Allpar Forums banner

ENGINE RPM @ VEHICLE SPEEDS

1978 7
Hello,

I am currently working out some kinks in our 90 Plymouth Sundance, 2.5 liter TBI, with the A413, 3 speed automatic transmission. The tachometer isn't currently working and my previous attempts to repair have failed (so far).

I have been told that while traveling with my 3 speed automatic transmission in 3rd gear @ 65 mph, the engine is turning "approximately" 2,800 rpm, near or at maximum torque.

What I would like a bit of help with is the following:

1) At what vehicle speed in 1st gear, is the engine making 2,800 rpm? Lets call this vehicle speed A.
2) At vehicle speed "A", if I shift manually into 2nd gear (without increasing the vehicle speed), what rpm is the engine turning (in second gear)?
3) At what vehicle speed in 2nd gear, is the engine speed 2,800 rpm? Lets call this vehicle speed B.
4) At vehicle speed "B", when I shift manually into 3rd gear (without increasing the vehicle speed), what rpm is the engine turning?
5) At what vehicle speed is the engine rotating 2,800 rpm in 3rd gear?

I don't expect anyone to know these numbers off the top of your heads, so I am actually asking you to, perhaps, today or tomorrow, while running a local errand or driving to work, if you (whomever doesn't mind) don't mind doing a stranger a small, seemingly ridiculous favor, to check these vehicle and engine rpm speed for me.
1 - 2 of 2 Posts

· Registered
Joined
·
1,147 Posts
You might get a few different answers if a few people actually try this out. :) Those are not normally published and since you have a lockup converter, you have to be sure what condition it is in. For example, when the engine is under load, like in going up a hill, the computer will not provide a lockup signal at the usual 43 MPH and the RPM's will run higher. IIRC, the lockup can only take place when you are in 3rd. For #5 you pretty much answered that yourself. I have noticed that at 70 MPH on my Spirit, I am running about 3050 RPM, but the factory tach could easily be off by 50 or more RPM.

If I get a chance tonight, I'll try to see what speed I am going in 2nd gear at 2800 RPM. It might be tough around here with the traffic congestion but we'll see how it goes.
 

· Registered
Joined
·
1,147 Posts
I can confirm the 42 MPH at 2800 in 2nd gear. That is about all I could do on the Spirit on my commute home and I couldn't stay at a constant speed for long because of tight traffic. It takes 35-40 minutes to go 8 miles in this urban sprawl, so we move pretty slow.
 
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top