what is the best rear end if you are looking for top end speed. I mean what axel and gear comgination

 

Depends where you want the top speed. A 2.73 ratio will give a higher hiway top speed than 4.10 gears however low end performance will suffer.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car
91 454SS daily driver
95 Homebuilt Harley

 

Stephen, isn't there something where too high of a rear gear won't give a higher speed, because the engine runs out of steam? How the heck is -that- calculated, I wonder?


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Lets say the engine red lines at 5000. The 2.73 gears may give it a top speed of 140 mph but the 4.10 gears will only be 100 (guessing but you get the idea).

Playing with gear ratios and tire sizes on the race track is a little different. The stock 3rd gen tire height is 26". If the engine only reaches 5000 rpm then 3.73's or 4.10's would let it reach red line at the end of the 1/4 mile. 2.73 would run out of track before the engine topped out. If the engine goes to 6500 like mine did, then the gearing or tire sizes need to be changed because the car is pulling for 1500 more rpm in each gear. When I had 3.27 gears and 26" tires, I shifted at 6500 and crossed the finish line at 5300. Switching to 4.10 gears and 28" tires I now cross the finish line at red line.

When you see cars in magazines with 4.56, 5.13 or lower gears, they usually have 30" tall tires or taller or the engines peak at 7000+ rpm.

If you could squeeze a 33" tall tire with 4.56 gears you could get the same top speed as having 2.73 gears and 26" tires (guessing again). The only difference would be that the 4.56 gears would multiply the torque more and get the car off the line quicker.

Lets say you want to run 200 mph on the salt flats. You would need a very high gear ration in the rear end. Something from 2.73 to 2.0 or 1:1. Maybe even overdrive in the rear end. The car would be a rear dog to get moving but once it did start moving you would be idleing at 80 mph. Now go one step further and take off the 26" tire and put on a 40". The taller tire would rotate less per mile than the 26" and give an extreamly high top speed. Depending where the engine red line is, it could be easy to run that fast however low speed driving would be non-existant. Maybe possible if the tranny's first gear was 20:1.

Another way to get a high top speed is with overdrive trannies. Standard OD is .7:1. If you could get .01 or lower then top speed would increase.