I have owned my share of new vehicles and rebuilt a number of engines. Every new vehicle or rebuilt comes with specific instructions for break in, quite often followed by a notice that performance will increase as the break in is completed. I can't honestly say I have noticed much improvement in any modern car engine.
The exception is my model T, the increase in performance is remarkable. The driveway up to my daughters place is gravel, long and steep, when I first started driving my 26 Tudor with a rebuilt engine she would struggle making it to the top, add a passenger and she would almost power out. Now after about 1000 miles that same driveway is a breeze, even with two passengers and and a 80 lb dog.
Not entirely sure why,...maybe with only 20 hp every little bit helps, that and I suppose the internal drag in the transmission is reduced as running time goes up.
The drag from new rings in freshly honed bores is considerable - and still, the seal isn't perfect, so as it wears in, it both gets less friction and less compression losses. And if the babbitt was't new, just tightened up, you may have had to pull start the car to overcome the drag - then it'll certainly pick up power after some miles.
Modern engines are built to higher precision, so running in isn't as needed as it was back in the day.. New Model T's had a sticker in the windshield calling for a maximum speed of 20 mph during the first 500 miles..
When I was a kid my folks bought a new 1951 Ford sedan then later a new 1957 Ford station wagon. I distinctly remember conversations about the "break in period". Now it's not even mentioned.
Newly built T engines always improve in performance when breaking in. Rings seat, friction reduces and everything seems to find its happy place. What can you tell us about the dog?
About ten years ago I rebuilt the engine on a Fordson model F tractor and could barely turn it over. Being considerably higher in displacement than a Model T and having an even more notorious history of breaking arms I decided that I should break it in before I cranked on it too much. I posted a video on youtube and titled it "1926 Fordson Tractor Compressed Air Break-in". Its complicated and corny but it worked and, while you wouldn't be inclined to duplicate it, you might enjoy seeing it. One of the interesting outcomes of the project was that it actually propelled ice and snow balls from the exhaust while it was running.
I remember these break in instructions for new cars too. (changing engine speeds, early break in oil change ect.) Doesn't happen today with moderns though. Usual recommendation for the first oil change is usually 3500 miles like all the others will be and just get in & drive wherever. Technology.
Dave Kahle, my internet supplier is being tempermental lately preventing me from downloading the compressed air break in.
I'll have a look at it at work tomorrow. Sounds interesting.
I have a Fordson tractor as well,...so I can relate to hard cranking .
The dog is a Golden Retriever "Curly"...he is our third of this breed
the other two were named "Moe and Larry"
Dave, when you are able to see the video you may also want to check out my "1919 Fordson Snowmobile" video as well. The videography is not very good but the tractor is cool. My border collie,Rena, loves to herd my tractors, grandchildren, and whatever else moves. I guess I have about thirty Fordsons by now, four Model T's and a couple Model A's. Apparently there is no cure.