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+--- Thread: 1981 300SD Engine RPM - Highway (/showthread.php?tid=3181)
1981 300SD Engine RPM - Highway - Mahone Bay - 12-16-2011
Hello,
I recently purchased my first Diesel powered vehicle a 1981 300SD. Fortunately it is in very tidy condition with only a few minor issues to be corrected. Great vehicle, I am very pleased.
I'm trying to get my head around the engine rpm at highway speeds. It pulls about 3000 RPM at 70 mph. This seems a touch high for a Diesel and a 3.07 axle ratio so I'm wondering if 4th gear is not engaging (it's an automatic).
Any thoughts?
Thanks and take care,
PK
RE: 1981 300SD Engine RPM - Highway - Captain America - 12-16-2011
Sounds right to me.
These things rev to 5000 rpm easy
RE: 1981 300SD Engine RPM - Highway - yankneck696 - 12-16-2011
The torque converter does not have a lock up function. Also, 4th gear is 1:1, not overdrive. And yeah, 3000 RPMs is just fine on the highway. Just imagine if you had a lock up converter & overdrive...
Ed
RE: 1981 300SD Engine RPM - Highway - Mahone Bay - 12-18-2011
Hello Captain America, Ed,
Gentlemen, thanks for info. Part of me figured the RPM was correct but then the 'Diesel' logic (low rev engine), kicked in. :-)
Captain America - great handle. :-)
Ed - fully agree, a lock-up torque converter would drop the RPM by some 200. Overdrive would be even better.
Both - I switched the original 14" alloys for the 15" alloys used on the Series II cars (same ET as Series I). This allowed me to go to a 215/65 tire which means the engine RPM came down by 6.8% (200 RPM). Which was one of the goals with this exercise. Another factor was the availability of 14" tires here (I live in Europe, Netherlands to be exact), it is very poor (no well known brands). So 15'' offers a broader selection here.
In case your wondering, the car is a US spec version. Originally sold to a couple from Texas (picked up in Germany and shipped to the US after a European tour), and was sold to someone from here in 2009. I purchased it from the 4th owner with a total of 100,000 miles and full service history. Still wears its original China Blue paint (very good condition).
Thanks again and take care,
PK
RE: 1981 300SD Engine RPM - Highway - larsalan - 12-18-2011
Adding the 15in wheels will allow you to fit the larger 2nd gen calipers/rotors too
RE: 1981 300SD Engine RPM - Highway - dieselboy - 12-18-2011
If you do a lot of highway driving you can put in a taller diff ratio. I run a 2.65:1 in my car and I like it. There's a few threads about what gear ratios were available.
RE: 1981 300SD Engine RPM - Highway - Captain America - 12-19-2011
No Problem, Rev her to the moon!
