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5/15/16 9:30am - Original Message: 'Cruising Speed'
Pappy's Toy Gold Member
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WILLIAMSTOWN, KY - USA

Vette(s):
Silver Anniversary 1978, L82?, 4-speed

Joined: 12/5/2002
Posts: 130
When cruising on the interstate at about 75 mph, I am pushing about 4 grand on my tack ('78 L82, 4 speed). How can I identify the gear ratio in my rear end and the type of 4 speed in my car? What are typical rpm readings when running at about 75 mph?

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Pappy's Toy
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5/15/16 12:15pm - Reply: 'Re: Cruising Speed'
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: 19448
'78 L82 w/4speed standard rear gear ratio was 3.70, with the option for a 3.36 ratio. With the rpms you're turning, I'd say you have the 3.70 gears. ALL 4 speeds have the same 4th gear ratio of 1 to 1, or direct drive. You could swap the rear gears for the 3.36 ratio and get your cruize rpms down to around 3000 @ 75mph or so, depending on tire size. Thumbs Up

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Joel Adams
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5/15/16 4:28pm - Reply: 'Re: Cruising Speed'
Pappy's Toy Gold Member
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WILLIAMSTOWN, KY - USA

Vette(s):
Silver Anniversary 1978, L82?, 4-speed

Joined: 12/5/2002
Posts: 130
Thanks for the info Joel. I kind of figured a 3.70 gear with the rpms I was pushing. It just makes it a little hard when cruising with a group on the interstate and I'm sure it doesn't help my gas consumption. I will have to consider my options; but since I just got her back on the road, I probably won't do anything this year. I just plan to enjoy her for a change instead of working on her.

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Pappy's Toy
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5/15/16 6:28pm - Reply: 'Re: Cruising Speed'
Jeffm Gold Member
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Sebago Lake, ME - USA

Vette(s):
1978 Silver Anniversary L82 4spd (M21) Red Leather. -1978 Pace Car L82 4spd (M21) 20k miles.

Joined: 2/15/2007
Posts: 962
'78 L82 4 speed here also and that rpm is probably about right. Don't hit the turnpike too often and only cruise at about 68 - 70 max and I thinks she tachs about 3500 at that.
A 5 speed will take care of that but I don't feel like spending that kind of money. 


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5/15/16 6:56pm - Reply: 'Re: Cruising Speed'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 862
I had the optional 3:08 in my Silver Anniv. L82 4-speed.  That would knock 600 rpm off your cruising rpm.

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5/15/16 10:06pm - Reply: 'Re: Cruising Speed'
Pappy's Toy Gold Member
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WILLIAMSTOWN, KY - USA

Vette(s):
Silver Anniversary 1978, L82?, 4-speed

Joined: 12/5/2002
Posts: 130
Thanks for the replies. I was curious if anyone else was in the same situation as I am in. I think for now I will just keep her at about 70 as Jeffm suggests for now.

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Pappy's Toy
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