Torque gets the car moving, horsepower keeps it moving.
367 vs 410 Engines Masters
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alone no but with rpm yes and what are torque and rpm together known as ? It's Hp
Nope
Think a bunch of torque applied on a bolt that won't move vs a running engine (tractor, car etc..) that produces torque and rpm aka runs. Your saying torque without movement moves your car and I'm saying torque with movement aka rpm which is again HP.
You can't separate the two there is no torque only engine, torque and rpm = power.
What a dyno's torque reading is the average force being created per revolution (rpm).
From idle to the point the engine can't spin higher what's being created is power and that power is made up of torque and rpm. There no way to just have torque only doing something only by itself.
PRH
Well-Known Member
I sure hope you guys can stretch this out for 10 pages or so.
I've enjoyed watching this thread as a recently retired OEM engine engineer (hint: it was not Chrysler!). But I thought I'd share some insight into how the OEM's engineer today's modern engines.
The physics:
Indicated power = friction power + brake power, or
Brake power (what we all care about! ) = indicated power - friction power. Brake power is what comes out at the crankshaft.
Indicated power can be computed from the P-V diagram (pressure-cyl volume trace). We can see the pressure created on the piston both before tdc (negative work due to spark timing lead) and after tdc (positive work due to combustion). We also see the negative work due to blowdown of the exhaust and negative work of the air induction process (pumping work). So we can integrate the P-V trace on the power stroke and get the indicated power. And we can lump everything else that does not come out at the crankshaft into friction power.
Friction power:
A bigger engine breathes deeper (more airflow) so the induction negative power is greater (higher pumping work). It also has more exhaust volume to blow down so again, more negative power. And all those parts rubbing together, valves going up and down, piston rings friction...all of this is the mechanical part of friction power. And you don't get a choice - you have to feed the mechanical friction monster as you raise rpm. In this simplified explanation, we also are lumping thermal losses into friction power. These are the losses due to the high combustion temps heating up parts and shedding to the coolant. Thermal losses can be considered close enough to each other for a stroker vs non-stroker. Obviously a longer stroke engine will have higher friction than a shorter stroke engine hence why they normally power peak at a lower rpm.
Ahhh, BUT that longer stroke inhales more air so it can make lots more indicated power of the piston pushing down on the crank. Even if sucking through the same straw (cyl head), it will inhale more air. If the straw is too small/more restrictive, the negative work just goes up and, since the mechanical friction is increasing with rpm, too small of a straw just moves the power peak even lower.
So the game is, within an engine's usable rpm range, where do we stop getting more brake power when the friction power gets high enough to negate the higher indicated power?
Clearly at lower rpm, the bigger engine has big gains in its lower speed output. But at some rpm, the increase in friction power will exceed the increased power due to airflow and the brake power will no longer be higher. And since friction power is a hyperbolic function (function of rpm squared), the power falls off pretty quick if the breathing up top is not so good.
Ahhh...but what about cam timing? The valve lift and IVC will determine where the longer stroke or shorter stroke breathes more efficiently so any cam chosen will favor one or the other engine. And the blowdown work (power) is a balance of wasting the cyl pressure before bdc (earlier EVO) and a later EVO that causes higher blowdown losses.
So in general, the larger engine will make a significant increase in torque where the rpm is lower and the friction is lower and the power increase at the high end is highly dependent on the breathing ability of the heads and cam. Within typical prod engine constraints, the bigger engine will always win. And if you want to play the "perfect gearing/rpm" setup for a drag race, the one that gets more area under the power curve will always win. And that will always be dependent on launch rpm and shift speeds. Can a lower power engine be perfectly set up to beat a higher powered engine? Theoretically yes but in all practicality, no.
So when we did new engines and looked at stroking them, we would get proportionally higher torque and slightly more power, just as you would expect. And fuel economy typically goes down due to more pumping losses (you only need so much power to push the car on the federal emissions/fuel economy test!) and higher friction.
I simplified this quite a bit but suspect some of you may not have seen this before. Just wanted to provoke some thought on the "why" behind a stroker.
And yep, I love my 408 "tractor motor" in the avatar. That's why I built it when I put this car together. Much broader operation range to get performance out of and don't have to have some theoretically perfect setup to get the most. 6200 rpm shift point suits me just fine. Now if only I had some TF heads instead of those Eddies.....haha
FWIW!
The physics:
Indicated power = friction power + brake power, or
Brake power (what we all care about! ) = indicated power - friction power. Brake power is what comes out at the crankshaft.
Indicated power can be computed from the P-V diagram (pressure-cyl volume trace). We can see the pressure created on the piston both before tdc (negative work due to spark timing lead) and after tdc (positive work due to combustion). We also see the negative work due to blowdown of the exhaust and negative work of the air induction process (pumping work). So we can integrate the P-V trace on the power stroke and get the indicated power. And we can lump everything else that does not come out at the crankshaft into friction power.
Friction power:
A bigger engine breathes deeper (more airflow) so the induction negative power is greater (higher pumping work). It also has more exhaust volume to blow down so again, more negative power. And all those parts rubbing together, valves going up and down, piston rings friction...all of this is the mechanical part of friction power. And you don't get a choice - you have to feed the mechanical friction monster as you raise rpm. In this simplified explanation, we also are lumping thermal losses into friction power. These are the losses due to the high combustion temps heating up parts and shedding to the coolant. Thermal losses can be considered close enough to each other for a stroker vs non-stroker. Obviously a longer stroke engine will have higher friction than a shorter stroke engine hence why they normally power peak at a lower rpm.
Ahhh, BUT that longer stroke inhales more air so it can make lots more indicated power of the piston pushing down on the crank. Even if sucking through the same straw (cyl head), it will inhale more air. If the straw is too small/more restrictive, the negative work just goes up and, since the mechanical friction is increasing with rpm, too small of a straw just moves the power peak even lower.
So the game is, within an engine's usable rpm range, where do we stop getting more brake power when the friction power gets high enough to negate the higher indicated power?
Clearly at lower rpm, the bigger engine has big gains in its lower speed output. But at some rpm, the increase in friction power will exceed the increased power due to airflow and the brake power will no longer be higher. And since friction power is a hyperbolic function (function of rpm squared), the power falls off pretty quick if the breathing up top is not so good.
Ahhh...but what about cam timing? The valve lift and IVC will determine where the longer stroke or shorter stroke breathes more efficiently so any cam chosen will favor one or the other engine. And the blowdown work (power) is a balance of wasting the cyl pressure before bdc (earlier EVO) and a later EVO that causes higher blowdown losses.
So in general, the larger engine will make a significant increase in torque where the rpm is lower and the friction is lower and the power increase at the high end is highly dependent on the breathing ability of the heads and cam. Within typical prod engine constraints, the bigger engine will always win. And if you want to play the "perfect gearing/rpm" setup for a drag race, the one that gets more area under the power curve will always win. And that will always be dependent on launch rpm and shift speeds. Can a lower power engine be perfectly set up to beat a higher powered engine? Theoretically yes but in all practicality, no.
So when we did new engines and looked at stroking them, we would get proportionally higher torque and slightly more power, just as you would expect. And fuel economy typically goes down due to more pumping losses (you only need so much power to push the car on the federal emissions/fuel economy test!) and higher friction.
I simplified this quite a bit but suspect some of you may not have seen this before. Just wanted to provoke some thought on the "why" behind a stroker.
And yep, I love my 408 "tractor motor" in the avatar. That's why I built it when I put this car together. Much broader operation range to get performance out of and don't have to have some theoretically perfect setup to get the most. 6200 rpm shift point suits me just fine. Now if only I had some TF heads instead of those Eddies.....haha
FWIW!
I get and agree with lot of what you said, you made a lot of interesting points.
For example here's the 431 hp - 410 vs 423 hp - 367 and 425 hp - 323 (post 28), I took 4 data points from each (Best I could), Peak hp, 500 rpm, 1000 rpm and 1500 rpm under peak should be a decent take of under the curve wish they had 500 rpm after peak to add but 1500 rpms is the meat of each engines powerband.
And yes the best average curves in this case went from largest to smallest cid but was a 15 hp average difference between the 323 vs 410 and a 6 hp average between 367 vs 410, to me that's very similar power curves.
410,
403 hp average, 1.17 lbs-ft per cid
431 hp @ 5500 rpm, 420 hp @ 5000 rpm, 395 hp @ 4500 rpm, 365 hp @ 4000 rpm
367,
397 hp average, 1.21 lbs-ft per cid
423 hp @ 5800 rpm, 415 hp @ 5300 rpm, 395 hp @ 4800 rpm, 355 hp @ 4300 rpm
323,
388 hp average, 1.19 lbs-ft per cid
425 hp @ 6200 rpm, 405 hp @ 5700 rpm, 378 hp @ 5200 rpm, 345 hp @ 4700 rpm
It's not necessary about perfect gearing, but people are acting like I'm nuts for suggesting engines of similar power the smaller engine will probably need deeper gearing to be in it's powerband.
This is one where people always assume the larger engine will always have the better under the curve like in this 367 vs 410 and even if they do it's not as great as people make it look like by comparing torque instead of the actual under the curve of each engine.
For example here's the 431 hp - 410 vs 423 hp - 367 and 425 hp - 323 (post 28), I took 4 data points from each (Best I could), Peak hp, 500 rpm, 1000 rpm and 1500 rpm under peak should be a decent take of under the curve wish they had 500 rpm after peak to add but 1500 rpms is the meat of each engines powerband.
And yes the best average curves in this case went from largest to smallest cid but was a 15 hp average difference between the 323 vs 410 and a 6 hp average between 367 vs 410, to me that's very similar power curves.
410,
403 hp average, 1.17 lbs-ft per cid
431 hp @ 5500 rpm, 420 hp @ 5000 rpm, 395 hp @ 4500 rpm, 365 hp @ 4000 rpm
367,
397 hp average, 1.21 lbs-ft per cid
423 hp @ 5800 rpm, 415 hp @ 5300 rpm, 395 hp @ 4800 rpm, 355 hp @ 4300 rpm
323,
388 hp average, 1.19 lbs-ft per cid
425 hp @ 6200 rpm, 405 hp @ 5700 rpm, 378 hp @ 5200 rpm, 345 hp @ 4700 rpm
Why people build them now matter what rpm your at power is just a foot step away.
It's like the stroker has free bonus power at lower rpms. You can see that extra power in the graph overlay.
Yes generally down in the lower rpms is mainly influenced by displacement as you go higher heads cam intake exhaust etc.. start playing a roll more and as you go up in rpm. Funny enough that 367 is actually doing very well at 3,000 rpms then the 410 takes off. But your main powerband is only about the top 2,500 rpms of each engine were the Top End of the engine usually has more to do with what your engine makes with a 4 gear it needs less rpms.
Also a smaller displacement done really well can also make good torque without a stroker it's just harder
Here's a pretty interesting build, a 371 that makes over 480 (486) lbs-ft by 4500 rpm and peak 495 lbs-ft by 4800 rpm and is making over 400 lbs-ft from 2500 - 6500 rpms.371ci Mopar Small Block - Deadly Weapon
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What I mean people treating torque as bonus power is some act like torque alone is a different kind of power than hp and it does one thing hp does another. A lot of people seem to equate hp with rpm's especially higher ones and torque with low rpm. I swear a lot think below 5252 rpms is torque moving your car and hp kicks in above that, probably cause that's what they see a dyno graph show, instead a dyno graph is showing two separate findings torque and rpm is what's measured by the dyno and the hp is the results calculated it's the ability of your engine, and is the main information, torque is not really needed on the graph seems to confuse more than inform them.
Icetech
Well-Known Member
so put on heads and a bit more cam that support those cubes better and the 410 beats it across the entire band.. crippling a motor then comparing it to one that is a more efficient combo doesn't make sense
I get the reasoning but ultimately it don't make sense to me.
Building the larger engine with better parts (for more power) isn't a fairer comparison. Of course it's gonna make more power, so would the smaller one with better parts, it only made it's power curve 300 rpms higher not like it was breathing much better.
Dynamic Displacement
323 x 6200 / 3456 = 579 cfm
367 x 5800 / 3456 = 616 cfm
410 x 5500 / 3456 = 652 cfm
This is what these engines are ruffly displacing (don't have VE%) this is what I call dynamic displacement cause these engine are only 323, 367, 410 on an engine stand doing nothing I call that static displacement, most 425 ish hp engine will flow (displace) a similar amount of air cause it takes a certain amount of air in a fairly narrow range to make 425 hp be it from a 2.0l or 572 technically they all become a similar displacement.
So a 425 hp 410 ain't under built it is what it is a 425 hp engine.
I said power, not torque. You can try to minimize the importance of torque but as I'm sure you know there is only one way to increase the horsepower at any given rpm. You have to produce more torque. There is no way around it. Hp and torque are not independent of each other. If you look at the graph and see that one motor is making more horsepower than the other at any given rpm it's because it's making more torque than the other motor at that rpm. You don't have to look at a torque curve to know that.
Darn right. Don't forget to add in the 25 year old BFGs.
This is another comparison done at peak hp. A single moment in time where the gap in power is the narrowest. It disregards the entire rest of the power curve. As if the motors only run at peak horsepower.
RAMM
Well-Known Member
That build was my favourite smallblock build of all time. Wish I still had the topend. It made 513ft/lbs on my dyno before I got greedy and went backwards on the intake a little bit. That engine was so solid on the DTS's at 2500rpm just hovering at 400+lbs for several seconds before the sweep. Oh and they even put the wrong peak HP number as it was actually 515 hp as indicated in the chart. J.RobYes generally down in the lower rpms is mainly influenced by displacement as you go higher heads cam intake exhaust etc.. start playing a roll more and as you go up in rpm. Funny enough that 367 is actually doing very well at 3,000 rpms then the 410 takes off. But your main powerband is only about the top 2,500 rpms of each engine were the Top End of the engine usually has more to do with what your engine makes with a 4 gear it needs less rpms.
Also a smaller displacement done really well can also make good torque without a stroker it's just harder
371ci Mopar Small Block - Deadly Weapon
Never said you didn't and agreed with you the 410 makes a lot of end power.
I'm very well aware of that fact, just said torque by itself don't tell you much hp tells you engines potential.
Hp is torque and rpm, basically torque is the average force per revolution, hp is the sum of all those revolutions.
I'm very well aware of that fact, what you don't want to see is they each have a different powerband the 425 hp 323, 423 hp 367 and the 431 hp 410 all have separate powerbands that start and stop at different rpm, generally smaller engines that make similar power than larger engines operate at higher rpms, 323 peaks @ 6,200 rpm, 367 peaks @ 5,800 rpm, 410 @ 5,500 rpm and when you compare each engine actual powerband to one another there very similar. And if you take advantage of each engine through gearing stall etc.. each car will be turning different rpms at any given mph so it don't matter if one engine makes more hp @ X rpm, what matters what power is being put to the ground at any given mph.
Yes of course you don't have to gear right still doesn't change they each engines powerband makes similar hp, I imagine behind that 410 crate there's all kinds of different gears and stalls being ran and given different performance but does that change they all have the same potential don't matter if the owner takes advantage of it or not it's still there ?
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Yes I showed the dynamic displacement at peak, but it's dynamic so it goes for every rpm the displacement will be different and same with throttle (VE%) gonna make it different still.
And for this case peak hp is when the engine demands the most air flow seemed more relevant since they were talking about more head flow and cam for the 410.
You think I don't care about under the curve hp but that's all I've been caring about each engines powerband, basically 2000 rpm under peak hp to 500 ish after peak hp (stall to shift points).
It's been one my favorites to read about, you definitely did a great job.
That is subjective. The more narrow you make the powerband used and the closer it is to far right of the curve the more similar they are. The wider the powerband used and or the more data that is included to the left the more difference that is seen between the 367 and 410. To some those power differences are substantial. Especially when they come with little or no cost. These are all the same points made in the video where they looked at the entire powerband.
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