My wagon has 4.10s and its LT1 has bolt-ons good for 425hp or so at the crank. It develops a thrumming noise starting at around 80mph. It persists or worsens as speeds increase, up to at least 100mph. I'd like to be able to cruise the interstate at 95mph, vibration free, and be able to burst up to 130+ without driveshaft-related issues.
From what I've read, the vibrations are because the driveshaft is being spun much faster with the 4.10 gears that it was with the stock 3.08s (or whatever they were).
The nearby Napa Auto in Cape Girardeau will balance driveshafts for $75, and I was thinking about going that route. From what I've read, a driveshaft that is balanced up to 8000rpm should be good for up to 150mph with 4.10s. Dynotech Aluminum Driveshaft Balancing Speed
I don't know up to what speed Napa will balance the the shaft to. I suppose I should call and ask!
Measuring from the center of the pivot point on the middle of the front u-joint to the pivot point on the center of the rear u-joint is just under 55". It's probably right at 55.5" between the edges of the pivot points.
Or, should I look into a P71 driveshaft? Would it be likely to meet my qualifications without needing anything besides possibly new u-joints (IE, not needing balancing)? I like the idea of just bolting in my original driveshaft after it's been balanced, rather than trying to find a P71, changing u-joints, etc. On the other hand, not having my car down for a few days waiting for the driveshaft to be balanced is a pro, too.
What do you guys think?