Is there anywhere that has an explaination of how the rear gears work, and why they do what they do.

I'm tring to figure all that stuff out...

 

Maybe you'll find something at http://www.howstuffworks.com ?

Basically the gear that connects to the driveshaft is called the pinion gear. That drives a ring gear. The ring gear is bolted onto a "carrier", which either be a posi, a locker, or an "open" differential. For a racetrack-only car, the carrier can be a spool. The axleshafts (left & right) slide into this carrier.

An open rear releases one wheel (usually the outside wheel) when the car turns. This is because on a turn, the outside wheels spin faster than the inside wheels. If the open rear didn't let one wheel "come along for the ride", the car would "plow" forwards. This is why spools aren't used on the street- a spool LOCKS the axleshafts together. Because of the spider gear design inside an open rear, when you go straight forward, only the rear right tire is driven, the left comes along for the ride. When you reverse, the left rear tire is driven, and the right comes along for a ride.

A posi/locker will also release one wheel on the turn. However, it senses when each wheel is turning at the same speed- and that's when it drives BOTH wheels. A posi uses clutches, and can "slip".

A locker uses interlocking gears, and can't slip. A locker is usually "clunky" to drive, since the gears keep slamming in and out of each other. A more espensive locker will be quieter. But, a locker proves the ultimate traction, since it can't slip.

Some lockers, like one by ARB, is air-activated. Meaning, you drive your truck on the road, and the locker acts like an open rear. Go off road, and pressurize the locker through a special fitting, and the axleshafts lock up.

A spool has no gears or clutches or cones or whatever on it. It's a solid chunk of steel that takes the axleshafts from the side, and the ring gear around the edge.

 

So how can the size of the gears cause goood or bad gas milage.

What the difference in feeling, and response

 

Rear gears affect the engine RPM. A lower rear gear is numerically higher, just like the low gears of a transmission are numerically higher.

So say I cruise down the highway at 50mph, and turn 2000 RPMs, in overdrive, with a 3.42 rear gear.

If I put in 3.73's, at that same 50mph, I might be turning 2300 RPM's, in overdrive.

That's where the gas mileage goes.

"Response"
A lower gear (like 3.73's) will make the car quicker, but not faster. That means your 0-60 and 1/4 will be quicker, but your top speed drops. This is related, again, to engine RPM. If I can wind my engine up faster, I'll move faster- but if I reach redline faster, the top speed is less.

A higher gear (like 3.08's) will make the car faster, but not quicker. It takes a while for the engine RPM's to rise. So it might take me longer to do the 1/4 mile, but when I reach redline in a higher gear, the top speed will be fast.

"Tuning"
There's something called a "powerband". This is the RPM range at which your camshaft was designed to operate at it's most powerful. You can usually feel this while driving; it seems like the "sweet spot" of the engine. For 1/4 mile racing, you want to cross the eyes (of the timers) while you're near/at your peak HP output. You can change the rear gear to accomodate this. Say, for example, I've got 3.23 rear gears, 26" tall tires, and my powerband is 3000 RPM to 5000 RPM. Now, say, with that combo, I'm crossing the 1/4 mile mark in 3rd gear, at 1800 RPM.

That's bad. I'm out of my powerband, so at 2200 RPM, I'm not making much HP.

Say I go through all the math, and decide I need 3.73 rear gears, and 25" tall rear tires. I might be able to finish the 1380 in 3rd gear, at 3800 RPM. That's better; I know when I'm in my powerband, I'm making more power, and the engine's performing better.

"Effective rear gear ratio".
Picture two circles, one larger than the other. The larger circle is the tire, smaller is the rear gear. Pick an "average" size circle, between the two. This could be thought of as your effective gear ratio.

Say I have a 3.42 rear gear, and change from a 26" tall rear tire, to a 28" tall rear tire. This will drop my "effective" gear ratio down to a 3.18! (This is the combo I used to run.) That's not cool at all. This basically suggests that my car would run the same as if I had a "actual" rear gear ratio of 3.18, and kept 26" tall rear tires on the car.

It works the other way, too. Say I had 3.42's, and went from a 26" tall tire to a 25" tall tire. I don't want to do the math now, but it could give me an effective ratio of 3.55- I just sped up my car, and only replaced the tires.

Search the net ( http://www.yahoo.com , or thirdgen.org) for more info on:

effective gear ratio
plus sizing

 

Class dismissed, Have a nice weekend students
I learned something, Tom.
THANKS

 

Dood that is exactly what I wanted to know.

I think I got it figured out now.
At least as much as I need to know.

It's just one of those things i see being discussed all the time, and I wasn't quite sure how it all worked.

Thanks for the info, I love the 6ixer board...

 

Did you ever go to http://www.howstuffworks.com ?

 

Ya I went there the ohter day.

That site is awesome. I wish I had know about it before. I'm getting all kinds of info off of there.

Thanks dood...

 

Wow. Tom that was excellent. I love reading your looooong posts. I am so dumb sometimes when it comes to this stuff. It never crossed my mind to change the tires to change the ratio... I like the idea though.

There is more stuff I learned this page is bookmarked now for just such things.

 

Glad you guys enjoy the lonnng messages! I don't know why, I love explaining things (as long as the person's willing to learn)! I offered to give a friend of a friend a wiring diagram to get his g-body some spark. He put a f-body 305 in it, and couldn't get spark. I saw him the next day, after typing up 1/2 the email, and he told me not to bother, he's having a shop do it. Typing up a GM diag chart is not fun.

Plus too I remember how when I started, I didn't have the 'net to help me out. Back in '94, the Internet was nothing like it is today. 'Fact, I think it was just "available" to government & educational institutions back then, I don't think the public had an idea of it, besides AOL 1.0. So I had to learn it all thru my dad, calling Summit Racing to see if parts (like exhaust) were available for my car, and by reading my GM service manual cover-to-cover. Just think how much faster I could've known about my car if the internet was around back then!

And that's probably why I also yell "call summit & ask!" or "do the work yourself!"

 

All I know is that you inspire me to learn more.

I like to know how my car works. and what I can do with it.
I'm glad that you help us out.

 

Even tho I own a Corvette ('74 kinda "low" model on the Corvette scale level, BFD) & hung out at Corvette Forum,
They were & are getting so damn "stuffy"
Man, here, it's real world
AND
It's fun to contribute, too.
Pain when all someone does is think that they have to make up a new name to get help from us.
Lame loser.