it again, if it's not 0-XX acceleration you're interested in, but just want more oomph in general that you think diff gears will get you, just wind out the engine more and delay upshifting with stock diff and get the same effect for free.

In my case , the FD itself is loud and the CF shaft make aircraft noise after 140km , the lsd itself have no change in noise , I can only hear very little bit chatter noise if I turn my steering wheel full lock and accelerate together .


I had a cusco rs lsd in S2000 , it last too long and I sold the car with it , over 30K+ mix with daily , autoX and track duty .

Here is two of my record video ,

[ame="http://youtu.be/tnrY4rrxaRE"]http://youtu.be/tnrY4rrxaRE[/ame]

The sudden loss of grip was cause by the lsd act up weird over bump and in wheel lift .

[ame="http://youtu.be/7qPlyFXZotk"]http://youtu.be/7qPlyFXZotk[/ame]

It was 5.1 FD , OEM diff. , Tein SRC with Super Pro sway bar front and rear , Tomei EL & over pipe + nameless muffled track pipe , 235/40R17 NT01 . Just for you to get a idea . I drive the car around if it is the day i work alone , i don't see any issue .

Hmm... I find it much easier to break the rear loose on a 1-2 shift with my 4.56 gears than with the stock 4.10. Acceleration is not always the goal...

I suppose you could achieve the same effect by revving the engine mid shift - but that is not something I want to do on a regular basis.

Has anyone used increasing the whee size to slightly lower the final drive?

I completely agree. I have a 5.29 with a 1.5way MFactory LSD.

Fun! I'm rocking the 4.88 with the MFactory 1.5 way. How do you like the diff?

The diff makes a lot of noise when it's cold under low speed and tight turns. More so when releasing. I've only had the diff on the car for about 2000km. It's mostly just for track use and driving to and from the track. Overall I wouldn't go back to a helical LSD for tracking. I also have the Whiteline diff and subframe bushings so the noise is transmitted to the chassis more so then without them.

I guess these may have to do with the lsd configuration , mine cusco is set to 1.5 way , minimum intial torque and lock , with motul 75W140 . More lock up = more noise ?


Those solid diff. & frame mount and diff. brace both make noise , with or without the FD or LSD , i have them and i like it very much , the noise just make the drive more exciting . That me only , other may hate it ...


Back to kbraun94 question , the car feel pull harder , more torque , more shifting , it is more fun for me but can't argue if it is actual faster .

My LSD is set up the same way. Minimum initial torque, full lock and I'm using the same oil. I have a Greddy diff cover and I change the oil every time I change the engine oil.

I completely agree, the car "feels" like it pulls harder, more shifting, more fun but I don't think the car is actually faster on the street. On the track it does make a difference though as you can hold different gears for different corners now but that's track dependent.

Smash the 4.3 and hit past 4.55.

if you cant floor it in 6th gear and get pressure, your FD is not too low.

4.3 fixes it and makes it able to daily drive and go on long trips still. Racing? rip that mofo. Crank it up. It cannot hurt with a 7400 RPM redline engine right?

Currently have a jrsc w/ hbp on 6AT frs. I'm thinking about going Cusco 5.1 FD w/ Cusco RS 1.5 way. Hopefully this setup will help me get off the lines faster and quicker corner exit speeds.

I wanna go 4.56 so I can leave like an automatic.

I'd just warn you that freeway suffers considerably. With a 4.88, I had to adjust my cruise speeds to be 15mph lower to avoid noise and heat soak. But if you have the JRSC you've got an oil cooler, so heat soak probably isn't an issue.

My intentions aren't for fwy driving.... lol

I have a daily for the freeways...


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AT has a taller transmission ratio , and much less worry about the gear shift , may be it work .I think this would be some interesting experiment ... I actually think that I can never FI the car with the 5.1 FD setup , because too busy with gear shift and traction issue .


I suggest you consider to spend a bit more get a 2nd used diff. for these , just in case if it too aggressive and you can sell off the diff. .


Please update if this is really happen .

Sounds about right. I've got the bushings (and lots of other bushings, including motor mounts) and even got the plates WPC treated before installing them. I've got the diff set to minimal preload and lock capacity as well! The thing is a monster in the corners though which makes all the train noises totally worth it!

I think if I was to do it again, I would save up for the OS Giken.

Will do. :thumbup: