Race motor break-in

[Zvoiture]

How do you break in a brand new motor in a race car (not street legal)?

steve77

[26th-Z]

Set it rich and let it run at a constant RPM below 3000 until it reaches temperature. Use colder plugs than the ones you plan to race with.

Avoid revving it or RPMs over 4000. Just let it run constant from cold to operation temperature several times (3 or 4). Continue to watch oil pressure and check for leaks. Make adjustments and tweak. Change the oil after your run-in.

[hmsports]

Good advice 26th-Z.

Once things are up to temp some guys will alternate between low and high RPM sessions during a single on-track session -- 10 minutes at 3000 and then 10 minutes at 4500 and then back down to 3000 for another 10 minutes.

My engine builder says that is not neccessary. He recommends simply running it for 30 minutes not to exceed 5000 RPM. He said that if you keep things at too constant of an RPM the rings won't seat as well as they could. With my last engine -- full IT prep -- I simply went out for my first practice session and took it easy. The engine is still really strong and shows no signs of leak-down problem, unexpected oil usage or shavings in the oil.

Slightly askew:

Question: Do you know how to break in a new manure spreader?

Answer: Take it out in the field and run the crap out of it :classic:

[26th-Z]

I wasn't real sure of RPM limits or time limits, so I was conservative with my numbers. Also, my old race engines didn't have fans and I didn't want to talk about an amount of run time without a fan! I always prefered to watch the temperature gauge. The variations in engine speed over the run-in period will be fine as long as it is not over-revved during this process. I always found that strong, long lasting engines resulted from a nice break-in / run-in. Have fun!

[240ZX]

For what it's worth, and I am not an expert on race engines, some engine builders believe that if the engine has been built correctly it should be broken in the way you intend to use it once you have oil pressure and operating temp. Reasoning behind this method is............as we all know, the higher the RPM the more the components grow due to heat and inertia (example: The higher the rpm, the more the rods will grow in length). So, if you break an engine in at say 3000 rpm and the rings take a set at that given rpm then what do you think will happen when you go up to 6000 rpm? The rings try to travel past the ridge that was incurred from the 3000 rpm break in, and can consequently result in broken rings. Just something to consider Steve. You might want to give Dave Rebello (Rebello Racing) a call for his opinion. Good luck there buddy!!!

[Phred]

I have spent many years "breaking in" ( I hate that term) engines.

The method actually varies depending on the state of tune or specs for a given engine. Probably 90% of these engines have been "run in" on an engine dyno, but the rest were run in on the track. First and most important is never let a new engine run at a constant speed without a load on it. Do not run it rich as stated in an earlier post. If these two things are combined, the rings will never have a chance to seat. The extra fuel will do nothing but wash down the cyl. wall and accelerate piston/cly. wear. Typically, on a dyno , the engine is partially loaded and run in the lower rpm range while it comes up to temp. Then its accelerated still under partial load while the timing is verified. The engine must be under load to take out all the "slack" in the drive components so the timimg will be stabilized and verified with a timing light. Being under load also causes the engine to produce more work, (torque) which creates heat and pressure within the cylinder. this pressure is what actually seats the rings. Most racing rings have very little "static pressure" which is the outward pressure the ring places against the cylinder wall at rest. When the engine is running, under load, the pressure in the cylinder is forced past the upper ring land and into the gap behind the ring. this extra pressure is what helps the ring to conform to the cylinder. At this point it is most important to note that synthetic oil is NOT to be used during engine break in. Especially with chrome rings. Synthetics are so good at lubricating, they will not allow the rings to seat into the cyl. After break in, change the oil and filter, and then put in the synthetic. If you have to break in your new engine on the track, an exhaust gas analizer or an EGT (exhaust gas temp.) gauge is very good insurance, and will keep you from burning down your nice new expensive race engine. As with the dyno, accelerate smoothly, then back off and let it breath. The more times you can do this the quicker the rings will seat. Rings come in many different sizes and alloys. The break in procedure for a 1/16 chrome ring will be much different from a 1mm steel or cast iron ring. Finally, if you can afford a race engine, you can afford to have it dyno'ed. It will be cheaper in the long run, produce more HP, and cause you less lost sleep.

Phred

[Ed]

Phred,

Great advice for a race engine. If you don't mind me asking, what about a street engine, using stock factory parts? What kind of "break in" would you recommend?

[Phred]

Hi Ed,

A street engine will benifit from a similar treatment as far as break in is conserned. Get it out on the back roads as soon as possible. Accelerate moderately through the gears, then let it coast down, and repeat. keep your eyes on the gauges, and take a look under hood frequently, to make sure all liquids are where there supposed to be. Try not to hold it at a steady rpm for at least a couple hundred miles. Run petrolium oil for at least the first 500 miles.

I think the factory replacement rings use a chrome top ring and a cast iron second. Which is a very durable combo. The problem many people have when they do a home rebuild, is replacing the rings without honing the cylinders. You might as well just hit yourself in the head with a hammer. To properly seat in, a chrome ring needs a honed surface with the correct grit stone and cross hatch pattern. There are tools called ball hones which rough up the surface and leave a cross hatch pattern. This is needed to allow the ring to "lap" itself into the cyl. While the cross hatch will microscopically hold oil to keep things from galling. But the ball hone will not properly "size" the cyl. like a ridged Sunnen type hone will. A ball hone follows the exsisting bore, while the Sunnen type will actually resize the cylinder. which is preferred. Even if your cyl. is enlarged a few thou., Its much easier for the ring to follow a straight hole than one that is slightly tapered or out of round. So when replacing rings, wether on a street or a race engine, have it properly honed. And if its a race engine, hone it with a torque or deck plate installed.

Phred

[TomoHawk]

Originally posted by Ed

Phred,

Great advice for a race engine. If you don't mind me asking, what about a street engine, using stock factory parts? What kind of "break in" would you recommend?

For street engines, we learned in tech school that you should avoid a constant RPM, so we drive around the neighborhood during off hours, accelerating moderately, then coasting to the next stop sign, etc. On longer roads, accelerate, coast, just no stopping. Driving at a constant RPM before a good break-in messes up the scratches from the cylinder honing and can mess up the seal of the rings.

So I avoided highway driving in my new car ( when I got it) for 1000 miles or so. Sounds like a lot, but I drive city street to work any way, and I figured on the calculator go about 1,000 miles back and forth to work in about a month.

After a good Break in, you drive any way you like.