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Discussion Starter #1
I have an 86 720 z24 race truck I just replaced my 2.25 sec gear tran w/ a 2.07 tranny tnen replaced my 4.38 rear diff w/ a3.54 rear diff and my driveshaft wont fii. Im a small girl and no male help. my orginal setup gave me final drive ratio 9.855 i was redlining 8000 halfway down the straight. the last two races i dnf because i felt i was going to blow the motor and my lap speed was dangerously slow. the orig setup was installed by a shop they said it was best one.
I race on a quartermile oval. im looking for 7 t0 1 thru 8.5 to 1 final

At first i didnt understand why i was reving so high. when i realized what the shop had installed i was furious. i try to do my own work at the same time realy understand whats going on mechanicly in my truck.

!st question should i rip out the 2.07 put the 2.25 back in and go with 3.90 rears? And do you have any tips on the remov and inst of the tranny? if i jack the trk up too high i dont have the strength to shove it back in there it seems you have to turn and push it back almost past the torsion bars to get it clear of the engine... HELP
 

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The 2.07 should have made second gear longer right? Along witht he 3.54 rear end instead of the 4.38
 

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Should be. The gear ratios convert engine rotations to drive shaft rotations. So 2.25 to 1 second gear would be two and a quarter engine rotations to make one full rotation of the drive shaft. Like on a nissan 5 speed transmission 1st gear is 3.32 to 1 so its real short. Second is 1.9 to 1 thats why second gear seems like it pulls forever in these cars. I'd be interested to know what transmission you're using and what gear ratios it had stock and what you're using now. Seems like if you are running lower gears now and getting slower times but over-reving the motor perhaps the clutch is to blame.
 

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Discussion Starter #9
the casing says zl71b and i am told it has a 1.85 second gear w/ a rear gear of 4.38 this combo im redlining 7500 halfway down the straightaway
not good I previously had a 2.25 second gear w/ 3.90 rear . not as fast off the line but i redlined at the end of the straigtaway ( better) anyone
familiar w the # zL71b
 

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Not familiar with that transmission but maybe consider a 4.11 rear end gear. Should be decently quick off the line but still give you some rpms on the straights.
 
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