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Originally Posted by RIWWP
(Post 4137171)
Series 9, episode 2. Can't find it on youtube. http://en.wikipedia.org/wiki/List_of_Top_Gear_episodes
http://www.topgear.com/uk/videos/coupe-shootout Richard's segment starts right around the 4.5 minute mark. |
Originally Posted by RIWWP
(Post 4137211)
So you are basically saying "steady state engine rpm is horrible for a tiny part of the engine, so you shouldn't do it, even though it's far better for every other part of the engine and car, and those benefits are not sufficient to outweigh the steady state engine problems."
? I still don't agree with that, but I'm just trying to understand your argument against highway driving. Physics (within the laws and rules that we humans know physics to operate) is never wrong. Usually when someone uses a pure physics perspective to argue a theory that is incorrect, it is because they are ignoring the physics of other factors. In your case, physics such as temperature equilibrium, ECU data loop becoming more refined, minimized heat cycles, etc... Perhaps you are in fact correct that steady state engine RPM is bad for the seals from a pure physics perspective, with "bad" being defined as "non-optimal wear." However, even at the base level I would say that the heat cycles associated with varying RPM is even worse. Thus making steady state still the best thing for it, even if it is still "bad." A laymans example would be if you are on the roof of a 2 story burning building, and have to jump off the roof, you have a choice of jumping onto a roof 1 story down, and then again from there to the ground, or the entire 2 stories at once. Neither will be very good for your body, but one stands out clearly as the better option, and the one people will recommend. Just using your own argument here. I still disagree with the fact that the seals are suffering any more under steady state RPM than they do at any other dynamic of engine operation. Completely disagree with it. You are still missing the point so let's simplify this. Take two wankle engines , engines only and run one consistently at 3k rpms for 10 days. Take the other and vary the rpms between 2500 and 3500 averaging 3k for 10 days. Now, and here is what you are missing, now take those engines and put them back in a car (or not whatever) and run them under daily driving conditions. Run them from 0-9k and so on etc and let's see which one performs better. My guess is that the one that ran for 10 days at 3k will have developed a "sweet spot" from constant wear and be a little off on the clearances outside 3k. The one that varied rpms will not have developed this wear zone. That's all I'm trying to state. |
Understood.
So what part of the engine do you think would show this "sweet spot" for 3k rpm? What about the engine, physically, wears at that RPM (range) and not another RPM range? Obviously the 3k was an example, so pick any RPM you want that is >500. What about the engine can possibly wear at one RPM and not wear at another RPM? |
The carbon accumulation comes from sources; oil and gasoline combustion.
Now I know it's for a very short burst so to speak, and I know the increased pressures created at WOT are behind the theory, but a high rpm, WOT run increases both oil injected and gasoline. Not sure about this but I think it's true the ECU decreases the A/F ratio during this kind of run. The two of which combine to produce more carbon. Especially oil injection. It's not a stretch to conclude that keeping fresh plugs, air filter, wires and coils would go a long way to limiting carbon build up. But this redlining so often puts additional stress on this engine. It would be very useful if Mazda would simply publish their findings on the topic. They don't need to recommend anything. Just simply publish what their experimentation has revealed. And to be sure they know exactly what the best thing to do is. |
Yes, as you go higher in the RPM at WOT, the ECU does shift more and more to the rich side. However, the compression is also increasing (we gain compression the faster the engine spins, hence the RPM correction chart for compression tests, and being able to run our engine at 9,000rpm without any apex seals, where lower RPM without apex seals will die.
Plus, gasoline acts differently at different combustion temperatures. Take a bit of gas (probably from your lawnmower's refill supply), pour it into a glass jar. Not much, maybe half a cup. Light it. As it burns off, watch the carbon buildup on the inside of the glass and especially around the rim. That is really low temp burn off. The hotter gasoline burns, the less carbon deposits are left behind. |
First, I'm not arguing for or against what you posted....and I'm not an expert on this topic...however I do recall from chemistry that a "perfect" hydrocarbon combustion produces two by products...water vapor and carbon dioxide.
I also recall the ideal mass ratio for that combustion is about 15:1. That is 15 mass units of air to 1 mass unit of the hydrocarbon (gasoline of course being the hydrocarbon in this instance). I don't recall if the air was to be pure O2 or atmospheric, not that it matters other than other compounds result from combustion....which would contribute to requiring more air, or purely O2 if that's the case. So then, having said that, an A/F ratio outside those parameters is going to produce less than perfect combustion with the other byproducts being carbon and carbon monoxide. This would lead one to believe that increasing A/F beyond that 15:1 ideal results in unwanted results from the chemical reaction. |
Yes, there is an impact of AFR on emissions. At a fundamental level, the more carbon leaving in the exhaust, the less carbon remaining in the engine.
http://www.planetcampbell.us/AFR_Emissions_Graph.jpg However, keep in mind the effects of the internal heat, the ability of the carbon to actually adhere to the surfaces, etc... Just because more carbon is being created does not mean that that carbon is being deposited on the internal surfaces. It could also be getting deposited on the interior length of the exhaust system. I admit I don't really know enough to take it further down the chemistry aspect. |
Interesting topic and discussion....and I'd have to crack the books to really take it much further. And for sure there was much more carbon residue on my exhaust tips when I drove the RX8 aggressively, as is there on the speed 3 I drive now. It suffers from another buildup problem that I'm afraid driving it hard only results in additional deposits.
Someone with Mazda contacts might want to get in touch with them to get information on this topic. Some may have already and I've not found it. |
Yes. I was actually about to post "I get more soot on my back bumper from high RPM driving than low cruising", but then realized I can't draw that correlation to the combustion dynamics, since I am quite simply using more fuel, so more soot will be present regardless.
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Originally Posted by RIWWP
(Post 4137374)
Understood.
So what part of the engine do you think would show this "sweet spot" for 3k rpm? What about the engine, physically, wears at that RPM (range) and not another RPM range? Obviously the 3k was an example, so pick any RPM you want that is >500. What about the engine can possibly wear at one RPM and not wear at another RPM? I'm just trying to make the point to change up the rpms every now and then to prevent any issues with keeping it the same rpm for an extended time such a a long cruise control. |
Agree, changing up RPM does help, when looked at over the life of the car. For a 8,330 mile drive around the country, cruise control is just fine, does not cause any actual harm, improves mileage, assists with protection from speeding citations, and other generally good stuff.
There is no harm from using cruise control, on any engine. |
Also consider impurities in the air in your build up. LA vs. Canadian countryside for example... wonder which has cleaner air...
Elevation, humidity, air temperature etc... Remember carbon deposits are just that, carbon. This means it will burn, it's just a matter of how high the melting point and boiling points are. |
Originally Posted by RIWWP
(Post 4137424)
Agree, changing up RPM does help, when looked at over the life of the car. For a 8,330 mile drive around the country, cruise control is just fine, does not cause any actual harm, improves mileage, assists with protection from speeding citations, and other generally good stuff.
There is no harm from using cruise control, on any engine. |
Oh also. Some new car manuals do state that both highway speeds and cruise control should be avoided with new car purchases for the first xx miles.
I think these are few and far between these days. |
Yes, the typical breakin period. I still believe that this always was a matter of making sure that the various flexible bits of the engine see all ranges of operation before the factory treatments wear off, so they don't go 20k before first seeing something more extreme and take a shock.
More and more manufacturers are backing away from a "break-in period" for their engines, because it matters less and less with modern engines. |
Originally Posted by Are-Ex-Eight
(Post 4137104)
DO NOT PREMIX a series II
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Sorry to the OP....
Damn, I best not let the engine sit at idol at all those traffic lights I sit at for hours on end. I'd hate to develop a sweet spot at 1K rpm. :) |
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