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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / April 2008Changing a V8 to a V4
I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this improve gas mileage? I only use this vehicle for short trips around town so losing 1/2 the horsepower will not bother me. Any thoughts?? Chief McGee <mcgeepby@mchsi.com> wrote in article <3SfLj.113592$yE1.94798@attbi_s21>... > I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this improve > gas mileage? I only use this vehicle for short trips around town so losing > 1/2 the horsepower will not bother me. Any thoughts?? If the subject didn't convince me, the terminology you used confirms that you don't know what you are talking about. Leave your automotive work to someone who knows what they are doing. If a smaller engine was an option for that vehicle you would be better off doing a swap to it. > I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this improve > gas mileage? I only use this vehicle for short trips around town so losing > 1/2 the horsepower will not bother me. Any thoughts?? The basic idea is actually okay, but like many things the devil is in the detail. You must "close off" those cylinders in some way. You cannot just take the pistons out since the crankcase oil would then go into the manifolds. You can actually leave the pistons in and find a way to hold the valves all open in those cylinders, then block off the manifold so that fuel does not get pumped through those cylinders. And which cylinders you disable makes a difference. There ARE some cars on the market now that do disable cylinders under light throttle. I believe these are port injected engines so the valves are disabled and those injectors shut down. On Apr 10, 10:01 am, Don Stauffer in Minnesota <stauf...@usfamily.net> wrote: > > I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this improve > > gas mileage? I only use this vehicle for short trips around town so losing [quoted text clipped - 11 lines] > light throttle. I believe these are port injected engines so the > valves are disabled and those injectors shut down. eh, not really - you'd still have an out of balance 4-cylinder. Unless you disabled them in the proper order, and *left the pistons, con rods, etc.* in the bores. (e.g., you couldn't disable cylinders 1-3-5-7 like you'd think would make sense on a typical V-8 with a firing order 1-8-4-3-6-5-7-2, but you *could* disable 2,3,5, and 8 and it might not be too rough. Physically removing the pistons and con rods would likely make the engine physically unbalanced, and would also leave open oiling holes on the rod journals not to mention no way of controlling lateral movement of the big ends of the con rods on the same journals as the removed rods.) AFAIK the real challenge in doing such a conversion would be retaining the valve lifters in their bores in the cylinders with the valves disabled - one would assume by removing the pushrods and rocker arms. If a lifter gets thrown from its bore, the engine will instantly lose most of its oil pressure, and that's bad. Even if you work around this I'm not sure how much real gain you'd see - you'd be removing the pumping losses from the disabled cylinders but you'd still have the frictional losses as you really can't remove most of the major mechanical components without serious modification, and it probably would be far easier simply to fabricate mounts to install a lighter, smaller engine without any missing parts. nate > On Apr 10, 10:01 am, Don Stauffer in Minnesota <stauf...@usfamily.net> > wrote: [quoted text clipped - 40 lines] > > nate Forgot to mention - you'd want to have the valves held *closed* not open. Despite what you'd think, leaving a column of air in a cylinder is no biggie; it takes work to compress it, yes, but you get it all back on the downstroke (minus losses, of course.) Pumping losses are gone forever, however. nate >> On Apr 10, 10:01 am, Don Stauffer in Minnesota <stauf...@usfamily.net> >> wrote: [quoted text clipped - 45 lines] > > nate And what do you do about the loss of air past the rings creating a vacuum in the cylinder above it? You will still have a LOT of loss in a typical V-8.  SignatureSteve W. Near Cooperstown, New York There is more money being spent on breast implants and Viagra today than on Alzheimer's research. This means that by 2040, there will be a large elderly population with perky boobs and huge erections and absolutely no recollection of what to do with them. >>> On Apr 10, 10:01 am, Don Stauffer in Minnesota <stauf...@usfamily.net> >>> wrote: [quoted text clipped - 52 lines] > > You will still have a LOT of loss in a typical V-8. The amount of mass in the cylinder will decrease over time until an equilibrium state is achieved. This means that the gas leakage when the pressure in the disabled cylinder is above atmospheric will be balanced by the leakage INTO the cylinder when the pressure drops below atmospheric. And yes, the equilibrium state will result in pressures near BDC being significantly below atmospheric. In this state the losses are actually very low; some mechanical friction from the ring contact and bearings, but this will be low due to the reduced pressures in the air-spring cylinders. This is why the displacement-on-demand systems are in production. They do work. >> Forgot to mention - you'd want to have the valves held *closed* not >> open. Despite what you'd think, leaving a column of air in a [quoted text clipped - 8 lines] > > You will still have a LOT of loss in a typical V-8. Believe it or not, Cadillac's V-8-6-4 of 1981 operated by holding the unused cylinder's valves closed at all times. Apparently there was no significant loss in efficiency from having the valves closed, but plenty of gain from reduced pumping losses. See the column "Mechanical Marvels" in the April 2008 issue of "Hemming's Classic Car" magazine. This article features the V-8-6-4. In 1981 I drove a new V-8-6-4 Seville on several occasions. Cylinder deactivation/activation was imperceptible, and it was fun to watch the dash readout show the change in the number of activated cylinders. When new and in correct adjustment, Cadillac's system worked very well. SignatureTegger >>> Forgot to mention - you'd want to have the valves held *closed* >>> not [quoted text clipped - 29 lines] > new and > in correct adjustment, Cadillac's system worked very well. The Cadillac system rarely worked well, and the real world gains in fuel economy never matched the claimed improvement (ditto for the current displacement on design systems from GM and Chrysler). Works good in the very predictable EPA tests, not so good in the real world (at least for some people). The only theoretical gain is from a reduction in pumping losses (not all that high at part throttle) and a slight improvement in thermal efficiency because the working cylinders are more fully charged. If / when individually controlled electrically operated valves become a real world everyday item, cylinder deactivation should be cheap, reliable, and effective. Current system are ..... Ed If you want four four cylinders, instead of eight cylinders in that vehicle.Put a factory manufactured four cylinder engine in there. cuhulin >>> Forgot to mention - you'd want to have the valves held *closed* not >>> open. Despite what you'd think, leaving a column of air in a [quoted text clipped - 10 lines] > Believe it or not, Cadillac's V-8-6-4 of 1981 operated by holding the > unused cylinder's valves closed at all times. As do the numerous systems in use today (Chrysler MDS, GM DoD, etc). The difference being that the Caddy V-8-6-4 used electric solenoids to release and re-engage the fulcrums of the rocker arms, and that system was very trouble prone. Today's systems divert oil pressure in a way that causes the lifters to either lift or not lift, and that system is EXTREMELY reliable. >> Forgot to mention - you'd want to have the valves held *closed* not >> open. Despite what you'd think, leaving a column of air in a cylinder [quoted text clipped - 6 lines] > And what do you do about the loss of air past the rings creating a > vacuum in the cylinder above it? Nothing at all. When the Chrysler MDS system and the GM DoD systems deactivate cylinders, all they do is keep the valves closed. Yes, there's a tiny leakage past the rings, but it just flat doesn't matter. So what if for 1/16 of the cycle there's negative pressure in the cylinder? Whatever air is in there always acts like a spring and you get >90% of the energy back on the other half of the cycle. > > On Apr 10, 10:01 am, Don Stauffer in Minnesota <stauf...@usfamily.net> > > wrote: [quoted text clipped - 48 lines] > > nate Right. That was my bad on valves being open. As you said, they should be closed. BTW, midget race cars have been powered for years by four cylinder engines made from V-8s. Most cut off one whole bank, but there have been a few that were cut athwartwise to create a V-4. Of course, the cranks were cut too. Don't know how well the balance was, but the things sure are powerful. There have been Chevs, Fords and Mopar engines treated this way. These are available in the market but they are FAR too expensive to use as an economy measure, though they do run on pure methanol. Lately I have been paying a lot less for methanol than gasoline, but of course the fuel consumption is twice what it is for gas, so it really is more expensive, even without the taxes. >> I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this >> improve [quoted text clipped - 10 lines] > a > way to hold the valves all open in those cylinders, No, no, no....you can't leve the valves open. If you do this multiple bad things will happen and you will makes the fuel economy worse becasue of pumping losses. If you want to deactivate four cylinders, you need to make sure both valves on those cylinders are CLOSED. With the valves closed, the air in a cylinder acts like a spring. This elimiates the pumping losses, and prevents blowing back stuff into the intake. As for which cylinder to deactivate....take a look at what Chrysler and GM do with their engines that have "displacement on demand." These V-8 deactivate 2 or 4 cylinders in order to improve fuel economy. Ed > then block off the > manifold so that fuel does not get pumped through those cylinders. [quoted text clipped - 4 lines] > light throttle. I believe these are port injected engines so the > valves are disabled and those injectors shut down. "C. E. White" <cewhite3@removemindspring.com> wrote in message news:47fe4ce6 > No, no, no....you can't leve the valves open. If you do this multiple bad > things will happen and you will makes the fuel economy worse becasue of > pumping losses. If you want to deactivate four cylinders, you need to make > sure both valves on those cylinders are CLOSED. With the valves closed, > the air in a cylinder acts like a spring. This elimiates the pumping > losses, and prevents blowing back stuff into the intake. When I was in college, I got to be friends with a mechanic who had a shop next door to where I lived. His son, a decent mechanic, was returning to town one night with his wife when he had a connecting rod problem with the old Dodge engine. He pulled off the road, jacked up the car, and dropped the pan. He removed the piston totally, jammed a rag up in the cylinder bore, and buttoned her up. He drove back home with no other modifications and made it just fine. This was a trip of some 60-70 miles. I would not have thought it possible, but it happened. > "C. E. White" <cewhite3@removemindspring.com> wrote in message > news:47fe4ce6 [quoted text clipped - 19 lines] > > I would not have thought it possible, but it happened. Probably wouldn't work for a modern engine, particularly a V-8. With a connecting rod missing on a V-8, the other rod on that journal would not be properly located and the oil flow path would be screwed up. Ed >> "C. E. White" <cewhite3@removemindspring.com> wrote in message >> news:47fe4ce6 [quoted text clipped - 23 lines] > connecting rod missing on a V-8, the other rod on that journal would not > be properly located and the oil flow path would be screwed up. Right. Some engines (most straight-sixes, for example) are balanced independent of the weight of the piston and conrod (the "bob weight."). But a v8 cannot be balanced independent of the bob weight. If you change from a heavy piston to a lighter one in a v8, you have to rebalance the whole rotating assembly. Not so with a straight six. > "C. E. White" <cewhi...@removemindspring.com> wrote in message news:47fe4ce6 > [quoted text clipped - 17 lines] > > I would not have thought it possible, but it happened. I'm skeptical as well; the lack of endplay control might not be a problem if, say, it were a seven main bearing six cylinder but I can't see how you'd keep from losing all oil pressure without plugging the hole in the crankshaft somehow. Of course, you may have been omitting a step like "he wiped down the crank with Brakleen and taped over the journal with a couple turns of metal duct tape" but the whole concept of the "repair" still makes me a little queasy :) nate "N8N" <njnagel@hotmail.com> wrote in message news:7292b385-8c22-4403-a2c8- Of course, you may have been omitting a step like "he wiped down the crank with Brakleen and taped over the journal with a couple turns of metal duct tape" but the whole concept of the "repair" still makes me a little queasy :) nate Did me too. But it happened.. That would have been in about 1964, and the Dodge would obviously have been several years older to have a con rod problem. I cannot see why he didnt essentially lose all oil pressure when he removed the con rod big end. Or, maybe he did. Maybe you can limp a long way with severely reduced oil pressure. A one way trip for that engine, Im sure. >> "C. E. White" <cewhi...@removemindspring.com> wrote in message news:47fe4ce6 >> [quoted text clipped - 28 lines] > > nate I have two uncles who did this as a stopgap measure to get home on two different vehicles. IIRC, both were straight 6's (one was an old GMC bus and the other was a Dodge car probably a /6.) They both made it a couple hundred miles, but it was apparently pretty ugly a drive. The engine needed a total overhaul anyway, in both cases they were probably 200,000 mile motors, so no concerns about long term damage, just didn't want to be stuck in Saskatchewan... Ray > I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this > improve gas mileage? I only use this vehicle for short trips around > town so losing 1/2 the horsepower will not bother me. Any thoughts?? I saw this done with a straight 6 many years ago, by removing the (solid) lifters. (Someone else mentioned the problems you'd run into doing it with hydraulic lifters.) I drove or rode in the car for a couple thousand miles in this condition, on a long trip. Running on 3 cylinders didn't change the gas mileage, it just reduced the power. On Apr 10, 2:59 pm, gringomasl...@yahoo.com wrote: > > I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this > > improve gas mileage? I only use this vehicle for short trips around [quoted text clipped - 5 lines] > miles in this condition, on a long trip. Running on 3 cylinders didn't > change the gas mileage, it just reduced the power. The issue is not solid vs. hydraulic (although hyd. lifters are *always* pressure fed, so it's good to think about) it's whether the lifters get positive, pressurized lubrication from the engine's oiling system. e.g. old Studebaker V-8s used solid lifters but also had oiling holes in the lifter bores, so that would not be a good engine to try to run with a pair of lifters removed. nate > On Apr 10, 2:59 pm, gringomasl...@yahoo.com wrote: >>> I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this [quoted text clipped - 14 lines] > > nate Other than the old splash lubed engines I cannot think of any engine made since about 1955 that doesn't have oil fed lifters. Even the Fords with external oiling to the rockers used an oil passage that fed the lifters. The 350 in the trolls post not only feeds the lifters but has a MAJOR oil passage the length of the block on both sides to send oil to the lifters an the top end of the engine. Pull even one lifter and you will lose oil pressure to feed that entire side of the engine. SignatureSteve W. Near Cooperstown, New York There is more money being spent on breast implants and Viagra today than on Alzheimer's research. This means that by 2040, there will be a large elderly population with perky boobs and huge erections and absolutely no recollection of what to do with them. The old Volvo B-18/B-20 had dry solid lifters. The valve train was lubricated through an oiling hole through the cylinder head that ended up in one of the rocker shaft pedestals. > > On Apr 10, 2:59 pm, gringomasl...@yahoo.com wrote: > >>> I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this [quoted text clipped - 22 lines] > the lifters an the top end of the engine. Pull even one lifter and you > will lose oil pressure to feed that entire side of the engine. Why would you remove the lifters? Removing the pushrods will not cause any problems in many engines. I did that to a chevy V8 40 years ago. It had a bad cam lobe so I disconected the 4 cylinders that were fed by the same barrel of the 2 barrel carb. As a 4 cylinder it ran and sounded like a tractor - slow acceleration but very steady sounded pretty good if you like that sound. It definitely did get better gas mileage since the bad cam was pretty much nullifying that half of the engine anyway. But gas was cheap and this was a station wagon so it was only run like that for a couple hundred miles until a good CAM was located. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > > > On Apr 10, 2:59 pm, gringomasl...@yahoo.com wrote: > > >>> I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this [quoted text clipped - 33 lines] > a station wagon so it was only run like that for a couple hundred miles > until a good CAM was located. It's not so much that you need to remove the lifters, it's that if they're loose in their bores, they might get smacked out of the lifter bore by the cam and then the engine would lose pressure. nate > It's not so much that you need to remove the lifters, it's that if > they're loose in their bores, they might get smacked out of the lifter > bore by the cam and then the engine would lose pressure. Lifters don't come out that easy. On an old engine you need to break thru a ring of varnish that formed that made them not slide easily out of the bore. Anyway I don't remember any problem with lifters or oil pressure and reversing it and getting it back to an eight was easy. And the engine ran excellent afterwards. If I recall (this was nearly 40 years ago) I first tried just removing the sparkplugs. It ran but was noisy and that didn't completely stop the flow of air and fuel thru the cylinders. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- I would not try to modify the existing engine. either 1) sell your vehicle and buy a vehicle with a smaller engine. Or 2) buy a new Dodge that will operate on the number of cylinders required. > On Apr 10, 2:59 pm, gringomasl...@yahoo.com wrote: >>> I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this [quoted text clipped - 14 lines] > > nate In fact, on many engines the oil "leak" you cause by removing a lifter is many many times greater than the "leak" you'd cause by removing a connecting rod! Take a Mopar or Ford v8- the lifters bores actually protrude into the main left and right bank oil galleys, so you essentially would de-pressurize the whole oiling system by leaving out one lifter. On the other hand, each rod bearing has a fairly small hole, and a healthy oil pump might easily keep up with the "leak" it would cause. At the other extreme, there's the slant-6. The solid lifter version oils the lifter bores by splash from the overhead, and oils the lifter/cam contact face by squirt from below. Removing a lifter wouldn't affect oil pressure or flow at all. > > On Apr 10, 2:59 pm, gringomasl...@yahoo.com wrote: > >>> I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this [quoted text clipped - 27 lines] > contact face by squirt from below. Removing a lifter wouldn't affect oil > pressure or flow at all. Was there ever a slant six with a hydraulic cam? nate In article <28e5966e-ecf9-4a6b-86cf-32ca5d98350f@a70g2000hsh.googlegroups.com>, > Was there ever a slant six with a hydraulic cam? > > nate 79 and newer. In the 1970s, I owned an ex Dolly Madison 1967 International walk in cube delivery van.The slant four International 152 cubic inch engine was the right hand bank of Internationals 304 cubic inch V8 engine, it had a five main bearings.Some International Scout vehicles also used the same engine.It wasen't a very smooth running engine either. cuhulin > Was there ever a slant six with a hydraulic cam? > > nate All of them from somewhere around 1978 onward through end-of-production (where's Stern when you need him?) And the way they managed to pressurize the lifters is amusing, to say the least. Putting a galley in the block to side-feed the lifters the usual way would have meant a big re-tooling, but the top-end was well supplied with oil via the rocker shaft. So they adopted a sort of "reverse Chevrolet" oiling system where pressurized oil was tapped from the rocker shaft, fed through a passage in the rocker arms, sent down hollow pushrods and into the lifters. Rube Goldberg smiled at that one, I'm sure, but it worked flawlessly (as did pretty much everything about the slant-six). Thanks gentleman for taking the time to answer my question. This is what I am I have gleamed so far. Using the firing order, I would remove from every other cylinder: the piston, connecting rod, pushrods and rocker arms. This should reduce drag from the rings, eliminate any pumping losses, and seal off the manifolds with the valves. I would leave the lifters in place (off the cam lobe) with Loctite and maybe a setscrew if there is room. I can manufacture a collar for the crankshaft journals to maintain oil pressure and locate the remaining rods. Maybe, cutoff the large end of the rod and use that. I would leave the sparkplug in, but, remove the wire. The whole point of this exercise is to improve the gas mileage for those driving vehicle with V8's. I'm thinking these cars/trucks have a lot more horsepower than they need to haul one person to work/store. Of course, if you need the HP for hauling a load, then you will just have to pay the price. And yes, you could just put in a smaller engine. But, the cost for that would in the thousands. You might as well spend that money on gas. Thanks again for your input. > I am thinking of disconnecting 4 pistons in my 350 Chevy. Will this improve > gas mileage? I only use this vehicle for short trips around town so losing > 1/2 the horsepower will not bother me. Any thoughts?? let us know how it works out for you > Thanks gentleman for taking the time to answer my question. This is what I > am I have gleamed so far. Using the firing order, I would remove from every [quoted text clipped - 18 lines] > losing > > 1/2 the horsepower will not bother me. Any thoughts?? The machine shop work for the conversion is likely to run quite a bit too, unless you have a very well-equipped shop yourself, in which case you could buy a well-used four, rebuild it yourself, and install it. > The machine shop work for the conversion is likely to run quite a bit > too, unless you have a very well-equipped shop yourself, in which case > you could buy a well-used four, rebuild it yourself, and install it. Yea, but where's the fun in that. PS. I own and operate a fully equipped machine shop. Just furnished converting a rotary engine for use on an airplane. I'm sure I can handle any machine work. But, I had completely over looked the oil pressure problem. That why I posted the question. Thanks again. >>The machine shop work for the conversion is likely to run quite a bit >>too, unless you have a very well-equipped shop yourself, in which case [quoted text clipped - 6 lines] > any machine work. But, I had completely over looked the oil pressure > problem. That why I posted the question. Thanks again. I still think that while it may be a "fun" project the balance issues and the weight of the unused portions of the block will make it less efficient and durable than, say, simply adapting a four or six cylinder engine. nate Signaturereplace "roosters" with "cox" to reply. http://members.cox.net/njnagel If you think it might be a fun project,,,,, Go for it. cuhulin > Thanks gentleman for taking the time to answer my question. This is what I > am I have gleamed so far. Using the firing order, I would remove from every [quoted text clipped - 12 lines] > that would in the thousands. You might as well spend that money on gas. > Thanks again for your input. You're still gonna need to pull the engine. Every car I've had with a V8 has a crossmember under the oilpan. Won't pulling rods off the crank kill the balance? Seriously, this sounds like a lot more work than buying a car with a smaller engine. "ray" <rollingviolation@domain.invalid.com> wrote in message news:Y4eMj.47129 > You're still gonna need to pull the engine. > Every car I've had with a V8 has a crossmember under the oilpan. > Won't pulling rods off the crank kill the balance? > Seriously, this sounds like a lot more work than buying a car with a > smaller engine. Yep, if you pull a rod and piston assemby off the crankshaft, you would have to make up a bob weight for best balance and to restrain the oil flow. In the example I gave, the piston was removed to keep the rod from going through the block on the way home, and was intended as a short term patch, not a cure. The kid got himself and wife home, but it was probably nip and tuck that they made it. Re another post, leaving lifters in a bore without a pushrod or whatever is not, IMO, a good idea. You could work out a situation to pull the lifter up off the cam face and hold it off, while still restraining oil flow, but if you leave that lifter banging off the cam and possible being slung out, that is not good hot rodding. > The whole point of this exercise is to improve the gas mileage for >those driving vehicle with V8's. I'm thinking these cars/trucks have a lot >more horsepower than they need to haul one person to work/store. Of course, >if you need the HP for hauling a load, then you will just have to pay the >price. And yes, you could just put in a smaller engine. But, the cost for >that would in the thousands. You might as well spend that money on gas. A flex-fuel project would be a far more workable vehicle. Plus... GM already brought back it's V4-6-8 with modern engine controls. If you really want the V4 concept the best route is probably getting one of those engines (and its associated control system bits) and put that in. (the new version of course) > Thanks gentleman for taking the time to answer my question. This is what I > am I have gleamed so far. Using the firing order, I would remove from every > other cylinder: the piston, connecting rod, pushrods and rocker arms. This > should reduce drag from the rings, eliminate any pumping losses, and seal > off the manifolds with the valves. And watch it shake itself to a million tiny bits because its now horribly mechanically imbalanced due to the missing weight of pistons and connecting rods...... > > Thanks gentleman for taking the time to answer my question. This is what I > > am I have gleamed so far. Using the firing order, I would remove from every [quoted text clipped - 5 lines] > horribly mechanically imbalanced due to the missing weight of pistons > and connecting rods...... Steve, could you expound on this. I can see that the large end of the rod affects balance because it is rotating. But, the small end and the piston are moving linearly. What exactly is meant by "mechanically imbalanced"? Thanks > > > Thanks gentleman for taking the time to answer my question. This is > what I [quoted text clipped - 14 lines] > are moving linearly. What exactly is meant by "mechanically imbalanced"? > Thanks I'm not Steve, but... If it's moving, it has a definite effect on balance. As-built, any given engine "expects" to be needing to move the piston, rod, and rings up and down the bore, along with having the large end of the rod spinning with the crank. Remove the weight of rod, piston, and rings, and you massively (err... no pun intended, but since it's laying there...) alter the balance of the engine. Pulling out pistons and rods is going to make at least SOME mess of the balance in pretty much any engine, but particularly so for the "V"s due to the fact that the masses are flying in two planes, rather than one. Straights and flats (like the old VW Bug or today's Subarus) as well as slants (which are effectively just a straight that's tilted) all have their pistons "only" going up and down (or in the case of a flat, "in and out") on a single plane of motion. Depending on where it is in the cycle, a V's pistons are moving either "up and out" or "down and in" - moving on two planes of motion simultaneously. Which complicates things quite a bit as far as balance goes. Take away some weight that's "supposed to be" moving up and out as another weight that compensates for is is supposed to be going down and in (or vice-versa) and the vibration is gonna get real ugly real fast, and it's only going to get worse the faster the crank spins. SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info >>> Thanks gentleman for taking the time to answer my question. This is > what I [quoted text clipped - 13 lines] > are moving linearly. What exactly is meant by "mechanically imbalanced"? > Thanks Grossly over-simplifying: A v8 crankshaft is (obviously) not straight. The big counterweights it has are there to balance out the mass of the big end of the connecting rods (as you mentioned) and ALSO to cancel out imbalances caused by the fact that the crank has to "push" or "pull" on the piston to get it to reverse its motion twice every turn of the crank. In a straight-six, flat four, and some other engine layouts, all those particular forces are cancelled out by another piston that is moving the equal-and-opposite way, and you just have a second-order effect because the pistons are at different places along the length of the crank. But in a typical v8 (we'll leave out the fact that there do exist "flat crank" v8s, but none are found in common production cars) the piston motion forces are NOT cancelled by other pistons, they're cancelled by deliberate addition of counterweights to the crank, and they have to be fine-tuned to match the actual weight of the pistons. So if you now remove some of those pistons or even replace them all with a lighter or heavier weight piston type, the crank will be out of balance. "Mechanical imbalance" just means that the shaft is out of balance. Like a washing machine with a quilt wadded up on one side in the spin cycle. |
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