Topic: 3.08 Posi
in Forum: C3 Driveline Components
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Leavenworth, KS - USA
Joined: 1/24/2007
Posts: 426
Vette(s): MM Red 1971 T-top,LS5,4-speed, black leather C5 seats, Hooker sidepipes.
Previous: 64 Coupe, 65 Roadster L76 / N14
Questions for the jury.
I haven't driven my baby enough yet to get a feel for this yet, but when I checked, I have a 3.08 posi rear end. This is mated to a 4-spd Muncie / LS5 motor. Question is, what can I expect? Better cruising and mileage? Poor take offs? Seems like a pretty high ratio. Isn't this pretty much standard for an A/T?
Is there an "ideal" or better ratio if my primary intend is to cruise? Thanx.
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Unless I'm mistaken w/a BBC its a good cruiser MPG gear however w/a 454 I cant see you having poor take offs. I had a Chevelle years back with a 396/325 and a 3:08 and it was just fine. If your racing I could see you going up in ratio but I think you'll be very satisfied.
Lifetime MemberThe "right" ratio is different for every person. A lower end ratio will result in lower RPMs while cruising. The downside is that the car loses some "punch" off the line. Going with a higher ratio gives you more punch, but also causes cruising RPM's to be higher. Choose based on what's most important to you.
Mike, if you want it good for cruising, leave it at 3.08:1. Any more and you start really sucking gas, not to mention running at high revs all the time.
Lifetime Member #116
Dave's '82 
Gold MemberI'd like to ditto what DaveM just said. My LT-1 has a 3:70 rear (M21 4spd), and at 70mph I'm running at about 3200RPM! Definitely not something you'd want to do on a long trip!
with an LS5 your not getting much in gas mileage anyway. If I had a BB i`d want to take off with my hair on fire.But it is a personal preference. I changed from 3;08`s to 3;55 . off the line is much better, and depending on the exhaust you have, cruising isn`t unbearable
It really is personal preference.
You could put in a six-speed to get a lower 1st gear for quicker off the line and a higher overdrive to bring the RPMs down when cruising, but you would need to look at the entire drive line.
Just another thing to think about.
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I agree with dwright (Dave).
I went from a dismal 2.72:1 to a 3.08:1. I'm very happy with that. It was a real slug off the line. Granted it's not a Titan II missile off the line, but the 3.08's made a big improvement and the rev's are still decent at highway speeds. Down the road when funding allows, I'll be investing in a Keisler 5 spd. kit. First gear will definitely help launch the car off the line a lot better, and the rev's should really drop down at highway speeds.
TKO500 5 spd.
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
My 81 has a 3:55 with the stock th350c. I love it BUT hiway gets a little combersome over 80mph..
I switched my3.08 gears to the 3.55 and with my SBC and TH400 it really sucked on a road trip, (like about 12mpg). I fixed it by going to the OD trans. Unless you really like burning rubber then stay with the 3.08's. Redwingvette 2007-03-19 16:30:21
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, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System
Dewitt radiator and dual electric fans
Borgeson Steering box
in Forum: C3 Driveline Components
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