'75 duster gearing issues

Same '75 duster as my last posts: '76 400 4 bbl w/ holley 4160, Mopar distributor, 727 auto, 8.75" rear end (trans and axle out of the same car
as the engine). The diff is open, and feels like it is geared high, like 2.7 or 2.9:1, pretty typical for '76. I would like to go with a limited slip rear with some lower gears, but I need to figure out which gears to go with. when I eventually finish the car and build the engine, I want to be able to outrun a viper in the quarter, but I don't want a car that will redline at 120 mph, since this car will see occasional street and perhaps some highway driving. As near as I can figure, 3.55:1 gearset times the car's 2.45 first gives me a final drive a little lower than the viper's (3.07 axle * 2.66 first) and a top speed approaching 160 assuming a 7000 rpm redline with the tires I am using (Yokohama avid S/T 255 series 27" overall diameter), but the viper has a manual and puts A LOT of power to the ground. I figure with this gearing and the fact that I have an automatic, I will need make between at least 560 lbs-ft. of torque at the flywheel to match the viper's power at the wheels. Is that feasible with this engine, running on pump gas? Would stroking the engine to 451 cubes help at all? Or should I go with lower gears like 3.91s or 4.10s and just deal with the lower top speed and higher rpms at highway speeds? 4.11s with the same tires and 7000 rpm redline would give me about 135 mph, and over 3000 rpm at 60mph. Thanks in advance for your advice!
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The 400 is a low compression motor Do you want to spend $15K-$20K to beat a Viper In a drag race your going to need the 4.10s with automatic & another 400 hp to beat a viper. A 451 stroker would be worth doing if you are rebuilding it, also going to need some aftermarket cyl heads good set of TTI headers, Have you considered a 5 speed (Kessler conversion)
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Hadn't thought about a 5 speed, but I did consider a gear vendors over/under drive unit for my torqueflite. Is the Kessler an actual conversion kit or would I have to track down parts to make it work? Also, would it be cheaper to go with forced induction like a centrifugal supercharger in order to make the necessary power rather than stroke the engine and spend money on the rest of the mods I would need if I kept the engine naturally aspirated?
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You want your cake and eat it too. The 4.10's are perfect 1/4mi gears for your combo. To run with a viper you will definately need at least a 5-speed or a gear vendors overdrive unit. The gear vendor unit would probably work better for you because you can overdrive every gear so with a 727 auto it would make it a 6-speed. With some nice 3.23 gears you could probably go over 150mph no problem (w/6-speed). I think you should sell the 400 and buy a 340 and stroke that to 416. Your car would handle better and it would be lighter and be able to make the same power as the 400 (even stroked). Forced induction is definately the way to go.
sackattack84 wrote:

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Also if you run that 400 to 7K RPM without internal upgrades you will be picking up the pieces, that's assuming you can get it to turn 7K. You would need to replace the crank & rods with aftermarket. As stock motor with mild cam limit it to 6K RPM The Kessler can be bought as a complete kit made specifically for your Duster. Has a low first gear allowing you to run 3.23/3.55 & Still launch the car. It gives you an overdrive 5th gear. If you have money to burn get the 5 speed & a big 600 hp small block from Ray Barton
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5 speed conversion www.keislerauto.com
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