Theory: Instantaneous Torque vs Mean Torque
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Theory: Instantaneous Torque vs Mean Torque
After doing a bit of reading earlier, I dawned upon an article about instantaneous torque as a percentage of mean torque. The main topic of discussion was the number of cylinders in the engine.
Starting on the basics, a one cylinder engine would produce one torque peak per cycle. But, on the compression stroke, negative torque would be "consumed" in order to push the piston up and compress the mixture.
Moving up to a 4 cylinder engine the number of torque peaks increases of course, but it also moves the torque "spectrum" a bit, the peaks are at less percentage of the mean, however, the minimums are "less negative" due to the inertia of the other 3 pistons during the combustion stroke of the given cylinder.
Once the number of cylinders reaches 8, there is no longer any negative instantaneous torque value, and the peaks still become nearer and nearer the mean.
Now, since the peaks become closer and closer together (measured as degrees in rotation of the crank), would it not make sense that the torque delivered by a v8 to the wheels would be much more linear than that of a 4cyl??
So, with the same displacement and VE, and if BSFC (TE) was constant, as the number of cylinders increases, torque will increase, correct?
This makes good sense to me as exemplified by the 300hp hybrid v8 made of two hayabusa engines welded together that pirate showed me some time ago....
Starting on the basics, a one cylinder engine would produce one torque peak per cycle. But, on the compression stroke, negative torque would be "consumed" in order to push the piston up and compress the mixture.
Moving up to a 4 cylinder engine the number of torque peaks increases of course, but it also moves the torque "spectrum" a bit, the peaks are at less percentage of the mean, however, the minimums are "less negative" due to the inertia of the other 3 pistons during the combustion stroke of the given cylinder.
Once the number of cylinders reaches 8, there is no longer any negative instantaneous torque value, and the peaks still become nearer and nearer the mean.
Now, since the peaks become closer and closer together (measured as degrees in rotation of the crank), would it not make sense that the torque delivered by a v8 to the wheels would be much more linear than that of a 4cyl??
So, with the same displacement and VE, and if BSFC (TE) was constant, as the number of cylinders increases, torque will increase, correct?
This makes good sense to me as exemplified by the 300hp hybrid v8 made of two hayabusa engines welded together that pirate showed me some time ago....
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Not exactly sure what the point of this thread is, or if youre just sharing some info that youve read, but anyway, yes, ive always just looked at it as that regarding a 4 cyl vs an 8 cyl, you get half as many TQ "pulses" per period of time, so the delivery is peaky. yet another reason most 4 cylinders need to be revved in order to make decent power.
Regarding the Hayabusy hybrid...
http://www.rst-v8.com
Regarding the Hayabusy hybrid...
http://www.rst-v8.com
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LOL yea you just read the **** out of me on that one....I really didn't have a question I was just looking to share/discuss this stuff....I tried to bs some sort of question there at the end....
How well does the shape of the instantaneous torque curve actually transfer to the wheels though?? Is that little negative torque blip actually ever there?
Its odd to think of it on that level...
Now, another thing I read into was about odd-firing engines, where the tq pulses build upon one another rather than fire in order. Is there anything worth looking into there?? I wonder if something like that would even be feasible for a 4 cylinder, or would the unbalanced forces on the crank be too much to overcome?
How well does the shape of the instantaneous torque curve actually transfer to the wheels though?? Is that little negative torque blip actually ever there?
Its odd to think of it on that level...
Now, another thing I read into was about odd-firing engines, where the tq pulses build upon one another rather than fire in order. Is there anything worth looking into there?? I wonder if something like that would even be feasible for a 4 cylinder, or would the unbalanced forces on the crank be too much to overcome?
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Re: Theory: Instantaneous Torque vs Mean Torque (bb4ever)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever »</TD></TR><TR><TD CLASS="quote">
....
Moving up to a 4 cylinder engine .... the peaks are at less percentage of the mean, however, the minimums are "less negative" due to the inertia of the other 3 pistons during the combustion stroke of the given cylinder.
....
</TD></TR></TABLE>
helping to explain why heavy pistons and rods still perform well compared to light pistons and rods. very light pistons are a benefit in terms of tensile loading but i wonder if they cost some power.
....
Moving up to a 4 cylinder engine .... the peaks are at less percentage of the mean, however, the minimums are "less negative" due to the inertia of the other 3 pistons during the combustion stroke of the given cylinder.
....
</TD></TR></TABLE>
helping to explain why heavy pistons and rods still perform well compared to light pistons and rods. very light pistons are a benefit in terms of tensile loading but i wonder if they cost some power.
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True, so can it be said that while lighter pistons and rods move the powerband up (which raises peak hp) and let the engine rev more "freely" as in faster; Heavier pistons and rods create less deviation between the torque peaks and minimums, therefore making more mean torque??
Does the same concept apply to lighter flywheels and crank pullies?
Does the same concept apply to lighter flywheels and crank pullies?
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Re: (bb4ever)
yes it should also apply
i have a question, if lightweight parts move your powerband up, then how would this affect low reving engine say a h22? it seems that the power falls of around 7500 +or-
if you use lightweight pistons,rods,lightend crank ,crank pully, flywheel
would power still fall off at 7500rpms? or maybe it might fall of harder than before?
or will it move your powerband to 8500rpms?(its a theatrical question)
i have a question, if lightweight parts move your powerband up, then how would this affect low reving engine say a h22? it seems that the power falls of around 7500 +or-
if you use lightweight pistons,rods,lightend crank ,crank pully, flywheel
would power still fall off at 7500rpms? or maybe it might fall of harder than before?
or will it move your powerband to 8500rpms?(its a theatrical question)
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Re: (alterdcreations)
When thinking of lite parts you should think of inertia, not TQ. It takes less time and energy to accelerate a lite part VS heavy. It also goes the other way, if you had a 100 lb. flywheel and got the engine to 8000 RPM put the engine in neutral, it would take longer to slow down than a 10 lb. flywheel. It is easier to stall a motor with a heavy flywheel than lite. It will also smooth out TQ peaks at low RPM's.IE it is easie to get a smooth idle with a heavy flywheel, and cams than a lite one.
Lite parts do ot necessarly move power to a higher RPM band, so much as extend the rev band.
Lite parts do ot necessarly move power to a higher RPM band, so much as extend the rev band.
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Re: Theory: Instantaneous Torque vs Mean Torque (bb4ever)
pointless thread bb4, did you just figure that out? you could have simply said v8's have more tq... 
if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties...
if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties...
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Re: Theory: Instantaneous Torque vs Mean Torque (blinx9900)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blinx9900 »</TD></TR><TR><TD CLASS="quote">pointless thread bb4, did you just figure that out? you could have simply said v8's have more tq... if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties... </TD></TR></TABLE>
go away.
if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties... </TD></TR></TABLE>go away.
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From: poopfacepartytime, ca, usa
Re: Theory: Instantaneous Torque vs Mean Torque (B.Rabbit)
are you upset cause i didnt invite you to my moms tea party? you can come too if you want gayboy... and dont pm me talking **** that dosent make sense...
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Aww still pissed you cant sell your ghetto itbs??
I would have loved you to explain why before reading this....oh but I forgot, you work for a huge turbo kit company so you must be a damn genious....thug life man
ON TOPIC:
Don, do lighter internals not lose torque down low due to less inertia at lower engine speeds?
I would have loved you to explain why before reading this....oh but I forgot, you work for a huge turbo kit company so you must be a damn genious....thug life man
ON TOPIC:
Don, do lighter internals not lose torque down low due to less inertia at lower engine speeds?
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Re: (bb4ever)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever »</TD></TR><TR><TD CLASS="quote">genious</TD></TR></TABLE>
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Re: Theory: Instantaneous Torque vs Mean Torque (blinx9900)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blinx9900 »</TD></TR><TR><TD CLASS="quote">pointless thread bb4, did you just figure that out? you could have simply said v8's have more tq... if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties... </TD></TR></TABLE>
you are an asshat. read the whole post before you go spouting off at the keyboard. he said with "with the same displacement and VE, and if BSFC (TE) was constant, as the number of cylinders increases, torque will increase, correct?". most v8's have a much larger displacement. so of course they make more torque then. but hes comparing say, a 2.0L I4 to a 2.0L V8.
interesting concept. what you said makes sense though, bb4.
in for more discussion.
if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties... </TD></TR></TABLE>you are an asshat. read the whole post before you go spouting off at the keyboard. he said with "with the same displacement and VE, and if BSFC (TE) was constant, as the number of cylinders increases, torque will increase, correct?". most v8's have a much larger displacement. so of course they make more torque then. but hes comparing say, a 2.0L I4 to a 2.0L V8.
interesting concept. what you said makes sense though, bb4.
in for more discussion.
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Re: (bb4ever)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF »</TD></TR><TR><TD CLASS="quote">When thinking of lite parts you should think of inertia, not TQ. It takes less time and energy to accelerate a lite part VS heavy. It also goes the other way, if you had a 100 lb. flywheel and got the engine to 8000 RPM put the engine in neutral, it would take longer to slow down than a 10 lb. flywheel. It is easier to stall a motor with a heavy flywheel than lite. It will also smooth out TQ peaks at low RPM's.IE it is easie to get a smooth idle with a heavy flywheel, and cams than a lite one.
Lite parts do ot necessarly move power to a higher RPM band, so much as extend the rev band. </TD></TR></TABLE>
so light parts mean more revs. with less inertia, the bearings are less stressed so less oppertunity to stack or spin bearings and longer sustained engine abuse
Lite parts do ot necessarly move power to a higher RPM band, so much as extend the rev band. </TD></TR></TABLE>
so light parts mean more revs. with less inertia, the bearings are less stressed so less oppertunity to stack or spin bearings and longer sustained engine abuse
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Re: (CONTROLLED CONFUSION)
This is hard to explain in a few paragraphs. Rod bearing wear should be less with lighter rods and pistons. This is on the transitions at TDC and BDC. Trying to pull down, or pushup a bowling ball compared to a baseball. A heavy flywheel or internals will store energy ( TQ, inertia or whatever) Example: Aheavy flyweel and internals at idle, let out the clutch, no throttle, the car will go foreward. Lite flywheel and internals it will stall. Now it will take longer to accelerate the heavy parts, but they will stay in motion longer, once at the same speed. Racing is about acceleration.
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Well explained.
Now, does what I said make sense? The lighter parts inside hold less inertia, therefore are able to aid less on the compression stroke, and lowering mean torque down low....correct?
Now, does what I said make sense? The lighter parts inside hold less inertia, therefore are able to aid less on the compression stroke, and lowering mean torque down low....correct?
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Re: (bb4ever)
Until you get into high RPM's then the cost of accelerating the parts is more than the stored inertia. A lite rotating assembly may make a few more BHP @ 8800, peak #, on the same motor, but alot more @ 9800. Overall it may make less peak TQ @ 6500. It just sustains the TQ longer.
I thought about an oil tanker VS a Boston Whaler. Same top speed or knots. Or a locamotive, once they are moving, get out of the way.
I thought about an oil tanker VS a Boston Whaler. Same top speed or knots. Or a locamotive, once they are moving, get out of the way.
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Re: (DonF)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF »</TD></TR><TR><TD CLASS="quote">Until you get into high RPM's then the cost of accelerating the parts is more than the stored inertia. A lite rotating assembly may make a few more BHP @ 8800, peak #, on the same motor, but alot more @ 9800. Overall it may make less peak TQ @ 6500. It just sustains the TQ longer. </TD></TR></TABLE>
Does this equal a longer powerband?
Does this equal a longer powerband?
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Re: Theory: Instantaneous Torque vs Mean Torque (bb4ever)
That's the whole point of a flywheel: to smooth out those torque pulses. However, I don't think the final effect is that of overall more torque. If anything the engine will run smoother, but I really don't think a torque difference would show up on a dyno.
As an example, look at the mazda MX-3, with a 1.8l V6. It makes a maximum of 115 lb-ft of torque. That's much less than a GSR motor, and about as much as a B-16.
In fact, lets look at some random V8. A 2002 Firebird LS1 motor. It makes 340 lb-ft out of 5.7l. That's a lot, but only 60 lb-ft/ liter. A GSR motor makes 71 lb-ft/ liter.
So in conclusion, a V8 does not produce more torque simply because its a V8. In fact, if its an American V8, it will probably produce less.
As an example, look at the mazda MX-3, with a 1.8l V6. It makes a maximum of 115 lb-ft of torque. That's much less than a GSR motor, and about as much as a B-16.
In fact, lets look at some random V8. A 2002 Firebird LS1 motor. It makes 340 lb-ft out of 5.7l. That's a lot, but only 60 lb-ft/ liter. A GSR motor makes 71 lb-ft/ liter.
So in conclusion, a V8 does not produce more torque simply because its a V8. In fact, if its an American V8, it will probably produce less.
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True, but is it safe to say that a v8 built to the same performance level as an I-4 will make better power?
That is assuming that both engines are equally efficient in all aspects (VE, TE, etc)...and I hate to use VE and TE and all the fancy acronyms like that but am I correct in saying that they are a good way to describe the overall quality in the design of an engine?
Modified by bb4ever at 11:10 AM 11/29/2006
That is assuming that both engines are equally efficient in all aspects (VE, TE, etc)...and I hate to use VE and TE and all the fancy acronyms like that but am I correct in saying that they are a good way to describe the overall quality in the design of an engine?
Modified by bb4ever at 11:10 AM 11/29/2006
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Re: (bb4ever)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever »</TD></TR><TR><TD CLASS="quote">True, but is it safe to say that a v8 built to the same performance level as an I-4 will make better power?
That is assuming that both engines are equally efficient in all aspects (VE, TE, etc)...and I hate to use VE and TE and all the fancy acronyms like that but am I correct in saying that they are a good way to describe the overall quality in the design of an engine?
</TD></TR></TABLE>
I guess I don't think so. Lets use another example of engines somewhat more closesly matched in their tune level: a 4 cylinder S2000 engine and a 12 cylinder McLaren F1 engine. I think we can all agree that a McLaren engine is just as highly tuned (similar VE, etc.) as the the S2000 engine. And it has 3 times the cylinders of the S2000. This is like your V8 point, except taken even further.
The S2000 makes 77lb-ft of torque. The McLaren, if scaled down to the same size, would make 75lb-ft.
So it looks like it doesn't make any difference. I can see a 2.0 V8 being able to rev much higher than a 4 cylinder (lighter pistons), therefore being able to make more power...but that's a separate discussion. As for torque...it doesn't look like the number of cylinders does anything. In fact, the data would even suggest it hurts it...but I think we'd be going too far saying that.
Anyways, I didn't know this when I entered this thread. In fact, I actually though it would make a difference....thanks for teaching me something new
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever »</TD></TR><TR><TD CLASS="quote">
pointless thread bb4, did you just figure that out? you could have simply said v8's have more tq... if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties...</TD></TR></TABLE>
Who the *** is this genius?
That is assuming that both engines are equally efficient in all aspects (VE, TE, etc)...and I hate to use VE and TE and all the fancy acronyms like that but am I correct in saying that they are a good way to describe the overall quality in the design of an engine?
</TD></TR></TABLE>
I guess I don't think so. Lets use another example of engines somewhat more closesly matched in their tune level: a 4 cylinder S2000 engine and a 12 cylinder McLaren F1 engine. I think we can all agree that a McLaren engine is just as highly tuned (similar VE, etc.) as the the S2000 engine. And it has 3 times the cylinders of the S2000. This is like your V8 point, except taken even further.
The S2000 makes 77lb-ft of torque. The McLaren, if scaled down to the same size, would make 75lb-ft.
So it looks like it doesn't make any difference. I can see a 2.0 V8 being able to rev much higher than a 4 cylinder (lighter pistons), therefore being able to make more power...but that's a separate discussion. As for torque...it doesn't look like the number of cylinders does anything. In fact, the data would even suggest it hurts it...but I think we'd be going too far saying that.
Anyways, I didn't know this when I entered this thread. In fact, I actually though it would make a difference....thanks for teaching me something new
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bb4ever »</TD></TR><TR><TD CLASS="quote">
pointless thread bb4, did you just figure that out? you could have simply said v8's have more tq... if you want to discuss things we all already know about you can hang out with my mom during one of her tea parties...</TD></TR></TABLE>
Who the *** is this genius?
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Re: (Lsos)
heres my interpretation from what everyone has said. so, in general i assume the work done during combustion is just like torque. now in the most simplified version, the work is going to be related to the swept volume. so a V8 2.0L and a I4 2.0L would produce nearly the same amount of work. but as you all were saying, the number of events/rev would be what governs the mean torque/work(whatever you wanna call it). so as you increase the number of cylinders keping everything else the same, it should absolutely raise your torque.
i didnt have a clue what you were trying to get at, and maybe for some people its just that easy. not everyone here is a god damn genius so if someone doesnt want to participate dont write a reply. damn! it was something i didnt really understand, now i do.
now imagine 3.0L V8 vtec, all motor. that **** would sound so insane.
i didnt have a clue what you were trying to get at, and maybe for some people its just that easy. not everyone here is a god damn genius so if someone doesnt want to participate dont write a reply. damn! it was something i didnt really understand, now i do.
now imagine 3.0L V8 vtec, all motor. that **** would sound so insane.
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Re: (bluedlude)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bluedlude »</TD></TR><TR><TD CLASS="quote"> so a V8 2.0L and a I4 2.0L would produce nearly the same amount of work. but as you all were saying, the number of events/rev would be what governs the mean torque/work(whatever you wanna call it). so as you increase the number of cylinders keping everything else the same, it should absolutely raise your torque.
</TD></TR></TABLE>
A 4 cylinder has half the events of an equal-volume 8 cylinder, but these events are twice as powerful. So in the end the average torque is the same. An 8 cylinder might deliver it smoother, but ultimately its the same.
Just as you said <TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">so a V8 2.0L and a I4 2.0L would produce nearly the same amount of work.</TD></TR></TABLE> If that's the case, and the rpms are equal, and you run it through the appropriate engineering formulas (don't ask me to confuse everyone by providing them) you will arrive at the result that they HAVE to have the same torque.
</TD></TR></TABLE>
A 4 cylinder has half the events of an equal-volume 8 cylinder, but these events are twice as powerful. So in the end the average torque is the same. An 8 cylinder might deliver it smoother, but ultimately its the same.
Just as you said <TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">so a V8 2.0L and a I4 2.0L would produce nearly the same amount of work.</TD></TR></TABLE> If that's the case, and the rpms are equal, and you run it through the appropriate engineering formulas (don't ask me to confuse everyone by providing them) you will arrive at the result that they HAVE to have the same torque.