My new-to-me ride has a freshly rebuilt engine. The cam has been broken in, and it's been tuned, but it doesn't have any street miles. I've never owned a car with a fresh engine before. What's the best procedure to break it in while driving it? I figured I'd put about 500 gentle miles on, both on surface streets and on the freeway, keeping speed/RPM varied. Then, change the oil and let 'er rip.

On fresh builds after break-in, I baby it for about the first 50-100 miles looking/listening for anything that's amiss, after that, drive it the way you intend on using it...if that means "balls to the wall" then so be it...if something is going to break, it's going to break regardless in the way you choose to run it

Use a good break in oil.
A shop I deal with suggested changing the oil in the first few 100 miles and check for metal in the oil / filter.
Then use break in oil again for at least 500 miles.

What do you suggest for break-in oil?

I would run it hard to set the rings, load on engine, wide open throttle blast from just over idle to 4,500 or so then completely let off. Do this for an hour or so off and on while you drive.

Here's an interesting read on that subject. "breakin secrets" at www.mototuneusa.com For motorcycle rings but applies to all & an excellent brief read. EDIT After reading this & some thought my take is: Brad Penn breakin oil/gun it many times during the breakin (read breakin secrets)/change oil to synthetic if desired/filter then drive it the way you intend/built it for (street/race/cruiser etc). You have 1 shot to get a quality ring/cam breakin & after that whats left to "breakin"??, nothing that I can see especially if it is true that the ring/cam breakin takes place completely (good/so so/bad) pretty much close to 100% only in the initial breakin procedure. (2 cents)

Don't run synthetic oil for the first few hundred miles or so. Go drive it like you stole it. No reason to take it easy.

Add me to the ... be gentle for about 50 miles varying the RPM and listen for noises then beat it like a rented mule. I would leave the break in oil in for a few hundred miles.

If it was broke in on an engine dyno then don't be afraid to drive it hard.

I wouldn't go to synthetic for a couple thousand miles though. I'm not sure what the new car makers do to go right to synthetic though ???

That ia what Ma Mopar recommends in thier race bible, break in the cam and seat the rings ASAP by on and off the throttle like mentioned above I've done it that way for years, no problems, babying it may glaze the cylinder walls insureing a long breakin on the rings or the rings may never seat properly Seat them rings right away

I run all new engines hard and with my bulk shop 5w-30 semi synth oil for a couple hundred miles then i switch to 5w-40 full synth. i build all my engines tight and have been very successful for many years. Only thing you are 'breaking in' are the rings and the tappets if they are flat tappets.

Put the inner springs back in.
Enjoy a few miles with the break-in oil (Brad Penn at the shop).
Change oil and filter.
Run as desired.

Todd break's them in thoroughly at the shop.
Pre and post inner spring we keep them warm to seat the rings.

I suspect and also have seen firsthand that most of Todd's customers as well as myself do the following on new engines:

Let the thermostat open and then the hammer drops!

Mike

same here. i don't understand why the decades old myth of "baby it for the first 1000 miles" still exists.

with my engine, roller cam, we started it on the dyno, set the timing, ran it for about 20 minutes at 1800 rpm or so. adjusted the valves, and started the WOT pulls. many thousands of miles later compression test reads just fine!

I had a friend that babied his freshly rebuilt Ford 302 for 950 miles , that was when it dropped a valved and put the piston into the oil pan ...

What do you think is done on a dyno? You're already way past "drop the hammer" time, IMO

My hemi was built and then went right to the dyno. After a few minutes of run time to get the timing dialed in it was right into pulls to 4500-5000 rpm. After a few more timing and fuel mixture adjustments, it was flogged like there was no tomorrow.

Bottom line: run it easy the first few miles making sure everything sounds right and then drive it like a rental!

Run it hard!

seat the rings!

I had an engine on the dyno stand and was expecting them to do a 20 minute cam break in. They said "no need. 2000 rpm or 5000 rpm, does the same thing...flings oil all over the tappets and gets them spinning in their bores to develop wear pattern. Just don't let it idle"

they started it up and set timing/fuel with it above 2000 rpm, then checked it over for leaks, and we went straight to making full RPM pulls.

after half a day we changed the oil and continued tweaking and tuning, and by the end of the day it definitely had 20 minutes of time on it.

If you have moly rings and a proper hone job then the rings were broke in before the cam was. Check for leaks, snug the intake and header bolts and drive it like you stole it.

the method described in the old DC race manual was for the stainless Dykes rings that were used in race hemi engines back then. If you are under 50 years old then you weren't born yet when that bulletin was written.

OK, here's a question I always wondered - if you are supposed to break the cam in for 20 mins (conventional wisdom) how does that affect the ring seating? Since you are not under load during this time does it just not affect the rings (neither seating them nor missing the only chance to do it?), so once you are done with the cam you can button it back together (inner springs back etc) and then take it out and break in the rings with load?

Or are you missing the opportunity to get a good ring seal by breaking in the cam first. Obviously I'm talking about the home garage setup here - on a dyno you can do both together.

Outstanding topic.
What about engines with roller tappets?

It occurs to me that it would be best to run the cam in on a different motor, or the original motor (if possible) before you pull it...

Useless info for the OP, but an interesting concept none the less