Rover V8 good for only 100k miles ?
Discussion
quote:
Just to prove I did read your post (which I think was pretty well spot on) I'll just make one minor quibble ...
Never looked inside a running engine to check, but I wouldn't expect the bore wear to vary with piston speed. Piston wear probably would, though.
Glad someone read it ...!
I think that there would be wear at the contact surfaces between the piston and the bore. Which it is that wears would depend on the realtive hardnesses of the two. I made a big assumption that the piston would be significantly harder than the bore, but in fact on reflection I've got nothing to base that assumption on.
In fact, it would make sense to make the piston softer as it'd be easier to replace a worn piston.
I was fairly sure that friction is proportional to speed. This is fact was because air resistance, which is essentially friction between air and the car, definitely does increase with speed. In fact with speed squared if we're being pedantic. But I have to admit that this may not apply to friction between solid surfaces - I didn't check, so I'll take your word.
Solids will be have differently than fluid/solids because with fluids, eg air, you get boundary layers ... this really is my specialist subject (or it was a few years ago) and I could go on at length about boundary layers ... they exist in cars in places but ...
Shutting up!
I've done a swift search - Peter you're essentially right, according to this link which explains things fairly clearly, friction wouldn't be affected by speed in the way I had assumed.
www.physics.nmt.edu/~raymond/ph13xbook/node226.html
However, in the case inside a cylinder the non-normal external force ('Fext' in the diagram in the link above) would have a normal (perpendicular) component and a parallel component.
In other words, the angled thrust from the con rod would mostly push up in the cylinder (parallel) but would also push against the side wall of the bore (normal).
This would have the effect of increasing the normal force between the bore and the piston. The force would increase as the engine went faster, increasing friction with engine speed.
The normal force - and hence friction - would also increase if the piston was heavier, as it would have more momentum (so you're right there as well).
I need to get out more ...
quote:
indeed a diffuser/undertray jobber for a Griff please
Doesn't make that much difference as most of the aerodynamic issues are at the front of the car anyway. The Griff is fairly clean underneath. The aerodynamic weaknesses are easy enough to solve (done it on the 520) but needed a 80mm front splitter, lowered the front by about 3 and a bit inches and run with a rubber front skirt that touches the ground. Slightly impractical though as there is not very much ground clearance.
Steve
Oh John, now you really have gone and done it, haven't you. How about helping with boundry layers inside the intake ports ? Nothing like keeping velocities up, so air/fuel mixture does not seperate. All those blind corners/changes in direction.....so many variables with different cam open/closing events, centerlines, etc..perhaps a little vortex added here or there might help,eh ? Works in the combustion chambers, how about ports ? I think I need a nice long walk !
Oh shit what have I said? 
Ok well mostly I know (knew!!) about water rather than air (says he ducking like mad
).
But (without looking it up) I'd reckon that boundary layers in air are unlikely to be more than say 1-2 mm thick at best. They tail off rather than stopping abruptly. It's very unlikely that you'd get any significant aerodynamic benefit from trying to make use of boundary layers, although I recall Lotus doing something in F1 in the 70s/80s - but that needed skirts that were a few mm from the ground.
Inside ports etc - again, with a gas, I doubt that boundary layer effects will be significant. However (this is true for water anyway!) a rougher surface will produce a slightly thicker boundary layer and hence more resistance to flow. But painting the insdies with something smooth would reduce the diameter by the thickness of the paint layer and that might be equally (in)significant.
That's why a golf ball has dimples incidentally: it promotes a boundary layer which reduces turbulence at the back, which reduces drag, so the ball can travel further. And of course that implies that what I said above isn't exactly true: there can be aerodynamic benefits from boundary layers. But these will be more significant to a golf ball than a car.
Hmm, if we extrapolate that principle to gas flows within an engine ... if there's somewhere that produes turbulence, then maybe that turbulence could be reduced by encouraging more of a boundary layer. Wire wool on the inside of the ports, anyone??
Inside the engine boundary layers will be significant in the oil lubricating the cylinders, and in fact lubricating anything. The boundary layers and hence resistance reduce as the viscosity reduces (which happens as the oil warms up). The boundary layers will transmit shear stresses between the moving components, and so will be largely responsible for the wear inside the engine - rather than direct metal to metal contact, which would in fact knacker the engine pretty quickly (so I wasn't quite right in one of my earlier posts now that I think about it).
That's why it's better to wait till the oil's warm before hitting the loud pedal too hard!
John.
Ok well mostly I know (knew!!) about water rather than air (says he ducking like mad
). But (without looking it up) I'd reckon that boundary layers in air are unlikely to be more than say 1-2 mm thick at best. They tail off rather than stopping abruptly. It's very unlikely that you'd get any significant aerodynamic benefit from trying to make use of boundary layers, although I recall Lotus doing something in F1 in the 70s/80s - but that needed skirts that were a few mm from the ground.
Inside ports etc - again, with a gas, I doubt that boundary layer effects will be significant. However (this is true for water anyway!) a rougher surface will produce a slightly thicker boundary layer and hence more resistance to flow. But painting the insdies with something smooth would reduce the diameter by the thickness of the paint layer and that might be equally (in)significant.
That's why a golf ball has dimples incidentally: it promotes a boundary layer which reduces turbulence at the back, which reduces drag, so the ball can travel further. And of course that implies that what I said above isn't exactly true: there can be aerodynamic benefits from boundary layers. But these will be more significant to a golf ball than a car.
Hmm, if we extrapolate that principle to gas flows within an engine ... if there's somewhere that produes turbulence, then maybe that turbulence could be reduced by encouraging more of a boundary layer. Wire wool on the inside of the ports, anyone??
Inside the engine boundary layers will be significant in the oil lubricating the cylinders, and in fact lubricating anything. The boundary layers and hence resistance reduce as the viscosity reduces (which happens as the oil warms up). The boundary layers will transmit shear stresses between the moving components, and so will be largely responsible for the wear inside the engine - rather than direct metal to metal contact, which would in fact knacker the engine pretty quickly (so I wasn't quite right in one of my earlier posts now that I think about it).
That's why it's better to wait till the oil's warm before hitting the loud pedal too hard!
John.
Some back to back tests on polished vs rough inlet ports were conducted by Dave Vizzard on A-series engine. He found that the same power was produced by both heads, but the polished inlet head used a measureable amount more fuel, the specific-fuel-consumption-per-braked-horse-power had increased. Not sure why this would be, but he surposed it to be due to reduced turbulence in the inlet tract causing fuel to "drop-out" of suspension in the inlet air. Any thoughts ??
quote:
Some back to back tests on polished vs rough inlet ports were conducted by Dave Vizzard on A-series engine. He found that the same power was produced by both heads, but the polished inlet head used a measureable amount more fuel, the specific-fuel-consumption-per-braked-horse-power had increased. Not sure why this would be, but he surposed it to be due to reduced turbulence in the inlet tract causing fuel to "drop-out" of suspension in the inlet air. Any thoughts ??
Reduced turbulence certainly could lead to fuel dropping out of suspension (if it's suspended not dissolved). Could the polished surface reduce turbulence? I don't know, maybe, I guess it'd have to depend on the geometry of the inlet tract.
But there certainly isn't a clear relationship that increased surface friction = thicker boundary layers = less turbulence = less drag, even if it works for a golf ball.
So Dave Vizzard could well be right. Since I don't actually know what an inlet tract is (enlightement, anyone?) I'm really not qualified to comment more.
On the golf ball example, the dimples work by encouraging a thicker boundary layer which in turn encourages the air stream to 'stick' to the ball and flow around the back of it, rather than departing off the top. This in turn reduces the area of turbulence, which would tend to occur in between the departing air streams. In fact, it's not the turbulence as such that causes drag but the lower air pressure in the same area causing a 'suction' effect (ever cycled close behind a bus? I managed 40mph with virtually no effort once, then realised, hey I'm 2 feet away and this thing is likely to stop!). The lower pressure is also responsible for the turbulence so the association is turbulence = drag.
Boundary layer, in case anyone is wondering:
When a solid object is moving through a fluid (gas or liquid) then the fluid molecules immediately adjacent to the solid surface do not move relative to it (ie thay are carried along with it). The fluid molecules that are a little bit away from the surface move slowly, but only a certain distance away from the surface do the fluid molecules move past the solid surface at the notional 'speed' of the solid object. The area in which the molecules are moving slower than full speed, or not at all, is the boundary layer.
>> Edited by JohnLow on Wednesday 15th May 23:08
Very good John, now you are starting to dig deeper ! Inlet tract = intake/injection runners (ports), and the intake ports in the cylinder head. BSFC increases due to fuel dropping out of suspension,sticking to port walls etc., so engine requires more fuel to produce power. In other words.....need X amount of fuel to coat ports, plus fuel to burn in combustion chambers = XX amount. Now if we can eliminate the seperation effect....same power less fuel used. Very important to American NASCAR builders, sometimes even more important than increased HP. The surface does have an effect on flow/swirl not only in the ports, but combustion chambers also. Not to be forgoten, the size of the port is very crucial to the speed of incoming charge. The larger the area, you get a corresponding decrease in flow velocity, thus allowing even more fuel to seperate (excluding turbo/supercharged engines). A vortex can be added, as in combustion chambers to increase swirl, move the boundry layer around, which in turn changes the direction of the incoming charge, such as when "turtles" are added to an engine to help poor fuel distribution cases. In the c/chamber case, it aids the flame front (propagation) in low swirl areas,such as piston crowns etc..Now with all these different ideas & thoughts flying around-this is what a tech site is all about ! Can anyone help John out ? I'm affraid he may suffer from the smoke from the ears syndrome soon ;>)
Was not implying that you had a problem understanding my "big words", but rather a weak try at humor, on my part. You and the others have been very helpful with tech information, and possibly unlike me I have to sometimes reach very far back into the memory bank,smelly book department, to dredge up long forgotten info (good or bad). This effort, along with the hour it is tried at, definately causes me to suffer from brain overload/smoke from ears syndrome sometimes. More power to you if this malady does not affect you...many thanks for your input......now where is that liquid to put out the fire in me ears :>) ALAN
Nonono ... I wasn't being entirely serious either! (we need a :tongueincheek: smiley!)
I did have to reread it a few times though!
I'm quite happy to answer questions if I know or can get close to the answer (beats working for a living!) - and I'll put my hand up if I haven't a clue.
Like now: Turtles?
(Incidentally a few paragraph spaces do make it easier on the eye)
I could take voluntary severance and retrain as a teacher!
>> Edited by JohnLow on Saturday 18th May 22:17
I did have to reread it a few times though!
I'm quite happy to answer questions if I know or can get close to the answer (beats working for a living!) - and I'll put my hand up if I haven't a clue.
Like now: Turtles?
(Incidentally a few paragraph spaces do make it easier on the eye)
I could take voluntary severance and retrain as a teacher! >> Edited by JohnLow on Saturday 18th May 22:17
Still treading water and monitoring the posts on this thread, most educational 
Silly questions to throw in here, why do petrol cars not have direct injection? Next silly question why does the rover V8 injection system work by banks, wouldn't it be more fuel efficient if it was sequential?
Harry
Awaiting the next lesson with sharp pencil at the ready
Silly questions to throw in here, why do petrol cars not have direct injection? Next silly question why does the rover V8 injection system work by banks, wouldn't it be more fuel efficient if it was sequential?
Harry
Awaiting the next lesson with sharp pencil at the ready
I'll happily put my hand up and say I have trouble with the big words; but then I did 4 languages at school and bugger-all science. 
Fat lot of good it did me, other than being able to ask for a blow-job in French (Pardonnez-moi, mademoiselle: est-ce que tu fait la pipe?)
But I digress... HarryW, I've pondered that Rover V8 injection thing as well: basically it's a very simple system with minimal data from sensors to tell it what's going on, one step up from a carb perhaps?. Modern cars use crank position, speed, TDC, knock, temperature, etc. and can figure out instantaneously what needs to be done. The Rover has temperature and a firing pulse from the distributor (OK, the later ones got a 'bit' more involved, but not much) and my guess is that it could, in effect, make do with one 'big' injector into the plenum, for all the accuracy it actually has; firing 4 at a time, when only one cylinder is actually drawing. An improvement on the old Bosch 'constant-dribble' K-Jetronic, then...;-)
Bearing in mind that the Sinclair ZX80 was new technology when the Rover ECU was designed, and modern cars have (roughly) a Pentium 2, you can see the computational difficulties!
On another tack, I had a mate who was an aerodynamicist for a missile manufacturer; he told me about the golf ball dimples. Apparently it had been proposed to cover an entire aircraft in dimples, but whether it's been done yet I know not...
Said mate's biggest claim to fame was writing off two TVRs!
W.
Fat lot of good it did me, other than being able to ask for a blow-job in French (Pardonnez-moi, mademoiselle: est-ce que tu fait la pipe?) But I digress... HarryW, I've pondered that Rover V8 injection thing as well: basically it's a very simple system with minimal data from sensors to tell it what's going on, one step up from a carb perhaps?. Modern cars use crank position, speed, TDC, knock, temperature, etc. and can figure out instantaneously what needs to be done. The Rover has temperature and a firing pulse from the distributor (OK, the later ones got a 'bit' more involved, but not much) and my guess is that it could, in effect, make do with one 'big' injector into the plenum, for all the accuracy it actually has; firing 4 at a time, when only one cylinder is actually drawing. An improvement on the old Bosch 'constant-dribble' K-Jetronic, then...;-)
Bearing in mind that the Sinclair ZX80 was new technology when the Rover ECU was designed, and modern cars have (roughly) a Pentium 2, you can see the computational difficulties!
On another tack, I had a mate who was an aerodynamicist for a missile manufacturer; he told me about the golf ball dimples. Apparently it had been proposed to cover an entire aircraft in dimples, but whether it's been done yet I know not...
Said mate's biggest claim to fame was writing off two TVRs!
W.
Wedg1e pretty much covered the injection portion, with the exception of your direct port question. The only experience I have is with an alcohol powered engine, equipped with down nozzles. Down nozzles (before the questions start), inject fuel directly into the cylinder head...same as direct diesel injection. The problem, clogging of nozzles,even with alky, so would assume the same or worse for gasoline powered engine. Yes the engine still has normal intake nozzles also upstream. "Paragraph" sometimes deleted when I have tunnel vision, and am only concerned with content of reply and not how it is formatted. Also indicates lack of higher education, as mine was all aquired in the back seat of a car ! "Turtles", invented by an American named Jean Dittmer. As the name implies, shaped like a turtle shell, with critter withdrawn ! Inserted into intake tracts, have the ability to change flow direction, and keep air/fuel mixture suspended. An invaluable tuning aid for engines with fuel distribution problems to one or more cylinders. When done properly, improved fuel mixture and atomization results, usually requiring a change in jetting. Just imagine a shell with small grooves milled into it, directing the mixture in another direction. Shallow groove,little change,large groove,big change. Just what you need to do on a rainy day, with nothing better to do than fiddle around with the flow bench. Oh yea, better make sure they a real SECURE to the engine, as when they become dislodged, they get swallowed by same ! Alan
>> Edited by MOTORMAN377 on Monday 20th May 02:05
>> Edited by MOTORMAN377 on Monday 20th May 02:05
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