The J20 (or J18 (rare) to G16B body swap.    

The non SPORT non 1999 and newer Sidekicks, Trackers and Vitara's are narrow frame cars.  (short list)
The wide frame was made to accommodate the bigger engines, even the V6.

The alternate to this, is why not just buy the wide frame car, say a 1999  Vitara or Tracker?
or move all parts and cut the drive shaft (rear prop) to fit.
why do all this work?,  and  swap cars  and not drive trains, but it can be fun......? (sadly, I too think of this as fun)
It's a Gen4 to Gen3 Vitara swap, (using world wide generic names, VITARA is the real name)
Unlike the J20 in to the J18 body, this swap is the most difficult of all.

Commentary on JARY post. By me.
G16B narrow frame Sidekicks Vitara's pre 1999 (and trackers) and.
Installing the J20 engines to  there. (or J18)
Eg. "Say  a 1999 J20 Vitara to 1996 Tracker was G16B "
I will not cover smog, if in calif?, they can fail you just (visual) with the wrong parts on car.  or CEL stuck on.
Even transmissions errors (slush pumps)P07xx DTCs.
Wrong cat, or mounted wrong, you fail in Calif.  (so  no comments on P.R of California or its hard fast rules)
The best post by JARY.(that I'm doing , rebuttals)

First off all the G16 sensors, harnesses , ECU , injectors and actuators are wrong. (5speed m/t) (a/t would  be a whole larger bag of snakes)
The Mounts, and flywheel do not match.  , everything is wrong, here.  (only the bells match, that be it)!

The J20 has a Hydraulic actuated clutch.  the older G16 car is cable clutch. (totally different)
if you moved the whole engine say J20 and manifolds, you need the J20 harnesses ECU and cluster from dash, MOVED.

my comments  in RED FONT., to original posters black.

begin orig:
Regarding the parts:

Exhaust:  obvious,  would need to custom or use  the newer system with J20 on donor.

Intake: Intake manifold could be any one year that you find, even from Aerio cars will fit (actually the J23A on 04-07 Aerio's have better flowing intakes that any other J series engine pre-07 and the injectors flow more fuel). It is important that you have access to the wiring harness and ECU that came with this intake manifold. I will explain.

ECU / Harness: As above...
It's all about connectors ;  The issue is not just connectors, the sensors on the end (or actuators) must actual work and match what the ECU NEEDS.  Most don't mix, here.
 2.0 vits and aerio.
J23 aerio's have the idle valve on the bottom of the throttle body while 2.0 aerio's as well as 2.0 vits have it on the intake manifold right where the plenum starts. (moving wires longer is not hard, the parts work different ,is what matters)

 Flow meters are very different too. on 1.8 and 2.0 J series engines (on any vehicle) they are integrated to the throttle body where as on J23's it is external and near the air filter box.
The air flow  profiles on the G16b and j20  are not even close to same so the ECU maps are too. WRONG.
The G16 ECU will never work with J20 injectors or sensors or actuators, VSV etc.
The G16 will never work right with the J20 MAF, or if using stock G16 maf, the stock MAF is no good at 2000CC, air flows.  Using a J20 MAF on a G16B ECU, will not work right. (will start and run)
why have a bigger engine, 400cc just to limit power with wrong MAF?

CKP/CMP(crank/cam angle sensors), though looking almost exactly the same on all three engines (pre 2007) are way different in pin out.  (some are hall , and others not) some have 3rd ground pins.
Some J18  on Esteem have totally radical differemt CKP, tone wheels. on crank, (have photo proof) you need to look there first.
The G16 runs a Distributor CMP, but the J20 runs a left rear cam CMP sensor, that work totally different, (radical)!  the J20 is twin cam the G16g is Single cam.


note: EGO's (0 sensor/lambda) and"EGO's" are basically the same (fixed typo ), though I do recommend getting this from the same vehicle too,  ( the sensor must match ECU, this is clear?)  EGO means  Exhaust Gas Oxy sensors. (0 )
The only tricky part of 0 is the  heater (the oxy pins are same) the heater currents can be different and might overload the ECU. Use the correct sensor in all cases.... Do not guess. Match them.
The EGR is totally different( and ISC), the old G16b is vacuum power EGR and exh back pressure sensed. the J20 is a simple electric drive motor and software load (maf+RPM = load) sensing (like new cars have today) vacuum bs ended in 1999. (blessings)
0s are easy to replace and is  a service item.(match your ecu)

Trans:  The hard nut to crack. , the 2wd 5 speed kick tranny is the best. (not true best, but sure lighter) There are no real 2wd advantages USED! (new, sure cheaper) (own both, and see, grin....???) I get 28mpg on both. It's not stronger at all.
Only the 1998 (narrow frame car) has unique  gearing (not 2wd) all 1998s.
The other ,early years ,have different gearing are only with 8valve and 16v engines , a fact, never on 2WD is this unique, I have a full parts list on all. (and have swapped internal parts many a time)
Yes, the 16v box runs better on the open highway, NO HILLS. It has a lower total ratio.  (by .86 to 0.80:1 fifth gear) the 16v box run 0.80:1 5th. This is it !
Pilot bearing issues, complex:
All that matters here is getting the trans pilot pinion tip to fit into fly center bearing.
I'm not sure the easy path here,  the J20 fly has different bolt pattern. 

G trans Bolts right up to the J series engine block and input shaft reaches well into the pilot bearing.(but don't fit) The J20 box had wider pilot bearing tip.. and will not fit G16 hole.
The J20 uses a diff, flywheel and larger ID pilot bearing, to match J20 transmissions, that are different.
The J20 has hydraulic  clutch lever on bell side for SLAVE cyl.

 For pilot bearing fit up, I made is the small  brass bushing I had to make to compensate for the thinner input shaft the 1.6 trans has (compared to the 1.8/2.0/2.3 on j series equipped cars).
 hand made on a lathe.  make od a tad tight, and ID loose by .002" (a hand made part)
I'm my opinion bushings have no life here,  If they run dry of grease and it will seize. YMMV. Mill the flywheel and put in the correct size ball bearing.
Might be ok, light duty off road, but not in city traffic.

Clutch / flywheel:
 As of right now, I'm using a J23 flywheel from a 04-07 Aerio.  (a brillant trick)
It's a 215mm flywheel that will accept a 1.6 Sidekick clutch system as well as Mitsubishi Mirage / Eclipse plate and disk -
 I actually am using an ACT MB012 plate and 4 puck lightweight disk made for Mitsubishi Eclipse without any problems, though I had to make my clutch hydraulic type since the 1.6 clutch cable would not hold tension. J20 and J18 flywheels are 200mm (there's an ACT clutch kit for the 2.0 Aerio that works well). They all will fit inside 1.6 sidekick bell housing without rubbing to the inner walls.
No mention of how  hard it was to fit clutch master cylinder to fire wall and linkages,  real hard.

note: I used a stock sidekick starter, but had to get the 2.0 vitara bell flexplate in order to work.

Engine mounts adapters:
 custom see link above..

It is imperative that you use a VITARA oil pan - either 1.8 or 2.0 - as the Aerio oil pan's belly is located on the front of the engine where as the vit's oil pan is towards the back, thus aerio oil pans will interfere with the steering rod.

EDIT: Adding throttle pedal info...

Throttle Pedal: In difference to the link posted below on a swap done by After market 4x4, I did not fix my stock pedal. I sourced a stock "sport" j18 kick throttle pedal and installed it on my kick. It bolts right up!!! and you then use the 1.8 throttle cable. Haven't compared the stock throttle pedal on the kick to that on a Baleno/Esteem 1.8 nor to any of the Aerio's, but there's a good chance they will work too.

I think that's about it.
 Be sure to find trouble along the way (what swap doesn't, right?) but it all will fall into place. You will notice how the Sidekick should have had this engine from factory instead of the 1.6L. it did, called a  J18 SPORT. 96/98'
end: great post.(jarysidekick)

Recap. : I love one liners.. short and sweet. How is this....?? J20 in to G16 bodies,,, not for the weekend DIY warriors. (faint at heart?)
by me:
1: wrong flywheel due to g16b having smaller trans pilot shaft tip. (Pilot bearing mod time)
2: wrong engine mounts (fitting wide frame engine to narrow frame VITARA/tracker/kick.)
Wrong Engine  harnesses and...
3: all sensors wrong (ECT / IAT might work wired right, some don't' , Suzuki run many different ECT world wide, so watch out)  Better?, all actuators and sensors are wrong.
4: wrong ISC (solenoid versus motor) drive, same with EGR main. (vacuum versus motor drive)
5: wrong IAC (cold air start, missing on J20 confuses J16b ECU)
6: wrong injectors
7: wrong MAF
8: wrong dash harnesses ,and wrong instrument cluster, to match j20 Ecu and VSS, (speeds and odometer) etc.  lots of pain here.
9: wrong ECU (keep the J20 ECU and all that it connects to, if savvy)
10: wrong clutch. and dealing with clutch linkage. (getting the G16 bell clutch levers happy with j20 clutch will be a challenge)
11: wrong pan. (can be)
12: wrong random VSV valves.  Evap , EGR , etc. wiring etc.
13: new induction routing (main suck air)
14: new exhaust pipes.  or simple hand made adapters. (the original being what, near 15 years old will be not much good?)
15: wrong throttle linkages.
16: The bolt pattern on the flywheel is different, making the wrong size pilot bearing fix , harder.

Why not move every thing,drive line wise and EFI wise, and then make custom length rear prop shaft.? total drive line swap and EFI +  new prop shaft
Cut prop and change length. (propeller shaft(s))
or sell the car, and buy a j20 car. a 99 VIT would do that..
No lie a fun project car, and has been done.

rev 1   ++++9-23-2015