Twin Turbo Engines as reliable as naturally aspirated engines?

[vinuneuro]

Originally Posted by JCL

Well, I think that SpeedR has a point, but I would use the word durability instead of reliability. A turbocharged engine will always be less durable than the same engine naturally aspirated, if you take advantage of and use the power available to you. More work taken out of the engine means that it won't last as long. In the real world of automotive engines, though, this is somewhat theoretical. With heavy duty industrial diesels, we often measure the gallons of fuel to overhaul. Take more power out of it, overhaul it sooner. With a modern car, though, lots of things are going to wear out or break before you need to change pistons and rings, so it is a theoretical issue not a real world one.

As for reliability, I think it is related far more to first-year (and second year) issues than it is to the turbochargers. I refused to buy my 3.0 twin turbo until BMW had two years of production behind them. Turned out to be a good plan, as well, engine of the year or not. I think the V8 twin turbo will go through the same cycle.

I also agree with others that heat is likely to be an issue on the V8. I am sure BMW will get it right, but there may be a string of TSBs until they do. Better to skip the beta testing phase.

Jeff, I don't think your point is valid, even regarding durability. Engineers take into account for the fact that a turbocharged engine is going to have operating conditions. For example the TT I6 engine isn't going to have the same rods as the NA engine, the TT engine will use forged pistons instead of cast, different head bolts, etc etc. Same goes regarding the heat issue, the cooling system is going to be larger and/or more efficient in a turbocharged engine. I know for a fact that diesel's use a different spec oil, but that also has to do with soot/emissions.

CAT C15, Cummins ISX, DD Series 60, etc are heavy-duty engines that produce 500+hp and 1500-2000lb-ft tq. Imagine how much heat is generated from that much work, and how high peak-cyl-pressures must be. They're still robust engines without any heat issues even in short-haul applications. The overhaul interval for these engines is 750,000-1,000,000 miles.

We're in a new era of engineering, since almsot everything can be simulated beforehand. Tolerances are tight, we have access to new modern materials, etc. There'r virtually no constraints you can't design around.

Imo, the only heat issue with any of these engines might come if the vehicle is tracked (maybe only to the point of endurance racing). As far as being a beta tester with BMW's goes, I think that's a non-issue with the latest gen of BMW's. BMW as a whole is more financially sound now, and I think they're putting more into development and validation. Don't think these new TT I6 engines have had any significant issue from the getgo.

[FSETH]

Originally Posted by vinuneuro

Jeff, I don't think your point is valid, even regarding durability. Engineers take into account for the fact that a turbocharged engine is going to have operating conditions. For example the TT I6 engine isn't going to have the same rods as the NA engine, the TT engine will use forged pistons instead of cast, different head bolts, etc etc. Same goes regarding the heat issue, the cooling system is going to be larger and/or more efficient in a turbocharged engine. I know for a fact that diesel's use a different spec oil, but that also has to do with soot/emissions.

CAT C15, Cummins ISX, DD Series 60, etc are heavy-duty engines that produce 500+hp and 1500-2000lb-ft tq. Imagine how much heat is generated from that much work, and how high peak-cyl-pressures must be. They're still robust engines without any heat issues even in short-haul applications. The overhaul interval for these engines is 750,000-1,000,000 miles.

We're in a new era of engineering, since almsot everything can be simulated beforehand. Tolerances are tight, we have access to new modern materials, etc. There'r virtually no constraints you can't design around.

Imo, the only heat issue with any of these engines might come if the vehicle is tracked (maybe only to the point of endurance racing). As far as being a beta tester with BMW's goes, I think that's a non-issue with the latest gen of BMW's. BMW as a whole is more financially sound now, and I think they're putting more into development and validation. Don't think these new TT I6 engines have had any significant issue from the getgo.

IMO Jeff does have a point. Engineers have the advantage of todays advanced testing techniques. However, they do not always get it right for one reason or another. It is possible to still have design flaws even with all of todays technology. They are also constrained by costs and the bean counters who want them to design parts just good enough to save money. The engineers at BMW could have put adequate oil coolers in the 335i to prevent the overheating issues many owners are dealing with, but they didn't. Who really knows why? So all design is not perfect and for those that wait for bugs like this to be worked out in a first year model, they will benefit from the work BMW does to correct the issue. Look back at the e46 M3 engine from 01-02 and the problems it had and that was an M engine! You know a lot of R & D went into designing that motor. I have to fully agree that waiting a year or two for the bugs to get worked out is still not a bad idea. The engineers can't get everything right the first time even with todays technology.

I wouldn't assume that just because engineers can design something to minimize any failures or weaknesses that it is always done that way. BMW is worried about the bottom line now just as much as they always have. Overall these engines have been reliable it has just been fuel pump and overheating issues. Only time will tell how well they last. I would assume they will be reliable and durable.

Another issue is if the TT is modified. The internal components of the e46 M3 motor were designed to be able to withstand more power and stress than the 335 motor and with tuning the 335 motor is going to be putting out more HP than a stock e46 M3. That could be a little scary. That is why you see tuners like Active selling 525 HP M3 turbos. That power would destroy a 335 engine.

[vinuneuro]

Originally Posted by FSETH

IMO Jeff does have a point. Engineers have the advantage of todays advanced testing techniques. However, they do not always get it right for one reason or another. It is possible to still have design flaws even with all of todays technology. They are also constrained by costs and the bean counters who want them to design parts just good enough to save money. The engineers at BMW could have put adequate oil coolers in the 335i to prevent the overheating issues many owners are dealing with, but they didn't. Who really knows why? So all design is not perfect and for those that wait for bugs like this to be worked out in a first year model, they will benefit from the work BMW does to correct the issue. Look back at the e46 M3 engine from 01-02 and the problems it had and that was an M engine! You know a lot of R & D went into designing that motor. I have to fully agree that waiting a year or two for the bugs to get worked out is still not a bad idea. The engineers can't get everything right the first time even with todays technology.

I wouldn't assume that just because engineers can design something to minimize any failures or weaknesses that it is always done that way. BMW is worried about the bottom line now just as much as they always have. Overall these engines have been reliable it has just been fuel pump and overheating issues. Only time will tell how well they last. I would assume they will be reliable and durable.

Another issue is if the TT is modified. The internal components of the e46 M3 motor were designed to be able to withstand more power and stress than the 335 motor and with tuning the 335 motor is going to be putting out more HP than a stock e46 M3. That could be a little scary. That is why you see tuners like Active selling 525 HP M3 turbos. That power would destroy a 335 engine.

Regarding the durability issue: you're basing your thoughts on quite a bit of speculation regarding the engine strength of the M3 v. the 335, and obviously only that. Based on what fact or logic do you think the M3 motor is stronger? Because it's been around and has given more 'tuners' to install a turbo or supercharger?

I'll start of saying that basically EVERY factory turbo engine comes with a ton of safe room in terms of increasing power output over what come from the factory. Whether it be the Toyota, Nissan, Subaru, Diesel, engines of the world. That's been proven time over again through history.

Comparing the M3 engine to the TT unit is about the worst comparison. A high-ouput 3.0L NA engine revving to 8,500 producing 333hp and a 3.0L TT engine producing 300hp and a ton more tq go about their business very differently and are built very differently. The M3 engine may have 500hp of strength in it (I wouldn't expect it to last 150k miles), but it's components weren't meant to do that.

Any high-revving motor is built with the lightest possible components since this allows the rotating assembly to rev that high and produce power that high. Less material of the same material is going to be weaker (with regard to the rods). In a motor like this, rotating assembly components are engineered to withstand high piston-velocities and the side-loading. The rods experience more of an elastic force. The pistons are going to be a different alloy, a lighter alloy. The bearings experience different conditions for the same reasons, they're built more to withstand higher piston-velocities. Clearances (bearing and piston-wall) will be tighter (permitting less heat, with regards to piston-wall).

In a turbo motor, it's the exact opposite. The pistons and rods don't experience the opposite (in direction) force of an elastic situation. Rather they're built more for sheer (not literally) strength. High-cyl-pressure is the issue here. The engine has heavier (more material) and stronger components. It's also easier to balance a lighter rotating assembly.

Now let's use some very simple logic. The Dinan reflash (which doesn't void the warranty) increases the power to 384 and tq to 421. You think that BMW would approve this enough without a significant surplus in the engine's capability? They're going increase power to 340hp for the Tii models, you think they're actually going to change components to withstand that? It doesn't cost BMW anymore than a little more in materials cost to increase strength and weight of the key components. On a high-revving motor though, weight (and in turn strength, bc it's the same material in both) is bad because it robs power once the revs climb. No such concern here.

As for the overheating issue, it's not actually an overheating issue but rather an issue of oil temp. The European spec oil can easily handle those temps. This issue also comes up only at the track (where the warranty is void anyway). Even still the previous gen 3.0L NA engine didn't have any issue from back in the day, and neither did the current 3.0L NA engine.

I'll be traveling out of the country for a few weeks, so this will be my last post here. Thanks for playing everyone.