They are related, but not necessarily synonymous.
I guess it just depends on how explicit you want to take the definition. Saying that they are synonymous, to me, is a fair description of it, but if you want to split hairs all day long I will agree with you that the definition doesn't exactly fit.
Not side-stepping here, just agreeing with you.My previous statement:
Volumetric efficiency and HP/L are essentially one in the same - you are basically just looking at efficiency from a different unit of measure. Note the use of the word essentially and basically. I understand and agree with your statement here: You can increase VE and not necessarily increase or decrease HP/L. You're leaving out necessary variables, and to say one denotes the other is a fallacy. All other parameters staying the same, increasing VE on an engine will always improve the power output. It is no different than comparing engine operation at half throttle vs. full throttle. If VE and HP/L were synonymous, increasing the timing would effect them both equally. VE does not change significantly with a bump in ignition timing, it does however change the thermal efficiency and HP/L significantly. This really goes back to the argument of whether the word synonymous is the best term to use. VE is a cause, HP/L is an effect. Timing advance is a cause, and it will affect HP/L. VE is a cause, and it will affect HP/L. Your logic stating that if VE and HP/L are synonymous that timing would affect them both equally is flawed. VE and HP/L are not both effects. VE and timing advance will both strongly influence HP/L: that's the logic you should comparitively analyze. As you stated, timing advance doesn't affect VE that much at all, however, you are limited by how much timing advance you can use with a given fuel octane and in this comparison of engines, it is presumed that both engines in stock form with stock ECU programs will be running a timing advance that offers a similar balance of power and knock resistance. In this case, the timing advance argument doesn't carry as much weight when comparing these two engines: it is presumed that although they may not be running the same exact timing advance, it will be as much timing advance as that particular engine will support with its given compression ratio and fuel octane: generate peak cylinder pressure at 14^ ATDC to provide the best conversion of pressure into mechanical torque, which will require different timing advance for the different compression ratios that these engines use. There are certainly many other variables within the engine that should be considered as well but it isn't like we are comparing a GSX-R engine to a 13B rotary: the VG and VQ have a lot of similarites. Again, the issue is you're leaving out variables, saying "all things being equal these are equal" and that's an oversimplification. A rarity for you, unless you're caught making some ridiculous statement and you need to fabricate a cute bit of logic to side step it. I didn't exhaustively state all of the variables as I was making a generalized statement about two very similar engines. I'm not dodging the reality of the variables you are talking about - I agree that they are there - we disagree on how much those other variables weigh into the generalized comparison I am making though - your personal jab is unjustified, BTW. VE and HP/L are related, but are not synonymous anymore than VE and TE or TE and HP/L are synonymous. Yes, they are related, and yet they all denote fundamentally different measurements of "efficiency" (some more valid than others). This goes back to my first response in this post. I really am not interested in debating the application of the word "synonymous" to our discussion when it appears that we both understand the limitations of its use in this discussion. It appears that we both agree that they are related, so I'll leave it at that. VE is nothing more or less than the amount of actual displacement relative to the volume of the engine. HP/L is horsepower per liter, or: VE = La / Ld
HP/L = HP / Ld Now you're claiming they are equal, so we can simplify to say Horsepower = Displacement. That's not what I am saying, no. I am saying that horsepower per litre has a lot to do with volumetric efficiency. FWIW: NASCAR has a device called a restrictor plate which goes between the carb and the intake manifold and it is there to reduce the VE of the engine. They know that by reducing the VE on a given engine, it will reduce the total power achievable by that engine and slow the cars down. In this post:
[ http://twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1827362 ] I note that it is a generalized method of looking at the performance of a given engine compared to another, but that one could go even further with the analysis. Although I didnt' state it explicitly, I am aware of the limitations with this approach just as you appear to be, but I dont think you are giving ample credit to the similarities of these two engines. The problem with that is readily evident - you've left off all the minutia that make engine development an engineering field. This is a pretty fundamental flaw in reasoning, and I don't really think you believe this so much as you want to shuck and jive enough to try to prove yourself correct, with an incorrect thesis - a hobby you practice on ttnet to no small degree. I'm not taking anything away from what actually goes on in engine development - those guys are going to do what they do regardless of what I say here. Perhaps you have interpreted the simplifications I have made as being all I think there is to it, which isn't the case. These two engines share a good bit of common design elements and to me, it isn't unfair or completely off-base to make a statement about how VE is playing a significant role in the differences we see. The VQ35 does make more power per litre than the VG30DE does as well as more overall power given that it has an additional 0.5L of displacement. Why does the VQ35 make more power per litre than the VG30? My suspicion is that it mostly due to the differences in the VE of the engines given that there are so many other similarities in their design. This is and has been really my only point. I was actually hoping that you would bring some evidence to the table to either confirm or refute my statement.....
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