904 LU in my 68 dart..or A-500

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Dakota_Don

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HI all, i have a 87 904 LU trans (needs rebuilt) and Id like the lower gear set, but would it be worth putting it into my 318 dart? I can rebuild it myself and get the TC rebuilt..

would it better MPG up top?

if i have 2.76 or 3.23 gears what would my ratio be in all gears even with the LU on. Post the formula plzz.. I also have an A-500 from a 95 Dakota I thought about using it, but i beleive the torsion bar mounting brace needs modified..and i am not to sure about that idea..

what are your thought?

The engine will be a 68 318 TRW forged flat tops, floating pins with magnum heads and either FI or a TQ carb and headers.. and maybe a 270H comp cam or the XE268 comp cam..

thanks for your input
 
I'll be sure to let you know, but don't wait for my report. Things will be a bit slow around here until warmer weather.
 
I hate to sound ignorant, I under stand the low first gear in the a998 and a999. What does LU stand for.
 
Dakota_Don said:
HI all, i have a 87 904 LU trans (needs rebuilt) and Id like the lower gear set, but would it be worth putting it into my 318 dart? I can rebuild it myself and get the TC rebuilt..

would it better MPG up top?

if i have 2.76 or 3.23 gears what would my ratio be in all gears even with the LU on. Post the formula plzz.. I also have an A-500 from a 95 Dakota I thought about using it, but i beleive the torsion bar mounting brace needs modified..and i am not to sure about that idea..

what are your thought?

The engine will be a 68 318 TRW forged flat tops, floating pins with magnum heads and either FI or a TQ carb and headers.. and maybe a 270H comp cam or the XE268 comp cam..

thanks for your input
Click to expand...

First of all if you do go with the TQ rather than FI then the cam is too big if you're looking for any kind of mileage and good cruising/street manners. Even with FI, combined with your rear gearing it is going to be pretty doggy on the low end (not terrible, but not very good either). Comp XE262 would be my choice.

As far as the transmission ratios go, you just multiply the rear-end ratio by the trans. gear ratios, which are 2.54 first, 1.54 second, and 1.00 third. That first gear is not that much lower than the old 904 first but it will help a bit. BTW the 904 should be perfectly fine behind your 318, especially if you rebuild it with good components.

With, say, 26-inch-tall rear tires and a cruising speed of 65 mph on the highway, you'll be turning ~2700 RPM with 3.23:1 rear gears. With 2.76's it would be around 2300 RPM which IMO isn't too big of a difference and you'd probably lose a good bit of torque with the 2.76's.
 
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