What rear gear?

[Double-D201]

My car is a 79 malibu 406 SBC afr aluminum heads 700r4 trans and a GN rear diff 3.42. All Stock suspension with a 255 et street tire cars best a 1.6 60 foot and a 12.3 ET at 108 mph. Over the winter I did some upgrades and moved up to a 275/60 rear. My question is what rear gear schould I run to drop my e.t.? 410 or should I go lower seeing as I'm running a 700r4

 

[Wageslave]

You may want to make a run or two with the new tire size before deciding to change rear ratios. What gear and RPM are you crossing the finish line at?

 

[lilbowtie]

Is the car strictly strip? If not are you worried about mileage? What camshaft-convertor?

 

[gnvair]

The problem with that transmission is the 3.06 first gear along with the low gear in the back will hit the tires very hard. You could try a lower gear, but the loss of traction could negate any positive gains. By comparison, the turbo 350 has a 2.52 first gear, turbo 400 has a 2.48 and the 2004r has a 2.74 first gear. The over drive transmissions have the lower first gear because they were originally designed for use with 2 series or low 3 series gears.

 

[Double-D201]

No not stricky a track car I drive it almost daily in the summer not to worried about fuel mileage. It's a 2500 stall converter I'm in 3rd gear going threw the traps not sure on rpm but not very high

 

[gnvair]

Do you have lock up torque converter or a non lock up with the proper block off in the pump?

 

[lilbowtie]

Kinda hard to determine a change w/o knowing where (and how much) power your making - you are currently going through the traps @ aprox 4900 rpm and the tire change would give you 5 more mph if you could still maintain 4900 rpm. That's only about 325 hp. What is your engine combo.

 

[bracketchev1221]

Like was said, ultimately you want to be just past peak power rpm at the stripe. What do you shift it at now? What is the average 60' time, there is a big difference between 1.69 and 1.60 in 60'.

 

[lilbowtie]

Another new-be, here then gone.