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Old 12-29-2006, 09:35 PM   #1
1970cuttass

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Default Rear End Gear Ratio Suggestions

I am running a 1970 Cutlass S with a 350, .030 over, brand new performance intake and exhaust, 750 cfm edelbrock, new TH350 with shift kit and 1500 stall. Im pretty sure stock its 2.73 or something like that and it really needs something new to wake it up. I guess im looking for something street/strip that really gets off the line. A friend suggested 3.73 or higher, i was wondering what this oldsmobile community thinks. Thanks.
 
Old 12-29-2006, 10:23 PM   #2
Psyco Diver 69

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I'm using a 3.73, but that came stock. I suggest 3.42 because it will still feel like adding 50hp but give decent hiway rpm.

For street/strip I would also suggest dumping the edelbrock. Its not that great, a holley or a quadrajet would be the best, quadrajet being the best overall. I would suggest a Preformer RPM intake amd I would add a 2000+ stall converter. What type of exhaust did you go with? Did you get headers too, if not get them, they make a huge difference. Did you upgrade from the points distributer yet?
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1972 Olds 442 - 350/th350/3.73 posi
1984 GMC Sierra - 305/TH700r4/3.42

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Old 12-29-2006, 11:10 PM   #3
1970cuttass

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I actually do have a performer rpm intake, i have hooker headers back to series 40 flowmaster. I also did go to the HEI distributor. I forgot to add i have a lunati braket master II cam. Thank you for the advice.
 
Old 12-29-2006, 11:25 PM   #4
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I ran that cam before, I would severly suggest a 2400-2500 stall converter and 3.42-3.73 rear gear to get it running at its best. That cam is pretty lumpy and quadrajet would make it run better at part throttle and cruising and still maintain a great top end. It would be a huge improvement over that edelbrock. My edelbrock did not like that cam at all, it ran good with my holley though
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1972 Olds 442 - 350/th350/3.73 posi
1984 GMC Sierra - 305/TH700r4/3.42

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Old 12-30-2006, 01:33 AM   #5
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i would go for the 3:42
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1984-olds cutlass supreme-307/TH200r4/3.73,15.06@88.26mph 2.065 60ft, street/strip
1980-gmc high seirra-350/SM465/NP205/1ton axles/4x4, frame-off resto-mod
 
Old 12-30-2006, 02:10 AM   #6
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Damn I have the exact same setup... 70 engine 355 w/bracket master 2 cam, but I have a 3000 stall, not a daily driver (and I don't care) and I plan on putting 3.90's in my rear..... I just hope my compressions good. I think we will be pleased if the compression is right. Should be a good combo..... unless Captjim says otherwise
 
Old 12-30-2006, 04:34 AM   #7
1970cuttass

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Mines more of a daily driver except for in the winter. I want to be able to drive it on the highway without winding too high.
 
Old 12-30-2006, 07:43 AM   #8
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Quote:
Originally Posted by 1970cuttass View Post
Mines more of a daily driver except for in the winter. I want to be able to drive it on the highway without winding too high.
4 speed should solve that.
 
Old 12-30-2006, 01:04 PM   #9
1970cuttass

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What do yall think about replacing the gears in my stock rear end? or should I go for a new housing, n axles and the whole deal?
 
Old 12-30-2006, 04:40 PM   #11
1970cuttass

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I bought the engine rebuilt so i forget what pistons it has, i doubt they are anything special.
 
Old 12-30-2006, 05:08 PM   #12
71CutlassConvertible

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If you have the original O-type 12 bolt then your gear ratio choices are very limited. Richmond Gear sells new gear sets in 3.42, 3.90 and 4.10 ratios only:
http://www.richmondgear.com/01pdfs/page11.pdf

Along with the gears you will need a different series carrier as the new gear sets are made to fit the original 3.08-3.23 ratio carrier.
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Old 12-30-2006, 08:07 PM   #14
1970cuttass

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Hmm.. the guy who had the engine rebuilt actually said it is supposed to make about a 10:1 compression, but i will definately look into it. What do you think about a used ford 9 inch with 3.50 ratio?
 
Old 12-31-2006, 12:39 AM   #15
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My engine was rebuilt with cast "factory replacement 10.25:1 pistons" and I calculate I actually have around 8.5:1.

Listen to what captjim is saying - he's been there and done that.
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Daily Driver - 355 cid, UltraDyne .485/.485, 217/221 cam, Performer RPM intake, 750 cfm QuadraJet, HEI, Heddman Headers, TH350/Hughes 2500 stall, 3.23 limited slip, BFG 245-60-14s on SSII wheels
 
Old 12-31-2006, 02:52 PM   #16
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Quote:
Originally Posted by captjim View Post
Here we go again. If cast replacement pistons were used, your compression ratio is not enough for that cam. That cam likes 10.0 or so, you are probably closer to 8 to 1. Do a cranking compression test.
How's that test done? Does the motor have to be out of the car?
 
Old 12-31-2006, 11:31 PM   #18
bigdan

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I had a 350 cutlass 4 barrel it had factory 10.0 to 1 CR with 3:42 it will give you a nice set up street -highway

you dont have overdrive so 3:42 is good compromise
i would install a 2200- stall torque converter you will be surpise how much difference off the line your car will act ...specially with that cam

I had a 1970 W-30 with 3:91 gears : good for strip and short trips on the road forget the highway olds dont like sustained high rpm

Dan
 
Old 01-11-2007, 06:42 PM   #19
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Greg@ Supercars Unlimited should have everything you need in your area! 3:42's are a very good all around gear
 
Old 01-13-2007, 12:13 PM   #20
tommy

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I put 3.42 in my car and they seem alright. Run about 2800 rpm at 60 mph with 28" tall tires. Would be nice to get the rpms lower but would also be nicer to have deeper gears. So the 3.42's were a good compromise. I eventually want to get an overdrive and deeper gears since this is my daily driver but the cost is a little high for me right now. 3.42 would probly be good for you too.
 
Old 01-13-2007, 02:35 PM   #21
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Which BMII cam did you use? Lunati makes 2 of them... a 214/224, and a 224/234... You may need a bigger stall... For rear gears I would run 3.23 or 3.43.


A 4 speed and an auto will have a cruise RPM within 10% of each other
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