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That is interesting about the knock sensors. Are there aftermarket "wideband" knock sensors available for the plethora of aftermarket rotating assemblies?
there are all kinds of gadgets and ways to use intuition to determine if an engine would be safe.
For dramatic example, If you have done a thousand or hundred thousands of tests on the same exact engine type, of varying displacement disregarding reliability, you would find a wide range of different ways of producing torque and monitoring the engine as these are all attempts to monitor something, whether it be knock timing pressure duty cycle, oil pressure. Our attempts to monitor and control torque output include how well we interpret the data among what we collect.
OK, well something is off. I'm overcalculating torque on the low end. The thick blue line is calculated HP, and the thick green line is calculated TQ. Thin red line is air flow in CFM, thin gray line is HP based off of pure air and gas converted to energy in a loss-less system, thin yellow line is TQ calculated off the gray "perfect" HP line. Once it hits 3600 RPM, it actually looks reasonable
Thanks for the link. They even called it a wideband knock sensor. That's pretty cool, really. The technology available to us these days is fascinating... as I type this on a phone that fits in my pocket and has more technology in it than what we landed on the moon with (arguably, or whatever).
But we can data log mass airflow, right? And this information could be graphed to the same scale as a dyno, right? Like a cfm vs rpm plot overlayed over the hp vs rpm dyno graph.
PS. I'm talking about actual logged data, not algorithm predictions. For the cfm vs hp vs rpm graph.
Last edited by DavidBoren; 10-28-2015 at 10:07 PM.
Thanks for the link. They even called it a wideband knock sensor. That's pretty cool, really. The technology available to us these days is fascinating... as I type this on a phone that fits in my pocket and has more technology in it than what we landed on the moon with (arguably, or whatever). But we can data log mass airflow, right? And this information could be graphed to the same scale as a dyno, right? Like a cfm vs rpm plot overlayed over the hp vs rpm dyno graph. PS. I'm talking about actual logged data, not algorithm predictions. For the cfm vs hp vs rpm graph.
I'm trying to get some airflow vs RPM logs. I can't put them on an actual dyno graph, because I don't have the data points, just the print out. But I'll see if I can find where I logged air vs RPM on a continuous run past 7k.
The motor peaked at 6800, so if airflow peaked then also, it would prove the point. Simply using VE x cylinder volume x RPM looks like air continues to increase past peak.
That kit looks neat. Will it integrate with my factory PCM or would it run like an AFR gauge, where you have to monitor it?
They were saying that a lot of modern ecu's have the capacity to use it, so I think you could replace your existing sensor with a wideband one. Their, that specific company's, standalone ecu has the capacity to tune it by crank degree, so it only listens when knock is probable, to help filter out white noise. I wonder if the Holley Dominator has **** like this.
Thanks for the link. They even called it a wideband knock sensor. That's pretty cool, really. The technology available to us these days is fascinating... as I type this on a phone that fits in my pocket and has more technology in it than what we landed on the moon with (arguably, or whatever).
After you asked "do they make a wideband knock sensor?" I internet searched "wideband knock sensor" and posted the first link to the first one I found. Essentially my point was more towards the function/use/availability of "fancy tech" to monitor our engines; whether they are useful or not is partially up to our ability to interpret data, implement the tech properly, and see through fluff.
But we can data log mass airflow, right?
That is what a MAF sensor does. Record your maf voltage and it gives you mass flow data. Make an engine mod and compare voltage logs (over time) to determine if the engine is flowing more air (potentially making more power). Keep in mind there are situations where tuning adjustments need to be made to take advantage of the changes, so just because you see an increase or decrease may or may not indicate a power change at the wheels (you would want a dynometer to back up findings)
The motor peaked at 6800, so if airflow peaked then also, it would prove the point. Simply using VE x cylinder volume x RPM looks like air continues to increase past peak.
How are you finding a decrease in airflow total mass after a peak horsepower is taken? Are you using the standard equation cidxrpm/3456 = CFM?
355x6000/3456 = 616cfm
355x7000/3456 = larger number
355x8000/3456 = even larger number
355x9000/3456 = even larger, larger number
Airflow (power output) peak keeps increasing because VE stays at 100% and RPM keeps going up.
If you are working with actual maf voltage data, keep in mind the voltage curve is parabolic, the closer you get to the edge of the voltage cap (around 5volts) the less resolution available (a small change to voltage equates more mass of airflow near the end of the voltage curve)
How are you finding a decrease in airflow total mass after a peak horsepower is taken? Are you using the standard equation cidxrpm/3456 = CFM?
355x6000/3456 = 616cfm
355x7000/3456 = larger number
355x8000/3456 = even larger number
355x9000/3456 = even larger, larger number
Airflow (power output) peak keeps increasing because VE stays at 100% and RPM keeps going up.
If you are working with actual maf voltage data, keep in mind the voltage curve is parabolic, the closer you get to the edge of the voltage cap (around 5volts) the less resolution available (a small change to voltage equates more mass of airflow near the end of the voltage curve)
See, that's the problem I keep running into. I didn't find that. I had originally thought peak HP was peak airflow, but it doesn't seem to play out. In an earlier post, I thought you sort of said the same thing - that peak HP is simply peak airflow. So, I have NOT been able to see where peak HP = peak airflow.
Originally Posted by Kingtal0n
The power peaks when the mass of air per unit time peaks.
I've used the CID x RPM/3456 formula, air keeps increasing
I've used VE x cylinder volume x RPM/4 (since there or 2 intake strokes per revolution out of 8 cylinders), air keeps increasing. I converted everything to CFM to specifically measure airflow per unit time
I wanted to see if the MAF logged air would show a peak, but unfortunately, I don't have any logs where I go past 6750. I thought I had one going to 7K, but it didn't save. But the airflow is on a steep enough curve that it looks like it would be still increasing past peak.
That was when I started looking at internal resistance as a potential culprit
It sucks, because we all know that there are at least a couple people on this forum who have this information. I'm not implying they are intentionally withholding the data, just unaware that we are looking for it.
For anyone reading this that has a date with the dyno, please record your air mass readings and try pull to 7500rpms, if you can. Please post your results in here.
I wanted to see if the MAF logged air would show a peak, but unfortunately, I don't have any logs where I go past 6750. I thought I had one going to 7K, but it didn't save. But the airflow is on a steep enough curve that it looks like it would be still increasing past peak.
That was when I started looking at internal resistance as a potential culprit
This might be of interest to you in comparing theoretical to real world. The only thing that might throw you off on this sheet is that the carburetor was about 50-100 CFM too small for this engine. If you notice, the manifold pressure gives that away as it gets past the torque peak. With a properly sized carburetor, this engine consumes about 20 more CFM at torque peak and about 50 more CFM at peak HP.
403 cubic inches. This engine achieved 1.75 Hp per CID.
Thank you speedtrigger! Although this is exactly what I was looking for, it clearly shows that the airflow continues to climb after peak hp, which takes a big, healthy dump right on our theory of peak horsepower occurring at peak airflow. Hmm...
This might be of interest to you in comparing theoretical to real world. The only thing that might throw you off on this sheet is that the carburetor was about 50-100 CFM too small for this engine. If you notice, the manifold pressure gives that away as it gets past the torque peak. With a properly sized carburetor, this engine consumes about 20 more CFM at torque peak and about 50 more CFM at peak HP.
403 cubic inches. This engine achieved 1.75 Hp per CID.
Thank you, Speedtigger!!! That was the information I was hoping to find in my logs somewhere. And that is what I'm seeing in calculations. Air and fuel continue to increase past peak power, but the power output drops, so it's something else. That's when I got back to the G-forces.
And in the name of keeping this somewhat scientific, this being your peer review process, the 0.8 multiplier in the piston/rod peak force equation... where and how was this number derived?
OK, I redid the thing by hand and found the 0.8 factor. It was 2Pi/8 or Pi/4. When I first did the calculation, I assumed linear by mistake. I realized I needed a 2xPi/8, and quick head-math (3.2/4=0.8) I threw 0.8 in there as a placeholder. Then, I got distracted and forgot to go back and fix it. I corrected it, but it made very little difference to the estimated curves. Less than 1%.
So, question for you - does friction increase or decrease with rotational speed? I know static friction is less than kinetic friction, but once it gets moving, does it stay constant? Does the oil thinning with heat reduce the drag? I can almost argue either point of view in my head. Help?
Friction increases with load. Load increases with engine speed.
The pistons and connecting rods are reciprocating. Valvetrain is reciprocating. If something is moving in one direction and you have to stop it and accelerate it in the other direction, that takes energy. The faster it is traveling and the more it weighs, the more energy it takes.
The power it takes for the engine to pump the air it needs increases with rpm.
The power it takes to run the oil pump increases with RPM. The power it takes to run the water pump increases with RPM. Oil windage deflecting off of the rotating assemble robs power and increases with RPM.
The volumetric efficiency of the engine decreases after peak torque.
Those are your players.
Last edited by speedtigger; 10-29-2015 at 12:48 PM.
The volumetric efficiency of the engine decreases after peak torque.
This is what I keep coming back to. It doesn't matter that air mass continues to climb after peak torque, because the volumetric efficiency is decreasing. At some point, probably right around peak power, the VE versus air mass fails to be capable of producing power.
Say your engine achieves 120% VE @ peak torque, and makes 500rwtq. Now let's say that it makes 400rwtq @ 100% VE... this will make sense in a minute.
Same scenario, now air mass continues to climb after peak torque, even though VE is falling.The engine continues to make power until the volumetric efficiency has dropped far enough that no matter how much more air mass you add, the engine is incapable of efficiently using any more air. Say your peak power is 600rwhp at this point.
As long as the engine is going, anything more than idle, the VE isn't going to fall below 100%, so after the power production peaks, it will fall off until you pretty much stabilize at whatever power your combination makes @ 100% VE, in this example 400rwtq, which let's say is 500rwhp.
Obviously, you would need one hell of a valvetrain to be able to run the dyno to a high enough rpm for the power curve to stabilize after peak power. On an engine that peaks around 6-6500rpms, the point of stabilizing is probably close to 9-10k.
That's my theory, at least. In the real world, there may never be a point of stabilization after peak power because of friction increasing with rpms. But the theory that volumetric efficiency will only fall back to 100% after peak torque, and the power will only fall back to whatever your combination makes at 100% VE, would actually account for the loss of power regardless of increasing air mass.
And that would imply that the number one contributor to power production is volumetric efficiency. Which actually back up a personal belief of mine, that power is a derivative of efficiency.
This is what I keep coming back to. It doesn't matter that air mass continues to climb after peak torque, because the volumetric efficiency is decreasing. At some point, probably right around peak power, the VE versus air mass fails to be capable of producing power.
Say your engine achieves 120% VE @ peak torque, and makes 500rwtq. Now let's say that it makes 400rwtq @ 100% VE... this will make sense in a minute.
Same scenario, now air mass continues to climb after peak torque, even though VE is falling.The engine continues to make power until the volumetric efficiency has dropped far enough that no matter how much more air mass you add, the engine is incapable of efficiently using any more air. Say your peak power is 600rwhp at this point.
As long as the engine is going, anything more than idle, the VE isn't going to fall below 100%, so after the power production peaks, it will fall off until you pretty much stabilize at whatever power your combination makes @ 100% VE, in this example 400rwtq, which let's say is 500rwhp.
Obviously, you would need one hell of a valvetrain to be able to run the dyno to a high enough rpm for the power curve to stabilize after peak power. On an engine that peaks around 6-6500rpms, the point of stabilizing is probably close to 9-10k.
That's my theory, at least. In the real world, there may never be a point of stabilization after peak power because of friction increasing with rpms. But the theory that volumetric efficiency will only fall back to 100% after peak torque, and the power will only fall back to whatever your combination makes at 100% VE, would actually account for the loss of power regardless of increasing air mass.
David. You picked that one thing out in that post and ignored all of the other stuff that explains the dynamic. Go back and read the post again. That whole post was to show you why the engine stops increasing in power after a certain point. It takes power to spin the engine. The higher the RPM, the more power it takes just to spin the engine. Friction and pumping losses use up the power before you can use it.
Throw a long block on an engine stand and put a hand crank on the snout of the crankshaft and get to spinning the engine. Tell me how many RPM you can manage. Now try to spin that thing 7000 RPM and let me know how you do.
10-28-2015, 05:52 PM
