Want to know how? Good, so do I! I'm baffled. But I'm sure the big brains on this forum can figure it out!
Here's the situation:
- New-to-me W116 300SD with 120k miles. Nice condition, but sat a lot last several years due to elderly original owner. I've done nothing so far except change fluids, adjust valves, check hoses. I'm sure injectors, turbo, etc. need attention still.
- Car has incredible acceleration: 11.9 secs to 60mph, measured multiple times with GPS and stopwatch. Chirps the tires on shift from 1st to 2nd. A real hoot to whip through the country roads.
- Transmission shifts smoothly through all 4 gears; no flaring or slipping, etc.
- No obvious engine mods (e.g., no Doktor Bert-esque tuning of cam, timing, ALDA, etc.)
- Tach is accurate (confirmed with touchless tach)
- Speedo reads 15-20mph high (e.g., reads 79 when GPS shows 60)
- High speeds require excessively high revs - e.g., approx 4,000 rpm at 70 mph. I'm afraid to push it above 78 as it sounds like it'll rpm itself to pieces. So highway cruising at modern speeds is virtually impossible.
I know what you're thinking, as I thought the same thing -- some acceleration junkie must have replaced the standard 3.07 rear diff with something significantly shorter like a 3.69 (and not recalibrated the speedo of course). So, I crawled under the rear to look at the stamp on the diff and it says. . . 3.07. Huh?!
I'd greatly appreciate folks' thoughts on what might produce the above characteristics in this car. And if anyone wants to drag race, just holler
. Thanks!