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That's because of oem gear spacing in which we are handicapped by. So it's not as simple as picking the next highest rear wheel torque number in the next gear. You must split the difference with the gear drop. As well as making sure the next gear provides more rear wheel torque on the shift.
So, knowing my 33% drop from 1st to 2nd....
7500 = 5019
7600 = 5086
7700 = 5153
So....your 7300rpm = 4885rpm, your first choice isn't bad.
There's also more to the average power calc. But it's a little controversial by some.
I was shown this "other" method by a current IHRA prostock racers. And it has proven to pick my combo up a little more (because of shift points). It's a calc that changes these averages a little.
And I prefer this "other" calc because it uses hp & tq !!
Hp is just a function of torque at a specific rpm essentially. Hp is the rate of which work is done or torque over a specified time interval. Thats why diesels usually have lower hp and higher torque and formula one cars have low torque and high hp at insane RPM's much like sport motorcycles for example. There is a formula that relates the two, and hp and torque are equal to each other at 5252RPM. Below that and torque is higher then hp and above that hp is higher then torque do to the high rate at which the crankshaft is rotating. On the contrary high rpm engines with little torque can still put a lot of torque to the wheels through taller gearing(higher numerically) that multiplies the torque and slows the rotation of the wheel. As far as creating torque the, easiest way is through a large displacement engine, which has more rotating mass and a high volume of air. You can in theory cheat this by using forced induction, and other ways of flowing more air like 4 valves per cylinder and a bunch of other advanced engine technologies. Engine efficiency is mainly a function of airflow through an engine, thats why for example a LSX engine work so well compared to LT1, the heads flow a lot of air. It is also true when comparing old 4.6 SOHC engines that lacked power because the heads flow poorly compared to the DOHC supercharged 4.6 in 2003-2004 Cobra Mustangs. To make more power you need to get air in and out faster, usually through better flowing heads and exhausts and larger valves faces, or cam duration to give it the most flow. Bumping up the timing and compression ratio also help the efficiency and as the more air you compress per unit volume the bigger bang you'll get. To make more RPM'S from an engine and increase Hp the best way is to use lighter valve train components for less rotating mass, and for pushrods using stuffer valve springs and stronger pushrods. The other thing is higher RPM motors usually have a shorter stroke and large bore, where as a low RPM diesel will likely have a larger stoke relative to the bore size.
I hate being argumentative and this is probably the last post I will make on this topic, but you have to shift where your gear splits maximize the horsepower curve, not the torque curve.
The goal is to shift at the RPM your HP on the right side of the curve (as the engine starts rolling off its power peak) meets the left side of the curve at the exact same HP figure on the way up. Shift too early and you fall way down on the next gear....shift too late and you would have the felt the car nose over a little as the power was lower past peak then where it shifted to. For example.....en engine makes say 500 HP peak.....if you shifted at 460 on the right side of the curve and the gear split put you back at 460 on the left side of the curve you nailed the optimal shiftpoint. If you shifted early at say 470 on the right side you may fall all the way back to 440 on the left and have to climb back up the curve....the trick is to ride the crest of the power curve. Shift late at say 450 on the right side of the curve and you would have slowed down some by not shifting soon enough even though it might hit 470 now on the way up (you would have felt the car lay down a little briefly).....its still best to try and split it perfectly so you feel the most constant rush of power. In manuals with varying gear spread transmissions that might mean a slightly different shiftpoint for each gear if your really splitting hairs and trying to extract the most from the combo.
Do this every gear down the 1320 and that means you maximized the most horsepower during the run which will net you your fastest trap speed and lowest ET if your able to effectively apply all that power to the ground (another topic entirely).
In the scenario LSHolic shows us I would say Darth's 7300 guess was right on or close but it depends on gear spread and converter efficiency as well.....its easy in a manual car....you just split the numbers....not many variables. If somehow shifting below 7K in that situation caused the vehicle in question to go faster, something is wrong with the car as it's accelerating down the track (something that's not being seen on the dyno in a static state test....such as not enough fuel pump to overcome the G-force).
LSHolic....what is your reasoning on why modified diesel applications with gobs of torque aren't running insane trap speeds if max torque were so important to acceleration.....you cant causally ignore that fact or the fact a motorcycle produces incredible results because it produces so many HP per liter (and minimal torque figures) and as a result flies down the racetrack due to its insane power to weight ratio.
I say it again.....Power to weight ratio is really the thing to leave this thread with if your concerned with improving your acceleration.....you can make more power or lose some weight.....or BOTH.....all of which help to achieve the nirvana/drug we refer to as acceleration.
Hello.....my name is Tony ("Hi Tony")......Im addicted to a drug called acceleration!!
Something is wrong. You know the formula. If torque is constant (and in your graph it is close) and the rpm goes up the HP has to follow. On your graph the blue line drops.
I think I found part of the issue with the modeling. I picked the 100-KPa line and ran straight across. Yesterday, I plugged in the MPVI and made 10 WOT pulls so I could get airflows. Plugged in the average airflows and here is what I got:
I still think it is calculating too much torque (blue line) on the low end, but it is pretty close to my last dyno pull from about 3600 to 7000. Below 3600 really doesn't matter anyway. HP (green line) is very close.
Again, what I'm seeing in the model is that the increase in g-forces exceeds the increased airflow at peak power. If I could find a way to express it mathematically, it would be something like:
HP = F(rpm) (F meaning function)
dHP = DAirFlow/drpm + DPistonAccel/drpm
Peak HP occurs at RPM where Dairflow/drpm + DPistonAccel/drm = 0
It could be shifted way too high of RPM. It's that torque on the high end that doesn't jibe with the horsepower. It drops a tiny bit but if I assume that's 425 at 5252 that's 425 HP. If it's approximately 450 TQ at 6,000 HP should be 514 HP and the same torque at 7000 would be ~600 HP. Plug in the numbers and see.
It could be shifted way too high of RPM. It's that torque on the high end that doesn't jibe with the horsepower. It drops a tiny bit but if I assume that's 425 at 5252 that's 425 HP. If it's approximately 450 TQ at 6,000 HP should be 514 HP and the same torque at 7000 would be ~600 HP. Plug in the numbers and see.
I guess I'm not following you. I removed the extraneous lines (that were really only there to show the change between loss-less and loss-full(?)) to help with the scaling of the calculated HP and TQ curves.
TQ is falling off pretty fast. The only reason HP continues to climb is the RPM increase.
Svede, does cleaning up the graph and posting the calcs help? If something is still messed up, tell me what RPM range.
Basically, compared to the actual dyno pull, the torque curve is flatter on the dyno. 400 pounds from 3800 to 6100, and it peaks at 417 vs 444. Nailed the HP number, though. 467 calculated vs 474 dyno.
I'm very familiar with shifting for most average hp.....it tends to look something like this in a manual car. And ultimately you end up with similar shift points when compared to the rear wheel torque method.
But, agree or disagree....rear wheel torque is what moves the car down the track. Thus is a very more accurate way to achieve proper shift points.
Personally, what's happens at the crank takes a back seat to what's happening at the wheels.
If it wasn't about tq multiplication and hp was the golden ticket, then rpm wouldn't matter as well as gearing. But...as we all know.....rpm and gearing are arguably more important than any other factor...aside from weight.
Like I said, overlay your g-meter with your torque graph profile....mirror image. And how does the g-meter correlate to the hp graph profile (when hp is peaking the graph is tapering down, just like the rear wheel tq shows you)
It's time to shift when the rear wheel torque in the next gear is greater than the one your leaving. That's what keeps the car pulling and the engine in its max acceleration zone.
And about your diesel example....what your missing is rpm. And I've said all along...I want max torque at the highest rpm my wallet can provide.
Because rpm allows more gear, more gear equals greater rear wheel torque, greater rear wheel torque equals greater acceleration...which means a quicker et.
And to throw the same comparison back at you....since its all about hp. In your world a F1 engine would rule the drag strip with its 800hp and measly 235ftlbs.
Remember Darins statement I quoted ?? Carrying the torque longer is key.
Do you notice the gradual leaning out of the engine, and with it the gradual spiking/jagged increase to the graph? This could be a sign of problems. I recommend using smoothing:0 to help diagnosis. Also, richen up the engine to see if the jaggedness goes away. You might also reduce timing.
IMO the engine started getting hot, if this is 93, and the timing was far enough forward to start giving rise to pressure spikes. If the engine has an oem head gasket it should be close to failure if you keep running it like this, otherwise, it will pit the head, deck and piston as high pressure spikes eat away at the chamber and piston. On the other hand it could just be something with the pickup or computer, or even software so that is why I suggest making these small adjustments and observing. It is a coincidence that both the a/f is leaning out and the sudden appearance of the beginnings of a jagged curve.
And about your diesel example....what your missing is rpm. And I've said all along...I want max torque at the highest rpm my wallet can provide.
.
This literally means you want max horsepower, as max horsepower is max torque at the highest rpm your wallet can provide.
In simplest terms, 2 horsepower will move an object with a given weight farther than 1 horsepower in the same amount of time. Engines do not just sit at one single number all the time though; so spending the most amount of time, "at the highest torque", "at the highest rpm" is what we are really after. In other words, most horsepower per unit time, or most weight moved the most distance in the shortest time.
If torque doesn't matter, how come a new shortbed Hemi Dodge Ram with the aerodynamics of a barn will outrun a high strung 9000 RPM screamer with no TQ Honda S2000 that has a BETTER power to weight ratio? Could it be the severe lack of low end torque made it difficult launch ?
2015 Ram hemi HP 395 TQ 410 Weight 5100 lbs per HP: 12.9 1/4:14.1
2000 S2000 HP 240 TQ 153 Weight 2750 lbs per HP: 11.5 1/4: 14.2
In simplest terms, 2 horsepower will move an object with a given weight farther than 1 horsepower in the same amount of time. Engines do not just sit at one single number all the time though; so spending the most amount of time, "at the highest torque", "at the highest rpm" is what we are really after. In other words, most horsepower per unit time, or most weight moved the most distance in the shortest time.
You just said what I'm struggling to calculate in the maths. Basically, you need to integrate. A reading is a moment in time. To know what it will do, you have to integrate over RPM and over time.
Similar to distance and velocity. Velocity is an instant in time. Distance traveled is velocity integrated over time.
Do you notice the gradual leaning out of the engine, and with it the gradual spiking/jagged increase to the graph? This could be a sign of problems. I recommend using smoothing:0 to help diagnosis. Also, richen up the engine to see if the jaggedness goes away. You might also reduce timing.
IMO the engine started getting hot, if this is 93, and the timing was far enough forward to start giving rise to pressure spikes. If the engine has an oem head gasket it should be close to failure if you keep running it like this, otherwise, it will pit the head, deck and piston as high pressure spikes eat away at the chamber and piston.
Tal0n, I very much appreciate the honest feedback. Unfortunately, it's 91 octane. CA / AZ gas sucks. I honestly thought the increased AFR at the end was just letting up on the throttle early. The jagged stuff at the top, he attributed to wheel balance, because he was not getting any KR. I'm actually only running 24 degrees of timing. That's where it made peak power. MLS head gasket. Injectors at ~70% duty cycle at 6800 rpm. ECT's stayed 197 and lower.
Now, all that said, I'm going back after getting the next round of mods done, probably mid-November, so I'll definitely look into those things while I'm there. I was actually thinking of taking it to a dynapack to bolt the hubs up and take the wheel balance out of the picture anyway. After reading your post, I'm thinking even more so.
I'm definitely going to stay out of the high end now until I get that stuff done. I can always just add fuel or cut timing myself, but I can't measure to know it helped or hurt. Since the jagged stuff doesn't start until 5500, I'm assuming it's not unsafe to drive in the low end and midrange?
In terms of practicality, there is a finite limit to the amount of cfm's any set displacement is capable of using within the rpm limitations of the LSx oiling system.
For us mere mortals, you know, hydraulic lifters and wet sump oiling, the practical rpm limit is 7k... 7500 in a darn good setup, and 8k if you're Jesus himself.
So, is there any benefits to having more cfm's than necessary for your goals? Say 500rwhp is your goal, and you want to achieve it below 7000rpms. 300cfm can support 500rwhp in a good hydraulic lifter/wet sump application.
AFR 205's are a quality piece, that flow 300cfm. 300cfm can support 370ci of displacement out to 7200rpms, or thereabouts. So, IN THEORY, afr205's SHOULD be capable of producing 500rwhp on a 6.2L before 7k. I haven't seen it happen, but I don't see why it wouldn't.
So, what is the benefits of adding bigger heads, with more cfm potential, when your goals can be met with less?
How important is port velocity vs runner volume?
Or is this an argument of peak power vs average power, and that's probably worthy of its own discussion.
To elaborate on this a bit more... It's all about the combination of parts and how well they interact with each other. THEN, once all the parts are working in concert with one another, it's a matter of how well that combination's performance meets your needs/goals/requirements.
In the name of efficiency, shouldn't you start with by defining your goals. Then select the lowest cfm's that will adequately meet your requirements. Find the smallest heads that flow your desired cfm's. Find the biggest displacement that those heads will support out to the projected redline for your application. Then you select your gears/stall/cam to make it behave how you want.
Or at least that's what makes sense to me. Granted, this assumes that you have an established power goal, and aren't just going for the most you can possibly get.
The most you can possibly get comes in the form of a superdeck block and a 4.5" crank. But that's just not available to us mere mortals, so it might as well not exist.
In terms of practicality, there is a finite limit to the amount of cfm's any set displacement is capable of using within the rpm limitations of the LSx oiling system.
For us mere mortals, you know, hydraulic lifters and wet sump oiling, the practical rpm limit is 7k... 7500 in a darn good setup, and 8k if you're Jesus himself.
So, is there any benefits to having more cfm's than necessary for your goals? Say 500rwhp is your goal, and you want to achieve it below 7000rpms. 300cfm can support 500rwhp in a good hydraulic lifter/wet sump application.
AFR 205's are a quality piece, that flow 300cfm. 300cfm can support 370ci of displacement out to 7200rpms, or thereabouts. So, IN THEORY, afr205's SHOULD be capable of producing 500rwhp on a 6.2L before 7k. I haven't seen it happen, but I don't see why it wouldn't.
So, what is the benefits of adding bigger heads, with more cfm potential, when your goals can be met with less?
How important is port velocity vs runner volume?
Or is this an argument of peak power vs average power, and that's probably worthy of its own discussion.
I mainly started the discussion, because I wanted to understand what was going on inside the motor that makes it peak when it does. It was intended to be purely academic. The discussion the happened was extremely helpful, but not what I expected at all - in a good way
Early on, I think we all agreed that peak TQ is peak cylinder fill. The problem was what corresponds to peak power?
Not peak airflow
Not peak fuel flow
So, I built a quick and dirty model in excel of the stuff I could think of in the engine that causes internal resistance. In the end, I think it is as "simple" as the work necessary to keep making the engine spin faster exceeds the work extracted by spinning faster. From the rough math, the best I can tell is that the acceleration of the pistons becomes incredibly high and becomes counter-productive.
Horsepower is basically a linear function (y=mx+b). x being its own function complicates it a bit, but y is linear.
the accelerative forces on the pistons are parabolic (y=f(x^2))
What I think I found is that the function is a derivative - in short, very close to what Tony said ("It's dynamic, not static"). You can't look at the point at which HP peaks and see anything, but if you look at the rates of change, it makes very good sense.
I'm going to start a new post to break up the train of thought, because it's going to get messy
This is going beyond the point of diminishing returns to the point of negative returns - in other words, you get less work out of the engine no matter how much more energy you add. In other words, beyond peak power, adding more energy simply makes it spin faster, but results in a LOSS of work output.
Imagine a point just below peak power, say 100-RPM lower, and another point just above peak power, say 100-RPM above peak. Now think of how much energy it takes to get from 100-RPM below peak to peak vs getting from peak to 100-RPM above peak. Intuitively, I think we can all agree "OK, it takes (edit) less energy to get from 6700 to 6800 vs getting from 6800 to 6900" The difference is that going from 6700 to 6800, the work output by the engine is still increasing, but going from 6800 to 6900, the work output of the engine is decreasing.
This is not intended to say anything about where to shift or torque at the wheels. Simply what is happening at the flywheel as an academic exercise
RPM..........6700........diff..........6800....... ..diff.........6900
CFM..........648.3.......+6.6.......654.9......... +6.8......660.7
Energy......933.6.......+9.5.......943.1.........+ 8.4......951.5
G-Forces...2309........+69........2378..........+71. ......2449
Net TQ......366.5......-4.2.........361.3.........-5.6.......355.7 Net HP......467.5......+0.3........467.8.........-0.4.......467.4
So, at peak power, the changes in internal forces that resist increases in speed are equal to the changes in energy input. The amount of energy needed to increase speed equals the resistance to increasing speed, and your net TQ is decreasing at a rate equal to RPM/5252. At its core, it's a derivative from Calculus I. Just got there the hard way.
Last edited by Darth_V8r; 10-28-2015 at 05:54 PM.
Reason: Correction in second paragraph due to being a moron
Intuitively, I think we can all agree "OK, it takes more energy to get from 6700 to 6800 vs getting from 6800 to 6900" The difference is that going from 6700 to 6800, the work output by the engine is still increasing, but going from 6800 to 6900, the work output of the engine is decreasing.
I think you have this reversed. It takes more energy to get from 68 to 69 than it does from 67 to 68. Moving from 4rpm to 5rpm takes more energy than from 2rpm to 3rpm right? Fuel economy decreases as engine RPM increases at identical cruising speeds, due to the parasitic nature of having to turn the same components faster (while still moving the same speed) This is why gearing plays such an important roll in fuel economy; you want the engine to be turning as slow as possible while you cruise at 80mph, while on the other hand, too low of an RPM will result with too much of a cylinder fill (necessary to have much more torque produced due to the lower RPM to meet the same demand for horsepower) giving rise to octane limitations (you now need to richen the air fuel ratio as the engine vacuum is decreasing to this region). Thus, keeping cylinder fill low enough to use a lean air fuel ratio while also turning the engine as slowly as possible is the goal for economy (minimizing parasitic loss due to rpm without ruining your BSFC by jacking up the air fuel ratio to keep things cool.)
Originally Posted by Darth_V8r
inside the motor that makes it peak when it does.
The power peaks when the mass of air per unit time peaks. Area under the curve has more to do with calculating how fast a vehicle will be, or how much gear you need to achieve your goal. Peak is simply peak airflow in terms of mass per unit time. We will make the largest amount of power, with the largest mass, of hot-as-possible air, that we can squeeze into the cylinder. The extra heat is energy and more energy will give you more output; the limitation here of course is octane, the unifying factor with all pump gas builds is that the fuel is poor quality, adding an element of surprise and danger to our combinations. A well thought out combination has safety features that allow for fluctuations in octane. And to add a little tid-bit, often you can push an engine "into the danger zone" on a dyno, what starts off as a couple jagged peaks can escalate into a significant spike that will give you a big fat peak number at the expense of your engine's insides.
We do not generally calculate limitation imposed by friction in any engine when consulting power output, because we already know that lighter parts, thinner oil, looser clearances all contribute and then engine has already been built by the time we arrive to this stage (the "lets make a dyno pass" stage) leaving us with only two main adjustments: air and fuel. Adjusting airflow (via boost controller or a throttle plate restriction or cam timing or runner length or other means) is adjusting power output. Peak airflow is peak power, in most if not all cases, unless there is something horribly wrong with the engine the way it was assembled or it was pushed outside of those critical parameters such as valvetrain limitations or piston speed.
Mathematically you may be able to derive such functions by using compressor wheel speed vs engine output (if the engine is on an engine dyno) or including drivetrain losses (if you have a compressor map and air temp, you can calculate mass of air moved via compressor wheel speed, take the difference from what you actually make to find how much you lost to the wheels or flywheel); however, none of that is necessary in a practical application because, again, the engine is already assembled, we have what we have, and now all thats left is to adjust for maximum output (or max economy or whatever the application calls for). I tend to look for max economy AND power, making the thin line a choice between a few extra decimals of safety in my compression ratio vs an extra MPG or two. In either case, if I want more power I just adjust my atmosphere; Everyone stuck in the "atmospheric rut" of using the natural pressure available is missing a significant chunk of useable engine output, in almost every application, regardless of whether we are economy or power focused (turbochargers tend to improve fuel economy).
In the name of efficiency, shouldn't you start with by defining your goals. Then select the lowest cfm's that will adequately meet your requirements. Find the smallest heads that flow your desired cfm's. Find the biggest displacement that those heads will support out to the projected redline for your application. Then you select your gears/stall/cam to make it behave how you want.
This is great advice for street cars. You are always looking for the smallest ports and lowest lift to get the best drivability and reliability out of your engine (street cars that care) while still maintaining your power goals. It is not uncommon to see 1200-1800 rwhp engines that achieve 28mpg in 3000lb vehicles that go hundred thousand miles with excellent street manners. There are also trade-offs between such things as exhaust size and design that can make or break a combination of any power level, as the exhaust gas is a critical component of clearing the cylinder, exerting a pull on the open exhaust valve if done right that is more powerful than the descending piston.
Tal0n, I very much appreciate the honest feedback. Unfortunately, it's 91 octane. CA / AZ gas sucks. I honestly thought the increased AFR at the end was just letting up on the throttle early. The jagged stuff at the top, he attributed to wheel balance, because he was not getting any KR. I'm actually only running 24 degrees of timing. That's where it made peak power. MLS head gasket. Injectors at ~70% duty cycle at 6800 rpm. ECT's stayed 197 and lower.
DO you have stock internals? Factory knock sensors may not work when you change your engine's internals. They are traditionally tuned to the frequency that the OEM manufacturer determined to be produced when the engine's octane:temperature threshold is exceeded, and those frequencies are related to the weight/shape/design of the original internals. I have had some engine's that I know were NOT knocking show me knock because of this, and others that didn't show me any when I knew it should have. Furthermore, once you start hearing the pinging/knock, generally that is also out of the range of the knock sensor, making it a device that you should use in addition to other tools to make a final judgement and also giving relevance to the noise produced by the exhaust system (you are more likely to hear mechanical/problem noise if the exhaust is quiet)
If you are using a mass airflow meter, shouldn't this be possible to track in data logs? Wouldn't you be able to witness the peak hp and peak air mass coinciding with one another? I would like to see an air mass vs hp dyno graph if anyone has one.
It makes sense, I am just a Neanderthal and like to see empirical evidence before subscribing my faith to it.
PS. I think this discussion just found its way back on course to its original intent. Save the shift point discussion for another thread, and let's just keep this thread going about the what's and why's of how peak torque and peak horsepower relate to the mechanicals of a running engine.
10-26-2015, 09:48 PM
