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Swap 3.23 to 3.55 rear end... Is it worth it?
#1633515
06/14/14 02:37 PM
06/14/14 02:37 PM
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Joined: Sep 2013
Posts: 464
KY
Telvis
OP
mopar
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OP
mopar
Joined: Sep 2013
Posts: 464
KY
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I want a little more torque from takeoff and thought about swapping my 3.23 sure grip for a set of 3.55 sure grip gears. I have also thought about putting the lower gear set into my 904. Thinking I might do one or both. How much highway speed driving will I sacrifice if I do the 3.55? Will it really benefit me much? Is it worth the swap? I can get a complete unit for $600. I figure I can sell my 3.23 set to pretty much absorb most of the cost.
I also have access to a set of 3.91 gears buy figure those would kill me at cruising speed. I have a 73 challenger with moderately built 69 340 with Edelbrock heads, Voodoo cam, about 10:1 compression. I have 15 inch wheels if that helps.
I am pretty sure I am going to do the 904 gear swap. I have a spare transmission and will do the swap and rebuild myself. Anyone do it? Is it worth it? Gearset and rebuild kit will cost me about $275... Not too bad to me if it gives me some extra torque on takeoff.
Last edited by Telvis; 06/14/14 02:54 PM.
That's King Weenie to you!
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: dangina]
#1633518
06/14/14 03:02 PM
06/14/14 03:02 PM
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Joined: Sep 2013
Posts: 464
KY
Telvis
OP
mopar
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OP
mopar
Joined: Sep 2013
Posts: 464
KY
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What about the 3.91 gears? The tool says about 700 rpm....seems like a lot to me...
That's King Weenie to you!
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: forphorty]
#1633519
06/14/14 03:05 PM
06/14/14 03:05 PM
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Joined: Sep 2004
Posts: 22,873
Chicken coop
dustergirl340
Chicken Little
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Chicken Little
Joined: Sep 2004
Posts: 22,873
Chicken coop
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Quote:
What engine? What torque converter do you have? If you have a stock converter, a swap to a good converter could be worth several tenths. Way bigger improvement than the gear swap you are considering. The 904 low gear set seems to be worth about a tenth on this site. The 3.23 to 3.55 swap might be worth a couple tenths. Just speculating here. Very application specific of course. IMO, the closer the converter is to being optimum for your combo, the less difference a small gear change will make.
Agreed 100%. I went from 3.23's to 3.91's and it made little difference at the track. More fun around town though.
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: forphorty]
#1633520
06/14/14 03:07 PM
06/14/14 03:07 PM
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Joined: Sep 2013
Posts: 464
KY
Telvis
OP
mopar
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OP
mopar
Joined: Sep 2013
Posts: 464
KY
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I was looking to get a different converter. I spoke with a guy at Turbo Action and he recommended the 904 lower gear set as a priority over a converter change. He said a converter would help but the lower gears and a converter would really help. He acted as though the gears were a better way to spend the money. He said the lower gear set would give me equivalent of a 3.60 gear in 1st. I have a TCI converter I got with the 904 when I bought it. I don't know the stall speed on it. Nothing wrong with the tranny and the converter seems to work fine. I just want more torque on takeoff.
I have a 73 challenger with moderately built 69 340, .030 over, Forged SpeedPro pistons with Edelbrock 60179 heads, Voodoo cam 60402, about 10:1 compression. I have 15 inch wheels.
Last edited by Telvis; 06/14/14 03:12 PM.
That's King Weenie to you!
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: FuryBoy]
#1633522
06/14/14 03:47 PM
06/14/14 03:47 PM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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I could see where 3.23's and 15" tires ain't giving you the low end you'd like. the 904 low gear would be going from a 2.45 to a 2.74 so your first gear overall ratio would be 8.85 (2.74X3.23) as opposed to 7.91 (2.45x3.23) plus I think 2nd gear might be a bit lower with the low gear set also but I ain't sure on that. I would make sure the eng is tuned right including the adv curve with a dual plane intake and the right carb then consider what guys have posted on more in depth changes. If you ain't out on the interstate alot I dont see a problem with 3.91's even. going from a 3.23 to a 3.55 is going to up the RPM's ~10% in all gears and the 904 low gearset is gonna up you ~12% in low gear. Just me I'd go with the low gear set plus a top notch converter if I took the trans out plus 3:55's plus super tune the eng & the components on it  EDIT Along with the low gear/better tc, a 3.73 742 clutch sure grip would be my hands down wish list. I had 4:10's with 14" tires in my first Mopar in 1975, a 440 GTX 4 sp convertible & that was toooo low. The next year I drove it to California & that was back when the speed limit was still 70 
Last edited by RapidRobert; 06/14/14 04:00 PM.
live every 24 hour block of time like it's your last day on earth
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: Telvis]
#1633524
06/14/14 04:18 PM
06/14/14 04:18 PM
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Joined: Jan 2005
Posts: 3,344
Central TX
roe
master
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master
Joined: Jan 2005
Posts: 3,344
Central TX
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I think you'll be surprised by the low gear set. In my sig car I had my trans rebuilt with a low gear set and the Transgo TF-2 shift kit, and even with the 2.76 peg leg, takeoff was noticeably better. Now I'm working on getting my hands on a 3.23 suregrip to go with the low gear set.
roe
Last edited by roe; 06/14/14 04:20 PM.
1971 Plymouth Satellite
408/904 8 3/4 3.23 SG
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: RapidRobert]
#1633533
06/14/14 07:18 PM
06/14/14 07:18 PM
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Joined: Oct 2009
Posts: 1,185
Nanaimo, BC
NOrrTH
super stock
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super stock
Joined: Oct 2009
Posts: 1,185
Nanaimo, BC
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I have 3:55's on my GTX, stock converter and 295 50 15's. Im on the highway a fair bit and its fine to me. im considering going to 3:73's. Any higher with my size tire would suck on the highway. 3:55's are about as high as you'd wanna go imo. My Challenger had 4:10's and that was horrible. People passing you looking at you funny because you are struggling at 50ish. No thanks.
'71 GTX N96 auto 3:55
'74 Challenger 440+6 4spd 4:10
'71 Duster 340 auto 4:10
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Re: Swap 3.23 to 3.55 rear end... Is it worth it?
[Re: Telvis]
#1633534
06/14/14 07:38 PM
06/14/14 07:38 PM
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Joined: Jan 2003
Posts: 3,575
The Netherlands
BigBlockMopar
master
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master
Joined: Jan 2003
Posts: 3,575
The Netherlands
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Quote:
Quote:
Ever considered going with an overdrive transmission and have best of both worlds?
Thought about it but seems like a PITA to do.
Removing a tranny, opening it up and changing only first gear and installing it again seems about the same PITA to me as just installing an overdrive transmission and do some remodelling on the transmission tunnel.
Especially on an already smallblock car imo it would be a no-brainer to fab an A500 under it and end up with a car that's much more fun to drive. Instead of trying to find a compromise in fixed gearratio's.
I installed an A518 (OD+LU) in my '73 Dart and everyday I'm enjoying the fact there's an (almost) 5-speed transmission in the car and still have 3.91 gears in the rearaxle.
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