For years I've been using the Apexi NEO piggy back system in my 1997 Toyota RAV4. This has the reliable 3SFE engine. (122cc). Now I'm interested in turbocharging it. How efficient is this PB tuning turbos? Any constructive criticism will be appreciated.

 

The NEO works best for minor corrections, such as small bolt ons or a non-adjustable chipped ECU that just needs a little adjustment to account for minor differences between your combo and the one used to develop the tune. They have some massive limitations on a turbo engine:

1. If you have tried to use larger injectors, the only way to get the NEO to correct for it is to cut the load signal. This does nothing to change the acceleration enrichment, which will likely dump too much fuel on throttle transients.

2. Changing the load signal moves both fuel and timing at the same time - and often trying to move one of these in the right direction will move the other in the wrong direction.

There were people in the '90s who did successfully run turbo builds on a NEO or other piggybacks, but these days there are much better tuning options available. You'll see better drivability and reliability on a properly tuned standalone.