How long does it take to do an engine/transmission swap?

Some vehicles were offered with 4, 6, and 8 cylinders and they all used the same transmissions and wiring harness. If that's the case, it shouldn't take too long. You and a friend should be able to do it over a weekend. If you're try to Frankenstein a Chevy V8 into Kia Sportage, it may take several month longer. Just fitting the larger engine in will be just one problem, then the transmission and crossmember will be another, exhaust and drive shaft, heavier springs and shocks, bigger radiator, the electrical stuff... Its not something just anyone can do. You wont get it done in 30 minutes like the guys on tv do. Good luck though, its good to see there are still guys out there that like to do stuff like that.

ask a mechanical engineer

and not a forum

It can be done in one day if all goes right; but most take about three days now. They have to reconnect the computer systems and all that other stuff; it  also depends on how many are doing the work and their skill at doing it.  Good Luck with that one pal!

I can do it. But you are asking to put in TWICE the engine size in a space meant for HALF OF IT. SO, it is no longer a simple swap.  This is a major modification meaning $$$ and time and welders, cutting torch, fabrication of custom parts aka a "pain in the a$$" job.  It won't be cheap and it now needs to be INSPECTED by DMV to certify it as road worthy.  It may fail.

. Swapping a 4 for another 4 is easy. Nothing really changed. So long as it is from the same make of vehicle. FORDS-FORDS, CHEVS-GM, Dodge-Dodge, Toy-toy, Honda-Honda.

. So like there really HAS TO BE A GOOD REASON why you want to go through the exercise...to come out with something similar to what was taken out.

Don't care what you WANT.  It is a matter of what is possible...and you pay cash in advance.

I can do it in 45 minutes. 

If it was designed to go there , probably best part of the day , but if you have to adapt brackets and move components to make it fit, it could take weeks.

Chances are , if you are asking here, you probably can’t do it yourself. 

If you ask a garage, at Labour rates upwards of £50/ hr you could easily run up a bill mire than the value of the car.

VWs had engines swapped in 4 minutes..

No one can say. If wiring harness, all in there, and Motor and Rear End Mounts  are the Same (Not likely),  maybe one afternoon.

How  long is a piece of string?    You may need radiator, suspension, brake upgrades Before it is even Practical to drive. Just swapping can be  one  afternoon or weeks  rewelding motor mounts, upgrading suspension,  hassles w/MVD, smog, etc etc..  I removed/replaced a Toy 4 banger and transaxle with a Kelley Come-Along, chainfall, and a stout Tree. 

A friend put a 350 in a Vega, not hard, But, it  twisted the unibody on hard acceleration.  Shattered every window. He won the drag race though, and the bet.

It would take you 73 days

Just how do you intend on "swapping" the motor and tranny? You'll need a new engine wiring harness and PCM for starters. Then there's the new axles and you'll also need to weld in new motor mounts. New exhaust system with the correct 02 sensors or the new motor will also be an expense. I'd buy a car with an 8 cylinder motor rather then crating a Frankenstein.

A lot depends upon parts availability, the car, the engines/transmissions, and skill.  A VW bug can be done in an afternoon, less if you have done it before.

Putting a larger engine into a cramped compartment might not be possible.  Check on line if it has been done.

"local motor vehicle administration" means nothing to us on Yahoo, since you give no clue where in the world you are.  Check with yours.