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5/26/12 8:56pm - Original Message: 'Gear Selection'
rod7515 Lifetime Member
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Red Lion, PA - USA

Vette(s):
1974 White 350 Corvette, TH400 Automatic 1972 Tangerine /Go Mango Convertible 383 Stroker, 2004r Automatic

Joined: 10/27/2006
Posts: 1172
Was wondering what RPM's I should be turning at 65 MPH in Overdrive with my 2004r trans with 3 different gear ratios/
I bought a set of 3:55, Thinking about 3:91 or 4:11. The rear wheels are 27" tall. 2004r trans and a 383 stroker. What is the highest RPM you would want to run going down the highway @65 if gas mileage meant nothing to you. I was thinking around 2500 rpms would be about the max for a long haul. Does anyone have the conversion chart for this.
Also is the rear out of an 81 the same or different then my 72. I found a set of 4:11 for an 81.

Thanks
Rodney


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5/26/12 10:04pm - Reply: 'Re: Gear Selection'
Sarge81 Lifetime Member
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WEST SENECA, NY - USA

Vette(s):
1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.

Joined: 12/3/2001
Posts: 2376
From the info you gave, I ran some numbers through an online engine rpm calculator. The 200R4 I believe has a .67 overdrive ratio.
At 65mph a:
3.55 = 1924 rpm approx.
3.91 = 2119 rpm
4.11 = 2227 rpm

'80-'82 differentials are the aluminum DANA 44. These are weaker that the cast iron units.
Gear sets from '80-'82 will not work in the older cast iron '79 and older corvette differentials.

Some guys with '80-'82 vette are adapting the cast iron units to the aluminum "batwing." Good upgrade if you going to be pushing some power.

Speaking of diff's. Not to get off the subject. I'm waiting for my differential for the '81 to come back from a fellow in Texas. I had him machine a left bearing cap out of billet steel and fit a C4 carrier w/posi unit. These are a weak points in the Aluminum Dana 44. I'm going with 3.54 gears. This should work good when I swap over to the "Baby LS1" engine.




|UPDATED|5/26/2012 7:04:00 PM (AZT)|/UPDATED|


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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




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5/26/12 11:00pm - Reply: 'Re: Gear Selection'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
Personally, I'd go with the 3.55, but the 3.91 would be ok too. I would not go to 4.11 if planning on running very many highway miles. Low ratio gearsets like that tend to get hot in use. I think Darryl's RPM/Gear ratio "chart" is prolly correct.
Also correct in that you cannot use gearsets designed for the Dana(aluminuminum) carrier in the iron carriers.
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5/27/12 10:38pm - Reply: 'Re: Gear Selection'
stingrayjim jr Lifetime Member
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SHELBYVILLE, TN - USA

Vette(s):
1976 L48 auto

1978 L82 4speed

1994 LT1 6speed

Joined: 7/5/2002
Posts: 3934
you can find a couple of different sites that has a calculator for such purposes... 
 
one neat one i found that has a display in real time of a tach and speedometer, along with gear selections, both rear gear and transmission, tire size selector,etc.. 
 
 
this one is a little more straight forward.. :)
 
just plug in your numbers.. :)


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StingrayJim
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Stingray's '76                             StingrayJr's '78                           Lil Red '94

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5/27/12 11:20pm - Reply: 'Re: Gear Selection'
rod7515 Lifetime Member
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Red Lion, PA - USA

Vette(s):
1974 White 350 Corvette, TH400 Automatic 1972 Tangerine /Go Mango Convertible 383 Stroker, 2004r Automatic

Joined: 10/27/2006
Posts: 1172
Thanks for the replies. I will start to look for a set of 3:70, 3:90 or 4:11. If I dont find any of these by the time I pull mine apart I will go with the 3:55 gears I bought. The overdrive looks to make a huge difference.
Thanks again for the responses
Rodney


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5/28/12 9:13am - Reply: 'Re: Gear Selection'
lukesvette Lifetime Member
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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

Joined: 5/18/2004
Posts: 6804
Very happy with my 3.70s. 65 MPH is at about 2000 RPM - engine is loafing and first gear converts to something like a 4.56 rear due to the lower first gear in the 700.

Those poor tires...Evil Smile


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5/28/12 10:05pm - Reply: 'Re: Gear Selection'
Redwingvette Lifetime Member
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Waterford, MI - USA

Vette(s):
1973 Red coupe

Joined: 9/13/2002
Posts: 1674
I am very happy with the 3.55 gear and my 200-R4 trans
With the better first and second gears for low end really helps with fast starts. Anything more and all I do is spin tires anyway.

200-4R: 2.74 first, 1.57 second, 1.00 third, .67 fourth

Turbo 400: 2.48 first, 1.48 second, 1.00 third.

Turbo 350: 2.52 first, 1.52 second, 1.00 third



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Brian - NCM Lifetime Member
          
73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, F-body seatbelts, Pioneer CD player
Magnaflow Exhuast System
Dewitt radiator and dual electric fans
Borgeson Steering box
Click here for Brian's Home Page 



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