This is just a general kind of question - in regards to new vehicles obviously engineers are given a quest to design a motor that is suitably quiet, reliable, sips fuel, doesn't cost too much to build, doesn't take up unnecessary space in the engine bay, doesn't weigh too much, is modular enough in design to be used in multiple applications and not just one or two vehicles, and of course it needs to be powerful with a nice powercurve.

I'm just looking for general information and discussion in this area because my dad has always said if Honda Civics were designed to only perform (acceleration and handling) as well as the Civics of 25 years ago, they could make them unbelievably reliable - but everyone demands to go fast and drive hard. Basically he's saying that the competition to be the fastest and most 'featureful' car in a given class is putting a serious hurting on reliability, too.

For example - if there wasn't such an unwritten rule right now that you must offer a 300+ horsepower V6 in your entry level premium brand sedan - and it was fine it manufacturers made a V6 that only output 220hp or whatever... then how would the design benefit? Could they extra great fuel economy out of the motor or maybe improve reliability substantially? Or would they have absolutely no reason to even make a V6 in the first place and instead would probably make a 4-cylinder of some sort?

 

Ok are you saying that if performance of the current Civic only had to be at the level of a 25 year old Civic that the car would be more reliable? If so then I would say yes. I think the parts would have less stress placed on them and would last longer due to that.

 

Right, that's what I'm getting at. But it was really only an example to give to show what I'm talking about. My dad used to say that because he had a Civic that was as old as I was until I was 18 and while the interior got kinda rough over the years, mechanically the car was like a swiss watch. His comment was basically if the next 25 years was only focused on things like fuel economy, reliability, and safety and not so much all of the gadgets and ultra powerful motors and such that cars today could be made to be nearly indestructible. Granted that might put car companies out of business after a couple of decades so they'd never do that... but...

I'm also wondering about fuel economy, production costs, emissions, etc... how are the constraints of today's market and government requirements hindering other aspects of engine design?

 

I've always thought about this as well. If a current 300+ hp 3.x L V6 was essentially detuned to ~220 hp in order to acheive better reliability and fuel economy, I see them being far less problematic than "ordinary," and I can see them lasting a lot longer. Unfortunately, this 3.x L V6 will be compared to other V6s of similar displacement and will be ripped apart by magazines and other publications if it doesn't perform.

 

Without a doubt, less power = more reliability. That's why lawn mower engines make a few HP from a few hundred cc's but run for decades without oil changes. But frankly, engine reliability is, by and large, not a significant problem with modern automobiles. You'll usually wear out the interior or rot out the body before a modern engine so much as smokes upon startup. Frankly, reliability is just not a problem - even the highest-performance mass-market engines of today are far more reliable than the toughest lumps from a couple decades ago.

Power and economy also share an inverse relationship, as more powerful engines need smaller throttle openings during normal usage. This increases pumping losses, and thus decreases efficiency. Cylinder deactivation helps here, and lean burn would also help if it weren't for the increase in oxides of nitrogen.

Once again, NVH is affected by power, since the characteristics required to increase specific output - aggressive valve event timing, high compression ratios, unrestrictive intake and exhaust tracts - are exactly the opposite of what makes for a smooth-running engine. The lightweight reciprocating parts and stiff blocks that are typically used in a higher-performance engine can be of some help in improving NVH, but that's not significant in the grand scheme of things. Then again, the sort of NVH created by a high-performance engine can be very pleasing to the enthusiast

Of any of these, the trade-off that's of greatest concern IMO is power vs. economy.

 

So, what are the problems with modern V6s? I'm unaware of any that are related to power output. The issues that do exist - Toyota's oil sludging, GM's intake problems - have little or nothing to do with specific output.

 

Nothing necessarily, I was basically trying to say what you stated in your first post that less power = better reliability

 

I think the push for power has done a lot for reliability, and if the same vehicles have to be able to stand up to a 300hp version, then the base 220hp version should be more reliable.
If you suddenly tomorrow dropped the output, you would see the increase in reliability, but if the next gen only needed to live up to 1/2 the power, I'd assume they would go with cheaper parts that could handle 1/2 the power, true?

 

Depends how good the engineering is If the vehicle is designed for a reasonable life expectancy, then yes, the parts would/should be adjusted accordingly.

Of course, how many engines die because the basic hard parts weren't designed correctly, and how many end up in the junkyard because some "minor" component (water pump, oil pump, hose, gasket, etc.) failed and started a catastrophic chain of events? Those sort of failures are often independent of engine output.


Gotcha

 

The problem with give a engine in the same car less power is you have to "drive it harder" to get the car not just to perfrom simlar, but you have to give it more gas when your going up a hill, etc. Now, if you drop HP relative to vehicle weight, than you could see a increase in mileage. Point being, back in the 80s you could get a Civic that got fourty somthing in town and fifty something on the highway. Sure the engine didn't have a lot of power, but the car didn't weight a lot either. The biggest enemy of gas mileage is weight. There was a Chrysler engineer, that wrote a book in the 90s, and he stated that it would be more cost effective to cut weight out of car than to try and make everything a hybrid.

I agree that a more powerful engine needs less restrictive intake and exhaust and that adds noise that no one wants to hear, but with everyone going to some kind of variable valve timing, more aggressive cams are not the problem they once were.

When it comes to reliablity, I don't really think there are any problems when it comes to high horsepower engines. Since just about everyone has some kind of 50k mile warranty, or longer, this is factored in and the OEs will not make an engine that will not be able to last. Today people are expecting engines and cars to last at least 100k miles, and expectations are only going up.

 

Slight detour here, but I gotta ask-

It is often said that diesel engines have lower pumping losses than gas engines due to the lack of a throttle. I'm having trouble figuring out the physics with this. Can anyone clue me in?

 

I don't know about GM's intake issue but from what I've read about the Toyota sludging issue, it was caused by the engineers creating the 'veins' in which oil flowed through certain parts of the block to be cooled to be too narrow. Somehow this translated into a benefit for fuel economy but I don't remember why. I just remember reading it. So not really specific output, but the sludge issue may have been over eager engineers trying to squeeze out an extra tenth of two of mpg?

It definitely makes a difference in the city but I was under the impression that on the highway, gearing, motor, and aerodynamics were the primary factors in fuel economy? Tire friction I suppose, too.


I'd say the average consumer would be pretty upset if their motor required major work at 100k miles. Seems like Dodge Ram 4.7 and 5.9s and Caddy Northstars both are notorious for requiring complete rebuilds around that mileage marker... and I sure don't hear anyone exactly 'ok' with that when it happens.

I know the 1UZ-FE in my old Lexus GS400 is supposed to be capable of 350 to 500k miles depending on usage, on average - but the thing nobody mentions is how much it costs to keep it running that long. The waterpump is deigned to be changed every 90 to 120k miles or so at quite a bit of expense (600 to 1200 dollars depending on who does it... timing belt is changed at the same time). The starter I don't think has an intended life expectancy but on that particular motor they seem to fail early - averaging around 100k miles before they need to be swapped, and they happen to be located underneath almost the entire top end of the motor - another 1200 dollar repair job. Plugs aren't cheap either.

So I guess the 500k mile 'expectancy' is really more like "no hard parts should fail before then but lots of modular accessory maintenance will be required in the meantime".

I wonder if companies are designing these things to bring in service department revenue after a while, or if they really just can't seem to make waterpumps, starters, and alternators that last any longer without costing a whole lot?

 

Diesel engines literally do not have a throttle blade; just a wide open pipe from the air filter to the intake ports. Gasoline engines, of course, do have throttle blades, so whenever they are at less than 100% throttle, they have a restriction blocking the intake tract.

Imagine trying to breathe through a straw vs. breathing through your wide open mouth. A gasoline engine at idle will have its throttle blade dang near closed, so each time a piston goes down with the intake valve open, you've got ~1 atmosphere of pressure outside the car, but it has to squeeze air though that tiny opening, so there is a large pressure drop before it gets to the intake port and cylinder. Same thing in part throttle situations. As in any fluid flow situation, the addition of a valve or bend or other change in geometry creates a pressure drop point and a flow restriction.

A diesel engine is controlled by how much fuel is added. Whether at idle, part "throttle" (fuel), or "WOT", the air doesn't meet that blade restriction. Of course, both engines have the restriction of the air filter, the intake assembly, and the intake valve. Of course, in reality, most/all modern diesels are turbocharged, so this little illustration isn't exactly representative.

Anyway, this is one of the reasons why upshifting early is helpful (or why skip shift is helpful). Keeping engine rpm down, and keeping the throttle blade open more, both aid in increasing fuel economy.

I'm not sure I'm really answering your question at the physics level (since I know you are a physics-oriented kinda guy ), so just tell me "no s*** sherlock" or something if you wanted a deeper answer.

 

Yeah, that doesn't really explain it for me. But, thanks, though. j/k

I'm missing some key point that I can't put my finger on. An engine is an air pump- a positive displacement air pump. A cylinder moves "X" volume of air on every cycle, regardless of manifold pressure. Everyone knows that a freer flowing engine will make more peak power.

But- consider this. I work with vacuum pumps in my line of work. They are also positive displacement pumps (basically roots blower style construction). They are driven by electric motors. If I flow more gas (let's say pure nitrogen) through them, the current draw goes up, because they are moving more nitrogen- a larger MASS of nitrogen. If I cut the flow to zero, so that they pull a hard vacuum, the current draw is lowest.

Which brings me to the throttle. If opening the throttle increases manifold pressure (and it does), and this, in turn, puts a higher pressure on the back side of the intake valve which, in turn, allows a larger MASS of air to be drawn into the cylinder (and it does)- how is it that moving this larger mass of air through the engine (which requires work from the engine to draw it in, and push it out) make it more efficient?

I can't reconcile technologies like cylinder deactivation against this "pumping loss" thing, in my head.

Mostly, it bugs me that, given the sort of high-tech, cutting-edge work that I'm involved in, I can't figure it out in my head. Surprisingly, Google isn't helping. There's a bunch of anecdotal examples, but no hard "this is why."


Sorry for the thread hijack, Kyle. To answer your question-

You could test this theory easily. Sure, cars today are more powerful, but there's nothing saying you have to tap all that power. If, for instance, you put a nanny program on an electronic throttled car to limit it to, say 40% throttle opening, you would reduce the peak power output, while basically holding all the other variables constant. For a 300hp V6 designed to withstand the periodic full-throttle romps for 100k+ miles, limiting power output would certainly improve lifetime.

One of the things your Dad may have been alluding to- so that you can have your 5.1 surround system, heated seats, etc, for just over 30k, the car designer may have spec'd lower price (and lower quality) CV joints/wheel bearings, window motors, etc, to fit all the features in at that price point. It's absolutely true. So, watch out for that ignition control module in that Audi that was made in China for Bosch, rather than made in Bosch- Reutlingen where the QC is tighter.

 

Just like in the city, in takes a certain amount of HP to keep the car moving at a certain speed. The less the vehicle weights, the less HP it is going to take to sustain cruising speed. While I agree with aeros playing a part on the highway, I don't think they have as much an impact at highway speeds as many people think. Sure they do play a role, but not as much as a role as 70mph compared to 150mph, like in racing. The aeros of any production car have to be used to keep the car on the ground at the speeds the OEs allow the car to go to. I think one of the biggest places light weight parts could be used to see great gains in mileage are in SUVs and Trucks. Seeing as there is such a big margin on those vehicles, there is room to spend more monee on exotic parts without hurting the bottom line. As with any exotic part, the problem is not so much making it work on a productin vehicle, but making it cost effective to work on the mass production scale, as compared to the exotic cars.



From what you said about the starter, I think that is more a problem with Toyota V8s, and I think the new 5.7 will suffer from it too. One of my instructors at school has a older Tundra with a 4.7 and says that it is common for the starter to go at 100k miles. So, I have to think that starters is once place where Toyota is cutting costs. With the water pump, I think it comes down to the seals that are used and the forces that ack on the shaft of the impeller. As not only does the seal have to survive coolant, that usually is not changed every 2-3 years like it should, it also has to survive the forces that are put on it from the impeller shaft. One way to get away from the shaft problem is to make the pump electric, but that will only drive the model price up.

I'm sure almost all OEs have the long last engine down, it is the other parts, especially the ones that interact with fluids that need routine change, that have long lasting problems. One of the problems that don't help parts is when you don't flush your coolant/transmission or even your brake fluid(bet you never heard of that one before). The more up to date you stay on maintaince the better off you are in the long run. Since most people rotate cars every 3 or so years, the original owners don't care too much about maintaince. I've heard of cars going 30k+ miles WITHOUT an oil change and people wonder why used cars don't last as long as new ones.

All in all, I think most people are satisfied with where cars are today with how many miles they are getting out of them, 100-150k miles. I think people looking at cars now are most interested in seeing what they can get for the dollar and how many features and bells and whisles they car get on a vehicle. I'm sure that the reliability will go up as computer handle more and more of the control of the vehicle, so I think any more gains made in those areas will come from more i computer control of the car since the computer does not abuse the car, even sometimes when the owner wants it to.