lets say the scenario is drag racing......

does the final rearend gear really make that much difference?

if you have a 3.90, you're looking at $100 for 4.10 gears.....

if you 3.90 or 4.10, you're looking at ~$400 for 4.33 gears....

is it really worth it?

 

Depends on what your doing with the car. Drag? Yeah, thats a big difference..

 

is a 4.1 to a 4.3 rearend swap worth one tenth in the 1/4 mile?

if so i'd say its worth it, other than the drawback of a higher cruise RPM on the highway.

 

Its worth more then 1 tenth. Think about the 60 ft time.

 

well how would the 60ft really be that much better? i mean that just means that your first gear is over faster, meaning thats time you lost because you shifted to second.. maybe im just looking at it the wrong way?

 

*sigh*

 

come on rat, explain yourself.

 

How about you explain yourself. a 3.9 gear to a 4.3 gear is going to get you down the strip alot faster. Period. Too bad its gonna kill your top end.

 

i dont have an explanation, thats why i was asking you.

 

Well its not going to kill most people's top end. How many people take thier car over 150mph even? I don't know too many people topping out 5th gear on a regular basis.

4.33 gears are going to improve acceleration everywhere. From 10mph-the top of 5th gear.

 

Honestly Bitchmill, you need tall-*** gears, especially since you run that gay-*** 1/8 mile. On the eighth, you need all the gear you can get..

 

there is a formula that you can use to figure out what your road speed will be at a specific RPM. You need the engine RPM, tranny gear ratio, tire size, and diff ratio. I'll see if I can find it. Its pretty cool to see the numbers for your self when you keep all the stuff the same and just change 1 variable, like the diff ratio, or tire size.

 

Unless you're a serious dragger, there's not much point in going from a 4.1 to a 4.3, it's pretty much unnoticable.

 

ok, I found it. X=multiply /=divide

Speed in mph = (Rear tire circumference in inches X engine rpm) / (Transmisison gear ratio X Differential ratio X 1056)

This is how you find tire circumference:

Circumference in inches = pi * (Wheel diameter + (2 * (Aspect ratio * Tread width in millimeters / 254)))

For example, given a 205/60 R15:
Wheel diameter = 15 in
Aspect ratio = 60
Tread width = 205 mm

Calculated circumference = 77.55 in

 

Changing the gearing changes the amount of force applied to the ground for the same engine torque. So changing from 3.9:1 to a 4.1:1 or 4.1:1 to a 4.3:1 increases accelerative force by ~5% (not really worth it), and changing from a 3.9:1 to a 4.3:1 increases accelerative force by ~10% (worth it).

Shorter gearing also improves throttle response, purely because the engine can generate more power at a given speed because it's at higher revs.

 

Now why would you say a 5% power increase isn't worth it. In my opinion 4.3 gears are awesome, other than the whole fuel consumption/cruise rpm thing. Now, before you start saying that I'm not going to notice it my first T2 hada 4.3 diff which will be swapped into my current T2 and I could DEFINATELY feel a significant improvement.

-David Guy

 

I say that because you have to find one (hard), pay for it (not cheap), swap it (major PITA) and put up with higher fuel consumption and engine noise, all for what is only going to be a relatively minor improvement in performance. I find it hard to believe the improvement could be called "significant". You might be lucky and find one cheap without much effort, and you might need to swap the diff anyway. But otherwise IMO it's just not worth it unless it's part of a major build-up.

 

what if your 390 dif case has a hairline crack and leaks, and thers a complete 410 in the garage?

 

if you want new gears get 4.60

4.60 and a full t04 setup will be all the drag car you can handle. Just about unbeatable on the street as well.
Last I knew Tripoint was still cutting gears for 500 bucks.

 

who sells 4.60?

 

There is a difference I can feel it in my car I have 390 now from an auto car in my broken rear i have 410 and they were noticably quicker

 

double post.

 

It's not like you can't smoke the tires with even a moderately modified TII and 4.10 gears....with 400rwhp you're spinning through third gear as it is. Why do you need it? If anything I'd go down to the 3.90s.

 

I'm sorry NZ, but you're wrong and this is why:

No, these are not hard to find, you call mazdatrix and they send them.

Ok, I don't find $400 (slightly more with tax and shipping) to be a whole hell of a lot for a nice performance upgrade

Dude, this takes less than a day if you're even remotely competent.

Um, ~350 rpm difference at cruise in the 80 mph range isn't a whole hell of a lot more fuel consumption, believe me, I know. And noise? Please. Again ~350 rpm is minor.

This is going to be a constant 5% multiplier to your power, if you up your power guess what? You'll still have a 5% increase, it's not static.

I think I've laid it all out, and to me thiss is a very significant modification. People always tend to think that if their turbocharged car isn't as fast as they would like it then they can either just up the boost or swap to a larger turbo but it isn't that simple. Look at dyno queens compared to roadrace beasts, dyno queens have one goal, make a shitton of power and have bragging rights, do they need ninja gear ratios? No. Do to they require correct sizing on wheels/tires? No. Do they need to be as light weight as possible? No. Do they even need suspension modifictions? No.

I guess my point is that many of these modifications are dismissed far too quickly due to the fact that our cars can make power very easily, and many members tend not to realize that you must take the whole picture into account, as well as a very very tight wallet which kills any sort of significant driveline modification. for example you see a fair amount of interest in creating a 9000+ rpm redline on roadrace cars, however how many peoplehave asked about running diff coolers for their rides? Not a whole hell of a lot.

This ends my (hopefully) informative little rant. Flame away if you so choose.

-David Guy

 

I'm a firm believer in "every little bit counts", even if it's 5% like stated above. Me personally I would jump all over a 4.30 gear. I don't really care about top end. My car is drag only anyways.

-Destin