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Best Diff gear ratio for SBC - 700r4 ?

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What would be best overall Differential gear ratio for 240z with SBC (350-400 HP) and 700r4 with 2800 Stall? Currently have R200 4:11 and gears are WAYY too short.. Looking for balance between launch/freeway RPMs.. Any suggestions?  Would it bog down too much at launch with 3:54 (already have) ? Any input appreciated!




Thank you,

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Hmm, are you sure you don't have a transmission problem? 3300-3500 makes sense for 3rd gear but you might have a bigger problem with that in your final gear. As silly as it sounds, are you also sure that it's a 700R4? I ask because I was sold a car with a Powerdrive only to find out it had a Turbo 350 in it. The guy wasn't feeling the first shift and assumed it was only shifting once. According to the numbers, the 3.54 gears should put you at 2200rpms but that assumes you don't have another issue.




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  • 1 month later...

406/700r/3.54's here. I have 235 60 15 drag radials.(pretty close to 26 inches) In third gear at 5k, I'm at about 108mph.

I don't have a speedo, so that is off the timeslip.


www.wallaceracing.com/Calculators.htm is a good source for gearing calculators.

Edited by Eric JB
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  • 2 weeks later...

I'm looking to do the same thing... 700R4 rebuilt about 2500 miles ago, about 3 grand at 65 MPH. I did a mpg on it last tank and I got a mixture of 21 city/hwy and getting on it pretty hard half of that time. I would like to improve the mileage a little more and imagine lowering that rpm range at highway speeds would help out. 

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  • 4 weeks later...

your obviously going to need to consider tire diameter, rear gear ratio and transmission gearing, generally your want the first gear in the transmission multiplied times the rear differential gear ratio to fall in the 10:1-10.5:1 range and cruise at a bit higher rpm that the torque converter stall speed in 1:1 gearing, if you have a over drive gear having a lock-up converter sure helps and a trans fluid cooler is almost mandatory if you have a high stall speed torque converter


you should ideally select a cam , tire diam. converter stall speed and differential gearing that put the engine rpm range in your power curve about 90% of the time



Edited by grumpyvette
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