Tach working OK??
Thread Starter
Instructor
Joined: Aug 2004
Posts: 119
Likes: 4
From: Sherwood Arkansas
Tach working OK??
Got a 96 LT-1 automatic. The Tach seems to be reading low. At 80mph its only showing 2000 rpm. Is this normal? I had the chevy dealer look at it while the car was in for other maintenance and they say it's operating ok. I would have thought 80mph would at least register 3000 prm????
Melting Slicks
Joined: May 2004
Posts: 2,286
Likes: 2
From: Stamping Ground KY
speed = RPM * 60 * tire circumference (miles) / (front gear * rear gear)
speed = 2000 * 60 * 0.00128799 / (0.70 * 2.59)
=85 mph
or you may have the optional performance rear gear (3.07)
=72 mph
I assumed you have 285/40-17 tires on the back.
Chevy put the steep last gear in the transmission to help with fuel economy, the engine is efficient up to about 2000 RPM... it's like they knew we'd speed
speed = 2000 * 60 * 0.00128799 / (0.70 * 2.59)
=85 mph
or you may have the optional performance rear gear (3.07)
=72 mph
I assumed you have 285/40-17 tires on the back.
Chevy put the steep last gear in the transmission to help with fuel economy, the engine is efficient up to about 2000 RPM... it's like they knew we'd speed
Intermediate
Joined: Jul 2004
Posts: 41
Likes: 0
My problem is exactly the opposite. I have a '91 vert and at 80 mph I'm at about 4,000 rpms, which seems high. Also, when I accelarate my tach goes off the map way past redline. I'm not sure of what gear ratio I have. What could be causing this and what do I need to do to fix it?
Melting Slicks
Joined: May 2004
Posts: 2,286
Likes: 2
From: Stamping Ground KY
Originally Posted by qdawg41
My problem is exactly the opposite. I have a '91 vert and at 80 mph I'm at about 4,000 rpms, which seems high. Also, when I accelarate my tach goes off the map way past redline. I'm not sure of what gear ratio I have. What could be causing this and what do I need to do to fix it?
I don't know the answer to your question.
Thread Starter
Instructor
Joined: Aug 2004
Posts: 119
Likes: 4
From: Sherwood Arkansas
Originally Posted by JCD
speed = RPM * 60 * tire circumference (miles) / (front gear * rear gear)
speed = 2000 * 60 * 0.00128799 / (0.70 * 2.59)
=85 mph
or you may have the optional performance rear gear (3.07)
=72 mph
I assumed you have 285/40-17 tires on the back.
Chevy put the steep last gear in the transmission to help with fuel economy, the engine is efficient up to about 2000 RPM... it's like they knew we'd speed
speed = 2000 * 60 * 0.00128799 / (0.70 * 2.59)
=85 mph
or you may have the optional performance rear gear (3.07)
=72 mph
I assumed you have 285/40-17 tires on the back.
Chevy put the steep last gear in the transmission to help with fuel economy, the engine is efficient up to about 2000 RPM... it's like they knew we'd speed
Thanks I talked to a friend that has an 89 manual and he sees the same thing in 6th gear as Im seeing in auto overdrive. At least I know it's not broke.
