. Will 4.10 gears be suitable for the TR 3650, or should I use 3.73?
I haven't had 4.10 gears but I really like my 3.73 with my t45. They make a decent balance of acceleration and power. Plenty easy to spin tires. I run out of 1st a little over 35. So that seems about right.
It doesn't rain much here and the roads are terrible when it does. It gets really dicey in the rain. 1st becomes almost useless.
I have almost 100hp more than stock. BigNSlow has more than that. So our opinions are skewed. He's rolling with a lot more torque too.
I would hate have a really short 1st gear though. As it is I can slip it in 2nd and roll slow at about 10mph also.
2. I've seen talk of a "forced lube" mod for the tailshaft on automatics when using 4.10 gears. Is this necessary for the 5 speed?
This isn't necessary on the auto or possible on the manual. In the manual you have no fluid pump to 'force' the lube. The manual relies on the gears themselves to sling the ATF all over the place inside the case. Yes, all of these Tremec trans, the T45 & the TR3650 both run ATF. Just plain off the shelf ATF.
The cheap fluid was one of the selling points for me when swapping to the manual. I wanted a cheap trans with cheap maintenance. $300 for the trans and a $20 fluid change with a longer interval than the auto. I'm sold.