what difference will gears make?

[69camarokid]

i have a 69 camaro with a 95 trans am LT1 and T56 in it. In the back it has a 10 bolt with stock gears, though to be honest i have no idea what the stock gears are.

Im gonna be going to 4.11s soon and i was wondering how big of a performace gain you guys thaought it would net me? how much time off my 0-60 and quarter mile

[carguy502]

Depends... If you are running 2.73s of 3.08s, then hell yes you will net lower 0-60 times. I have heard that 4.11s are the way to go in stock 4th gens, so as long as you rear tires are not too big or small, you should have some fun.
Best,
Don

[69camarokid]

Depends... If you are running 2.73s of 3.08s, then hell yes you will net lower 0-60 times. I have heard that 4.11s are the way to go in stock 4th gens, so as long as you rear tires are not too big or small, you should have some fun.
Best,
Don

i dont know what my stock gears are... but it runs really low RPMs in 6th so i think theyre freeways gears. Im running a 245 tire in the rear on 8 inch rims

[BA.]

since you're in sunny socal, jack up the rear of the car to get both wheels off the ground, mark your driveshaft with tape or chaulk and then count the driveshaft revolutions as you turn your rear wheel around 2 times. that'll be your gear ratio.

Then we can tell you how for sure how much a kick in the ass the new gearing will be!

[mikey]

George @ rockland standard gear told me not to go with anything lower than a 3:73 or 3:90. He said that a lower gear like 4:11 or 4:56 developes a harmonic vibration on the drive shaft. He said while it will be fine for short trips to cruise nights ect. It will really drive you nuts on a long trip. You can get any tech info youneed or want from him here.
http://www.rocklandstandard.com/transzilla.asp

[b-man]

since you're in sunny socal, jack up the rear of the car to get both wheels off the ground, mark your driveshaft with tape or chaulk and then count the driveshaft revolutions as you turn your rear wheel around 2 times. that'll be your gear ratio.

Then we can tell you how for sure how much a kick in the ass the new gearing will be!

On an open rear to check the gear ratio you need to hold one drum from moving, easiest way if it's still in the car is to leave one tire on the ground.

Turn the driveshaft and count the turns of the driveshaft, you need to make the drum that's still free (or the tire that's off the ground) turn exactly two full revolutions. This is due to the 2:1 ratio of the differential side gears and spider gears.

A little more than 2 and 3/4 turns of the shaft, you have 2.78s, a little more than 3 turns = 3.08s, about 3 and 1/4 turns _3.23s, etc.

Eyballing it might not give you accurate results, use some chalk or make a scribe mark on the driveshaft, rear end, drum, tire, ground, etc.

Posi rear - BOTH tires off the ground, count driveshaft turns for ONE full tire revolution. This assumes you have posi that's in good shape.

Open rear - ONE tire off the ground, count driveshaft turns for TWO full tire revolutions.

This method also works great when you're in the junkyard or at the swap meet and you want to make a quick ratio check before bothering to tear it down to do a closer inspection.

I also think that 4.11s will be a little to deep, something like 3.55 gears (or maybe 3.73 at the most) will be better out of the hole and help control wheelspin yet still be a very nice highway/economy gear in 6th.

This will put your gearing close to the original factory gearing, I'm pretty sure your drivetrain came from a car that had a 3.42 rear gear.

[69camarokid]

On an open rear to check the gear ratio you need to hold one drum from moving, easiest way if it's still in the car is to leave one tire on the ground.

Turn the driveshaft and count the turns of the driveshaft, you need to make the drum that's still free (or the tire that's off the ground) turn exactly two full revolutions. This is due to the 2:1 ratio of the differential side gears and spider gears.

this is very helpful since i do not have a posi (YET) and i had doen the single rotation before in an attempt to figure out the gear ratio and it had been nearly 1:1 ( i believe... it was about 3 years ago).
this method makes more sense, ill check it tomorrow morning and post it up.

thank you for the info! its a big help!

[79-TA]

Switching gear ratios is often referred to as "waking a car up" and for good reason.

Basically, you get more torque multipliacation (f=ma, so more accelation) and it allows the engine to rev more freely so you get into the powerband more quickly.

Freeway cruising rpm suffers immensely, but that's the compromise you make for the performance gain.

[Rhino]

i dont know what my stock gears are... but it runs really low RPMs in 6th so i think theyre freeways gears. Im running a 245 tire in the rear on 8 inch rims

Do you know what RPM your engine runs in 6th at a given RPM? Knowing that, and your over all tire size you can calculate the gear ratio.

[69camarokid]

Do you know what RPM your engine runs in 6th at a given RPM? Knowing that, and your over all tire size you can calculate the gear ratio.

unfortunately i just got the car running in the last few weeks but some things arnt done yet... IE my rpm gauge doesnt work. I have a RPM gauge set up for my old turbo 350 automatic and i now have a t56 6speed in the car. I have yet to find a place that sells a cable to allow my RRPM gauge to work. I tried classic industries since theyre right down the street and they tried to sell me some 350 dollar converter piece..... ummm yeah, no!

so no i have no idea what my RPMs are.

[gmjj13]

i think you mean speedo?

almost sounds like it'd be cheaper to buy an electric speedo than a 350 dollar convertor...

[69camarokid]

yeah your right, i did mean speedo... although my RPM gauge alaso doesnt work hahaha

[69camarokid]

ok... so. Did my gear check and had a little over 3 rotations meaning imore than likely have 3.08s out back. This basically brings me back to the question of whether or not to go with 3.73s or 4.11s. I know the 3.73 give me a better freeway cruising and the 4.11s give ,e better excelleration. But as this is my first time swapping gears, and my first build id like to hear from the voices of experience.

I should also mention im running a stock 1995 trans am T56 6 speed manual transmission. So keep that in mind. Ive head that since my tranny has dual overdrive the 4.11s would be fine. What do you guys think?

thanks

[79-TA]

Calculating speed isn't that hard if you know your setup. You'll need to know your transmission's gear ratios (in this case the top gear is the ratio of interest), your rear end gear ratio, and your rear tire circumference and then pick an engine rpm or vehicle speed. It just comes down to simple unit conversion.

Man, I'd go crazy if my tach didn't work. Would that T56 have the 0.50 overdrive or the 0.62?


So, starting with an engine rpm, here's the process:
- Take the rpm of your choice and divide by the top gear's ratio
- Divide again by the rear end ratio (to be more exact, use the ring and pinion tooth numbers as a fraction)
Note that the units are still in terms of revolutions per minute here and we're trying to end up with miles per hour. Now we need the tire circumference so we can convert from revolutions to inches.
- multiply by the tire's circumference

If you know the tire's diameter, the circumference is just pi x diameter. If not, the diameter can be found with the p-metrics on the sidewall. Take the width in mm and divide by 25.2 to convert to inches. multiply this number by the aspect ratio and divide by 100 and then multiply by 2. Lastly, add the wheel diameter, the last number, and that is the overall tire diameter. Now either write this number down to plug in or make sure you keep your order of operations straight when using it.

Now that we've multiplied by the tire's circumference, we have inches per minute, so we'll just convert minutes to hours by multiplying by 60 (multiplying because it is in the denominator.) Then just divide by 12 and then divide by 5280 and you'll have good ol' mph.

For example

((2000 rev/min) / (0.50 rev/rev x 4.11 rev/rev)) x ((((245 mm/25.4 mm/in) x 2 x 0.45) + 17)x pi) x (60 min/hour) / ((12 in/foot) x (5280 feet/mile)) = 74.35 mph

with 3.73's it'd be 81.92 mph

with the 0.62 overdrive . . . I have no idea what size your tires actually are without all 3 basic specs

((2000 rev/min) / (0.62 rev/rev x 4.11 rev/rev)) x ((((245/25.4) x 2 x 0.45) + 17)x pi) in/rev / 1056 = 59.97 mph

with 3.73's it'd be 66.08 mph

since the conversions on the end aren't going to change, you can simpilify that to just dividing by 1056. (60/12 x 5280 = 1/1056)

if you plug something like this into excel, you can quickly have a spreadsheet of all sorts of speeds at given rpms or rpms at given speeds. I haven't done anything to take tire growth at speed into account, but the change isn't large. Of course, you can also go from mph to rpm when this equation is rearranged a bit. And then if you're not feeling ambitious, there are plenty of online calculators, but they don't make spreadsheets for you like excel.



You're transmission has a pretty tall overdrive so that even with 4.11's your cruising rpm is good. I like the 3.73's since they'd let you cruise at 72.5 mph at a calm 2200 rpm. But if a couple hundred rpm more on the highway wouldn't bother you, then have fun with the 4.11's. It all depends on how you want to drive the car.

[wicked68]

you also need to look at your engine horsepower - (this does not apply here since I think you are probably only running about 300 with that engine stock) but if you had big hp with those size tires or even something a bit bigger you would not want to go that big on a rear either.

I run 700 rwhp and I have a 3.23 and we are actually putting taller tires on it to lengthen the gears abit and give it a bit more top end - since my car loves the top end of the hp curve.

if I went 4.11 to lower my 60 foot times I would be having a hard time hooking up since I dont have full tubs and would be risking killing my tranny with the shock as well.

[69camarokid]

haha after reading all that i feel like im back in school again! i love it haha

Im actually an engineering major at cal state LA right now with an emphasis on industrial production in transporation... so i remember some of this math, but the refresher is a big help.

My trans has a .50 6th gear. And the engine is a cammed LT1 with most bolt on goodies. A buddy withthe same year engine and same cam is putting down 345 RWHP with no tune. im tuned so at least that much. Im not too incredibly worried about my top end. I just want a quarter mile time in the 12s that i can drive every day.

[79-TA]

With the 0.50 overdrive, the 4.11's are a no-brainer. That's a final drive ratio of 2.06!!!

[79-TA]

Wicked68 makes a good point about tire limitations with the more aggressive first gear.

350 rwhp is right in the ballpark for what you'll need to sneak into the 12's without a drag-specific set up so far as I can tell. Sounds like fun!

Anyway, here's (most of) what I whipped up on excel for my own car one night. I thought it answered quite a few questions. Perhaps you should try it as well.

[69camarokid]

alrighty then....

did the math.. thanks again for taking the time to write that all out. IT was a big help and gave me a chance tofeel all brainiac like.. lol

so i anted my cruising RPM to be atleast 2500 RPMS or under so i did my equations set at 2500 RPMs to see what speed that would land me.

4.11s in 6th gear at 2500RPMs nets me 86.82MPH on a 24 inch tall tire

3.73s in 6th gear at 2500RPMs nets me 95.66MPH on a 24 inch tall tire

hmmm if im already up to 86MPH in 6th with 4.11s at only 2500RPMs then i think ill be ok with them...

everyone else agree?

[79-TA]

Sounds good, definitely agreed. 4.11's with a 0.50 overdrive still gives a crazy tall top gear. What are the p-metrics on your tires? 24 inches seems a bit small, but the larger diameter will only reduce rpm at a given speed. From a freeway cruising standpoint, 4.11's will be no probem at all.

Now that you'll be multiplying torque at nearly 11:1 in 1st gear, you'll have to worry about keeping things stuck to the ground