It's sorta hard to follow a post like that with my own ill-conceived ideas but I'll back up and take a swing at a point you quoted me on, arnie, and see if this makes sense to you:

Well, no. 100% VE is defined as what's trapped inside the cylinder as the intake valve closes being exactly equal to the theoretical volume of the cylinder. As the intake valve snaps shut let's say you have achieved exactly 100% VE- not more, not less. 100% of the cylinder's theoretical volume is then trapped in the cylinder but the piston is already XX degrees up the bore at the point the intake valve closes. From that point compression begins- the exact same point from which DCR is calculated. i.e. at 100% VE inside the cylinder the pure and exact compression number defined by the engine's calculated DCR is achieved.

That's the thinking that was behind that response. And if you buy that then I also have a bridge in Brooklyn I could sell you cheap. Seriously, I think I'm probably right about that. And IF I'm right about that then you'll see why I say that you would need something well over 100% VE to get all the way up to the SCR number. Like a supercharger, probably. The rest of my thinking kinda flows from there.

Everything else, I'm not even going to try to argue with or add to SStrokerAce's post.

 

Notice the change... with that you have it right.

100% VE basically takes "boost" in the form of intake pulse tuning to achive so yeah you do need something to get there.

Bret

 

I'm getting a little cross-talk from a previous post.

Is Effective Compression calculated using SCR and VE (figured after the intake valve closes)?

 

Wouldn't SCR after the valve closes be DCR?

Effecitive compression is hard to know without dyno tests on the motor at multiple RPM points so don't worry about it because you really can't know what it is for a motor without that.

Bret

 

Bret, as you apparently have taken the time to read my 'dribble', you deserve at least, the same consideration. I have thus studied each sentence of your post, with the following comments...

If 'cylinder pressure' and 'BMEP' are different, I can accept that. I'm concerned with what (pressure) generates the most torque. (That IS the focus of this thread.) Torque is generated from pressure exerted on the piston."in street motors it's less likely to occur at peak TQ where VE is highest but at lower RPM..." Even with OTHER areas of concern, it does not diminish the critical area at peak torque. My interpretation of 'max VE/peak torque/most efficient' has me envisoning the 'air pump' with the ignited air/fuel charge exerting the most push (pressure) possible on the piston. This is what is known as peak torque generation. Yes, as RPM implies, it has a time element. However, there is still enuf time for the ignited charge to generate the most pressure, which translates into peak torque. The higher the pressure, the greater the need for octane. I trust you do not believe this is true.As noted above, this thread is dealing with the pressure required to generate torque, the focus of this thread. Reardless, by stating "Max Cylinder Pressure does follow the same trend as BMEP but it's also related to the STATIC Compression Ratio", are you stating, octane requirement does not increase with an INCREASE of torque at agiven RPM?Good read. BMEP is tied to torque. Octane is tied to 'max cylinder pressure'. Is this tied to my arguement? My arguement? The relativeness of DCR with octane limited fuel, in engines generating DIFFERENT levels of torque at the same RPM, but without all the variables noted just above. In my case, doesn't BOTH BMEP and 'Max Cyl. Pressure change, as the torque generated changes?Hmmm, I wonder bout that, as well as question that.
I agree.Yes, but have no part in my arguement, in this thread. By intent, to make it easier to focus on the real issue of this thread, all variables were kept out of it. Although common to street engines, these variables mask the characteristic of pressure at peak torque. Without these variables to cloud my point, it is easier to realize, efficiency is greatest at peak torque, and the possibility of detonation is also greatest at peak torque. Now if we STILL disagree on these basic points, I do not see the purpose for further posting on this subject, by either of us. In my arguement, the VE is NOT the same, and the torque generated is NOT the same.OK, let's use that engine as an example, and compare it to if/when it had a higher duration cam that generated a lower DCR. Using the torque curve as reference, pick a common RPM point to the two engines, that has the greatest difference in torque readings. Would Mindgame need to make any allowances for any octane deficiency, with the lower DCR/higher duration cam, at the point?

 

Right from everything I have seen it's not true for BMEP, but for Max Pressure seen in the cylinder.

correct.... BMEP is directly related to TQ output, you can have the same TQ per L and the same BMEP but different Max Pressures in the cylinder.

Problem is you can't take out these variables and only judge this situation based on one of them... especially the intake port temps, you have to work with what you are given in terms of changing port temps relative to velocity and RPM. That's what makes engines fun EVERYTHING is related to EVERYTHING else.

Total motor efficentcy is at peak TQ but not always every component of efficentcy. VE can and does happen after peak TQ in a lot of race motors.

All I can say is that detonation CAN occur at peak TQ but it does not always... if it doesn't happen at peak TQ but does other places in the TQ curve how do you explain that? I've seen it lots of times.

In your situation where VE and TQ are not the same WTF are we even talking about here? I'm talking about the same DCR with different SCR and different effective RPM bands which is exactly what you were talking about in another post... if your VE and TQ numbers are lower, something is wrong in the motor combination and it's most likely sonic choke in the head and intake port causing the lower VE and TQ numbers... I started with a situation where the TQ numbers with the smaller cam were pushing the limits of detonation, and then threw more cam and SCR at it. If you want to throw more variables in there how can we know what is going on in terms of octane requirement and DCR? You can't. Going with lower VE and TQ per L is going to lower the BMEP and usually the Max Pressure in the cylinders and not give us accurate results of what we are looking for.

As for Mindgames example.... if you kept the same SCR and added cam that made the IVC point later and lowered DCR you would have less detonation... so you wouldn't have to worry about it. The motor would have lower BMEP and maybe equal Max Pressures in the cylinder. I can't just take a point on the curve, but comment on the whole curve because as I said detonation doesn't always happen at peak TQ, but could safely say that his propensity for detonation would decrease with a lowering of the DCR. My example above was with similar DCR with only changes in the cam and the SCR, if you only change the cam then you are going to be fine because the max cylinder pressure is very dependant on the DCR/SCR to causing detonation problems.

Bret

 

Bret, I understand and am aware of other variables. The point of removing them, was to get you (and others) to focus on the crux of my argument, which isn’t altered with their removal. That being torque generated, and tendency to detonate. With other variables to cloud the real issue here, it's tougher to focus on that. Bret, have you thot about entering into politics? Is the timing (really) correct at/for all load conditions? I trust you are referring to my quote, "In my arguement, the VE is NOT the same, and the torque generated is NOT the same." Even if we approach it from the ‘angle’ you prefer, it shouldn’t really matter technically, providing the focus remains on the subject. Regardless, I thot I started this thread, and consequently, set the parameters. Somehow, I feel I’ve lost control of true focus of this thread. I figured by reading my post(s), you were aware of what (I) was talking about. :scratching head: Bret, please don’t do this to me. I trust it was unintentional.

I've become aware of a thread on another forum, that is 'advanced' in it's own rite. That thread ironically, makes reference to this very Camaro forum thread. Thus, I believe it is appropriate to make reference to THAT thread here. http://speedtalk.com/forum/viewtopic.php?t=1372 Apparently, I'm not the ‘maverick’ I thot I was.

I also believe it is important (in general) to 'think outside of the box', in regards to established or accepted facts (?) or practices. Obviously, I'm referring to various DCR sites on the net. Remember, it was that 'thinking outside of the box' that brought attention to the fact the earth was round, and not flat. Closer to home, just cuz it is a viable website, does not automatically make it accurate. Of course, that would apply to favorable or supportive websites as well, wouldn't it? In that frame of mind, each is entitled to believe what they prefer to accept.

 

Round, maybe, but not necessarily spherical, or so say some of us.

http://www.alaska.net/~clund/e_djubl...rthsociety.htm

 

Not one to pat myself on the back but since my name was brought up..... Since this whole DCR thing came up in this forum (maybe a couple of years ago) I've put together 6 LT1's and a couple of gen 1 small blocks. Using DCR as a guideline and staying in the 8.5-9.1 range, I've yet to put one together that showed any signs of detonation. These were all pump gas daily drivers that see mid 90's F in the summer.

When Chuck (PRED) worked the 15º heads for my last engine I got a chance to ask him a little more about DCR. The jist of the conversation was that DCR is nothing more than a guideline for planning a build. I was also told that the VE plays its part in the equation but that there was no exact science in all of it.

I think there's a tendency to read into things a little too much. If we sit around contemplating every nuance of how an engine works then we'll never get around to building one. A guy like me who doesn't have a means of testing theories like I'd really like to is more than happy to push the textbooks aside and pick up the wrench every once in a while. Keeps the head from exploding.

Besides that... I'm no professional but my stuff usually ends up putting down more HP/TQ than alot of guys who are. So yeah... I just patted myself on the back.

-Mindgame

 

Interesting link, Jon!