3.25 or 3.45 diff???

[BP1]

I am switching out my 3.64 diff for different one and am being offered either a 3.45 of a 3.25 version (non LSD). I have a FI 3.5L with a Paul Burke N21 cam with Megasquirt. Most driving is street with maybe 10-20% freeway and love the 2nd and 3rd gear pulls I currently have. Would I regret going to a 3.25 from a 3.64? The 3.45 seems like the safe choice. Thanks in advance....BOB

 

[BP1]

Oops

Oops...I left out that I have a 5 speed.

 

[HB Chris]

Bob,

The 3.25 is wasted with a five speed, your b35 will pull fine with a 3.45, it's what I have. 3000 rpm equals 77 mph.

 

[teahead]

Why switch out? 3.64 seems like a good rear ratio w/a 5-speed.

 

[sfdon]

3.5 liter
9:1 compression
Cam
Gear ratios are matched to engines also

3.64 is a 3speed auto ratio

 

[Mike Goble]

I have a 3.25 rear ratio in my 3.5l Bavarious and I like it. I do a lot of driving at 80+ mph and it keeps the rpm under 3000. If I am on a road with a reduced speed limit I just keep it in 4th. The 3.25 also gives you a longer 1st gear, something I like over the previous stock ratio.

 

[teahead]

I'd keep the 3.64 personally for better torque multiplication at low speeds.

But if you must change, and you want lower highway RPMs, go w/3.25. You won't find hardly any difference going with a 3.45.

RPM calculator:

https://www.ringpinion.com/calculators/Calc_RPM.aspx

 

[HB Chris]

And all US 3.0 coupes came with the 3.64, stick and auto. The 2800CS at least early on had the 3.45.