While out on my run last night I was pondering the issues I'm having w/ my new clutch (arrghhh!). I then began to wonder, "How do race cars break in their clutches when they can't drive them easy on the street first?" So that then expanded to other items such as engines, rear end (gears), etc.
If the car isn't street legal, and you need to put in 500 miles or so on a specified part to break it in, what do you track only guys do? Are the items you use 'race only'? i.e. they don't require the same breakin proceedures and come near 'ready to use'? What methods are used on a clutch, or even an engine, when you can't put in those easy miles before beating on it?

Dyno ... if you have access ...

I too am pondering this as I become closer and closer to not renewing my registration on my car.

With a clutch, just back it up and down your driveway a few times and let it cool. Do this for several days and you will get it seated. Think of it like wearing brake pads and new rotors together. It takes a short while and the surfaces begin to mate (wear in). Just be careful not to get the clutch too hot.

for a clutch, its not the number of miles, it's the number of gear change's or starts from a stop. manufactures will tell you 500 miles assuming you will make a number of gear changes durring that distance. i've broke in clutch's by doing a 4000 rpm clutch drop w/ a nasty burnout and not driven a single mile prior. clutch worked perfect for a very long time. RR is not as demanding as drag racing on a clutch. just do some (4-5) 2-3K "lurches" then let it cool. should be fine.
as for a motor, well as mitch said, a dyno is best. but you could always use the "jackstand" dyno to do what you can. same goes for the rear end. w/ the diff, you just want to drive "normal" and let the teeth wear in to each other, but the most important thing is the heat cycling. thats what make the metal hard and strong. i believe the corrct term is "work hardining". you don't want to get them too hot too quick or for too long.

I would have thought a no load break in would be bad ...

Not sure where I came up with that idea ...

I also suspect a 'no load' break in would be insufficent. You wouldn't generate the required heat, if in fact, work hardening is required. Also you wouldn't be loading up on the parts the same way as if you had significant resistance. I know the clutch really isn't mileage related but is based on engage/disengage cycles, mileage is just a simple rule of thumb. I'm thinking here more of a general discussion for race car break-in than on, say, the clutch specifically. There are a number of different components that require break-in. Not to mention components/systems that need to be cycled in actual conditions to verify that they are tuned correctly, installed correctly, free of defects, etc.

I typically rent the track for a session or two the day before a race and run some moderate speeds to break in stuff like a tranny or engine.....as for the rest.....

GO FOR IT!

I can relate to all of this having essentially replaced everything on my CMC car at one time or the other. Two seasons ago I decided to change gear ratios and posi. The car dynoed fine and my sponsor ran it on his own dyno (a smog dyno) also to help with break-in. I went to Thunderhill for a test day a week before our first race at California Speedway. First lap I babied it, going into turn one on the second lap *BANG* and lots of noises you know ain't the good kind. My new gears and posi were not set up right and this is not something that showed up on the dyno. So, I was faced with a decision, whether or not to go to California Speedway without a test day to see if the new gear set and posi was going to be good. I decided not to, and that turned out to be a great decision as that is our highest speed track (150mph+ on the banking) and doing that with a new gearset would be really foolish. Heat cycling and not too much at one time for new components is the name of the game.

Test days are gold - I teach and earn track time at Thunderhill, perhaps other tracks offer the same deal? I also instruct for NCRC for free track time during that day, other organizations like NASA have that same deal. This is ideal for keeping your skills sharp and those all important break-in days!

When I got the SPEC 3 clutch I have now put it the break in went like this.. "Honey can you go grocery getting in my car?"



I then went to the drag strip 3 days and 50 miles later and the SCCA meet the day after that. When I bud was driving my car during this past weekend SCCA run he said he liked the grabbiness. It grabs like a beast. I hope it lasts a while because the car is my daily driver.

... most that I know that are racers will take a new engine around the track at say 2000 rpms for a 2 mile lap, then a 3000, then a 4000 then let it set an cool. If head/valves were done, then a few snaps of the throttle to insure the valves seats are seated.
change the oil and filter then go racing.