I restoring a 1966 Jetstar 88, 2 door. I'm putting in olds 403 and 400 tyranny. Cuz original drive train is gone. Has anyone done this. Thinking I got moved crossmember, different drive shift. But do I have to cut floor and make a bigger trans tunnel? Any help or advice greatly appreciated thanks.

 

The 1966 J88 is the same B-body platform and frame as all other 1966 Olds 88s. The TH400 was an available option that year, so it clears the floorpan just fine, and the frame should already have the holes for the crossmember. The problem is that the 1965-76 full size cars use a long tail TH400. If the TH400 you have came with the 403, it is almost certainly a short tail version. The problem with this is that the driveshaft gets too long, which means that the "critical speed" (the driveshaft RPMs where excessive vibration starts) becomes too low. No amount of balancing will fix this, it's a structural limit on the driveshaft tube. A larger diameter tube fixes this if it fits in the tunnel. You'll need to have a custom driveshaft fabricated in any case. The other problem is the exhaust manifolds if you plan to run dual exhaust. The 1965-70 full size cars use a rear steer configuration, which puts the steering box in the way for the driver side exhaust pipe. The factory dual exhaust cars used a special LH manifold that routes up and over the steering box. This was only offered on big block engines - Olds never offered dual exhaust on the small blocks in the full size cars. Others have successfully used this special BBO manifold on a small block. Repros are available.