1983/1984 300SD: MPH for RPM
 

I'm on a road trip in Oregon and Washington. Today I was driving 80 MPH at 3800 RPM. The RPM seems high for that speed. Can anyone with a similar car let me know what their car does?

It would be nice to know the RPMs at 60, 70, and 80 mph for these 300SDs.

Thanks!

Hmm. That sounds like you are in third...

80 mph should be around 3200

Rear ratio should be 3.07:1
Top gear transmission is 1:1
Tires are around 195-75R14 (put tire size here) use ratio calculator on the web. Figure 200 rpm higher than it comes up with to account for TC slippage

I found you should be around 3400 at 80 - standard rear end, stock tires, auto trans.

The fuel injection pump timing on my car is retarded. Going 80 mph is almost maxed out. It did get 24.9 mpg today, mostly at 65-70 mph. Going 80 mph it was getting about 22 mpg, but that was mixed 50% with in town driving before the road trip.

I'm thinking of stopping in at Oregon Fuel Injection in Eugene, Oregon. They want the car for a day and a half to remove the IP, test & adjust it, then reinstall and adjust the timing. Estimated cost $750 to $1000, plus hotel nights. OUCH.

According to the tachometer, my car does 5000rpm @ 75mph in 4th gear, with a standard (manual) transmission. That being said, I don't think I've ever seen two tachometers show the same rpm at any given speed in these cars

3800 at 80mph in a 3.07 with stock wheels sounds pretty close, the tach might be off a bit. I usually run around 3400 at 75mph in our '82 300SD's.

My 420sel with a 2.47 diff is about 2950rpm at 80....so 3700ish is about right for a 3.07.

The 85's have a 2.88 differential which does drop a few hundred rpm off and helps a bit.

Mine likes to show 6000 rpm at idle. Or 0. Or anything in between.

I have been running about 3000 RPM at roughly 65 MPH

3800 at 80 sounds about right to me with the 307 or 288 diff...not a lot of difference there. I think my 350 SDL was around 3700 at 80 so with a 307 3800 sounds about right.

I stopped in Oregon Fuel Injection in Eugene, Oregon. It was just going to take too long and cost too much.

The car is running ok at speed. At 70 mph it was going at 3550 rpm. I'll adjust the IP timing when I get home. Today it got 25.25 mpg.

Been running 2900rpm for 65mph, 3200-3300for 72mph.
Ran 90mph at just under 4000 for 20miles ( running late for work)
All with 3.07 and 205x14 bundts tires/wheels. All correct with gps

84 300SD, 162k. Average honest mpg 28-30, respectively

3,000 RPM @ 70 mph - 83 300SD

Same here 1983 300SD 3000rpm @70mph