3:55 to 3:91 RPM difference ?

[Racer57]

I have 3:55 gears with a Tremec 5 speed. 70mph is about 2,000rpm. If I install 3:91, high many rpm will I gain ? More than 500 ? I'm thinking about doing it, just for the fun of the launches at stop lights. 

[RUNCHARGER]

Just a skosh over 10%. So 2000 will become 2210 or so. If you'd prefer around 2500 a 4.30 would be a better choice. Changing gear is a lot of $$$ for 200RPM.

[kawahonda]

200ish.

But that 200ish can be annoying when you're "skating by" doing 65 MPH. Better to be at 3200 than 3400.

3.73s here, and it's a perfect mix of town + highway cruises. In your case, 3.73 would be a waste of money over 3.55....

With a 5 speed, you have much more liberty to go even bigger. 2,000 RPM at 70 MPH is nothing! I bet you could go bigger...

Find out what your max "cruising" speed is, then choose the gears to account for that. I'm not aware of any Mopar engine that can't sustain anywhere in the 2000 range for a long period of time, so you may have more room than you think.

[Brads70]

I found this fun to play with to determine gear ratio's. You can chance all the values to suit...

https://www.blocklayer.com/rpm-gear.aspx?saved=bl_T56_with_295_50_15


There is also this one in the reference section!
https://www.e-bodies.org/resources/rpm-speed-gear-tire-size-calculator/