Ok, I've seen a variety of methods for running in a new engine. Mainly drive it like you stole it for the first 20 miles to seat the rings in properly or take the gentle touch and granny it for 1000 miles. Both schools of thought only agree on one thing and that's not to hold it at a constant speed for the first while.

So what's everyone's idea here then?

 

Somewhere in between those two extremes will do the job, and don't let the engine labour.

 

I did a fair bit of research on this when I bought my Spec C.

Like you, I came across the two methods you listed, but also came across another one which says to gradually increase revs as the miles build and not to keep it at a constant rpm.

Sounds most logical and it was stated by experienced engine builders. So that was what I went for.

 

To add to this the bearings do not need ran in! Just the rings and possibly new camshafts if fitted

 

Is it just rings and bearings that are new?

My school of thought is and was when I rebuilt my engine, run it gently for 20 miles steadily in creasing revs up to 3k to make sure everything is ok. Then get out and check for leaks or weird sounds, drive it normally all being well increase in 1k rpm increments up to 5k rpm until about 50 miles had been covered, then go home and drop the oil and change filter, I used the cheapest branded 10/40 mineral oil I could find for this.

Then I put some of the good stuff in and drove it through the rev ranges up to 6k rpm until I hit 250 ish miles and dropped it again then drove back from Croatia via Milan 1400 miles Dropped the oil again drove it around for a few weeks and gave it death on a Track day at Donnington and drove it home and stripped the car for parts, engine was fine.

 

On most modern engines you are really just bedding the rings in, and cams if they are new. Cheap mineral oil or running oil first, drive it normally but under 3500 for around 100-200 miles, vary the speed/revs. Change the oil and filter to a semi synthetic and gradually allow more revs and boost for the next 500, change to the brand and grade you will be using all the time, job done.
Ive tried all sorts and for my rally car, it just went straight on the dyno with semi in. There will be various thoughts about running in, the only real thing not to do is put a fully synthetic in first, as that won't allow the rings to bed in to the bores. I also think being too cautious is also not the best, let it get hot and under some strain to get the bores/rings bedding in.
When I was into bikes, the Guys that had motocrossers, just revved them wide open for 30 seconds and off to go :-)

 

I use this in the rear of my car when running in