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7/22/13 8:44pm - Original Message: 'Engine RPM'
RedVetteinprogress
Former Member
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West Bend, WI - USA

Vette(s):
1985 silver coupe & 1975 red coupe

Joined: 3/18/2010
Posts: 46
I've got a question for you guys. I bought a 1981 Vette recently and I'm wondering what's up with the engine RPM. The car is bone stock and when I'm cruising at 60MPH my tach is showing about 2800 RPM. The car is three speed auto and is supposed to have a 2:87 rear end in it. Does the indicated RPM seem high for what I have? Thanks for the help, Darrell

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7/22/13 10:11pm - Reply: 'Re: Engine RPM'
dyoes
Former Member
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Zachary, LA - USA

Vette(s):
1974 L-48 Auto. Just your basic Vette. GM crate motor w/vortec heads and intake. Crane cam. Scorpion rockers, Edelbrock carb. Lots of parts still in boxes... :(

Joined: 1/27/2013
Posts: 201
This is just a swag, of course, but the rpm calculator from

http://www.powerblocktv.com/resources/

shows about 2280 RPM.


That's assuming you have a TH400 auto (1:1 final drive) with 265/50R15 tires (diameter of 25.4").  Kind of scares me about what my TH400 with 4.11 gears will run when it's finished...  Might be time to invest in a ring and pinion.

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7/22/13 10:26pm - Reply: 'Re: Engine RPM'
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: 19449
'81 will have a 350C trans, with lock-up torque converter....assuming it is still stock. 60mph @ 2800 rpms does sound a little high, also assuming the tach is accurate. My guess is the lock-up is not working. A functioning LU would drop the rpms around 200 or so.
It sounds like you may not be 100% sure of the rear diff ratio. The stock '81 ratio for automatic was 2:81, but it may have been changed.....





|UPDATED|7/22/2013 7:26:29 PM (AZT)|/UPDATED|


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