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Topic: What ratio to use???

in Forum: C3 Driveline Components


What ratio to use???

Posted: 7/7/03 11:09am Message 1 of 9
Former Member
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Canada
Joined: 6/27/2002
Posts: 13
Vette(s): 1969 Corvette Coupe 350-350 H.P. Monza Red, Black leather interior
It's been a blast getting my engine back (350-350 hp). I had it totally rebuilt with all new components from Active Engines here in Toronto. (Activeengines.com) What a difference!!! |bouncy| |thumb|
The guys at Active told me I'm running 3:08 in the rear and that is find if I plan on cruising on the highway (at 150mph..). He said I may want something more aggresive to really feel the pull of this motor. |headscratch| Any suggestions..
|saluteflag| |cheers|


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What ratio to use???

Posted: 7/8/03 8:36am Message 2 of 9
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Eastern part of, CT - USA
Joined: 1/29/2002
Posts: 319
Vette(s): White 73 convertible - 350/auto, A/C PS, PB, PW, leather, t/t, two tops Also had a 69 t-top 20 years ago
I guess it depends on your driving habbits and tranny. I have 3.08 gears and turn 3000 RPM at just about 75 MPH with 235/60R15 tires and an automatic. It is soft at the bottom, but I drive 75% highway so I don't mind.

I think 3.23 would be a good compromise for an auto tranny, and 3.4? with a standard tranny.

If you do mostly city driving, 3.40 with an auto and 3.55 with a standard.

Drag racing requires gears matched to the trap speed you plan on achieving.

Joe

PS, an overdrive tranny throws all the above out the window.

|UPDATED|7/8/2003 8:36:56 AM|/UPDATED|



What ratio to use???

Posted: 7/7/03 3:02pm Message 3 of 9
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Toledo, OH - USA
Joined: 9/4/2002
Posts: 147
Vette(s): 1976 Stingray, L48 auto Buckskin/Buckskin Leather originally. Numbers matching.
Like Joe said, you need to look at what your mpg needs are, and what your desired cruise rpm range is.
Personally I would recommend 3:55's, unless you do alot of highway. 3:55's will get decent milage, and should plant you in your seat when your right foot gets heavy. I wouldn't use anything lower than 3:40-42. My last Camaro ran a 3:42 with a very mild 350/auto, and it wasn't bad out of the hole, but definately not fast from a stand still. I will be swapping out a 3:36 for a 3:70-73 since I don't plan on putting any highway miles on my '76. Had considered 3:90, but I'm not sure I could afford to drive it then. |wink|
My theory is that most of the fast factory small block cars from the late 60's early 70's seemed to be equipted with 3:55-3:90 gears, automatics and manuals, and since that is the type of performance that I am looking for, that seems to be a good place to start. |cheers|

|UPDATED|7/7/2003 3:02:35 PM|/UPDATED|



'76 L48 Auto Project |IMG|http://www.freewebs.com/privategod/Mine2a.JPG |/IMG|

What ratio to use???

Posted: 7/7/03 7:51pm Message 4 of 9
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Portland, TN - USA
Joined: 4/29/2003
Posts: 805
Vette(s): 1972 Coupe Anything, but Stock and more mods to come! SSBC Force 10 Brakes, 3.73, TH350, 355 CID, Rack and Pinion, Vette Brakes suspension front and rear.
I just swapped mine over to 3.73. Did my math at ringpinion.com. They have a RPM calculator. It will get you in the ballpark. Choose a gear based on your driving habits. Is it 80% cruise and 20 drag/stop light to stop light or around town. You need to decide from their. The last thing you want to do is throw in a set of 3.90's and then decide you want to go on a cross country cruise. You'll regret it.

I chose 3.73 because I can live with the higher RPM's for right now until I do an overdrive swap.


What ratio to use???

Posted: 7/8/03 5:07am Message 5 of 9
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DOWNINGTOWN, PA - USA
Joined: 11/24/2001
Posts: 962
Vette(s): 1969 Monza Red Black Conv / Black Vinal hardtop 454/480 Tremec 5 Speed 308 Posi.Black Leather Interior, PS, PW, Air cond., tilt/tele,AM/FM Cass.-5 Pack CD, Hurst Shifter, side pipes 2004 Yellow convertible with black top and black interior
I have a 308 gear set currently. At 70 mph I am doing about 2900 rpm. Since I drive it to work at high(er) speeds, it is a good set up. However, when I change over to my 454 I think I will try to find a complete differential set up with either 373s or 411 gears. If I feel like going to the track, it won't be all that hard to change over the whole differential and then swap it back in later. I figure I will cut an access over the differential to get the top bolts from inside the car.
I won't worry about stop light 'drags' with the 308s. With over 400 foot pounds of torque at the rear wheels, I should be ok stop light to stop light.


What ratio to use???

Posted: 7/8/03 7:11am Message 6 of 9
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Toledo, OH - USA
Joined: 9/4/2002
Posts: 147
Vette(s): 1976 Stingray, L48 auto Buckskin/Buckskin Leather originally. Numbers matching.
Glenn, that was what I was planning originally, I picked up a complete rear frame and suspension from some guy who back halfed his 74 BB to pro-street. The current differential was a new replacement and has virtually no miles. I don't know about switching back and forth now, as it was a pain just getting the unit out of the bare(no body)frame. Unless the is a secret to making it easier, I guess I'll just have to stick with one ratio.

|UPDATED|7/8/2003 7:11:04 AM|/UPDATED|



'76 L48 Auto Project |IMG|http://www.freewebs.com/privategod/Mine2a.JPG |/IMG|

What ratio to use???

Posted: 7/10/03 5:33am Message 7 of 9
Former Member
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DOWNINGTOWN, PA - USA
Joined: 11/24/2001
Posts: 962
Vette(s): 1969 Monza Red Black Conv / Black Vinal hardtop 454/480 Tremec 5 Speed 308 Posi.Black Leather Interior, PS, PW, Air cond., tilt/tele,AM/FM Cass.-5 Pack CD, Hurst Shifter, side pipes 2004 Yellow convertible with black top and black interior
Please understand that I have not actually done this before. I am going by other club members who race their cars. According to them, the 'secret' to quicker swaps is cutting an access into the rear deck ( behind the seats ).
Depending on what these guy are doing at the time, they seem to do a lot or swapping of the differentials so I guess it has to be a better alternative than opening it up and doing gear and shim changes.
When I get the 454 into the car and buy another differential, I'll post the results. Unfortunately my attorney does not appear to be in any hurry filing the paperwork to get the engine back |frown|


What ratio to use???

Posted: 7/10/03 10:05am Message 8 of 9
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Joined: 6/16/2003
Posts: 252
I have a 3.70 in mine with a 700R4 transmission and 255/16 tires. It has a 90 model Tuned-Port engine. It runs about 2200 rpm at 70, I don't know exactly because my tach is off. I recently took a 300 mile mostly-highway round trip and got just over 22 mpg, I get around 18 mpg in town. The overdrive gives me an effective 2.59 rear ratio if I had a direct transmission. I agree with the other replies, it all depends on what you want to do with the car and if you have overdrive. If you don't have overdrive and want to drag race you may want a 4.11, if you want to cruise the 3.08 is probably fine. If you want a little of both then a 3.42 or 3.55 is probably good. If I had it to do over again, I would probably get a 3.42 with the overdrive in mine. Then I could get close to 2000 rpm at 70.
As far as physically changing rearends goes, I have done it a few times in the car. It is not terribly hard, the worst part in my opinion is dealing with the spring. It is not something I would want to do very often if I could help it. I would never cut a hole in the floor to get the upper bolts. Instead, I just take the upper crossmember out with the chunk bolted on. Take the 2 bolts out and use a pickle-fork (tie-rod) wedge to separate the crossmember bushing from the frame hat. The rearend and crossmember come out together without much problem then.


What ratio to use???

Posted: 12/2/03 1:37am Message 9 of 9
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Oakland, ME - USA
Joined: 10/4/2003
Posts: 12
Vette(s): 1977, 350, 4sd, coupe
My 180 hp '77 L-48 has a 3.70 gear and turns right around 2800 at 60 mph in 4th gear. I get about 15 mpg when I behave myself, which isn't very often. At 80 mph on the interstate it's buzzing, as I recall, about 3600 rpm's. I think a day long cruise at that engine speed would become a little tiring, but the 3.70's are great fun on back roads and for blasting up through the gears, and makes the car seem more powerful than it really is. It's perfect for the way I want to drive my car. My brother has an '81 Camaro with a 350 4 spd as well, but his engine is more powerful, about 285 hp, and has 3.08 gears. It's about the same weight as mine. But there is no doubt that my car is quicker and definitely feels it, too. I'm keeping the 3.70's for sure. Along with the other comments posted, this may help you decide what gears to go with. Good luck! |thumb|


in Forum: C3 Driveline Components


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