3.64 Diff - Quite the Diff-erence!

[AaronMaguire]

All,

Has anyone else done this diff swap to a 3.64 with stock wheels/tire profile?

I'm contemplating doing the diff swap on my 3.0si / roadster / 6MT. I'm debating between the 3.64 and the 3.46 with a lean towards the 3.64. My "complaint" about the 3.0si is that acceleration to ~60 MPH feels sluggish.

When I'm in 3rd gear, 3K RPM / between 60-80MPH the engine/car has such urgency that small pushes on the pedal almost get the car to leap forward which is an intoxicating feeling. Below 3K the car feels sleepy to me so I figured this change will put the engine more in the upper RPM power band more quickly.

Currently I have stock wheels (18") and tires and if I make any changes, I might actually go down to 17" for slight ride improvement, lower wheel mass and better tire options.

I've played around with online gearing calculator (https://www.blocklayer.com/rpm-gear) entering in all my data with the 3.64 and it seems like I'd go from ~2800 RPM @ 70 MH to about 3100 RPM @ 70 MPH. This doesn't seem horrible.

I went with the 3.46.
I've found that this is short enough for me. Any shorter and I'd be too high in the rev range at 60mph (100kmh where I'm from).
My 3.0 e85 has never felt sluggish and now on the track at the end of the straight at Sandown in Melbourne at 185kmh (115mph) I'm changing into 5th which makes turn 1 a pain when having to change down to 3rd. That's my only complaint.

Otherwise the 3.46 ratio works very well for me.
I'm running OEM 18" wheels and tyres.

Hope this helps.