red_stapler said:500cc / cyl is about optimal for combustion FWIW.
How about 500cc spread across 8 cylinders?
red_stapler said:500cc / cyl is about optimal for combustion FWIW.
How about 500cc spread across 8 cylinders?
red_stapler said:500cc / cyl is about optimal for combustion FWIW.
I tried plugging 90deg V engines into the game Automation, and all else being equal it seemed to think that the V6 would be lighter and make more power due to a higher knock threshold. V8 would be much smoother though.
I thought knock threshold was down to bore diameter and combustion chamber shape, which also go hand in hand - an undersquare engine will have a less flat combustion chamber than oversquare, for the same compression ratio.
One engineer who spent a lot of time studying detonation preferred to keep bore diameter under 83mm in Hondas because the small gains in displacement and breathing were lost in reduced detonaton resistance.
This may have already been discussed, I haven’t read the whole thread, but wasn’t the last 265 V8 built in 1956? I know the ‘57 models were already 283. Unless you’ve got a ‘55 or ‘56 Chevy and are trying to stay all original, I’d avoid the 265 at all costs. The first ones had several shortcomings.
ProDarwin said:Streetwiseguy said:There is something to be said for the larger valves of the 6, but it is more than offset by the volume available through the extra two valves.
I know nothing about the GM engines discussed, but in a theoretical sense with the same stroke, the available valve area would be the same.
The V8 would have more ring contact area (friction) and more cylinder wall area to lose heat to (bad for efficiency, but good for max power).
This. Years ago, when print media was king, Kevin Cameron would write wonderful technical columns in Cycle World. This is exactly how he answered the question about why Harley Davidson V twins will win any battle of MPG’s against similar sized machines. It isn’t uncommon for a fully dressed HD to reach 55 to 60 MPG. No 4 cylinder motorcycle of that size can even come close. Even when riden just as leisurely.
The 4.3L V8 was used on and off all the way up through the late 90s in varying flavors.
The early 50s version were the 265 (3.875 bore)
The 70s version was the 262 (3.671 bore). It wasn't used much, but it was a smogtastic way to get a V8 in a Monza, Vega, or Ventura.
The 90s version (L99 baby LT1) was the 263 (3.74 bore)
A 401 CJ said:ProDarwin said:Streetwiseguy said:There is something to be said for the larger valves of the 6, but it is more than offset by the volume available through the extra two valves.
I know nothing about the GM engines discussed, but in a theoretical sense with the same stroke, the available valve area would be the same.
The V8 would have more ring contact area (friction) and more cylinder wall area to lose heat to (bad for efficiency, but good for max power).
This. Years ago, when print media was king, Kevin Cameron would write wonderful technical columns in Cycle World. This is exactly how he answered the question about why Harley Davidson V twins will win any battle of MPG’s against similar sized machines. It isn’t uncommon for a fully dressed HD to reach 55 to 60 MPG. No 4 cylinder motorcycle of that size can even come close. Even when riden just as leisurely.
This is an excellent example of the lack of clarity to the original question. Sure, a long stroke lazy twin gets better mileage, but the shirt stroke four cylinder will be faster.
What is the better engine? Depends on the intended use.
In reply to barefootskater :
Its a 4 cyl normie...
red_stapler said:500cc / cyl is about optimal for combustion FWIW.
Yes, this is why the largest and most efficient tanker engine is 3620 cylinders. https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C :)
Note that overall efficiency on those engines is nuts. That one achieves 50% thermal efficiency, which is significantly higher than most (all?) automotive engines.
^ glad it's a diesel. I'd hate to change 3000 spark plugs.
ProDarwin said:red_stapler said:500cc / cyl is about optimal for combustion FWIW.
Yes, this is why the largest and most efficient tanker engine is 3620 cylinders. https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C :)
Note that overall efficiency on those engines is nuts. That one achieves 50% thermal efficiency, which is significantly higher than most (all?) automotive engines.
Here's what I was thinking of:
A 401 CJ said:ProDarwin said:Streetwiseguy said:There is something to be said for the larger valves of the 6, but it is more than offset by the volume available through the extra two valves.
I know nothing about the GM engines discussed, but in a theoretical sense with the same stroke, the available valve area would be the same.
The V8 would have more ring contact area (friction) and more cylinder wall area to lose heat to (bad for efficiency, but good for max power).
This. Years ago, when print media was king, Kevin Cameron would write wonderful technical columns in Cycle World. This is exactly how he answered the question about why Harley Davidson V twins will win any battle of MPG’s against similar sized machines. It isn’t uncommon for a fully dressed HD to reach 55 to 60 MPG. No 4 cylinder motorcycle of that size can even come close. Even when riden just as leisurely.
I'd like to dive into this a bit more.
Re: valve area... let's say you have the two engines we are discussing side by side. The V8 with the smaller bore and the V6 with the bigger bore. Let's also assume that the V8 has the same total valve area (proporotionally smaller valves, but more of them) The V8 will still run out of breath sooner due to valve shrouding. I'll draw an exaggerated picture to demonstrate why.
Re: heat/surface area. I wont say you're wrong, but this flies in the face of everything I've learned. Shedding heat kills power. You want to keep all the heat IN the cylinder where it can help to maintain cylinder pressure. This is why aluminum heads need more compression to make the same power as iron heads. I don't understand why cooler combustion would make more power. Cooler, denser intake charge, sure.... but not combustion. Making power means keeping things as hot as possible without damaging things.
Here is the exaggerated picture. On the V8 you see the area where the blue arrow points. That circumferential area is smaller on a small bore because the sides of the cylinder curve in faster. Even if they have the same displacement and the same total valve area across all cylinders, the smaller bore will actually flow less. The problem is, even if you increase valve size in the smaller bore, you can easily make things worse. You add flow area, but put that flow area even closer to the walls. Increasing bore size while keeping the same valve area often increases net flow because you're pulling the walls away from the valve.
All other things being equal (total valve area, etc) the V6 will make more power - if for no other reason than it can flow more net air for a given valve total area than the small bore V8.
red_stapler said:Here's what I was thinking of:
I appreciate their attempt in the article, but then they compared apples and oranges. A lumpy-cammed race-designed 6.2L with a sky-high torque peak vs a twin turbo 4.0L isn't really a viable comparison. I would want to see that article with both of those engines naturally aspirated. You can tweak turbos to provide boost wherever you want, and a twin turbo can cover the whole RPM range.
All Mercedes did was replace displacement with forced induction. That article is more about how turbos can overcome the reduced flow of smaller bores
ProDarwin said:red_stapler said:500cc / cyl is about optimal for combustion FWIW.
Yes, this is why the largest and most efficient tanker engine is 3620 cylinders. https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C :)
Note that overall efficiency on those engines is nuts. That one achieves 50% thermal efficiency, which is significantly higher than most (all?) automotive engines.
Different priorities.
For automotive engines, an undersquare 500cc/cyl is ideal for the 10-25hp idling around they spend 99% of their life at.
Obviously, a cargo ship has somewhat different priorities
Pete. (l33t FS) said:ProDarwin said:red_stapler said:500cc / cyl is about optimal for combustion FWIW.
Yes, this is why the largest and most efficient tanker engine is 3620 cylinders. https://en.wikipedia.org/wiki/W%C3%A4rtsil%C3%A4-Sulzer_RTA96-C :)
Note that overall efficiency on those engines is nuts. That one achieves 50% thermal efficiency, which is significantly higher than most (all?) automotive engines.
Different priorities.
For automotive engines, an undersquare 500cc/cyl is ideal for the 10-25hp idling around they spend 99% of their life at.
Obviously, a cargo ship has somewhat different priorities
Different fuel types too.
Curtis73 (Forum Supporter) said:red_stapler said:Here's what I was thinking of:
I appreciate their attempt in the article, but then they compared apples and oranges. A lumpy-cammed race-designed 6.2L with a sky-high torque peak vs a twin turbo 4.0L isn't really a viable comparison. I would want to see that article with both of those engines naturally aspirated. You can tweak turbos to provide boost wherever you want, and a twin turbo can cover the whole RPM range.
All Mercedes did was replace displacement with forced induction. That article is more about how turbos can overcome the reduced flow of smaller bores
Yes, that article is comparing all kinds of variables, and certainly not combustion efficiency. Thermal efficiency is discussed most, but packaging, power curve, etc. are all covered there.
I think this is the most important text though:
500-cc-displacement intervals align nicely with existing global taxation statutes
Note how all the brands listed are European brands.
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