ok thanks alot kyphur, ur really helping me to see this ...well i already spend 50+ a week on gas now lol and its tight...yeah those RPMS sound about right for me too..i do hit 58-60 at 2000 RPM...so going down a full gear will drop the top end speed by quite a bit then...by them having lower speeds at higher RPMs, how does that make them faster off the line? and why would racers do that if it hurts there top speed and have to strees the engine more by going to such high RPMs to go fast? it seems like they'd want to have higher gears like mine so they can go faster while having lower RPMs?

 

I'll make a comment on the 700r4 as I mentioned in your other thread. Your final drive ratio will be about 2.6 with the overdrive in the 700r4 along with a 3.73 rear end, which brings you pretty close to the same final ratio you have now of 2.52 or so. Overdrive works wonders sometimes, and if you shoot for a 3.42 you final drive would be 2.39, even better. And the steep first gear of the 700 (3.06) will make up a lot in the take off as well.

It helps off the line to have lower gears because it gets them going faster. Think of it this way: in a manual transmission, can you take off better in second or third gear better as opposed to first? Lower gears just make it easier for the engine to turn the wheels, which helps it get going.

Race cars are built for a specific purpose, so they know what range they need. For instance, someone like NASCAR can only go so fast in the turns, so they need the right gearing to get them as fast as possible in the straight away, while still being able to control it in the turns and take off ASAP. If thegearing was too high, it would bog it down just enough for someone to breeze by. A 1/4 mile car would be made to go as hard as it can off the line without topping-out before it reaches the 1/4 mile mark. You want to be able to take off hard, but you don't want to make such a low gear that you top out fast. Their main goal is to find the perfect gearing, low enough to take off well, while still being high enough to get them the top speed they need.

 

just what Bobarian91 said. The drag racers want to be able to get up to speed fast and since they don't have a long distance that they have to travel then they don't have to really worry about their top end speed being sustainable. They want to be passing the line right about when they run out of gear.

 

I found this link to a gear ratio calculator and comparison. Nevermind that it has rice information in it. You can load up your own. The configuration in there right now is with my TH400 and gear setup with a 2.52 rear end vs. a th700r4 with a 3.42 rear end setup.

 

Pretty good explanation bobarian. I couldn't have said it better....well, almost!
A little more about why racers go with a lower rear gear. An engine that's built up for racing has the capabilities to rev the rpm's considerably higher than a "stock" engine can. The lower gearing will make the car jump faster off the line, and top end speed will be met by the engine winding high. Neither gas mileage, nor wear and tear on the engine is an important factor. That all comes with the territory. The bottom line is, what does it take to get to the finish line faster.

 

Camaro69> Exactly

I also just found this site which gears for most popular transmissions and final gear ratios for the starting gears (first and second) with their respective rear end ratios.

 

thanks everyone for all your help and clarification ..that helps alot! i will save up for an overdrive trannie with 3.73 rear gears..i cant wait to get a new more powerful engine and a new trannie