3.91s in my 340 now!

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I love the 3.91's in my 340 '68 Dart. 4.10's would probably be better though since I run a 275/60/15 tire, but it's just a street cruiser. 340's love a short gear and a good converter, that's for sure.
 
318willrun said:
when a torque converter is advertised as a "3200 stahl" (or any other rpm range they pick), that is in a certain situation with a certain engine. So if somebody says "3200 stahl" and that is behind a 440 making 500 ft lbs of torque, your 340 might only see 2500 rpm's of stahl out of that same converter.

... And what that means to you is with that combo, and not enough stahl and gears... it will feel lazy up to a certain point, till it builds rpm's.
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Thank you for the explanation. This car (now with the 3.91 gears) doesn’t feel lazy, at all.
 
If your 340 was doggy with 3.23s and a 3200, something in the combo was not right. Either the cylinder pressure was/is quite low, or the ignition timing was late, or like Willrun suggested, the stall was off.
However,
3.91s will bring the shifts closer together , time-wise, which also seems to feel faster, and 3.91s are getting close to being perfect for most streeters; 65mph in Second being about 5100 rpm.
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I have had a lotta 340 A"s, always with a 4-speed, and usually with either 3.23s or 3.55s; and with the 340 factory cam, the only one that ever impressed me was the very first one I purchased, in fall of 1970. IIRC tho 4.10s went in at the beginning of the Second summer.
Currently, I run the Commando manual-trans, with 3.55s, and a hi-pressure 360 with a modest 276/286/110cam.(230/237@050)
The starter gear is 10.97, about the same as 4.10s with the standard 2.66 low trans. Between the mega-torque 360, the BFGs, and the super-starter gear, she's a real tirefryer.
But as others have said, the GVod makes those 3.55s to be 2.77s, for cruising 65@2240rpm. The best of both worlds.
And I haven't even mentioned gear-splitting.........
 
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AJ/FormS said:
If your 340 was doggy with 3.23s and a 3200, something in the combo was not right. Either the cylinder pressure was/is quite low, or the ignition timing was late, or like Willrun suggested, the stall was off.
However,
3.91s will bring the shifts closer together , time-wise, which also seems to feel faster, and 3.91s are getting close to being perfect for most streeters; 65mph in Second being about 5100 rpm.
*********************************
I have had a lotta 340 A"s, always with a 4-speed, and usually with either 3.23s or 3.55s; and with the 340 factory cam, the only one that ever impressed me was the very first one I purchased, in fall of 1970. IIRC tho 4.10s went in at the beginning of the Second summer.
Currently, I run the Commando manual-trans, with 3.55s, and a hi-pressure 360 with a modest 276/286/110cam.(230/237@050)
The starter gear is 10.97, about the same as 4.10s with the standard 2.66 low trans. Between the mega-torque 360, the BFGs, and the super-starter gear, she's a real tirefryer.
But as others have said, the GVod makes those 3.55s to be 2.77s, for cruising 65@2240rpm. The best of both worlds.
And I haven't even mentioned gear-splitting.........
Click to expand...
It was only "doggy" out of the hole. But that was unacceptable to me. If I romp on it (with the 3.91s) cruising at 60 or so, it will push you back in your seat.
 
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.
 
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Just today I pulled the 4:30's out of my 340 Challenger... Bolted in a set of 3:55's... But then you need the whole story... I pulled the 518 O/D... And put in a TKO with a 3.27 1st gear.... So it's actually a deeper 1st gear & a taller high gear.... It was a lotta fun before.. Should be a blast when I'm done...
 
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