Ah, infinity. That one map that everybody hates to drive on, yet knowing how to drive it can make or break your lap times. So, being one of the only avid drivers who actually LIKES infinity, I figure I can share some tips to shave several seconds off your lap time.
First off, at the start it is generally wise to grab a hog and a gunner and then back up for about 1 second before rushing for the nav so that by the time you get out, everyone else has already rocketed each other into oblivion and no one will notice the hog that slips out a few seconds late.
It is best to take the ditch for the first run because as long as you can avoid hitting the trees and rocks, you will pull slightly ahead in terms of lap time. I would suggest that you practice taking this route in your own server alone so that you can go through the whole ditch without hitting any trees or rocks head on. Getting through this area without even brushing up against anything will shave a full second off your end lap time.
The jumps are pretty straight forward, just take it straight or jump off towards the right slightly if someone is shooting rockets back at the jump in the hopes of hitting you. Keep driving normally until you reach the "Fat man's squeeze". Here, let your finger of the gas for just a split second and then turn, and then put your finger on the gas again. This will help you avoid flipping and maximize your speed to a safe limit.
At blue base, pretty much just drive as straight as possible unless there are rockets coming at you, in which case you should drive slightly to the right under the base's overhang, because they will usually be shooting towards the left to avoid shooting the dirt mound.
At the little oil refinery place (the big place with all the pipes) do NOT cut through the center. Instead, go the right of the refinery and then slow down when taking the turn around the big dirt mound here using the same strategy used at "Fat man's squeeze".
Use the same strategy for the jumps that you used before, except jump off towards the right if someone is shooting back.
With the final home stretch, take the inside tunnel and then where the road curves slightly to the right then back to the left, just cut across that turn to save about half a second.
Here, just zip on through the lap nav and keep in mind your time may not be that great because you had to hold back a little at the start. On your next lap, you should be able to sit back and enjoy a 101 lap time or so! If you keep up these strategies and practice, you can cut it down to 100 and maybe even the "legendary" 99 lap time!! Happy driving!
Sonic