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Thread: The Technical Questions Thread

  1. #136
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    Manufacturers hook the engine up, run them on the red line for a few minutes and then put them into your car.
    As far as I know, you only get one chance to get enough pressure in the cylinder to get a good piston ring seal which means full throttle. If someone has some alternative theory on how to get a good seal it would be interesting to hear it.

  2. #137
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    Yes, I've heard that theory as well. Which one is best?

  3. #138
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    Quote Originally Posted by Matra et Alpine View Post
    Based on factu, not opinion or single instances.
    Your view is based on what ?
    meaning that you have seen an engine that had trouble solely caused because it was run hard (after it was fully warm) but before the recommended run-in milage was achieved?



    Quote Originally Posted by Matra
    Overhaul ? New cams, followers, rings,
    Yes yes and yes.
    Quote Originally Posted by Matra
    liners,
    Didn't replace them but I got the engine re-honed.
    Quote Originally Posted by Matra
    bearings,
    the majority of them yes.
    Quote Originally Posted by Matra
    oil pump,
    Nope it was in pristine condition but it was apparently changed 5K kms before I overhauled it.
    Quote Originally Posted by Matra
    valve stems, valve seats, valves
    I replaced the valves and spings valve seats are original.
    Quote Originally Posted by Matra
    If all of those then you've run a risk.
    I'm not worried in the least.

    Quote Originally Posted by Matra
    So the fact that someone has lived to 100 and smoked all his/her life is justification for everyoen believing that smoking doesn't harm us ?
    no but I haven't seen much proof that running an engine hard (when warmed) before run-in milage is complete will lead to damage later on.

    Quote Originally Posted by Matra
    Compared to what ?
    Obviously compared to how it felt before being overhauled... Silly Matra
    Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
    Engine torque is an illusion.

  4. #139
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    Quote Originally Posted by H12 View Post
    Manufacturers hook the engine up, run them on the red line for a few minutes and then put them into your car.
    As far as I know, you only get one chance to get enough pressure in the cylinder to get a good piston ring seal which means full throttle. If someone has some alternative theory on how to get a good seal it would be interesting to hear it.
    You don't get a good seal unless you run the engine at WOT under load. Revving it in neutral does no good. Also Manufacturers do alittle more then just rev it to redline for a few minutes.
    Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
    Engine torque is an illusion.

  5. #140
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    Quote Originally Posted by hightower99 View Post
    meaning that you have seen an engine that had trouble solely caused because it was run hard (after it was fully warm) but before the recommended run-in milage was achieved?
    Lots of them. I've worked on cars for 40 years
    Poor oil consumption, rattly, leaks.
    Less common now as many engines are manufactured by seperate factory and they do the run-in and use pre-treatments to replace the need for 100s of miles of "care".
    no but I haven't seen much proof that running an engine hard (when warmed) before run-in milage is complete will lead to damage later on.
    Glad you're happy to have the risk.
    You really should have discussed it with an engine builder though who would have advised proper procedures. I pointed out one I had to do only last year in replacing cam in Ford CVH....... Performance cam MANUFACTURER stated instructions were a 20 minute - NO LOAD - at 5000 revs.
    Obviously compared to how it felt before being overhauled... Silly Matra
    Well that's not a very good comparison IS It ( hence not silly ).

    Really ht, at the high prices of petrol, you really need to stop pouring it over yourself

    If an engine DIDN'T feel "better" after an overhaul I'd be very VERY concerned. BUT, a more appropriate comparison would be with a new engine or another - properly bedded in - engine.

    Silly .... burning .... .... ht
    "A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'

  6. #141
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    Quote Originally Posted by Matra et Alpine View Post
    If an engine DIDN'T feel "better" after an overhaul I'd be very VERY concerned. BUT, a more appropriate comparison would be with a new engine or another - properly bedded in - engine.

    Silly .... burning .... .... ht
    I agree completely. One thing I'd like to add though- the only accurate comparison would be between properly run in engines and those that are not, both from the same factory. But to be truly certain you'd need to do this thousands of times.



    Which, incidently, is exactly what auto manufacturers have done. And they recommend run-in procedures.

  7. #142
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    Quote Originally Posted by Matra et Alpine View Post
    Lots of them. I've worked on cars for 40 years
    Poor oil consumption, rattly, leaks.
    Less common now as many engines are manufactured by seperate factory and they do the run-in and use pre-treatments to replace the need for 100s of miles of "care".
    Really? You sure that the sole cause of the damage was running the engine hard (we are not talking overloading the engine or stupid driving) after the engine was warm but before the manufacturers procedure was performed? I find that hard to believe.

    Quote Originally Posted by Matra
    Glad you're happy to have the risk.
    You really should have discussed it with an engine builder though who would have advised proper procedures. I pointed out one I had to do only last year in replacing cam in Ford CVH....... Performance cam MANUFACTURER stated instructions were a 20 minute - NO LOAD - at 5000 revs.
    Well I trusted the experiance of Motoman Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power
    granted motorcycle and car engines can be different beasts. Also if I got new cams and the manufacturers said they neede 20 mins no load at 5000RPM I would ask them why?... Why does a cam need to run at 5000RPM under no load? vibration issues?

    Quote Originally Posted by Matra
    Well that's not a very good comparison IS It ( hence not silly ).

    If an engine DIDN'T feel "better" after an overhaul I'd be very VERY concerned. BUT, a more appropriate comparison would be with a new engine or another - properly bedded in - engine.
    I overhauled it more to see how it looked and because I wanted to make sure that it wouldn't break on me. It didn't need it but it certainly feels much better now, much more free-revving, feels better at low rpm and at redline. doesn't drink oil at all (I change it often though) emissions improved (one of the oil control rings wasn't working properly). On top of that it feels better than the 5 other 325i (owned by friends) I have driven (same chassis and a max age difference of 2 years).

    Of course that is all subjective but I always seem to stay ahead of the others.
    Last edited by hightower99; 07-29-2007 at 07:41 AM.
    Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
    Engine torque is an illusion.

  8. #143
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    Hey guys I don't remember which thread it was but there was an argument and HP/L came up. Someone said that this is a frivolous point was just looking to see both sides of the argument, any information would be appreciated thanks.

  9. #144
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    Quote Originally Posted by Viper007 View Post
    Hey guys I don't remember which thread it was but there was an argument and HP/L came up. Someone said that this is a frivolous point was just looking to see both sides of the argument, any information would be appreciated thanks.
    Last edited by Quiggs; 08-04-2007 at 03:09 PM.
    [O o)O=\x/=O(o O]

    The things we do for girls who won't sleep with us.

    Patrick says:
    dads is too long so it wont fit
    so i took hers out
    and put mine in

  10. #145
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    DO a search and browse the threads so we don't have to go into ALL the details (again)

    Summarising .... hp/l is an engineering goal and used to judge possible solutions and maintenance schedules, materials and lubrication needs.
    It's a techie thing that has sadly been hijacked by fanboys the world over and abused
    "A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'

  11. #146
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    nooh..the onslought of ls7 vs vtec will be unbearable!
    autozine.org

  12. #147
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    Ok, I'm here to hijack this thread again, with many questions.

    If diesel fuel is more energy dense in terms of both mass and volume, why is it that most n naturally aspirated diesel engines produce less energy than similarly sized naturally aspirated gasoline engines?

    Why do diesel engines not use spark plugs? Why doesn't someone make a diesel engine with spark plugs and a smaller compression ratio - is this less effcient? Does the combustion that comes from compression of the gas promote a more through burn? Why doesn't someone make a gasoline engine with a sufficiently high compression ratio so that spark plugs are not needed?

    Is it possible for a two-stroke engine to have a camshaft?

    Why don't we see any two-stroke diesels in the automobile market? They would produce nearly twice the power of a four-stroke diesel and would still return a relatively good fuel economy, would they not?

    That's all I can think of for now, if any of my questions sound stupid, keep in mind I am only learning about engines and have a somewhat limited grasp on how they function.

  13. #148
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    Quote Originally Posted by Kitdy View Post
    If diesel fuel is more energy dense in terms of both mass and volume, why is it that most n naturally aspirated diesel engines produce less energy than similarly sized naturally aspirated gasoline engines?
    I think you mean to ask why NA diesel engines make less peak power than similarly sized NA petrol engines right? The simple answer is that because diesel engines are designed to be stronger they cannot rev as high (ever noticed that diesel engines almost never rev past 5000RPM?). There are ofcourse other factors like: because they are designed with a higher compression ratio the valve system cannot be properly optimized for high RPM flow ect. ect.

    Quote Originally Posted by Kitdy
    Why do diesel engines not use spark plugs?
    I think you have misunderstood something if you have to ask this question. A diesel engine is not called a diesel engine simply because it burns diesel fuel but because it is a Heterogenous Compression Ignition engine that works according to the Diesel cycle (as opposed to the Otto cycle that petrol engines use).


    Quote Originally Posted by Kitdy
    Why doesn't someone make a diesel engine with spark plugs and a smaller compression ratio - is this less effcient?
    Yes it is less efficient. Higher compression ratio = higher efficiency.


    Quote Originally Posted by Kitdy
    Does the combustion that comes from compression of the gas promote a more through burn?
    Depends when talking about lean mixtures yes when talking about stoichiometric or rich mixtures then no.


    Quote Originally Posted by Kitdy
    Why doesn't someone make a gasoline engine with a sufficiently high compression ratio so that spark plugs are not needed?
    This is actually being done it is called a HCCI engine (Homogenous Charge Compression Ignition).

    Quote Originally Posted by Kitdy
    Is it possible for a two-stroke engine to have a camshaft?
    Yes ofcourse but why?

    Quote Originally Posted by Kitdy
    Why don't we see any two-stroke diesels in the automobile market? They would produce nearly twice the power of a four-stroke diesel and would still return a relatively good fuel economy, would they not?
    I am not sure why two-stroke diesel engines don't appear in cars I would imagine it has something to do with emissions?
    Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
    Engine torque is an illusion.

  14. #149
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    Quote Originally Posted by Kitdy View Post
    Ok, I'm here to hijack this thread again, with many questions.

    If diesel fuel is more energy dense in terms of both mass and volume, why is it that most n naturally aspirated diesel engines produce less energy than similarly sized naturally aspirated gasoline engines?
    diesel has a lower calarific value (MJ/Kg) than petrol and hence will release less energy under similar burning conditions.

    Quote Originally Posted by Kitdy View Post
    Why do diesel engines not use spark plugs? Why doesn't someone make a diesel engine with spark plugs and a smaller compression ratio - is this less effcient? Does the combustion that comes from compression of the gas promote a more through burn? Why doesn't someone make a gasoline engine with a sufficiently high compression ratio so that spark plugs are not needed?
    diesel burns different to petrol. while petrol has more energy, it has more unpredictable combustion characteristics. a higher compression ratio is of course desirable and this is the key to diesel fuel economy. Thermal efficincy of diesel is 30% compared to 25% (roughly) for petrol. So basically because diesel fuel is more stable at higher temperatures than more volatile petrol which needs a spark plug to ensure near-instantaneus fuel burning of entire mixture. nderstanding that petrol is a ideally a constant volume combustion (instant) and diesel is a constant pressure (burns through downstroke) combustion helps, but this is harder to visualise

    without spark plugs and too high compression ratio (incresed fuel temp.) knocking occurs in a petrol engine. Thats when parts of the fuel/air mixture react too early. However this is detonating, not burning, creating supersonic soundwaves. This is relevant because more advanced petrol engines use ionic knock control to listen out for this sypmtom in order to allow the ECU to get the latest spark ignition in order to acheive more efficiency...

    In a diesel engine the same thing simply results in progressive burning of diesel fuel droplets releasing a steady supply of heat energy.


    Quote Originally Posted by Kitdy View Post
    Is it possible for a two-stroke engine to have a camshaft?

    Why don't we see any two-stroke diesels in the automobile market? They would produce nearly twice the power of a four-stroke diesel and would still return a relatively good fuel economy, would they not?
    emmisions and refienent are the main issues. since 2 stroke uses porting timing is critical and only one rpm is catered for really. perhaps someone could cover this in better detail.

    just ask if you need some points expanded..
    Last edited by jediali; 12-16-2007 at 03:56 PM.
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  15. #150
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    heterogeneous - occurs in petrols and throttles air supply and adds appropriate fuel quantity (ideally stoichiometric, 14.7:1) therefore cylinder size does not necesarily represent air/fuel mixture volume entering hence lesser volumetric efficiency.

    homogeneus - always allows fuel provision of air to cylinders, this time accelerator adjusts fuel deliverd through injectors (usually direct into cylinders) therefore maximising volumetric efficiency and reducing unburnt fuel.

    in theory both these engines at WOT (wide open throttle) would be similar in intake delivery.

    Quote Originally Posted by hightower99 View Post
    This is actually being done it is called a HCCI engine (Homogenous Charge Compression Ignition).
    clever stuff this...worth looking out for. vauxhall are running this as we speak. this has been allowable through advancements in ECU and engine tolerances. I also think it has a lot to with good combustion chamber where there are no hot spots (hottest point of combustion chamber which sets of fuel to early - usually the exhaust valve or something else sticking out).
    Last edited by jediali; 12-17-2007 at 08:16 AM.
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