3.91s in my 340 now!

-
Rude72*

Rude72*

Well-Known Member
Joined
May 4, 2024
Messages
115
Reaction score
41
Location
Wauseon, OH
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.
 
I also have a 72 340 Duster that originally had 3.23s and have swapped to 3.91s. Although my 340 is now 422” and I run a 4 speed. In my opinion 3.91 and a 4 speed are a match made in heaven for a street car.
 
SSG_Karg said:
I also have a 72 340 Duster that originally had 3.23s and have swapped to 3.91s. Although my 340 is now 422” and I run a 4 speed. In my opinion 3.91 and a 4 speed are a match made in heaven for a street car.
Click to expand...
Man, do I wish I had a 4 speed tranny! 3,500 RPM around 60 mph is a little steep, but I would never go back to the 3.23s. It's not a daily driver and I won't be driving all over the place for car shows... a couple times a year I might be making an hour to an hour and a half drive. Thanks for sharing!
 
I put 3.91s in Vixen for a short time. I really enjoyed it behind the hot slant 6, but with 13" tires it was buzzin goin down the road, so I put the 3.23s back in.
 
RustyRatRod said:
I put 3.91s in Vixen for a short time. I really enjoyed it behind the hot slant 6, but with 13" tires it was buzzin goin down the road, so I put the 3.23s back in.
Click to expand...
thats probably. what Ill do. 3.91 in my 70 Dart. I also have a 741 case 3.23 and a 2.94.
3.91s for a while, 2.94s long cross country trip
3.23s rathole spare stash
 
Rude72* said:
Man, do I wish I had a 4 speed tranny! 3,500 RPM around 60 mph is a little steep, but I would never go back to the 3.23s. It's not a daily driver and I won't be driving all over the place for car shows... a couple times a year I might be making an hour to an hour and a half drive. Thanks for sharing!
Click to expand...
I’m running right about 3000rpm at 60mph with a 275/60-15 rear tire.
 
SSG_Karg said:
I’m running right about 3000rpm at 60mph with a 275/60-15 rear tire.
Click to expand...
That sounds about right. I've got 245/60/14 on the rear. Blasted 14" rims! lol But I don't care. I don't take long trips (60-90 minutes) more than a couple times or so a year. So I am TOTALLY cool with the 3.91s. Waaaay more fun to drive! It's cool that when I'm doing 60 and I stand on it, it still pushes you back in the seat! Too cool!
 
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.
Click to expand...
Are you actually getting 3200 rpm's of stahl? I might think not, and then the single plain intake with that .284/484 cam (I think that's what it is) it was a little lazy till it hit a "point" in the rpm band.
 
318willrun said:
Are you actually getting 3200 rpm's of stahl? I might think not, and then the single plain intake with that .284/484 cam (I think that's what it is) it was a little lazy till it hit a "point" in the rpm band.
Click to expand...
Well, I have no idea what your speaking of. I am a novice. I know barely s*** about motors and performance-related topics. Just being honest.
 
RustyRatRod said:
It's gonna be classic sho nuff when I swap in the Ford T5 five speed and Ford 9" with 4.11s. lol
Click to expand...
I love that concept! I've been teasing the idea of a t5 in place of the full crash box in my 33 straight eight. Fifth gear would be a huge help with the mid-high 4 series gears in it. ( i can't remember offhand the exact ratio. 4.5x or lower)
 
33IMP said:
I love that concept! I've been teasing the idea of a t5 in place of the full crash box in my 33 straight eight. Fifth gear would be a huge help with the mid-high 4 series gears in it. ( i can't remember offhand the exact ratio. 4.5x or lower)
Click to expand...
It will make the 4.11s into 2.79s.
 
Rude72* said:
Well, I have no idea what your speaking of. I am a novice. I know barely s*** about motors and performance-related topics. Just being honest.
Click to expand...
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.
 
Last edited:
33IMP said:
3.20s or thereabouts with 30" tall tires would work for me. I think first in the T5 might be lower than in my 3sp crashbox too.
Click to expand...
They use a couple of different 1st ratios. Mine is 3.35:1.
 
You must log in or register to reply here.
-

Back
Top