Hey dudes,

If I change out those 3.08 gears in the stock 10 bolt to 3.55s what can I expect to happen to the rest of the drivetrain being stock and all? Could it hurt my performance? I know it sounds dumb but I have heard some crazy stuff before. It is just a stock 307. 10 bolt's a peg-leg. Thanks guys.

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69 Post

JOHN
1969 Chevelle

www.geocities.com/w_surfer99/index.html (http://www.geocities.com/w_surfer99/index.html)

www.celdivision.com (http://www.celdivision.com) Art For The Big Boys!

The 3.55's are a good cruising gear and will give a little more UMPH of the line than the 3.08's. You will bring the cruising RPM up as well though. What size tire are you planning on running?

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1970 chevelle
406 - TH-350 - soon to be 411's
engine (http://www.chevelles.com/showroom/engine.jpg)
Interior (http://www.chevelles.com/showroom/interior.jpg)

"I didn't get pulled over for going over the speed limit, i got pulled over for getting there faster than anyone else"

You shouldn't have any problems with the 3.55 gear. You'll notice a bit more RPM's at highway speed, and maybe even a little more interior noise because of it. Your gas mileage will drop a bit, probably not very noticable, and you should feel like you have a bit more power during take-off. Other than that, this won't be a major switch.

It should be reasonably noticeable, but just go the extra mile and get 3.73's. You will definitely notice a considerable difference.

Its still a 307 so it wont be a scary change, but always be looking toward the future with your changes....this one is worth looking into now

The tire's bfg radial 275/60-15

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69 Post

JOHN
1969 Chevelle

www.geocities.com/w_surfer99/index.html (http://www.geocities.com/w_surfer99/index.html)

www.celdivision.com (http://www.celdivision.com) Art For The Big Boys!

One thing it won't hurt performance. Is this a change four future intentions? You will have to change the speedometer gear in the trans if you want the speedo to read correctly.
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Undee's70SS (http://www.chevelles.com/showroom/undee70ss02.jpg)

[This message has been edited by undee70ss (edited 01-24-2002).]

[This message has been edited by undee70ss (edited 01-25-2002).]

Went from 3.08's to 3.73's and a Locker. It was quite noticible. As long as you don't plan on long trips, the 3.73's are the way to go. For suggestios if you want to add some more 307 juice. I just completed mine. Look for it in this forum. I spent around $1,000 in parts, but they can all be moved to a 350 later if wanted.

Dude,
With those tall tires (my 275-50-15s are 28" tall) you'll be fine with either 3.55 or 3.73 rear gears.
For me I'd go 3.73 if I had it to do today.
But I'm currently using 4.10s.

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ACES member:#3722
68 SS-396 (http://www.chevelles.com/showroom/thad68velle.jpg) Best E.T. 13.533@106 m.p.h.
68 SS-396 (http://www.chevelles.com/showroom/thad68velle2.jpg) 4 gears & 4.10s
1st Car (http://www.chevelles.com/showroom/thads68bu.jpg) 1984-86, original 6cyl, then 74-350, then 327, then 454 :)
68 Corvette (http://www.chevelles.com/showroom/thads68vette.jpg) In the Family for 20 years.

For street cars I like 3:55s with 14" tires and 3:73s with 15s. 3:73s and a 200R4 would be a great combo if you can swing the trans swap also.

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Dave
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
68/72 chevelles
55/57/61 chevies
TC member #493
Never forget Earnhardt!

Interesting that you should ask if it could hurt performance. Unless you have had your Velle on a chassis dyno the gears may make no change other than extra engine noise from higher rpms - I say this because sometimes gear changes with such a tame engine only serve to get the engine past the fat part of its powerband more quickly, which hurts acceleration. 3.08's aren't all that bad (note my sig line), but normally I would expect 3.55/3.73 gears to be helpful.

You didn't ask, but if it were me I would instead install a PowerTrax perfromance locker - they are an easy one man driveway install. That way, with those tires, you could launch it as hard as you wanted to and not waste any time spinning the wheel(s).

Thomas

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"Bomber" '67 El Camino, Beater comes back to life.
Was 350/TH350 14.90 @ 93mph, 360,000+ miles on car.
Now 406 roller, 340rwhp, more hp coming, 3.08 gears.
Street radials, left in drive, 13.20 e.t.@108.35 mph.
8/1/01 added Plum Mist '67 to collection
ProCharger D-2R 468 under construction.

QUOTE:
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You didn't ask, but if it were me I would instead install a PowerTrax perfromance locker - they are an easy one man driveway install. That way, with those tires, you could launch it as hard as you wanted to and not waste any time spinning the wheel(s).
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What's the difference between a locker and POSI? I know that a POSI has friction clutches to keep both wheels spinning. How does a locker work? What makes it lock up? I am not looking for faster launches. I am looking for better traction in snow and slippery stuff.

Mike

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Mike Novak
'71 Chevelle convertible
red daily driver

As I posted above, I am currently running 3.73 gears, 28" tires and a Locker. The locker acts just like a spool on the straight away. But when you take a corner, it unlocks and "ratchets" as to allow the outside wheel turn slower than the inside. This way it doesn't shred your tires. It takes a little getting use to. I have an older unit from about 4 years ago. They have newer ones that are supposedly quieter. I will say that I only hear mine click when cutting the wheel really sharp and going very slow. I will say one thing. If you install one, don't let a mechanic working on it tell you that something is missing teeth causing a "ratcheting" noise. Just happened this weekend. Scared the hell out of me until I realized the sound he was describing. He never heard of a locker before.