3.73 thoughts on 260whp turbo?
 

I'm on a 2018 brz with the 4.3 final drive. What's everyones' thoughts' on going down to a 3.73 if I'm not making too much power?

I'd use the 3.73 either to raise your grip, or for 1/4mile driving to hold a gear longer. I do not think 260whp merits a 3.73. I'm selling mine because it really just makes the car piggishly slow, and I think under 350whp it'll only make you feel slower.

What kinda turbo and how much power are you making? That doesn't seem good. Would you happen to have any videos?

I don't have my turbo installed yet, I installed it on my NA car. There is one video on Youtube of BRZoomTX running it on his 400+ WHP car.

I have experience with other cars and changing the diff to try for longer gears. You can certainly do it, but you'll be surprised how much torque you lose by lengthening the gearing if you're not making enough to take advantage

Yeah his car is ridiculously fast. My first gear is so useless rn lol. On a site note, how much are you selling your diff for?

It's already sold locally, sorry.

It really would be a great tool for helping minimize wheel spin in 2nd, but I think 1st really is a matter of tire, contact patch and boost by gear settings. I definitely don't mean to discourage the 3.73, but I feel that the cost to benefit ratio is not there unless you're going for bigger power.

eventually i'll go for e85 and go for around 320whp. what about at that power?

Choosing a proper FD is highly dependent on your power levels and your usage for the car. Like autox, track, drag, street pulls etc. if it can prevent an extra upshift in the straights or down shifts in the corners it may be a good choice.

Going from 4.3 to 3.73 your gears will be 15.5% longer, also the same amount of less torque multiplication from the gear. So whatever your currently topping a gear out at multiply by 1.155 and see what your new redline speed is per gear. You may find out you just made 5th too long /high of speed for your power and now it’s useless.

A 3.9-4.1 may be a better option for sub 350whp

thanks guys.. I think i'll just stick to my 4.3 then and save that cash for something else such as e85.

86TOYO2k17: or if NA, imho by then close ratio gearset might be better option, as in making longer just 1st & 2nd.

@incutebus: I have it as a factory option in the early European models and I don't make too much power either. It works great on the autobahn with a really strong 5th gear for performance (stronger than the 4.3 fd 6th gear) and a much better overdrive 6th gear for economy. Porsche's are using similar or even longer final drive ratios for decades.

how is your acceleration in 2nd 3rd and 4th?

Personally I like it because it doesn't break traction easy. Power delivery is smoother and longer in same gear. However, it is a setup for high speed driving. The 2nd gear for example tops approximately at 103kph or 64 mph.

I'll be at 450whp soon, thinking about upgrading the fd.. Friend says the torque feel and pulls will feel a lot different. Curious to see how it is with the stock fd lol. Friday is the big day for my tune.

I retained the stock 4.1 (2013) FD all the way up to 550 whp 480 wtq while boosting the FA20. 1st and 2nd were useless (as far as punching the car, driving around was absolutely fine).

When boosting the car, setting it so that the torque does not all come up too low helps a lot.

Now I have an LS swap and I needed to swap down to 3.73, because the down low torque from the LS (over 320 wtq at 2500 RPMs) made first and second too short and undrivable. Like others have said, it depends on use, power curve and power range.

Thats a lot of power xD What size turbo when you were 550whp? Curious because my current setup is using a gt2871r lol

GTX3076R

Which option is best for you is highly dependent on what you use the car for and what benefit you are trying to achieve from switching a FD. If you just care about acceleration to an arbitrary number going as aggressive as you can before becoming traction limited would generally be the best, but there are plenty of trade offs. A lot of things to consider. Deciding what you want to achieve by switching FDs, or what your use of the car is, can then determine what FD would be best for you.

On stock Tire at 7400RPM these are the top speed of each gear for these 4 FDs.

4.3FD 3.73FD 3.909FD 4.1FD
35 / 40 / 38 / 36
58 / 66 / 63 / 60
82 / 94 / 90 / 86
104 / 120 / 114 / 109
126 / 145 / 139 / 132
164 / 190 / 181 / 172

for a fast fun high speed run, based on this just looking at 5th gear, for 260whp i would say a 4.1-4.3 would be best, at 320whp a 3.909 to 4.1 could be good and still pull hard to top of 5th. To have a usable 5th with a 3.73 you would really want at least 400whp+

also an ls300 has a 3.909 read diff for around 300$ and swaps in pretty easy.

going e85 soon, used that money towards flexfuel instead. I'm sure I'll be more happy.