torque vs. hp
01-13-2003 | 03:29 AM
#31
Senior Member
Joined: May 2002
Posts: 177
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I think I have the right idea about what VE is, I think my lack of complete understanding is the impact of running at a higher VE on wear & tear of components vs just pushing an engine with a lower VE a little further to compensate for the lower VE.
I do understand that some potential side effects of a high VE can have an impact on part reliablity, like increased likelyhood of detonation. However for this discussion, lets assume compression is low enough, or high enough ocatane fuel is being used, that this is not an issue.
I do understand that some potential side effects of a high VE can have an impact on part reliablity, like increased likelyhood of detonation. However for this discussion, lets assume compression is low enough, or high enough ocatane fuel is being used, that this is not an issue.
01-13-2003 | 07:00 AM
#32
Senior Member
Joined: Jul 2001
Posts: 691
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From: parkville, md
Vehicle: 1997 accent L
VE has absolutely NOTHING to do with engine wear.
Volumetric Efficientcy is simply how much air you actually pull into the cylinder vs. how much room there is at BDC (bottom dead center). For example, if you have a 1 cylinder motor with 100cc displacemnt, and you only fill that cylinder 85cc of air, you're running a VE of 85% at that point in time.
And now to relate it to HP and torque: where ever you have your highest VE is most likely near your torque peak. If your torque peaks at 2200rpm, or if it peaks at 12200rpm, thats where the air is flowing into the engine its best. Engines with good torque down low, like Hyundai's engines or any truck engine, have highest VE values early in the rev range (like the alphaIII's peak at 3800rpm). Engines with peaky engines, like the honda B series engine which typically peak at ~7000rpm, have the highest VE at the upper reaches of the tach.
How do you make torque down low? Small ports, long strokes, long intake runners, and small diameter intake/exhuast piping, small TB's, and really mild cam lobes to keep up the intake charge/exhuast charge veloctiy at low engine speeds. If you build an engine this way, it will have good torque in the low revs, but the "ooph" will fade toward redline making the engine feel outta breath.
How do you make lots of top end power? Large ports, short strokes, short intake runners, large diameter piping, large TB's, and big mother cam lobes to be able to flow the massive amount of air the engine's gonna be sucking in at 9000rpm. If you build an engine this way, it will suck at low engine speeds simply because the velocity of the intake and exhuast charges are just not there. However, cross into the magical land at the top of the tach, and all hell breaks loose and the engine devours more and more air.
An engine is built for a certain VE in a certain rev range. If you build an engine to run reliably at 9000rpm, it will, but unless you keep it there it may not last as long as one would like . If you build the engine for power down low, then try to rev the snot outta it, it will not last. An engine will only last if you use it the way it was built to be run.
VTEC and variable lift/timing systems throw this off significantly, as it allows you to run small duration cams for low revs, then switch over to the larger lobes/different timing setup at a certain rpm (or constantly change timing as with the new BMW 7 series engine) to maximize VE in two different areas of the rev range. Forced Induction does sorta the same thing, except instead of changing the valve lift or timing or both in an effort to increase VE, it simply rams more air down the engine throat.
Volumetric Efficientcy is simply how much air you actually pull into the cylinder vs. how much room there is at BDC (bottom dead center). For example, if you have a 1 cylinder motor with 100cc displacemnt, and you only fill that cylinder 85cc of air, you're running a VE of 85% at that point in time.
And now to relate it to HP and torque: where ever you have your highest VE is most likely near your torque peak. If your torque peaks at 2200rpm, or if it peaks at 12200rpm, thats where the air is flowing into the engine its best. Engines with good torque down low, like Hyundai's engines or any truck engine, have highest VE values early in the rev range (like the alphaIII's peak at 3800rpm). Engines with peaky engines, like the honda B series engine which typically peak at ~7000rpm, have the highest VE at the upper reaches of the tach.
How do you make torque down low? Small ports, long strokes, long intake runners, and small diameter intake/exhuast piping, small TB's, and really mild cam lobes to keep up the intake charge/exhuast charge veloctiy at low engine speeds. If you build an engine this way, it will have good torque in the low revs, but the "ooph" will fade toward redline making the engine feel outta breath.
How do you make lots of top end power? Large ports, short strokes, short intake runners, large diameter piping, large TB's, and big mother cam lobes to be able to flow the massive amount of air the engine's gonna be sucking in at 9000rpm. If you build an engine this way, it will suck at low engine speeds simply because the velocity of the intake and exhuast charges are just not there. However, cross into the magical land at the top of the tach, and all hell breaks loose and the engine devours more and more air.
An engine is built for a certain VE in a certain rev range. If you build an engine to run reliably at 9000rpm, it will, but unless you keep it there it may not last as long as one would like . If you build the engine for power down low, then try to rev the snot outta it, it will not last. An engine will only last if you use it the way it was built to be run.
VTEC and variable lift/timing systems throw this off significantly, as it allows you to run small duration cams for low revs, then switch over to the larger lobes/different timing setup at a certain rpm (or constantly change timing as with the new BMW 7 series engine) to maximize VE in two different areas of the rev range. Forced Induction does sorta the same thing, except instead of changing the valve lift or timing or both in an effort to increase VE, it simply rams more air down the engine throat.
01-13-2003 | 09:54 PM
#34
Senior Member
Joined: May 2002
Posts: 177
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QUOTE
skierd:
BTW, my name is Dave. I OWnZ jOo. tongue.gif
No doubt you could...BTW, my name is Dave. I OWnZ jOo. tongue.gif
However if you look at my post, you will notice that I said I knew what VE was, and wanted to know what impact that had on engine wear.
Mostly you explained what VE was, and how to move the point of maximum VE up and down the rev range.
I will take a guess here, that "owning" would be proving, or disproving a point with loads facts, or a particularly well thought out explanation, or something like that. Since neither Turbulence or I had any question on what VE was, was this particular "OWning" the statement:
VE has absolutely NOTHING to do with engine wear.
If so, I think your claims of ownership are pretty weak in this particular case. smile.gif
I did notice one thing, you had said;
Volumetric Efficientcy is simply how much air you actually pull into the cylinder vs. how much room there is at BDC (bottom dead center).
Whereas I had thought VE was the mass of the air in the combustion chamber and cylinder just after intake valve closes, vs the theoretical mass of air filling the combustion chamber and cylinder (BDC), at the current temperature and atmospheric pressure.
I am assuming you were just presenting a simplified explanation, but how close was mine to the truth?
01-14-2003 | 01:50 AM
#37
Member
Joined: Oct 2001
Posts: 91
Likes: 0
here's a copy of the hp and torq dyno for my beta engine from the weekend:
http://ca.msnusers.com/99mini/shoebox.msnw...hoto&PhotoID=10
the torq peaks at about 5000 rpm and the hp peaks at about 6000 rpm. the dyno shop told me in quarter mile acceleration from a dead stop, i should be shifting at peak torq (5000 rpm), but if i'm already driving fast on the hiway, and want to pass someone ASAP, i should shift at peak hp (6000 rpm).
i don't really understand the diffence. i'd guess it has something to do with momentum. if you are accelerating from a standing stop, you have no momentum going for you, so torq is important, but if you're already doing 200 mph on some NASCAR track, you have tons of momentum, and hp is what matters. not sure, just a guess.
(PS i just noticed the hp and torq don't cross at 5200 rpm, which i thought was pretty common. guess it's the aftermarket cams.)
EDIT...the dyno fella had a small plastic box (2" wide by 1/2" high) mounted to the instrument panel of one of his sport bikes. it had 2 small lites, one flashes when the bike hits max torq, and other lite flashes when the bike hits max hp. gotta get me one of those. he said it cost about $140 CDN.
[ January 14, 2003, 09:05 AM: Message edited by: 99mini ]
http://ca.msnusers.com/99mini/shoebox.msnw...hoto&PhotoID=10
the torq peaks at about 5000 rpm and the hp peaks at about 6000 rpm. the dyno shop told me in quarter mile acceleration from a dead stop, i should be shifting at peak torq (5000 rpm), but if i'm already driving fast on the hiway, and want to pass someone ASAP, i should shift at peak hp (6000 rpm).
i don't really understand the diffence. i'd guess it has something to do with momentum. if you are accelerating from a standing stop, you have no momentum going for you, so torq is important, but if you're already doing 200 mph on some NASCAR track, you have tons of momentum, and hp is what matters. not sure, just a guess.
(PS i just noticed the hp and torq don't cross at 5200 rpm, which i thought was pretty common. guess it's the aftermarket cams.)
EDIT...the dyno fella had a small plastic box (2" wide by 1/2" high) mounted to the instrument panel of one of his sport bikes. it had 2 small lites, one flashes when the bike hits max torq, and other lite flashes when the bike hits max hp. gotta get me one of those. he said it cost about $140 CDN.
[ January 14, 2003, 09:05 AM: Message edited by: 99mini ]
