Andoskyy

iTrader: (1)

interesting article...i always like to hear both sides of the story...

http://www.mototuneusa.com/break_in_secrets.htm

kickin8

iTrader: (1)

thanks for the info. interesting article!

Adnectere

I'm a traditionalist, so I'd take it easy for 500-1000. Not many guys here are going to go the hard break-in route. So stick to this for your ease of concern.

If you go the hard break-in route, you can do it pretty much immediately. Some cars have it this way from the factory. One of my friends' dad picked up a 997 turbo from the factory and asked about the break in. The engineer said "Break in? What is that? We put that in there for you Americans because you insist."

Break-in was more important in the days of non-hydraulic cams because the lobes had to mesh with the lifters. You typically ran it above 2500 for 20 minutes or so just to get a good surface on those two alone.

Nowadays, the majority is rings, as properly stated above. The concept of break-in is that different surfaces which have not previously had contact need to run against each other and develop friction and mate. A cam and its lifters mate; piston rings and a cylinder wall mate; the parts of a motor which touch will wear against each other and the proper amount and direction of wear is what you are attempting to go for.


Pistons see high temperatures and pressures, but their very grain structure does not change, certainly not forged pistons that are formed under tons of pressure. Certainly their structure changes meaning the piston expands, but not their inherent formulation.

Cosworth was just about the best engine manufacturer ever for high performance naturally aspirated motors; bike motors are that if there is a classification for them. I'm sure there's a little more in their piston design than choosing an alloy; positioning the pin hole, the ring land, face, and skirt and their designs along with ring design & hone have great impacts as well. Peak power is not everything, it's just 1 design criteria.

Turbo headers get hot, they always do. There's an old saying that all turbo headers crack and break from heat cycling, high-quality ones just buy you more time. Pistons don't crack and break from heat cycling, they break from inertial loads that cause fatigue.

The car break-in is more than just the motor; tires, brakes, & transmissions also need break-in, but we typically ignore these.

Does anyone know if the factory does any break-in? As mentioned earlier, Porsche does specific break-ins on the car so when you get the keys it's ready. Does Lexus?

rhsmd

i keep it around 70-75 mph, and no hard starts from tthe line.
my saleman said that the car can take it.

LexusIS-TL

I'm doing that right now. I admit I went 80mph quite a few times already but they were never over 3,000 RPMs. It was a gradual acceleration as I do a lot of freeway driving. Rule of thumb is to burn it in at 1,000 miles. Forget the manual. 500 mile brakes break in period.

lobuxracer

iTrader: (2)

I attended a special seminar at US Steel some years ago for promising high school students. Grain structure is dramatically affected by heat. Saying grain structure is inherent in the formulation ignores heat treating, and ALL metal alloys are affected by heat treatment.

Of considerable consequence is not just the amount of heat, but the method and rate of cooling. Your comment would seem to indicate you have not studied this area of metallurgy.

Adnectere

lobuxracer: You're right (and I'm not metallurgist). The amount of heat, rate it goes into an object, how long it stays there, and the rate it leaves all affect it. I think you're misunderstanding what I mean when I say normal operation and then some form of heat treatment. Metal treatments, be they hot, cold, or non-temperature related (like shot-peening) will affect the metal's inherent formulation and realign its molecules. This realigning is done because the given method used will produce better results during a specific type of operation. These forms of metal treatment are done and they permanently reform the item's molecules. Simply heating a piston as it runs doesn't permanently alter its structure, it merely temporarily spreads its molecules since that's what happens as it heats.

Grain structure in pistons and in forged pistons was mentioned earlier. The grain structure is denser in forged pistons, for example, because that grain structure is packed in during its pressing. The presses use thousands of tons of force and normal operation creates maybe 4000 lbs or 2 tons of force on a piston/con-rod assembly. When you use thousands to create it and you use 2 tops in normal operation, well I seriously doubt that it changes that piston, especially permanently.

As for temperatures of the piston itself glowing cherry like an exhaust tube, I'm going to seriously disagree. Included are photos from an MIT book and they show "bomb tests" or photographs of a typical combustion. Nowhere in it is the piston cherry red. The edge of the piston in the last series glows because "[it is] probably caused by lubricating oil thrown off by the piston." The exhaust tubing shown also isn't heated as such during normal operation; that's at least 30 seconds of full throttle on a 1000+hp motor.

lobuxracer

iTrader: (2)

Are the pictures CI or SI? 1000 hp sounds like a lot until you've seen an engine that makes 1000 hp all day long, not just for a few seconds at WOT. I have a piston from just such an engine that I use for a stool in my garage.

No, the piston top will not glow cherry red. If it did, the engine would be severely preigniting and suffering irreparable damage. There is however, a very large temperature differential between the top and the skirts since most of the heat is conducted away from the piston to the cylinder walls through the skirts (unless there is an oil jet underneath the piston crown - a common technology on high performance CI and SI engines.)

The top of the piston is in a plastic state at full load. The strength of the piston's alloy will determine a lot in this state. Under most "normal" operation, this kind of heating never happens. Only at WOT, only at full load. BTW, oil jets help the pistons retain strength at temperature by removing heat and allow the engine to make power that would otherwise melt through the crowns. You have seen a holed piston?

When the metal heats, the grain changes. When it cools, it changes again. The point of the break-in procedure is to force this change in a predictable way and give the piston the opportunity to retain its shape. After about five or six cycles (final cycle at WOT with full load), the grain stabilises, and break-in is complete.

Pistons are not cylindrical. They have a very complex shape; they are designed to become as nearly cylindrical in service as possible, AND to provide the strongest possible support for the ring pack so the rings stay in normal contact with the cylinder walls to both retain the combustion pressures and control oil migration. When the pistons are heated too rapidly, they can lose their shape when cooled. If they are heat cycled with increasing thermal loading followed by cooling sessions, they tend to retain their shape and do the things they are meant to do.

You can't do this with the casting process, and the forging process can't do it either. Certainly those processes result in a predictable grain structure, but the final structure doesn't happen until they've been fully heat cycled. Take a peek at any text on aluminium tempering, and it's pretty clear there are any number of ways to get aluminium alloys harder using heating, cooling, and through mechanical means. All that is happening with a piston in service is the final step in arriving at a finished product.

FWIW, redlining a new engine with no load isn't a big deal for anything but the rings. There is so little pressure required to spin the crank and drive the accessories that it really doesn't hurt anything in a modern engine. It's the loading during break-in determining how the engine will perform over its service life. Motoman and I agree. Get it done straight away, and be methodical about it for best results.

Oh, here's a picture of a piston from a 1000 hp engine. Maximum rpm is 610. It weighs 68 lbs, and yes, it has 6 rings in the pack. Enjoy!

Adnectere

Good conversations lobux. A lot of your info is a given. Here's my take on other portions.

"See the orange glow? What do you suppose the top of the piston looks like at this load? "
I figured you meant the piston looked similar with a glow like the exhaust. We're agreed it doesn't then.

1000 hp at WOT for a few seconds is far more of a task than 1000 hp all day. 1000 hp all day would dictate low rpms, high torque applications. Some ocean-goers have 200,000++ hp motors with cylinders you can stand inside. I like the picture btw. I only bring up the 1000 hp motor number because the only time I've seen a blown motor have the cherry exhaust were 2 vids of a blown 427 (lingenfelter 1000 rwhp) and a renault f1 motor. Both were on an engine dyno and to get to that higher street level requires a lot of effort and heat. I don't really think it's going to be possible to reach that glow on the street ...and probably not even on a track - there's a reason that pic is taken on the engine dyno instead of actual operation (kudos to anyone who can show us a pic of an exhaust like that in operation). Without an excessive bmep you won't get heat like that. Which means our larger displacement (I'm guessing yours is about 10k cubic inches) won't suffer a similar fate. I'd also argue (although probably you will agree 100%) that from an engineering standpoint, that's probably a better motor.

As far as piston cooling goes, it's an overall systematic approach to cooling. A change not related to the piston will affect its heat; be that a valve guide or almost any other component. That means a well designed system or a poorly designed system is an A-Z concept instead of just jets. I know what you are getting at though.

The grain is denser when you forge a piston versus casting it. I doubt operation changes that, but I don't have info for or against so I'm open. Can you give me scientific proof or a thesis at least? We are agreed on various methods of permanently altering pistons via treatment before installation. I doubt this information is available.

I will strongly argue against redlining a new engine with no load; if it were under full load I would probably relatively disagree, but no load is just plain stupid. Free-revving any motor is a bad idea. Slap anyone you see doing it.

lobuxracer

iTrader: (2)

I wish I had a picture of a mini-sprint I used to work on. We had a tuning problem, but the entire exhaust was dull red while the car was on the track that night. It was running WAY TOO hot. Nothing like the orange hot on the dyno shot in my avatar.

I would suggest anyone getting an exhaust hot enough to glow red/orange on the street is a Darwin Award contender.

Unfortunately, I can't discuss certain information about piston design. I've had some interesting conversations with a contact at Mahle, but nothing I can quote without harming the relationship.

We certainly agree about grain and density in the manufacturing process, and operation does not siginificantly increase a cast piston's density. If it did, no one would bother with forging. It's not simple or cheap.

I grew up with the same admonition - NEVER redline an unloaded engine. Strangely enough, I've seen service manuals telling me to do this for testing, especially in the motorcycle world. I've also been told mean piston speed is the primary limiting factor in engine speed, yet I've seen very short duration operation well beyond the long accepted 20 m/sec with modern piston alloys, and even had reasonably knowledgable people tell me the valvetrain is the only limiting factor these days. Sometimes I think I'm just getting too old for all this stuff.

clubfoot

Very good discussion here, has anyone considered the chemical reaction as well i.e. aluminium oxided formation / thickness. Aluminium oxide forms naturally as a protective layer, but what are the effects of burning fuel mixed with air, under pressure in a combustion chamber on the metallurgy of the piston?

Just a thought don't mean to drag on a thread about break-in.

Adnectere

If you get a motor set up wrong, it can definitely run hot.

If you have confidential information on pistons at startup, that's fine - I wouldn't ask you to reveal your sources.

Whoever told you not to free-rev was right. Anytime the motor revs without a load is dangerous. The higher up you go in rpms, the more the tensile inertial loads are. It doesn't take an enormous amount to accelerate an engine without a load. 10-15% throttle should easily redline the motor. All it takes to accelerate the motor to a higher rpm is the overcoming of friction; once you reach a higher rpm where the friction equals your imep you will stop revving higher. Redlining a motor and holding it means that you are only producing enough combustion to overcome the fmep at that point.


Obviously you know your stuff, so you know that the inertial loads, specifically the tensile loads in a motor, go up with the rpms in a squared fashion. The tensile loads on a piston/con-rod assembly specifically are the most dangerous. You can counterbalance some of them by more power loads, ie more air/fuel being burned. In fact, a motor at high rpms is going to live longer on 100% throttle than it is at 15% throttle because the extra combustion gases are counterbalancing the tensile loads.

You mentioned sprint cars; I'm sure you've seen some cars blow their motors. It never happens under full power load, it happens right before a corner when the driver lifts the throttle at a high rpm. In that motor, all the tensile loads are acting on it without any counterbalancing by compressive combustion gases and the forces break it, usually in the piston/con-rod, occasionally in the crank. Sprint cars have a habit of doing that.

Here's something put a better way by someone wiser than me. The problem is that free-reving the motor doesn't instantly destroy a motor - it, like a woman, remembers everything you ever did to it.

Those tensile loads are fatigue loads whereas compressive loads by combustion are not. Everytime the car runs high rpms you are feeding loads into it that the motor doesn't forget or forgive and the only way to counterbalance is with lots of bmep. That's why I said those major motors like the one whose piston you showed were better engineered; with good bmeps, larger displacements, and lower rpms you are going to be running that motor for a longer timeframe before it breaks because your tensile loads are so small and are well-balanced.

Mean piston speed is the major limiting factor for both longevity and rpms at the most basic level. Remember piston speed takes into account stroke specifically but good engineers will also include a coefficient based on the motors' bore size. That means that a larger motor running lower rpms may have the same stresses that a smaller motor running higher rpms has. It's not a piston "speed" but rather a piston "acceleration" that limits the max rpms (i have a feeling you know this). As the piston has a higher velocity from BDC to TDC and vice versa, it takes more force to slow it down and then reaccelerate it. Those forces are the tensile loads aforementioned (in the upper half, compressive in the lower half, but we only care about the upper half). If you increase rpms or bore/stroke/mass you will increase the force needed to decelerate/stop/reaccelerate the piston. Any motor that goes past 20 m/sec is short-term. You can blow right past that momentarily, but the motor never forgets. The problem exacerbates the higher the rpms you turn and the bigger the motor. That's ultimately the failure point - when a rod breaks from excess acceleration, conveniently referred to as mean piston speed.

And the valvetrain is A limiting factor. If you are willing to run a motor until destruction in 5 seconds, say during a drag race, your major concern is the previous paragraph. The valvetrain is a longevity concern more associated with the street and extended use. As you increase rpms, getting the valves to seat requires more and more force and the force exerted on the valve/seat is directly proportional to its lifetime. The heavier the valvetrain and the higher the rpms, the more force you will need and eventually you run into a scenario where your operation life is just dismally small, maybe 25k before a rebuild.

Back to that boat motor being better. Now if we can find a way to stick 10k cubes under a hood.

LexusIS-TL

I've put on 700 miles exactly already and the car's a week old!!!!!! I didn't over rev it, but I do drive fast on the freeway. I'm averaging like 70-80mph!!!!

This car's got guts. I was driving home today when I almost missed my exit. I poured it on and wow. I can't even begin to imagine what it's like for the IS350.

Adnectere

TRDCorolla - I'm guessing that was your last car; you'll notice a difference with the IS from it. The first time you notice is when you do WOT and go through peak hp. Later on you'll notice it in daily driving; the 250 has much more torque especially with these short gearboxes. You can always go to the dealer and test a 350.

For that matter, I'm due to pick up my IS350 in May when it gets delivered and I'm curious how I'm going to feel about it then. I think it'll take a few months to vibe with the car and then I could post something realistic. I will say that I picked it over it's closest competitor, a twin turbo 335i for several reasons. I could post them if anyone gives a *#($.

As far as chemistry goes, gas is a lot like cigarettes, what goes in is completely different versus what comes out. Most of the chemistry goes into figuring out what objects remain after combustion and which ones are harmful; then steps are taken to lessen the emissions in each particular category. The fun part is when you change one thing for the better and it makes another get worse. If you really care, pick up "The Internal Combustion Engine in Theory & Practice" - volume 1 has a chapter devoted to this subject. That's probably the best motor book I've ever come across and I highly recommend it - anytime you get into a question you'll find the answer in it. I'm not even going to crack open the chapter and deal with anything in it because it's absolutely hellish. You can torture yourself. As far as anything actually being left behind in the motor, I'm not sure there. Everything I've come across has been focused on what happens when the chemicals dissociate after combustion. I'm not sure it truthfully matters any.

Dabigman

Hah! So 1000HP huh, how much torque? Like 8000lb because it has to high with slugs that big! Is this from a diesel-electric locomotive?