My 71 2800CS automatic runs at about 1400rpm and when I shift in gear it drops to about 800rpm, is that normal?
Running Weber carbs if that has anything to do with it?
Running Weber carbs if that has anything to do with it?
Idle drop from park to running gear
- Thread starter autowerks
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Too high. Try around 950 rpm. 1000 if you have ac.
Is it normal for rpm to drop that much though?
I'm working from memory here, but I seem to recall that when I removed my auto there was a connecting rod from a mechanism in the transmission to the bell crank. I believe this was intended to cause the tranny to downshift whenever you mash the pedal to the floor, so it is supposed to be loose unless the pedal is fully depressed. Because it is also connected to your linkage to the carburetor, you might check whether the length of this rod is influencing the drop you are seeing. A simple way to do this would be to disconnect your linkage all together and determine idle rpm without the linkage. If my theory is right, your car will idle around 800 rpm with the linkage disconnected.
when I put the car in drive from park the rpm drops 500, is that normal? I,ll check the transmissions linkage and see, thanks Joe
It has been a while since my 5-speed conversion but it makes sense that the CS being an open loop system when you go from park to drive you increase the load on the engine so the RPMs have to drop. I agree that 1400 sounds too high.
nashvillecat
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It might be normal . . . for your setup. Typically, engaging an automatic transmission in gear, engages the torque converter and this will necessarily cause idle speed reduction. That said, a 600 rpm drop is not necessarily abnormal, since you may have a torque converter with an unusually low stall speed or something else that might account for parasitic power loss at idle, e.g., air conditioning, power steering pump, charging alternator etc. Often, aftermarket air conditioning systems incorporate an idle solenoid that increased idle speed with air condition compressor engagement. If yours is so equipped, that might account for some of the drop in idle speed when the automatic transmission is also engaged. It is also possible that your tachometer readings are off.
If your carburetors are providing an excessively lean or rich mixture, the engine labors more than at optimum setup so that the drag imparted by an engaged transmission at near idle speed is more dramatic than normal. This is somewhat analogous to sea level engine operation for an engine setup for optimum high altitude operation or even a sticky or not fully disengaged choke.
Try lowering the idle speed, you may find the drop in rpm is not proportional due to the function of the torque converter
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Thanks guys, will play with idle setting a bit and let you know!
The car has Sanden A/C compressor with original set up, choke seems to operate normal!
The car has Sanden A/C compressor with original set up, choke seems to operate normal!
Mike Goble
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You want to make sure that your idle timing is correct. At 1400 rpm you may already be up on the mechanical curve.