OK guys I got a little new feed back. My proctologist buddy (DR Boost) and i have been discussing gear ratios for over a year now. He was interested in trying a 3.73 in his GN. I told him alot of guys say it supposedly doesn't work. I used my arguments with him like in my above post. He just went to a 9" ford and I let him try my center section with a 3.25 gear and a detroit locker set up. His old set up was the stock GN 3.42 with clutch type posi. He said you can tell the locker really couples the two tire together under straight line driving, he said it feels really solid and he likes that. He said the 3.25 gear makes the car feel like it has more torque. He said you can tell the motor is getting loaded down more and he said the motor is responding positively to this. We'll have to wait and see if he'll ever try a 3.73.
One thing to keep in mind is that the old proctologist has a pretty stout motor. From what I've read and seen a motor that makes lots of torque will like a numerically lower gear ratio. It just seams like a motor like that needs to grunt against the gear, it needs to be loaded down, and buy doing that it allows the motor to do what it does best which is generating torque.
Torque is the actual FORCE that accelerates a car. Horse power is not measured it is calculated, because its a function of force over time. HP = TQ X RPM / 5250. Below 5250 rpms TQ is always higher than HP and above 5250 RPM HP is always higher than TQ.
Torque is the rotational force applied around an axis. Imagine if you welded a regular old hex nut in the center of the end of your axle. If you took and put 100 pounds on the end of a 3' long breaker bar parallel to the ground you would have 300 ft-lbs of torque trying to rotate your axle(3' X 100 lbs = 300 ft-lbs, and yes its that simple). If you put the same 100 lbs on the end of a 4' breaker bar you would now have 400 ft-lbs trying to rotate the axle. Holly COW! imagine a 50' breaker bar 50' x 100 lbs = 5000 ft-lbs of rotational force with only 100 pounds actually put into it. You can easily see how some one could get real greedy in a hurry.
A gear ratio is the mechanical equivlent of the breaker bar above. A 3.00 ratio would be exactly like the 3' bar, 4.00 gear for the 4' bar, and 50.00 gear for the 50' bar. From this you can see why you would want to run a numerically high number gear ratio. Lets say we take the car out of park, use the three bars (say they all weigh nothing to keep it simple), and place the 100 pound weight on the end. Lets say with the 3' bar the car moves forward slowly until the bar hits the ground, the 4' moves the car a little quicker, and the 50' bar drops like there was never any thing attached to it. This is because you will eventually hit a point to where the weight is only going to drop so fast. The 50' bar / 100# weight combo only puts the 5000 ft-lbs of force into the axle when your trying to hold it from rotating or only allowing it to ratate slower than the weights trying to drop. If you allowed it to rotate to fast then the weight and bar combo will never put the 5000 ft-lbs of torque into the axle.....basically you never allowed it to be loaded down.
My physics is a little fuzzy because that was way to many beers and a whole lot of hair follicles ago, but here goes. Moving a car of 3500# 1320' represents a certain amount of work, and HP is the rate at which the force is generated that can be used to do the work ( I probably have that a little messed up in my wording). This is why more HP makes you run a quicker ET. You generated the force at a quicker rate therefore it take less time to do the work (move the 3500# car 1320'). When you gererate the force at a fast enough rate you can and need to go to a numerically higher gear ratio to take full advantage of it.
Now that I probably got that above stuff half F'd up I'll try to make the concept seam simple. Ltes say I go down to my dust and cobweb covered weight set. I'm going to bench press to do some "WORK", I'm going to move 3500# 1320 feet. Lets say 1 bench press moves the weight 2 feet. I could do this work by: (you have to assume you never get tired, you just lift a certain weight at a certain speed based on your strength, or FORCE your muscles can generate.)
bench pressing 10# 660 repititions, and do 350 sets of that.
or: 100# 660 reps, 35 sets
or: 175# 660 reps, 20 sets
or: 350# 660 reps, 10 sets.
You should be able to see from the above that there will be different amount of times required to do the same amount of work. The 10# reps would take forever because you would have to do it 231,000 times. each rep might go pretty quick but your arms would be basically free wheeling and they are only going to go so fast. 350#'s is no way in hell but lets pretend the bar very slowing moved up, you only had to do it 6,600 times, but it moved sooo slow that it took forever. Probably for me the 175# senerio would get done the quickest. It would be the best compromise between loading down my muscles and the speed I could do each rep.
Thats what we get into when looking at gear ratios, We are looking into the optimum compromise between the mechanical advantage of the gear ratio, and engine loading. This will all be affected by the complete combonation of the exact car in question. We are lucky enough to have feed back from similar cars which points us towards the 3.23 to 3.42 range as being the sweet spot. With out more testing or feed back we have to assume that this is correct. You're actually lucky compared to me. I have to try to pick a gear ratio for a stage 2 combo that I have no idea what rpm the motor is going to want to be shifted at, no idea how much power its going to make (700?, 800? 1000?), hell I don't even know how much the damn things going to weigh.
If your running a stock cam motor and running 118mph then I don't think I would try a 3.73. If you where hitting OD then I would go lower than 3.23 if you weren't hitting OD then the 3.45 may be pretty decent. If you do go to the 3.45 and your palnning on doing some thing that makes the MPH go up you will probably want to go to a different cam to increase the rpm range of your motor to stay out of over drive (if your'e running a stock cam now).
HTH: I'm going to bed now, Jason
.. hehe
