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 .