selecting the rear gear after trans swap

grumpyvette

Administrator
Staff member
octanejunkie said:
Been a while since I've posted here, busy with work and life, but now my truck is coming back into focus and I've started spending $$ on it again; so now more questions!

I've been weekend-driving the truck in my sig w 3:42 gears for 4 years. Gears were chosen when truck had a TH-350 trans, now it has a 700R4 w OD.

With 31" tires and a 3.06:1 first gear ratio in the 700R4 I'm thinking 4.10 gears might be too much, but overall 3.73 might be not enough difference to make the cost of the swap worthwhile - then I found a set of 3.90 gears at summit...

Any thoughts?



theres several factors to consider, like what the trucks used for (towing, cruising etc.)what is the current engine rpm while cruising at 70 mph, on trips what is the lowest rpm range the engine easily tows and accelerates easily from while towing a load, is the engine mileage or performance the prime factor your looking to improve?
what is your trans fluid temperature on long trips? do you need a trans fluid cooler? if the trans fluid temp frequently exceeds 170F YOU DO!


these links should be helpful

http://www.wallaceracing.com/gearcalc.php

http://www.wallaceracing.com/gear-speed.php

http://www.msgpio.com/manuals/mshift/mods.html

viewtopic.php?f=71&t=555

viewtopic.php?f=71&t=741

viewtopic.php?f=71&t=1715

viewtopic.php?f=71&t=662

AS a general rule, a performance street cars rear gear ratio multiplied by the transmissions first gear ratio should fall in the 10:1-10.5:1 range with tire diameters in the 25"-28" diam. range
gmtransgeart.png


http://www.cprparts.com/HPcalculator.html

http://www.wallaceracing.com/et-hp-mph.php

http://www.ajdesigner.com/fl_horsepower_trap_speed/horsepower_trap_speed.php

http://www.gregraven.org/hotwater/calculators/qm-from-wt-hp.php

http://users.erols.com/srweiss/calcehp.htm


related info threads
http://garage.grumpysperformance.co...electing-a-torque-converter-stall-speed.1715/

http://garage.grumpysperformance.co...late-gear-ratios-and-when-to-shift-calcs.555/

http://garage.grumpysperformance.co...earing-and-trans-choice-made-correctly.11697/

http://garage.grumpysperformance.co...hing-the-drive-train-to-the-engine-combo.741/

http://garage.grumpysperformance.com/index.php?threads/select-a-gear-ratio-or-trans-or-both.10493/
 
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