Actually all they sell you is a ring and pinion. I was refering to a complete diff. So now you're disassembling and reassembling the diff as well...
IMO $400 for the equivalent of an extra 9-10hp on a turbo is not much bang for your buck. It might be worth it if you'd already done a lot of the easier stuff, but you could build quite a nice 3" exhaust for $400 that would make 30-40hp. Compared to an exposed pod filter, a decent cold air intake and heat shield could have a similar effect for $20-30.
I consider myself quite a bit more than remotely competent, but if I was stuck in my garage with basic tools (and that's most people here) I would definitely allow more than just one day to remove, disassemble, reassemble and reinstall an FC's diff. And I didn't actually say it was a difficult or time-consuming job, I just said it was a PITA.
Um, yes it is. That's the beauty of a turbo'd engine. It doesn't take much extra boost to get 10hp, and a simple boost controller can be made for ~10% of the cost of that ring and pinion set. A turbo upgrade costs more, but will get you a helluva lot more than 10hp. NA's are a different story. It's harder to make the same gains, so shorter ratios are more worthwhile.
Why would I?

So get one. Apparently it's cheap and easy...

 

don't spend 400 bucks on 4.30 spend the 400 on 4.60 gears.

if you have 2 300 rwhp cars and they are running in a straight line the guy with the lower gears is going to win ever time in a drag race. A guy around here in Northern VA races 3rd gens and he runs 4.60 in all of his street cars and also his drag car that hit 9 seconds.

 

Actually NZ I've found that it isn't always that simple. You start throwing huge turbos and more boost at your car then you'll have a car that: A. Isn't fun to drive around on the street. and B. will get it's *** handed to it by a crx on a canyon road or a very tight road course.

-David Guy

 

I don't see how an increase in power can decrease handling? With the right driver, more power will always equal faster lap times. And why does it matter that a turbo is adding the power instead of a higher gear ratio?

 

It doesn't decrease handling, however it will tweak your powerband to a point that it becomes unwieldy. Just look at Mani and his Supra, he steps down to a smaller turbo, putting down ~450 horses and steps up to a higher final drive whenever he road races. I use this example mainly due to the fact that most high horsepower supras tend to have a horrible dyno plot/torque area and very high peak numbers, I am not comparing an rx7 to a supra.

-David Guy

 

where can you buy the 4.60?

 

I don't see how (once your car makes power) gearing can change 1/4 mile times at all...

if my car makes enough power to be able to not get traction at all in 1st (and 2nd on demand), how is MORE torque to the ground going to help me?

 

Werd. Its not always helpful for traction limited cars. But your car will be trying to accelerate faster. But once you get going, you better watch out.

See I personally don't like setting a car up for drag racing. Wide soft-sidewall tires, heavy flywheels, and soft suspension setups are not things that make cars fun to drive. Its hard as hell to launch a Carrera GT, but do you think Porsche cares that the car could get better 60' times?

 

The difference between a 4.10 and a 4.30 would actually be very noticable, being that with that setup, a stock s5 N/A could probably give a s5 TII a run for its money in 0-60 times. Just for all you kids, thats a 40 HP handicap that is overcome by sheer gearing ratios, that and the N/A powerband is longer then the TII's, so that would give a slight advantage.

Personally, I would want a 4.30 in my rear end for around town and racing, but a 4.10 or 3.90 for highway (or the occasional "testing" of the local radar speed boxes)

 

well once you solve your traction problem the gearing would make a huge difference in straight line acceleration. All of these 1/4 improvement assume you are keeping traction to the wheels, which is something you should be doing if you want to go fast anywhere

 

Where can you get 4.60 gears?

 

dude the main problem with all this is you just spin your gears that much worse. You have to be a master of hte launch before you even THINK about that. I've lost to 200 HP hondas with a 400 RWHP car because of that before.

 

There's so much misinformation here it's sad...

My GTUs gets 25-31mpg (varies on which type of gas I put in) freeway driving at 80mph (4k rpm), this is definatly not far off from my 4.1 '87 sport (26-29), at 80mph. As far as acceleration, my GTUs accelerates dead even with the 4.1's, the only gear I ever can pull on anyone is 3rd, and even that has it's limits. The difference is NOT noticable at all. I've driven in countless different FC's with all sorts of gearing, and the only real noticable difference was going from 3.9 to 4.3, or similar.

 

Well I have to say I deffinetly notice the 390 to 410 difference in 3rd gear. This seems so wierd that some people have a hard time understanding it. If you are goin all out drag and don't care about gas mileage or top speed (Only a concern for those of you whose cars hit there top speed at redline) then get the smallest(largest Number) gears you can find. Many dage muscle cars use from 5.0 and up. I thing sonicrat and NZ convertible have this topic coverd tho

 

Thank you, it was very informative. Nice to see an informative post w/ out major flamage.

 

For the record, taller gears will give a turbo motor more load which will help spool.

Taller ratios would let the turbo do the work by using torque for a longer period of time.

 

 

Yes, if you're running a larger turbo then sometimes upping the ratio hurts more than it helps however with a properly sized turbo you shouldn't really have any issues with a 4.3.

-David Guy

 

But we're not talking about huge turbos here. Why would you even bring it up in a discussion about shortening the diff ratio by a paltry 5%?

And simply increasing the boost with your existing turbo will have absolutely zero negative effect on drivability or turbo lag. Quite the opposite in fact.

 

I'm sorry man...but you must be a horrible driver if thats the case.

-Joe

 

I am going from 3.9 to 4.3 in my vert this week. I'll let everyone know what my butt thinks about it when I get it done.

BTW, it has always been my understanding, and the formula posted bears this out, that the torque produced at the flywheel gets multiplied through the gears, so not only does the 4.3 provide more actual torque to the ground, it helps the most in the lower gears where the ratio is the shortest, and low end/ low speed torque is what the rotary needs the most help with.

I'm planning on staying NA and 5-10% means alot to me.

 

you can get 4.60 gears cut from Tripoint last I checked.

 

"For the record, taller gears will give a turbo motor more load which will help spool.
Taller ratios would let the turbo do the work by using torque for a longer period of time."

150FC wins with this comment. Lower gears are always better for racing. You just have to come to a point where you figure out if your car is a daily driver/highway long distance runner or a street/weekend racer.
You can't have the best of both worlds. If you want to best of both worlds buy a Jap street bike

 

Nobody mentions putting smaller tires on the back, ie. going from 205/60 15's to 205 50 15's. That shortens the wheel diameter by like 1". Isn't that pretty much the same effect as putting in lower rear gears?

200 ft-lb at engine * 3.475 = 695 ft-lb at the driveshaft
695 ft-lb *4.1 = 2849.5 ft-lb at the half-shafts
or
695 ft-lb *4.3 = 2988.5 ft-lb at the half-shafts

139 ft-lb gain at the wheel by switching from 4.1 to 4.3 rear gears.

Force at tire contact patch:
Torque = Force * Distance
Force = Torque / Distance

2849.5 / 1.029 = 2849.5 lbs of force with 205 60 15 wheels
2849.5 / 0.9625 = 2960.5 lbs of force with 195 50 15 wheels

163 lbs of force change

Go here for more info on power and gear ratios:
http://www.allpar.com/eek/hp-vs-torque.html

Dave



Dave

 

FWIW, gearing doesn't change power, only torque. (Not contradicting Dave, above)