Theory: Instantaneous Torque vs Mean Torque - Honda-Tech

mgags7 · 11-23-2006, 08:18 PM

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....

Combustion Contraption · 11-23-2006, 10:16 PM

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

mgags7 · 11-23-2006, 10:32 PM

LOL yea you just read the shit 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?

mike_belben@yahoo.com · 11-24-2006, 05:00 AM

Quote:

Originally Posted by bb4ever

....

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.

....

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.

mgags7 · 11-24-2006, 08:41 AM

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?

alterdcreations · 11-24-2006, 09:27 AM

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)

DonF · 11-24-2006, 09:49 AM

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.

blinx9900 · 11-24-2006, 10:22 AM

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...

98vtec · 11-24-2006, 10:24 AM

Quote:

Originally Posted by blinx9900

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...

go away.

blinx9900 · 11-24-2006, 10:40 AM

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 shit that dosent make sense...

mgags7 · 11-24-2006, 12:48 PM

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?

blinx9900 · 11-24-2006, 01:10 PM

Quote:

Originally Posted by bb4ever

genious

GSRCRXsi · 11-24-2006, 01:11 PM

Quote:

Originally Posted by blinx9900

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...

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.

CONTROLLED CONFUSION · 11-24-2006, 01:15 PM

Quote:

Originally Posted by DonF

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.

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

DonF · 11-24-2006, 01:42 PM

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.

mgags7 · 11-24-2006, 01:50 PM

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?

DonF · 11-24-2006, 02:41 PM

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.

petty$rep · 11-24-2006, 07:32 PM

Quote:

Originally Posted by DonF

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.

Does this equal a longer powerband?

mgags7 · 11-25-2006, 08:21 AM

"Sustains the TQ longer"

^^could he put it any more plainly....yes that means a longer powerband....

Lsos · 11-29-2006, 07:03 AM

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.

mgags7 · 11-29-2006, 07:51 AM

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

black_EM1 · 11-29-2006, 08:00 AM

Yea, I'm in for this one.

Lsos · 11-29-2006, 11:40 AM

Quote:

Originally Posted by bb4ever

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?

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 cyli

11-23-2006, 08:18 PM	#1
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	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.... __________________ Matt ███

11-23-2006, 10:16 PM	#2
Combustion Contraption Senior Member Join Date: Jan 2003 Location: So Cal Posts: 8,534	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 __________________ EARL LASKEY, YOU WILL BE MISSED CCCylinderheads.com Check out the INDUCTION SPECIAL Matco Doublebay Toolbox FOR SALE Click Here!

11-23-2006, 10:32 PM	#3
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	LOL yea you just read the shit 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? __________________ Matt ███

11-24-2006, 08:41 AM	#5
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	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? __________________ Matt ███

11-24-2006, 09:27 AM	#6
alterdcreations Senior Member Join Date: Feb 2006 Location: Single camshafting for now in, N.Y. Posts: 3,223	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) __________________ http://images.honda-tech.com/set1/smile/emcocktl.gif http://images.honda-tech.com/set1/smile/emdgust.gif

11-24-2006, 09:49 AM	#7
DonF Senior Member Join Date: May 2002 Location: Atl. Beach, fl, duval Posts: 4,701	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.

11-24-2006, 10:22 AM	#8
blinx9900 Senior Member Join Date: Sep 2006 Location: poopfacepartytime, ca, usa Posts: 5,072	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... __________________ ek9.org <--- a place for the ek/ej lovers [b]FS: Racing Hart C2's 17x7 4x100 otaku squad member #004 http://images.honda-tech.com/set1/smile/emsmile.gif

11-24-2006, 10:40 AM	#10
blinx9900 Senior Member Join Date: Sep 2006 Location: poopfacepartytime, ca, usa Posts: 5,072	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 shit that dosent make sense... __________________ ek9.org <--- a place for the ek/ej lovers [b]FS: Racing Hart C2's 17x7 4x100 otaku squad member #004 http://images.honda-tech.com/set1/smile/emsmile.gif

11-24-2006, 12:48 PM	#11
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	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? __________________ Matt ███

11-24-2006, 01:42 PM	#15
DonF Senior Member Join Date: May 2002 Location: Atl. Beach, fl, duval Posts: 4,701	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.

11-24-2006, 01:50 PM	#16
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	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? __________________ Matt ███

11-24-2006, 02:41 PM	#17
DonF Senior Member Join Date: May 2002 Location: Atl. Beach, fl, duval Posts: 4,701	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.

11-25-2006, 08:21 AM	#19
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	"Sustains the TQ longer" ^^could he put it any more plainly....yes that means a longer powerband.... __________________ Matt ███

11-29-2006, 07:03 AM	#20
Lsos Join Date: Oct 2001 Location: VA Beach Posts: 1,654	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. __________________ 1989 CRX, B16A.... RIP 12-10-01 1991 CRX DX 2002 S2000

11-29-2006, 07:51 AM	#21
mgags7 Senior Member Join Date: Mar 2004 Location: Between headphones, NC Posts: 14,382	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 __________________ Matt ███

11-29-2006, 08:00 AM	#22
black_EM1 Senior Member Join Date: Dec 2004 Location: www.Kills.com, ShutUpYouRetard Posts: 2,441	Re: (bb4ever) Yea, I'm in for this one. __________________ -Charles- [ B00STED EM1 CREW #27] Kills Pirate. For Life. PeakBoost powered. 418hp/259tq@17psi PoorMan's R 336hp/223tq@15psi Bone Stock B18C