Yes this has been covered in blistering detail on many websites, but for those new to this site/issue...
First, I don't pretend to be an expert, but I have rebuilt several engines and think I remember some of the basics. This will obviously be tainted with my own personal opinions. And being an engineer, I have also found some of the physics and chemistry behind this interesting. So, don't take just my opinion, you can find a lot of info on the internet about this topic.
There are many "camps" on this topic. I couldn't possibly cover them all but here are a few.
Camp 1. Smash it from the get go. This camp subscribes to the theory that if it is a good engine and you want maximum performance, you need to romp them from the start. After all, this is what racers do.
Camp 2. Drive it normally. This camp believes that you want to break in the engine the way you are going to drive it 90% of the time. After all, we aren't all racers.
Camp 3. Follow the manual. This camp believes the manufacturer knows best what the procedure is. After all, they designed the thing.
Camp 4. This is a myth. Todays engines and materials don't require breaking in. It used to be true, but the quality and precision of current manufacturing techniques makes this a non-issue. After all, this is the 21st century.
What is break in? The engine has to "break-in". Break in involves the process by which the moving metal parts wear into each other. While bearings and bushings wear together, the primary parts for consideration during break-in are the piston rings/cylinder bores. Camp one also believes its a good idea to weed out weak parts on day one.
The pistons have rings, both compression and oil. These rings and the cylinder bores must fit very closely together or the engine will not have proper compression and lubrication. Outside of the obvious benefit of lubrication, the rings also serve to scrape the oil off the bores on the down stroke so that oil is not burned during combustion. When the rings are not properly "seated" in the cylinder bores, full design compression is not achieved. When compression is not achieved, performance and gas mileage is adversely affected.
The internal combustion engine works by compressing an air/fuel mixture and igniting it. Basically a self contained explosion. The explosive force moves the piston which is connected to a crankshaft through piston rods. Thus the lateral movement of the piston is translated into rotational movement. If the compression is not correct, the explosion is weak.
A word about compression and octane. Higher octane fuels require higher compression. Higher octane fuels provide more power and burn better. With that said, a lower compression engine cannot make use of the extra energy in high octane fuels because they never achieve sufficient compression.
So one of the impacts of break in is obvious. You want the rings to seat to the cylinder walls. The rings and the cylinder walls are not perfectly round. They are very close, but not exactly. Therefore the cylinder walls are "cross-hatched". Which weeds out camp four because cylinders are still cross hatched. This cross-hatching is what allows the rings and the cylinder walls to wear together in shape very quickly. If the walls were perfectly smooth, it would take a very long time, if ever, for the rings and cylinder walls to wear together in a matched shape. In older engines where the rings are worn out, they will consume more fuel, burn oil and lose power. But these cross hatchings only serve their purpose for a short time. The "sharp edges" from the hatching wears off. The time it takes to wear off depends upon the materials of the rings, and cylinders. Also, maximum throttle and load can hamper the break in process. At maximum throttle and full load, the pressures inside the cylinder are at their highest and cause blow by. Among other things, blow by forces the rings into the piston and away from the cylinder walls. Exactly what we don't want for the break in process.
As the piston moves up and down the cylinder, the piston and cylinder vibrate. Very small amounts, but they do vibrate. And they vibrate differently at different rpms. That is to say the vibration profile changes with rpm. So if you run at a constant speed/rpm, the engine will take a "set" to a specific rpm/speed. This weeds out camp one unless you are a racer and want an engine that only works best at highest rpm. This also weeds out camp two because we do occasionally want high rpm performance, depends on definition of "normal" driving. For the rest of us,what we want is an engine that will achieve compression at all rpms.
Lets combine all this and say that during break-in (the first few thousand miles) you do not want to drive at a constant speed/rpm. You do not want to go to full throttle/load. What you want is to constantly vary your rpm's throughout the throttle/load range but staying away from max throttle/load at first ending up at primarily max throttle/load towards the end of break in.
To stay within the manual recommendations, first 1200 miles keep rpms under 4000-4500 and maybe a few excursions into full throttle. After that, gradually increase rpm range to 6000 with several excursions into full throttle. Find a road late at night with few people cause the constant accelerating/decelerating will drive people nuts. And obviously, you can't do this up/down yo-yo thing all the time, but do it. It works. Avoid driving for long periods without doing it. What is long periods? Tough to say but I try to avoid 5 minutes or so of constant speed driving at first then gradually lengthening the time to 15 minutes. Use the Ds and L modes to help with this. If you want to venture out of camp three, accelerate the mileage IE instead of 1200 miles, use 500 instead.
A note about the VQ35DE and it's computer control. The VQ used in the MO and the 350Z has a computer that "learns" the way you drive. (It is akin to a kalman filter by my way of thinking for those engineers out there.) As it breaks in and you drive differently, the computer will adapt and change how much power it provides you by way of changing how much fuel it provides. It senses the engine rpms and the throttle positions with respect to time. Given the VQ has VVT, it probably also changes that.
The affect you are looking for is that the car should get "stronger". I don't know how else to put it. But as the engine breaks in and you increase your excursions into full throttle/load, as a result of the rings seating/break in and the ECU, the engine creates more power and it just feels stronger (butt-dyno).
It has been proposed (not confirmed) that the computer also kicks in more aggressively based on ODO miles.
Some of my experiences...
First let me say that I broke in my 350Z and my MO with this process and I am very pleased with the results.
Secondly, this process was taught to me by my father who rebuilt more engines than I will ever know and was into racing at one time (until mother threatened to divorce him). Some of the engines I have rebuilt for myself/friends worth mentioning include the 280Z, 390 Ford, 383 Magnum - Dodge Superbee, 460 Ford. The 280 was amazing. With over a 100,000 miles you could still see the hatch marks in the bores. The dealer service rep I talked to at the time claimed the bores on the datsuns were nitrided (never confirmed). The 390 Ford was straight forward, 80,000 miles but I had to hone the bores, re-hatch, and get oversized pistons. The 383 I learned about chrome rings and Rislone. The 460 had only 1200 miles on it. My friend replaced the stock cast iron intake manifold with an aluminum edlebrock when he bought it, but forgot to clean it out first. Must have had sand in it because the engine lost compression big time. When we took the engine apart, you could see a worn lip in the cylinders and wear on the pistons. Only 1200 miles! Needless to say it's now closer to a 490 and after many years and miles of reliable service my friend can still melt the tires.
All the engines I rebuilt were broken in using my fathers tried and true method. Followed each up with wet and dry compression tests to make sure the rings and valves seated. All I can say is, it works.
First, I don't pretend to be an expert, but I have rebuilt several engines and think I remember some of the basics. This will obviously be tainted with my own personal opinions. And being an engineer, I have also found some of the physics and chemistry behind this interesting. So, don't take just my opinion, you can find a lot of info on the internet about this topic.
There are many "camps" on this topic. I couldn't possibly cover them all but here are a few.
Camp 1. Smash it from the get go. This camp subscribes to the theory that if it is a good engine and you want maximum performance, you need to romp them from the start. After all, this is what racers do.
Camp 2. Drive it normally. This camp believes that you want to break in the engine the way you are going to drive it 90% of the time. After all, we aren't all racers.
Camp 3. Follow the manual. This camp believes the manufacturer knows best what the procedure is. After all, they designed the thing.
Camp 4. This is a myth. Todays engines and materials don't require breaking in. It used to be true, but the quality and precision of current manufacturing techniques makes this a non-issue. After all, this is the 21st century.
What is break in? The engine has to "break-in". Break in involves the process by which the moving metal parts wear into each other. While bearings and bushings wear together, the primary parts for consideration during break-in are the piston rings/cylinder bores. Camp one also believes its a good idea to weed out weak parts on day one.
The pistons have rings, both compression and oil. These rings and the cylinder bores must fit very closely together or the engine will not have proper compression and lubrication. Outside of the obvious benefit of lubrication, the rings also serve to scrape the oil off the bores on the down stroke so that oil is not burned during combustion. When the rings are not properly "seated" in the cylinder bores, full design compression is not achieved. When compression is not achieved, performance and gas mileage is adversely affected.
The internal combustion engine works by compressing an air/fuel mixture and igniting it. Basically a self contained explosion. The explosive force moves the piston which is connected to a crankshaft through piston rods. Thus the lateral movement of the piston is translated into rotational movement. If the compression is not correct, the explosion is weak.
A word about compression and octane. Higher octane fuels require higher compression. Higher octane fuels provide more power and burn better. With that said, a lower compression engine cannot make use of the extra energy in high octane fuels because they never achieve sufficient compression.
So one of the impacts of break in is obvious. You want the rings to seat to the cylinder walls. The rings and the cylinder walls are not perfectly round. They are very close, but not exactly. Therefore the cylinder walls are "cross-hatched". Which weeds out camp four because cylinders are still cross hatched. This cross-hatching is what allows the rings and the cylinder walls to wear together in shape very quickly. If the walls were perfectly smooth, it would take a very long time, if ever, for the rings and cylinder walls to wear together in a matched shape. In older engines where the rings are worn out, they will consume more fuel, burn oil and lose power. But these cross hatchings only serve their purpose for a short time. The "sharp edges" from the hatching wears off. The time it takes to wear off depends upon the materials of the rings, and cylinders. Also, maximum throttle and load can hamper the break in process. At maximum throttle and full load, the pressures inside the cylinder are at their highest and cause blow by. Among other things, blow by forces the rings into the piston and away from the cylinder walls. Exactly what we don't want for the break in process.
As the piston moves up and down the cylinder, the piston and cylinder vibrate. Very small amounts, but they do vibrate. And they vibrate differently at different rpms. That is to say the vibration profile changes with rpm. So if you run at a constant speed/rpm, the engine will take a "set" to a specific rpm/speed. This weeds out camp one unless you are a racer and want an engine that only works best at highest rpm. This also weeds out camp two because we do occasionally want high rpm performance, depends on definition of "normal" driving. For the rest of us,what we want is an engine that will achieve compression at all rpms.
Lets combine all this and say that during break-in (the first few thousand miles) you do not want to drive at a constant speed/rpm. You do not want to go to full throttle/load. What you want is to constantly vary your rpm's throughout the throttle/load range but staying away from max throttle/load at first ending up at primarily max throttle/load towards the end of break in.
To stay within the manual recommendations, first 1200 miles keep rpms under 4000-4500 and maybe a few excursions into full throttle. After that, gradually increase rpm range to 6000 with several excursions into full throttle. Find a road late at night with few people cause the constant accelerating/decelerating will drive people nuts. And obviously, you can't do this up/down yo-yo thing all the time, but do it. It works. Avoid driving for long periods without doing it. What is long periods? Tough to say but I try to avoid 5 minutes or so of constant speed driving at first then gradually lengthening the time to 15 minutes. Use the Ds and L modes to help with this. If you want to venture out of camp three, accelerate the mileage IE instead of 1200 miles, use 500 instead.
A note about the VQ35DE and it's computer control. The VQ used in the MO and the 350Z has a computer that "learns" the way you drive. (It is akin to a kalman filter by my way of thinking for those engineers out there.) As it breaks in and you drive differently, the computer will adapt and change how much power it provides you by way of changing how much fuel it provides. It senses the engine rpms and the throttle positions with respect to time. Given the VQ has VVT, it probably also changes that.
The affect you are looking for is that the car should get "stronger". I don't know how else to put it. But as the engine breaks in and you increase your excursions into full throttle/load, as a result of the rings seating/break in and the ECU, the engine creates more power and it just feels stronger (butt-dyno).
It has been proposed (not confirmed) that the computer also kicks in more aggressively based on ODO miles.
Some of my experiences...
First let me say that I broke in my 350Z and my MO with this process and I am very pleased with the results.
Secondly, this process was taught to me by my father who rebuilt more engines than I will ever know and was into racing at one time (until mother threatened to divorce him). Some of the engines I have rebuilt for myself/friends worth mentioning include the 280Z, 390 Ford, 383 Magnum - Dodge Superbee, 460 Ford. The 280 was amazing. With over a 100,000 miles you could still see the hatch marks in the bores. The dealer service rep I talked to at the time claimed the bores on the datsuns were nitrided (never confirmed). The 390 Ford was straight forward, 80,000 miles but I had to hone the bores, re-hatch, and get oversized pistons. The 383 I learned about chrome rings and Rislone. The 460 had only 1200 miles on it. My friend replaced the stock cast iron intake manifold with an aluminum edlebrock when he bought it, but forgot to clean it out first. Must have had sand in it because the engine lost compression big time. When we took the engine apart, you could see a worn lip in the cylinders and wear on the pistons. Only 1200 miles! Needless to say it's now closer to a 490 and after many years and miles of reliable service my friend can still melt the tires.
All the engines I rebuilt were broken in using my fathers tried and true method. Followed each up with wet and dry compression tests to make sure the rings and valves seated. All I can say is, it works.
