general questions?

[Nozler]

A few quick questions:

Transmission gears:
Say I have a transmission gear with a ratio of 2.
Is that 2 turns of the driveshaft for every one of the engines
or
1 turn of the driveshaft for every 2 turns of the engine?

Rear end gear ratio of 2.
Is that 2 turns of the axle for every turn of the driveshaft
or
2 turns of the driveshaft for every turn of the axle?

What is the difference between overdrive or 4th gear? Is overdrive just a fancy name for the 4th gear?

 

[93Ranger]

let me work my way backwards.

overdrive is basically 5th gear. it lowers your gear ratio even more, thus creating ****y accel. but great mileage, and the ability to go faster. 4th gear is just that, 4th gear, better accel than 5th, but worse mileage.

now, a rear end ratio of 2:1 would mean that 2 turns of the wheels for every 1 turn of the tranny output shaft. so if you had 4.10:1 back end ratio, you would have 4 wheel turns for every 1 turn of the output shaft. so a higher back end ratio = quick accel. low top end
lower back end ratio = slow accel. high top end

transmission gearing means that you get 2 engine turns for 1 tranny spin. the Tachometer says what your engine revolutions is. now, getting 4,000 RPM's needs to be reduced inorder to extract any power out of the engine. it is downgeared by your transmission to increase torque, but the back end down gears it even more increasing torque. so when you see a car with 200 HP, but 350 Ft Lbs of torque (not possible, but it is good for an example), you know it has fairly low gears.

car companies found that if the HP and the Torque are fairly matched, then it will be a good match for a daily driver.

some guy on a forum i visit had a Jeep TJ that he set a rock crawling gear so it had a roughly, 65.3:1 in 4lo. NOT a daily driver. he could put it in 1st, drop the clutch, stomp the brakes, and sit there and chirp the rear wheels. talk about torque **insert Tim Allen power grunt here**

 

[Nozler]

How about torque converter stall speeds?

I understand the torque convertor to transfer power from the engine to the tranny but not at everyspeed. Otherwise your brakes would be fighting the engine at a stop light. But when you are at a stop light, the engine is at low rpm and below the torque convertors stall speed.

My question is if the above is correct then why does the engine move the explorer even when still at very low rpms, like if you just let off the brake at a stop light and didn't press the gas?
Is the torque convertor stall rate when the total power is transfered?
So for faster takeoffs for dragsters, I high stall rating would be wanted
and
for towing, a low stall speed would be wanted?

Correct? Wrong? Why?

 

[Stephen S]

Originally posted by 93Ranger

now, a rear end ratio of 2:1 would mean that 2 turns of the wheels for every 1 turn of the tranny output shaft. so if you had 4.10:1 back end ratio, you would have 4 wheel turns for every 1 turn of the output shaft.

You sure about this?? Using the axle ratio (4.10:1) means for every 4.10 rotations of the driveshaft, the tires/axle rotate 1 time. This is why race cars have high ratios (maybe 3.08:1??) and rock crawlers use low ratios (4.56:1). The lower the gearing, the easier it is to turn big tires. Anyway, an axle ratio is (driveshaft revs:axle revs).

I'm pretty sure you are right about the transmission gearing. When your engine is spinning 4000 RPM, your transmission gears that down to get power from it. Tranny ratio of 2:1 for example would mean 2 engine revs for every 1 tranny rev. (engine revs:trannyrevs).

 

[Alec]

One correction though:
the 96 automatic only has 4 gears, so OD is the 4th gear.

The ratios are approximately (not exact I know, so don't kill me Robert)
1st: 2.5:1
2nd: 1.5:1
3rd: 1:1
4th(OD): .78:1

The first number represents the engine, the second number represents the driveshaft.

In the rearend gears, the first number represents the driveshaft, and the second number represents the axle.

 

[yob_yeknom]

To clear up overdrive a little bit. Overdrive is no certain gear, nor is it necessarily your last gear. An overdrive gear is any gear with a less than 1:1 ratio.

 

[93Ranger]

Originally posted by Stephen S


You sure about this?? Using the axle ratio (4.10:1) means for every 4.10 rotations of the driveshaft, the tires/axle rotate 1 time. This is why race cars have high ratios (maybe 3.08:1??) and rock crawlers use low ratios (4.56:1). The lower the gearing, the easier it is to turn big tires. Anyway, an axle ratio is (driveshaft revs:axle revs).

I'm pretty sure you are right about the transmission gearing. When your engine is spinning 4000 RPM, your transmission gears that down to get power from it. Tranny ratio of 2:1 for example would mean 2 engine revs for every 1 tranny rev. (engine revs:trannyrevs).

um... thats what i said? 4.10 back end means this: the wheel's will spin 4.10 times for one spin of the tranny output shaft. if it were the other way around, and 4.10 spins of the output shaft for every wheel rotation, then the lower the first number, the faster the wheel's would spin, and that is the exact opposite of what happens.

your analogy of your racecar:rock crawler is entirely correct.

a stock car (not drag, but oval track) is geared at something low likw 3.0 or something like that. that gives you poor accel (but with that many ponies, it doesnt matter), but a high top end, thats why these cars can sustain 180 MPH for several miles without redlining and melting the engine.

correct me if im wrong.

for torque stall converters, i believe they are like this:

the engine in an automatic vehicle (use an explorer as an example) needs to spin or else it will stall out. but if it is spinning, then it will fight the brakes at lights and whatnot.

so what they do, is set up a system that is like a clutch. it doesnt grab below a certain RPM, this saves the tranny, brakes and engine. once you get on the gas, it'll grab and the car will accelerate.

a high stall speed means that you can take off right at your peak RPM range. the problem with that, espically in a daily driver, is that if you have a high stall speed and you let off the brake, it will start to roll back a bit until you reach that RPM, and it will engage.

again, correct me if i am wrong.

 

[Stephen S]

Originally posted by 93Ranger


um... thats what i said? 4.10 back end means this: the wheel's will spin 4.10 times for one spin of the tranny output shaft. if it were the other way around, and 4.10 spins of the output shaft for every wheel rotation, then the lower the first number, the faster the wheel's would spin, and that is the exact opposite of what happens.

We may not be understanding one another, or may be arguing around the same point. But a 4.10:1 rear end means that the tires/wheels/axle will rotate ONCE for every 4.1 rotations of the tranny output shaft/driveshaft. The transmission output shaft/driveshaft rotates faster than the wheels/tires/axles do. The ratio is 4.10 driveshaft revs to every 1 wheel rev. (Driveshaft revs:wheel revs)

If you don't believe me, go jack up the rear end of your truck and manually spin a rear wheel ONE full revolution, and notice how many times your driveshaft turns.

 

[Nozler]

my engine idles around 900, out of gear and 750-800 when in gear(auto). If I left off of the brake, the car starts moving forward even though it is slow. I assume the stall speed isn't 800 b/c then it would be way too low. I think.
So is the stall speed rating when there is a 100% power transfer?

 

[nosaj122081]

Originally posted by Nozler
my engine idles around 900, out of gear and 750-800 when in gear(auto). If I left off of the brake, the car starts moving forward even though it is slow. I assume the stall speed isn't 800 b/c then it would be way too low. I think.
So is the stall speed rating when there is a 100% power transfer?

Its a little hard to explain.... Right now I have an 11 inch converter (gonna put a 10" converter in this summer) in my Mach. When you let off the brakes, it will creep along, it doesn't let the tranny slip at idle. When I punch the gas, it "flashes" to about 2200 RPM before it grabs. Most aftermarket converters are measured more towards their flash speed, although it is different for every car.

To check the stall speed of your converter you gotta powerbrake it. Watch the tach, the speed when the tires start spinning is the stall speed. Its probably slightly over 1000 RPM, but I'm not sure, my Explorer is a 5 speed.

Sorry for being confusing, its alot simplier when you see it in action.

 

[Robert]

Originally posted by 93Ranger


um... thats what i said? 4.10 back end means this: the wheel's will spin 4.10 times for one spin of the tranny output shaft. if it were the other way around, and 4.10 spins of the output shaft for every wheel rotation, then the lower the first number, the faster the wheel's would spin, and that is the exact opposite of what happens.
. . .
again, correct me if i am wrong.

OK Stephen is correct. Put in a mathematical way, let's use 4th gear as an example since it typically offers a 1:1 ratio for sake of ease. Driving along the interstate in 4th gear at 2500 RPM with 30" tires and a 4.10 axle. If what you were saying was correct 93Ranger, your rear tires would be turning at 10250 RPM with your driveshaft turning at 2500 RPM (2500 x 4.1). Ok, now using basic mathematics we can calculate the CIRCUMFERANCE of the 30" tire to be approximately 94.2" (Pi x D). So if the tire is turning at 10250 RPM, we can figure that it is covering 965550" in one minute. Divide by 12 to convert it into feet yields 80462.5'. Divide it again by 5280 to convert it into miles and you end up with 15.239 miles. So if what you were saying was correct, you would be traveling at 15.239 miles in one minute or put another way 914.34 MPH. Did I make it easier to understand? Probably not

 

[Stephen S]

Originally posted by Robert

Ok, now using basic mathematics we can calculate the diamter of the 30" tire to be approximately 94.2" (Pi x D).

Thanks for backing me up, but isn't the diameter of a 30" tire, um, 30". I understand that you are meaning the circumference of the tire, and then the linear distance that the tire will travel in one revolution, so I'm just picking on you. I didn't check your numbers, but your process seems right. Nice work.

 

[Robert]

Originally posted by Stephen S


Thanks for backing me up, but isn't the diameter of a 30" tire, um, 30". I understand that you are meaning the circumference of the tire, and then the linear distance that the tire will travel in one revolution, so I'm just picking on you. I didn't check your numbers, but your process seems right. Nice work.

And to think it took until November of last year before I made my first mistake of '01

 

[Stephen S]

Off to an early start huh??