Rpm at 55 mph
Thread Starter
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
Rpm at 55 mph
I posted awhile back about my "up shift" light coming on in my 87 convertible.
I know nothing about the cars past since the owner died before I bought it. I know it has a 383 stoker engine. I know it runs strong.
But the light keeps coming on for "upshifting" at 55 mph or so. The cars turning over 1900 rpms at 55 mph. What rear end does the thing have to be doing that? I found another thread on here where someone mentioned putting a 3.54 rear end in their car and having the upshift light and around the same rpms. So Im guessing the guy put a 3.54 rear end in it? Its a 700r4 automatic car.
The tcc seems to be locking up right as in giving it gas only raises the rpms if the speed increases too and doesn't drop when letting off the pedal.
So what rpm should I be seeing normally at 55 mph?
I know nothing about the cars past since the owner died before I bought it. I know it has a 383 stoker engine. I know it runs strong.
But the light keeps coming on for "upshifting" at 55 mph or so. The cars turning over 1900 rpms at 55 mph. What rear end does the thing have to be doing that? I found another thread on here where someone mentioned putting a 3.54 rear end in their car and having the upshift light and around the same rpms. So Im guessing the guy put a 3.54 rear end in it? Its a 700r4 automatic car.
The tcc seems to be locking up right as in giving it gas only raises the rpms if the speed increases too and doesn't drop when letting off the pedal.
So what rpm should I be seeing normally at 55 mph?
Team Owner
Joined: Sep 2003
Posts: 25,357
Likes: 2,729
I posted awhile back about my "up shift" light coming on in my 87 convertible.
I know nothing about the cars past since the owner died before I bought it. I know it has a 383 stoker engine. I know it runs strong.
But the light keeps coming on for "upshifting" at 55 mph or so. The cars turning over 1900 rpms at 55 mph. What rear end does the thing have to be doing that? I found another thread on here where someone mentioned putting a 3.54 rear end in their car and having the upshift light and around the same rpms. So Im guessing the guy put a 3.54 rear end in it? Its a 700r4 automatic car.
The tcc seems to be locking up right as in giving it gas only raises the rpms if the speed increases too and doesn't drop when letting off the pedal.
So what rpm should I be seeing normally at 55 mph?
I know nothing about the cars past since the owner died before I bought it. I know it has a 383 stoker engine. I know it runs strong.
But the light keeps coming on for "upshifting" at 55 mph or so. The cars turning over 1900 rpms at 55 mph. What rear end does the thing have to be doing that? I found another thread on here where someone mentioned putting a 3.54 rear end in their car and having the upshift light and around the same rpms. So Im guessing the guy put a 3.54 rear end in it? Its a 700r4 automatic car.
The tcc seems to be locking up right as in giving it gas only raises the rpms if the speed increases too and doesn't drop when letting off the pedal.
So what rpm should I be seeing normally at 55 mph?
Post back with RPM @ 55 MPH with the GPS and also mention your tire size. With MPH, RPM and tire size the axle ratio should be easy to compute. Is the rear a stock D36 or has it been changed to a D44?
Instructor
Joined: Aug 2014
Posts: 144
Likes: 2
From: Ca
I posted awhile back about my "up shift" light coming on in my 87 convertible.
I know nothing about the cars past since the owner died before I bought it. I know it has a 383 stoker engine. I know it runs strong.
But the light keeps coming on for "upshifting" at 55 mph or so. The cars turning over 1900 rpms at 55 mph. What rear end does the thing have to be doing that? I found another thread on here where someone mentioned putting a 3.54 rear end in their car and having the upshift light and around the same rpms. So Im guessing the guy put a 3.54 rear end in it? Its a 700r4 automatic car.
The tcc seems to be locking up right as in giving it gas only raises the rpms if the speed increases too and doesn't drop when letting off the pedal.
So what rpm should I be seeing normally at 55 mph?
I know nothing about the cars past since the owner died before I bought it. I know it has a 383 stoker engine. I know it runs strong.
But the light keeps coming on for "upshifting" at 55 mph or so. The cars turning over 1900 rpms at 55 mph. What rear end does the thing have to be doing that? I found another thread on here where someone mentioned putting a 3.54 rear end in their car and having the upshift light and around the same rpms. So Im guessing the guy put a 3.54 rear end in it? Its a 700r4 automatic car.
The tcc seems to be locking up right as in giving it gas only raises the rpms if the speed increases too and doesn't drop when letting off the pedal.
So what rpm should I be seeing normally at 55 mph?
Thread Starter
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
Check your tach with a scanner and see how accurate the tach actually is. Check your speedometer with a GPS for accuracy. Disregarding the OE speedometer what does the tach read when the GPS reports 55 MPH in 3D gear NOT OD. Do all of your confirmations using 3D and NOT OD.
Post back with RPM @ 55 MPH with the GPS and also mention your tire size. With MPH, RPM and tire size the axle ratio should be easy to compute. Is the rear a stock D36 or has it been changed to a D44?
Post back with RPM @ 55 MPH with the GPS and also mention your tire size. With MPH, RPM and tire size the axle ratio should be easy to compute. Is the rear a stock D36 or has it been changed to a D44?
I tried to see what rear end it has after finding a pic of the difference in the d36 and d44 but I cant see the top of the rear end to tell. Going to have to jack it up and crawl under there to know for sure.
Thread Starter
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
I counted the gears and its in 4th at 1900 and the converter seems to be locked up but I'll try faster and see what happens.
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Team Owner
Joined: Sep 2003
Posts: 25,357
Likes: 2,729
A test would be maybe 2000 RPM,
1 = 13.5, 2 = 25.3, 3 = 41.3, 4 = 59
or 3000 RPM
1 = 20.3, 2 = 38, 3 = 62, 4 = 88.5
Those #'s are using advertised diameter of a 255 so there will be a discrepancy because of the rolling radius.
Last edited by WVZR-1; Jan 31, 2015 at 08:20 PM.
Burning Brakes
Joined: Mar 2012
Posts: 768
Likes: 22
From: California
FL Events Coordinator
St. Jude Donor'13
Relly? I am not the original poster, but my from what I believe is stock 1989, my car goes into overdrive at about 38mph and comes out of it at around 33mph. Also, my car runs at about 1900 RPM's at about 57-58. Does that mean I have 3.73 gears in my car also? I thought I had the stock 2.59. My car is a 700r4 if that helps.
Safety Car
Joined: Sep 2001
Posts: 4,137
Likes: 531
From: Glenbeulah Wi
Relly? I am not the original poster, but my from what I believe is stock 1989, my car goes into overdrive at about 38mph and comes out of it at around 33mph. Also, my car runs at about 1900 RPM's at about 57-58. Does that mean I have 3.73 gears in my car also? I thought I had the stock 2.59. My car is a 700r4 if that helps.
1 revolution of the rear tires is 6.754 ft
4840/6.754 = 716.56 RPM of the rear axle at 55 mph
1900 RPM /.7 overdrive ratio of the 700 R4 = 2714 driveshaft RPM
2714 driveshaft RPM / 716.56 tire RPM = 3.78 rear axle ratio or approx. 3.73 or 3.75 gears.
My guess is you are not in overdrive instead you are feeling your torque convertor lock up at 38 MPH. if you were in drive (3 rd gear) you would be running 1900 RPM at 57 MPH with 2.59 gears.
Last edited by bjankuski; Feb 3, 2015 at 11:55 AM.
Burning Brakes
Joined: Mar 2012
Posts: 768
Likes: 22
From: California
FL Events Coordinator
St. Jude Donor'13
55 MPH = 4840 ft/min
1 revolution of the rear tires is 6.754 ft
4840/6.754 = 716.56 RPM of the rear axle at 55 mph
1900 RPM /.7 overdrive ratio of the 700 R4 = 2714 driveshaft RPM
2714 driveshaft RPM / 716.56 tire RPM = 3.78 rear axle ratio or approx. 3.73 or 3.75 gears.
My guess is you are not in overdrive instead you are feeling your torque convertor lock up at 38 MPH. if you were in drive (3 rd gear) you would be running 1900 RPM at 57 MPH with 2.59 gears.
1 revolution of the rear tires is 6.754 ft
4840/6.754 = 716.56 RPM of the rear axle at 55 mph
1900 RPM /.7 overdrive ratio of the 700 R4 = 2714 driveshaft RPM
2714 driveshaft RPM / 716.56 tire RPM = 3.78 rear axle ratio or approx. 3.73 or 3.75 gears.
My guess is you are not in overdrive instead you are feeling your torque convertor lock up at 38 MPH. if you were in drive (3 rd gear) you would be running 1900 RPM at 57 MPH with 2.59 gears.
Safety Car
Joined: Aug 2013
Posts: 4,424
Likes: 603
From: Minneapolis Mn
I thought the upshift light was only wired on manual transmission cars. According to your info, this is an automatic so IMO that means it was converted from manual to auto or there's a short or screwup in the wiring.
Thread Starter
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
From what Ive read its normal for the automatic cars to have the upshift light in the L98 models at least.
Safety Car
Joined: Sep 2001
Posts: 4,137
Likes: 531
From: Glenbeulah Wi
Safety Car
Joined: Sep 2001
Posts: 4,137
Likes: 531
From: Glenbeulah Wi
-The transmission shift MPH are controlled by the transmission so I am not sure when your car should shift into overdrive. what I can tell you is if you were in overdrive at 60 MPH with the torque convertor lock-up, and 2.59 gears your engine RPM would be 1420 RPM.
Last edited by bjankuski; Feb 5, 2015 at 01:10 PM.