Tranny

My friend has a '90 240, and he was wanting to know if the transmission from a DOHC would be any different than his on the SOHC. And if it was different in a better way, would it fit...without much fab?
And also, we buried the speedo at 115 yesterday in 4th gear, when I geared to 5th it "nose-dived" and we slowed down tremendously. Was this because of the gearing or fuel cut( 5th gear sensor thing i've heard about)?
Those are the mans exact words so, help us out.

probably the speed limiter.

Would some sort of piggy back work? To eliminate the limits???

HKS has one for the speed limit and rpm limiter. You can eliminate the speed limit by cutting one of the wires on the ecu. Ask someone else on here because I forgot which one.

it the 8th wire from the left, green with yellow stripe I think..check out 240sx.org