Is it normal for my Vette 1977 stock 350 L48 Automatic to tach so high at highway speeds? It seems awful high to me. Around 55mph it's about 2500 rpm and 65mph around 3000 rpm. Also, when I turn it on to start the needle on tach does not go all the way down to 0. It stays at 4 rpm. So could that be throwing it off by 4 rpm. Is this a problem that I need to address? When I had my 68 350 4spd it tach around 1600 at 55mph.

Here is a rear gear/rpm calculator.

I plugged in 3000fpm, 3.55 rear gear, and 27" tall tires and got 68 mph.

Same but with 26.5" tall tires I got 66.6 mph.

https://www.angelfire.com/fl/procrastination/rear.html

I always thought my '75 tach was high, then when I put EFI on, it has a built-in tach, and I found that at highway speeds the Vette tach read over 1000 RPM high!  And this was after I had replaced the electronic board on it.

Assuming it has the 3.55 rear gears, as most automatics did, 3000rpms would not be excessive. My '74 with 3.36 gears tachs around 3200rpm at 75mph.

Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

If it's an electronic tach then indicating ~400 rpm w/ engine off is normal. The rpm at any road speed is governed by rear end gear ratio and tire circumference.  Do the calculations and see if it's off. 

My 3:55 gears give 66 mph @ 3,000 rpm.

1973 L-82 4 spd

My '78 Silver Anniversary with 3.08 gear, Turbo 350 trans and 27.1" diameter P255-60R15 Radial T/A's does 70 at 2,700 & 75+ at 2,900.  In contrast, my '85 Monte Carlo SS with 3.73 gear, TH200R4 in overdrive and same tire does 70 at 2,200.  500 rpm difference makes the SS cheaper on gas for long trips, just not quite as fun!  Can carry alot of luggage though so its a trade-off.  😀