Black 600 HP 944 Turbo in Excellence!
03-08-2003, 03:15 AM
#61
Race Director
Wow... two big names duking it out on the same thread... <img src="http://www.gururacing.net/ImagesMisc/Graemlins/Graemlin-CowTow.gif" alt=" - " />
Somehow these dicussions always seem to steer towards the topic of balance-shafts, and the benefits or disadvantages of removing them. My personal opinion is that they don't make that much of a difference either way in performance. First one has to have an understanding of the background behind why and how balance-shafts work (see pictures & equations here): <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=11;t=000339;p=2#000017" target="_blank">Balance Shafts</a>.
Chris is right in that balance-shafts does nothing with rotational balance of the crank & pistons. And Scott is also right in that lightening the crank & attached parts will throw the balance-shafts out of whack... just a little...
The balance-shafts combat the shake of the engine as a whole, not of individual parts. This shake rocks the engine front-to-back like bucking horse and there's a similar sideways shake as well. There is also a rotational component since the crank is always spinning in the same direction.
Mitshubishi improved on the original British Lanchester design of opposing balance-shafts by raising and lowering the shafts relative to the crank. This has the additional benefit of removing the rotational shake.
As already discussed, the benefits and gains of having the balance-shafts in place or removed is minor for performance. The weight-savings can be valuable in a very lightweight car. The HP-gains are minimal (although if we're talking about the same car you tested a month or so ago, Chris, wasn't it 2.5hp across the board?).
So I think this issue comes down to personal-preference. We can debate theoretical factors all day long in black & white terms, but as the real-world numbers show, the actual performance difference is negligible.
"I just typed a VERY LONG reply and accidentally pressed the back button on the browser and whooosh! - Gone!"
Don't you just HATE IT when that happens <img src="http://www.gururacing.net/ImagesMisc/Graemlins/Graemlin-nonono.gif" alt=" - " />? Sometimes, if I know it's going to be along construction, I'll prepare it in MS-Word or something so I can save it along the way.
Somehow these dicussions always seem to steer towards the topic of balance-shafts, and the benefits or disadvantages of removing them. My personal opinion is that they don't make that much of a difference either way in performance. First one has to have an understanding of the background behind why and how balance-shafts work (see pictures & equations here): <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=11;t=000339;p=2#000017" target="_blank">Balance Shafts</a>.
Chris is right in that balance-shafts does nothing with rotational balance of the crank & pistons. And Scott is also right in that lightening the crank & attached parts will throw the balance-shafts out of whack... just a little...
The balance-shafts combat the shake of the engine as a whole, not of individual parts. This shake rocks the engine front-to-back like bucking horse and there's a similar sideways shake as well. There is also a rotational component since the crank is always spinning in the same direction.
Mitshubishi improved on the original British Lanchester design of opposing balance-shafts by raising and lowering the shafts relative to the crank. This has the additional benefit of removing the rotational shake.
As already discussed, the benefits and gains of having the balance-shafts in place or removed is minor for performance. The weight-savings can be valuable in a very lightweight car. The HP-gains are minimal (although if we're talking about the same car you tested a month or so ago, Chris, wasn't it 2.5hp across the board?).
So I think this issue comes down to personal-preference. We can debate theoretical factors all day long in black & white terms, but as the real-world numbers show, the actual performance difference is negligible.
"I just typed a VERY LONG reply and accidentally pressed the back button on the browser and whooosh! - Gone!"
Don't you just HATE IT when that happens <img src="http://www.gururacing.net/ImagesMisc/Graemlins/Graemlin-nonono.gif" alt=" - " />? Sometimes, if I know it's going to be along construction, I'll prepare it in MS-Word or something so I can save it along the way.
03-11-2003, 02:03 AM
#62
Instructor
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Chris and I are hardly duking it out. In fact, I support his view, as he supports mine to relatively the same degree.
Without question balance shafts make for a smoother "feeling" engine. And heck, when you fork out the dough for what one of these cars cost new, then you want a smooth running machine, not a tractor. So, do balance shafts have a place? - Yes. Do I endorse running the stock balance shafts on a highly modified engine? - No.
As I have mentioned in my earlier post, the stock balance shafts are virtually useless in a 9000 RPM engine with a 30% lighter rotating assembly. However, balance shafts can be retained in a higher than stock horsepower, but primarily stock based engine that is modestly modified with engine management, increased RPM, headwork, and an onslaught of bolt on power adders. My point? - Well, once you significantly change the lower end internals you have pretty much rendered the stock balance shafts useless anyway, so why retain them?
While the power gains are relatively small, I still opt for the weight reduction, a few extra HP, elimination of several potential leak areas, and one less belt, and two less rollers to fail.
In short, Chris and I may see things a bit differently, but surely we appreciate each other's views and understand each other's take on things.
Over the years, as fellow professionals, Chris and I have shared/exchanged our thoughts with the list, and with each other, on several topics - Some we agree on, some we don't, but that does not change the fact that I still respect him for his knowledge, experience, and his opinions - Perhaps he feels the same about me?
In short, Chris does what works for him, I do what works for me. Is he or I right or wrong? - The answer is not black and white in this case.
Do secondary harmonics exist? - Yes. Can they be "eliminated" - No. Can they be lessened to a tolerable level? - Yes. Are balance shafts effective in reducing the "effects" of secondary harmonics? - Yes. Are "stock" balance shafts effective in highly modified engines with significantly lightened rotating assemblies? - Not in my experience.
As most of you already know, the rotating assemblies of the stock engine are quite heavy. When doing the math to determine the evil forces at work, you will find that by reducing the piston and rod weight and machining the crank (counterweights) to accommodate the lighter arrangement, you reduce the effects of the secondary harmonics.
Can you eliminate the secondary harmonics? - No, they are inherent in all inline four cylinder engines and can't be eliminated, (not even with balance shafts) but they can be effectively reduced/controlled through either means.
The rule of thumb has always been that inline 4 cylinder engines under 2L could run without balance shafts. That's because the secondary harmonics are not very strong in smaller displacement engines, but why?...
Well, the relationship linking the reduction of secondary harmonics and displacement is somewhat misleading, but here is how it all started...
As a general rule, smaller displacement engines have smaller pistons, shorter rods, less stroke, and smaller, lighter, cranks with smaller, lighter counterweights. But what would happen if you built a smaller displacement engine with very heavy rods and pistons? You guessed right, the secondary harmonics would begin to become an issue.
So, by reducing the weight of the "opposing" rotating components in a larger displacement engine, you "effectively" reduce the effects of the secondary harmonics, and do so to a degree that makes them tolerable, much like the way they behave in a smaller displacement engine.
Without question balance shafts make for a smoother "feeling" engine. And heck, when you fork out the dough for what one of these cars cost new, then you want a smooth running machine, not a tractor. So, do balance shafts have a place? - Yes. Do I endorse running the stock balance shafts on a highly modified engine? - No.
As I have mentioned in my earlier post, the stock balance shafts are virtually useless in a 9000 RPM engine with a 30% lighter rotating assembly. However, balance shafts can be retained in a higher than stock horsepower, but primarily stock based engine that is modestly modified with engine management, increased RPM, headwork, and an onslaught of bolt on power adders. My point? - Well, once you significantly change the lower end internals you have pretty much rendered the stock balance shafts useless anyway, so why retain them?
While the power gains are relatively small, I still opt for the weight reduction, a few extra HP, elimination of several potential leak areas, and one less belt, and two less rollers to fail.
In short, Chris and I may see things a bit differently, but surely we appreciate each other's views and understand each other's take on things.
Over the years, as fellow professionals, Chris and I have shared/exchanged our thoughts with the list, and with each other, on several topics - Some we agree on, some we don't, but that does not change the fact that I still respect him for his knowledge, experience, and his opinions - Perhaps he feels the same about me?
In short, Chris does what works for him, I do what works for me. Is he or I right or wrong? - The answer is not black and white in this case.
Do secondary harmonics exist? - Yes. Can they be "eliminated" - No. Can they be lessened to a tolerable level? - Yes. Are balance shafts effective in reducing the "effects" of secondary harmonics? - Yes. Are "stock" balance shafts effective in highly modified engines with significantly lightened rotating assemblies? - Not in my experience.
As most of you already know, the rotating assemblies of the stock engine are quite heavy. When doing the math to determine the evil forces at work, you will find that by reducing the piston and rod weight and machining the crank (counterweights) to accommodate the lighter arrangement, you reduce the effects of the secondary harmonics.
Can you eliminate the secondary harmonics? - No, they are inherent in all inline four cylinder engines and can't be eliminated, (not even with balance shafts) but they can be effectively reduced/controlled through either means.
The rule of thumb has always been that inline 4 cylinder engines under 2L could run without balance shafts. That's because the secondary harmonics are not very strong in smaller displacement engines, but why?...
Well, the relationship linking the reduction of secondary harmonics and displacement is somewhat misleading, but here is how it all started...
As a general rule, smaller displacement engines have smaller pistons, shorter rods, less stroke, and smaller, lighter, cranks with smaller, lighter counterweights. But what would happen if you built a smaller displacement engine with very heavy rods and pistons? You guessed right, the secondary harmonics would begin to become an issue.
So, by reducing the weight of the "opposing" rotating components in a larger displacement engine, you "effectively" reduce the effects of the secondary harmonics, and do so to a degree that makes them tolerable, much like the way they behave in a smaller displacement engine.
03-11-2003, 02:07 AM
#63
Instructor
Join Date: Jun 2001
Location: Assonet, MA
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By the way, thanks for the tip Danno - I used Microsoft Word to type my post, then just cut and pasted into the form before sending it.
Many sites still retain the form data when you navigate with the back and forward buttons - I learned the hard way that this is not one of them - DOH!
Many sites still retain the form data when you navigate with the back and forward buttons - I learned the hard way that this is not one of them - DOH!
