3.91s in my 340 now!

Rude72* said

Hey guys...

I have a '72 340 Duster with a few engine mods (Holley 750, bored .030 over, Mopar performance purple cam/P4120235, Hooker comp headers, Edlebrock Torker II intake, 2.5" exhausts with Flowmaster mufflers). It has a Mopar 727-A three speed auto trans with a 3200 RPM Stahl Speed Trans Specialties converter and B&M shift kit with Hurst Quarterstick. It originally had 3.23s in it when I bought it, but it seemed (to me at least) that it was kinda "doggin" it coming out of the hole. Well, that certainly has changed! I was wondering if anyone else out there is running 3.91s with their 340s and how you're liking/disliking it.

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Hey Rude72,
I am running a very similar combo.
1972 Duster
340 with 284/484 Purple cam
750 Edelbrock on LD340 intake
TTI shorty headers, dual 2.5” exhaust
3200 stall FTI Performance torque converter
727-A non lockup trans
8-3/4 Sure grip with 3.91 gears
255/60r15 (27” tall)

Edited to add more due to a glitch:

My car responds well to the foot with the 3.91s and requires no downshift if already going 40+ mph when mashing the gas as it is already in top gear and it’s powerband, putting me nicely back in my seat. Highway is 3500-4000 rpm depending on if uphill or downhill. And no shortage of passing power if needed because engine is good to 6000 rpm. I would not go with any less gear in this setup, I think 3.91 is the sweet spot.