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Thread: Holden Captiva - Opinions?

  1. #41
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 12:42 PM, John_H wrote:

    > The distinct lack of a respectable power band in the rotary will be
    > the main factor... along with a wide ratio gearbox that won't anything
    > like provide the step ratios needed to utilise the rote's power band.
    >
    > Since I can't be bothered chasing them up how about you provide the
    > respective maximum power and maximum torque figures with their
    > corresponding rpm. The transmission ratios would also be useful.


    I'll have to get back to you with those as I don't have them here handy,
    or the time to find them right now either.

    > At that point I'd expect the answer to be very obvious (to me at
    > least).
    >
    > And FFS don't snip the figures you've already provided as they're also
    > a vital part of the story, even if you have omitted the most important
    > bits. :)


    What are you on about?





    --
    --
    Regards,
    Noddy.

  2. #42
    Ext User(D Walford) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/2013 12:24 PM, John_H wrote:
    > D Walford wrote:
    >> On 24/07/2013 8:24 AM, John_H wrote:
    >>> D Walford wrote:
    >>>>
    >>>> It is if both vehicles tow exactly the same weight, they both have 126kw
    >>>> and the Forester's kerb weight is 235kg less so it already had a power
    >>>> to weight advantage yet its towing performance is abysmal.
    >>>
    >>> Because of the gearing.
    >>>
    >>> Even though the final drive ratios are similar, because the Hilux
    >>> develops it's maximum power (and torque) at lower revs it's
    >>> effectively much lower geared.
    >>>

    >>
    >> That's an odd way of looking at it.

    >
    > Only to some it would seem! :)
    >
    > Perhaps you've never heard of, or else don't understand, the concepts
    > of under gearing and over gearing, which are the design factors that
    > have the most influence on a car's performance in relation to the
    > final drive ratio.
    >
    > It used to be common practice in competition cars (the serious ones at
    > any rate), and probably still is, to change their axle ratios to suit
    > the type of competition or even to suit a particular race track. It
    > involves selecting the axle ratio that matches the maximum power revs
    > (not torque) to the maximum speed expected to be attained.
    >
    > For example, if setting up car for a quarter mile drag race the ideal
    > ratio is the one where it just hits maximum revs as it crosses the
    > line. (Noddy may or may not agree.) :)
    >
    > As it applies to road cars an overgeared car is one that's too high
    > geared to ever attain its potential maximum speed in top gear. The
    > term 'overdrive', which you've almost certainly heard, implies that
    > situation... ie a gear ratio which over gears the car.
    >
    > An undergeared car is one that will exceed it's maximum power rpm (not
    > torque) in its highest gear. It's also the one I'd expect to have the
    > best performance through all of its gears.
    >
    > Getting back to your examples, most modern petrol engined road cars
    > are overgeared (because they're geared for economy rather than optimum
    > performance) as is your Forester.
    >
    > Diesels are mostly undergeared, and especially commercials, ranging
    > from utes to prime movers. It's done solely for performance and
    > economy isn't such an issue since diesels are at their most efficient
    > when operating within their power band. It's also the reason why
    > diesels with lower maximum power outputs can have similar performance
    > to their petrol engined counterparts (and nothing to do with maximum
    > torque).
    >
    > You could easily verify what I'm telling you by comparing the maximum
    > power revs of both (and not the maximum torque revs) against their
    > likely maximum speeds in the absence of a speed limiter. In any case
    > your Forester almost certainly won't hit the speed limiter in top gear
    > whereas your Hilux almost certainly will, which also reflects their
    > gearing status.
    >
    > If you've managed to get this far, it's the reason why you can't
    > simply replace a 500kW diesel with a 500kW V8 petrol engine and get
    > the same performance through all of the gears... which is what seems
    > to bother Noddy.
    >
    > It's also the reason why your Hilux is better suited to towing than
    > your Forester (and has SFA to do with their respective maximum torque
    > figures). Put higher ratio diffs in the Forester and it will be more
    > than a match for the Hilux, in spite of its lower maximum torque
    > figure.


    Lowering the diff ratio would certainly help the Foresters towing
    ability and there is no doubt that it is over geared to improve economy
    but it would still need to be revved a lot higher whilst using a lot
    more fuel which still means that the Hilux would do a better job towing.
    Best thing I could do to the Forester would be be fit a turbo:-)
    You also seem to be saying that the torque figures quoted by
    manufacturers are meaningless?


    --
    Daryl

  3. #43
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 8:24 AM, John_H wrote:

    > Then you still don't get it!


    If you're saying that I'm not buying the theoretical physics as being
    the case in every real world example, then yeah I'm not :)

    > The diesel with 1500Nm of torque will also bog down under maximum load
    > once the revs drop below the power band.


    I wasn't arguing that point. I was simply saying that one third of the
    torque won't do the same amount of work.

    > Once we've established the relevance you may then wish to discuss
    > precisely why the 'torque monster' you built couldn't possibly achieve
    > the outputs claimed, since the bmep (which is also a theoretical
    > figure, derived from torque) isn't likely to have matched NASCAR's
    > best for comparable engines (as it did, based on dyno measurements
    > that don't stand up to the established theory).


    How do you know it couldn't have? Nascar engines aren't formula one :)

    > I chose that example because it demonstrates what is obviously your
    > perception of torque, based no doubt on a mechanic's intuition,
    > whereas mine's based on the physics textbook! :)


    I hear where your coming from, but your physics text book would have us
    believe that makes bugger all difference to anything.




    --
    --
    Regards,
    Noddy.

  4. #44
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 2:10 PM, John_H wrote:

    > Ignoring forced induction (only because it obfuscates the basics)...
    > when you modify an engine for performance what do you expect to
    > increase... torque or power?


    It depends totally on what the requirements are, but generally it's for
    power as that plays the most significant role in acceleration.

    > If the answer does happens to be torque you might also explain what
    > you need to do to increase it significantly (excluding forced
    > induction).


    Increase the stroke and play with rod ratios basically.


    --
    --
    Regards,
    Noddy.

  5. #45
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 12:24 PM, John_H wrote:

    > For example, if setting up car for a quarter mile drag race the ideal
    > ratio is the one where it just hits maximum revs as it crosses the
    > line. (Noddy may or may not agree.) :)


    Not completely, but it's close enough :)

    > If you've managed to get this far, it's the reason why you can't
    > simply replace a 500kW diesel with a 500kW V8 petrol engine and get
    > the same performance through all of the gears... which is what seems
    > to bother Noddy.


    It doesn't bother me at all, as I'm not talking about that.

    > It's also the reason why your Hilux is better suited to towing than
    > your Forester (and has SFA to do with their respective maximum torque
    > figures). Put higher ratio diffs in the Forester and it will be more
    > than a match for the Hilux, in spite of its lower maximum torque
    > figure.


    What you're saying on the one hand is that torque means jack, but on the
    other you need to change gear ratio's to allow for the lack of it :)



    --
    --
    Regards,
    Noddy.

  6. #46
    Ext User(John_H) Guest

    Re: Holden Captiva - Opinions?

    D Walford wrote:
    >
    >You also seem to be saying that the torque figures quoted by
    >manufacturers are meaningless?


    They're only meaningless when quoted in the absence of revs (as Noddy
    has done in the Roadpacer example)... which is the whole point I've
    repeatedly tried to make from the outset that you both appear to have
    missed! :(

    *The main significance of the maximum torque figure is where it occurs
    in the rev range relative to maximum power, which is what determines
    the engine's power band.*

    When Noddy comes good with the vital information he omitted I might be
    able to demonstrate why (but I won't be holding my breath). :)

    --
    John H

  7. #47
    Ext User(John_H) Guest

    Re: Holden Captiva - Opinions?

    Noddy wrote:
    >On 24/07/13 12:42 PM, John_H wrote:
    >>
    >> And FFS don't snip the figures you've already provided as they're also
    >> a vital part of the story, even if you have omitted the most important
    >> bits. :)

    >
    >What are you on about?


    You quoted the power and torque figures in isolation of revs which
    makes them meaningless in the context of comparing the performance of
    the two engines. However the rest of figures you quoted (and have now
    snipped) will become relevant once the revs are known!

    --
    John H

  8. #48
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 5:26 PM, John_H wrote:

    > You quoted the power and torque figures in isolation of revs which
    > makes them meaningless in the context of comparing the performance of
    > the two engines.


    I quoted those because they were all that I could find at the time. Revs
    weren't mentioned otherwise I would have quoted them. It makes no
    difference to me.

    > However the rest of figures you quoted (and have now
    > snipped) will become relevant once the revs are known!


    I suspect it'll only make a difference to you though. To me it doesn't
    matter where the engines make their respective power or if the chassis
    are geared to suit them. In the race between zero and flat out even a
    direct drive set-up will hit it's straps eventually.

    "All else being equal" comparisons don't really work here because the
    theoretical physics won't permit all else to actually *be* equal. So,
    even if you provided an optimally geared chassis to suit the 500hp car
    engine It *still* wouldn't be capable of doing the same work as a 500hp
    diesel making three times the torque.

    In my opinion.




    --
    --
    Regards,
    Noddy.

  9. #49
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 5:26 PM, John_H wrote:

    > They're only meaningless when quoted in the absence of revs (as Noddy
    > has done in the Roadpacer example)... which is the whole point I've
    > repeatedly tried to make from the outset that you both appear to have
    > missed! :(


    Not missed John. Just don't think it's relevant.

    > *The main significance of the maximum torque figure is where it occurs
    > in the rev range relative to maximum power, which is what determines
    > the engine's power band.*


    I think you're getting lost in the technicalities. It doesn't matter if
    you have to rev the engine to 1500rpm or 5000rpm to make it work to it's
    maximum, and I wasn't interested in *how* you had to go about making the
    engine work.

    What I *was* interested in was how well the 500hp petrol engine could
    manage doing the same work while dealing with only one third of the
    torque output, and the differences in how the two engines had to work to
    make their power is irrelevant to me.

    > When Noddy comes good with the vital information he omitted I might be
    > able to demonstrate why (but I won't be holding my breath). :)


    As you please. I'll try finding the specs after dinner :)



    --
    --
    Regards,
    Noddy.

  10. #50
    Ext User(D Walford) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/2013 5:26 PM, John_H wrote:
    > D Walford wrote:
    >>
    >> You also seem to be saying that the torque figures quoted by
    >> manufacturers are meaningless?

    >
    > They're only meaningless when quoted in the absence of revs (as Noddy
    > has done in the Roadpacer example)... which is the whole point I've
    > repeatedly tried to make from the outset that you both appear to have
    > missed! :(


    I haven't missed it at all, for example the quoted maximum torque of the
    Hilux is at 1400rpm and the Forester 4400rpm so the Hilux power band is
    between 1400-3600rpm and the Foresters 4400 -6000rpm which makes the
    Hilux's power band wider and a lot more useful.

    >
    > *The main significance of the maximum torque figure is where it occurs
    > in the rev range relative to maximum power, which is what determines
    > the engine's power band.*
    >
    > When Noddy comes good with the vital information he omitted I might be
    > able to demonstrate why (but I won't be holding my breath). :)
    >

    I hope he knows what you are talking about because I don't.

    --
    Daryl

  11. #51
    Ext User(jonz) Guest

    Re: Holden Captiva - Opinions?

    On 7/24/2013 5:26 PM, John_H wrote:
    > Noddy wrote:
    >> On 24/07/13 12:42 PM, John_H wrote:
    >>>
    >>> And FFS don't snip the figures you've already provided as they're also
    >>> a vital part of the story, even if you have omitted the most important
    >>> bits. :)

    >>
    >> What are you on about?

    >
    > You quoted the power and torque figures in isolation of revs which
    > makes them meaningless in the context of comparing the performance of
    > the two engines. However the rest of figures you quoted (and have now
    > snipped) will become relevant once the revs are known!

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    A wee reminder, The _real_ world is still here, semantics, and theory,
    tend to cloud the outcome.
    >



    --
    “Usenet is like a herd of performing elephants with diarrhea- massive,
    difficult to redirect, awe-inspiring, entertaining, and a source of mind
    boggling amounts of excrement when you least expect it”

  12. #52
    Ext User(John_H) Guest

    Re: Holden Captiva - Opinions?

    Noddy wrote:
    >On 24/07/13 8:24 AM, John_H wrote:
    >
    >> Then you still don't get it!

    >
    >If you're saying that I'm not buying the theoretical physics as being
    >the case in every real world example, then yeah I'm not :)


    The theoretical physics you're apparently having a problem with has
    been long proven, going right back to James Watt, and Isaac Newton
    before that!

    >> The diesel with 1500Nm of torque will also bog down under maximum load
    >> once the revs drop below the power band.

    >
    >I wasn't arguing that point. I was simply saying that one third of the
    >torque won't do the same amount of work.


    Of course it will, power is the rate of work (by definition) not
    torque.

    >> Once we've established the relevance you may then wish to discuss
    >> precisely why the 'torque monster' you built couldn't possibly achieve
    >> the outputs claimed, since the bmep (which is also a theoretical
    >> figure, derived from torque) isn't likely to have matched NASCAR's
    >> best for comparable engines (as it did, based on dyno measurements
    >> that don't stand up to the established theory).

    >
    >How do you know it couldn't have? Nascar engines aren't formula one :)


    Their bmep figures (calculated from torque) have been widely
    published... google should find them. The specific torque figure
    derived from the torque value you provided (which was something
    significantly in excess of 90Nm per litre IIRC) would've made your
    engine a potential NASCAR winner, even if its maximum power output
    wouldn't... the only difference being down to revs! Actually NASCAR's
    claimed bmep figures are also regarded with some suspicion among those
    who take note of such things, since they are right up there with F1.

    >> I chose that example because it demonstrates what is obviously your
    >> perception of torque, based no doubt on a mechanic's intuition,
    >> whereas mine's based on the physics textbook! :)

    >
    >I hear where your coming from, but your physics text book would have us
    >believe that makes bugger all difference to anything.


    Especially if you happen to base your belief as to the significance of
    torque on the technical irrelevance that's often propagated by
    motoring journos and sales droids... ie torque and power figures
    quoted in the absence of the corresponding revs! :)

    --
    John H

  13. #53
    Ext User(John_H) Guest

    Re: Holden Captiva - Opinions?

    Noddy wrote:
    >On 24/07/13 2:10 PM, John_H wrote:
    >
    >> Ignoring forced induction (only because it obfuscates the basics)...
    >> when you modify an engine for performance what do you expect to
    >> increase... torque or power?

    >
    >It depends totally on what the requirements are, but generally it's for
    >power as that plays the most significant role in acceleration.


    Other than the power band, which is related to the revs at which
    maximum torque occurs, power is the only significant factor affecting
    acceleration (all other things remaining equal). You could even
    compensate for any reduction in the width of the power band by
    changing the gearbox ratios (ie making them closer).

    >> If the answer does happens to be torque you might also explain what
    >> you need to do to increase it significantly (excluding forced
    >> induction).

    >
    >Increase the stroke and play with rod ratios basically.


    Indeed, because the only way you can significantly change the maximum
    torque produced is to increase the displacement. Even so the specific
    torque (and bmep) won't change significantly from that which is
    inherent to the engines design (since it's directly related to the
    volumetric efficiency).

    In the absence of a signicant torque increase (ie the displacement is
    unchanged) any increase in performance can only come from increasing
    the revs at which maximum power occurs.

    --
    John H

  14. #54
    Ext User(Jason James) Guest

    Re: Holden Captiva - Opinions?

    Noddy wrote:
    > "Jason James" <h6tgf22l@outlook.com> wrote in message
    > news:kskgto$s3i$1@dont-email.me...
    >
    >> Years ago I was given a 3 on the tree Falcon XT ute to travel up the Blue
    >> mountains to Katoomba. What I didn't bank on was how goey the ute was. Put
    >> it back to 2nd, and it'd rocket up the passing lane. It had a 200 cube 6
    >> IIRC, and it wasn't till later, a mechanic in the mechanical service bay,
    >> told me its secret [the XT that is] It had a commercial ratio diff in
    >> it,..circa 4.3 : 1. I was suitable impressed by my new-found knowledge.

    >
    > Perhaps.
    >
    > Apart from the GT there were 4 ratios in the Falcon/Fairlane range in those
    > days, and they were 2.93, 3.23, 3.5 and 4.0:1. 4.0 was about the physical
    > limit of what would fit in a Borg Warner "tin hat" housing at the time and
    > there was nothing shorter than that. Ratios varied according to the model,
    > but there were options available.
    >
    > The number of permutations was considerable depending on the engine and
    > trans combination, but basically the only ratio that *wasn't* available as
    > standard in a commercial was the 3.23, which was reserved specifically for
    > the 221 powered manual Falcon sedans and Fairlanes.
    >
    > As far as commercials go, the main difference was the axle housing itself,
    > as it had thicker tubing material to accommodate the increased load
    > capacity. Standard "off the shelf" ratios for utes and vans were 4.0 for
    > the188 powered base models, 3.5 for the 221 powered "Falcon 500" models, and
    > 2.93 for the V8 jobs. Of those, the only one with an "official" option was
    > the 221, which could be had with the 4.0 if you wanted it. Hardly anyone
    > ever did, as a 4.0:1 rear axle in a Falcon ute or van gave it a freeway
    > cruise of around 3500rpm @ 60 miles per hour, which would have been enough
    > to drive anyone nuts in about 8 minutes :)
    >
    > Incidentally, the 200 cube engine finished it's production run in the XR
    > Falcon range, so if that's what it had then it was an XR ute rather than an
    > XT.


    Gotcha,..it's all too long ago now, but the Falcon did haul-arse, which
    is why I have soft-spot for the early Ford 6s. I drove an XT Van for
    years in the west. Reliable as the day is long. It was *always* serviced
    on time with BP Vannelas (sp) On the long dirt roads back then, we'd
    compare our driving expertise by seeing who could do the longest 4-wheel
    drift around a sweeping dirt-corner. My friend along for the drive had
    the 3 L Capri I used to adjust the rocker-clearance on.

    Mad as a cut-snake behind the wheel. He'd go back to Sydney, as did I
    and we took turns with our cars. He'd cruise at 140kph around the back
    roads with his 2 "Mother" spotties on. More than once I told him to slow
    down,..but he seemed to have the magic-touch come handling,..so I'd lie
    in the back and suck on a beer, trying to shut-out the flashing Flora
    along the way.

    Jason




  15. #55
    Ext User(Clocky) Guest

    Re: Holden Captiva - Opinions?

    John_H wrote:
    > Noddy wrote:
    >> On 24/07/13 8:24 AM, John_H wrote:
    >>
    >>> Then you still don't get it!

    >>
    >> If you're saying that I'm not buying the theoretical physics as being
    >> the case in every real world example, then yeah I'm not :)

    >
    > The theoretical physics you're apparently having a problem with has
    > been long proven, going right back to James Watt, and Isaac Newton
    > before that!
    >
    >>> The diesel with 1500Nm of torque will also bog down under maximum load
    >>> once the revs drop below the power band.

    >>
    >> I wasn't arguing that point. I was simply saying that one third of the
    >> torque won't do the same amount of work.

    >
    > Of course it will, power is the rate of work (by definition) not
    > torque.
    >
    >>> Once we've established the relevance you may then wish to discuss
    >>> precisely why the 'torque monster' you built couldn't possibly achieve
    >>> the outputs claimed, since the bmep (which is also a theoretical
    >>> figure, derived from torque) isn't likely to have matched NASCAR's
    >>> best for comparable engines (as it did, based on dyno measurements
    >>> that don't stand up to the established theory).

    >>
    >> How do you know it couldn't have? Nascar engines aren't formula one :)

    >
    > Their bmep figures (calculated from torque) have been widely
    > published... google should find them. The specific torque figure
    > derived from the torque value you provided (which was something
    > significantly in excess of 90Nm per litre IIRC) would've made your
    > engine a potential NASCAR winner, even if its maximum power output
    > wouldn't... the only difference being down to revs! Actually NASCAR's
    > claimed bmep figures are also regarded with some suspicion among those
    > who take note of such things, since they are right up there with F1.
    >
    >>> I chose that example because it demonstrates what is obviously your
    >>> perception of torque, based no doubt on a mechanic's intuition,
    >>> whereas mine's based on the physics textbook! :)

    >>
    >> I hear where your coming from, but your physics text book would have us
    >> believe that makes bugger all difference to anything.

    >
    > Especially if you happen to base your belief as to the significance of
    > torque on the technical irrelevance that's often propagated by
    > motoring journos and sales droids... ie torque and power figures
    > quoted in the absence of the corresponding revs! :)
    >


    Let me just add that the Captiva figures I posted were at 2000rpm.



  16. #56
    Ext User(Xeno Lith) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/2013 6:35 PM, Jason James wrote:
    > Noddy wrote:
    >> "Jason James" <h6tgf22l@outlook.com> wrote in message
    >> news:kskgto$s3i$1@dont-email.me...
    >>
    >>> Years ago I was given a 3 on the tree Falcon XT ute to travel up the
    >>> Blue
    >>> mountains to Katoomba. What I didn't bank on was how goey the ute
    >>> was. Put
    >>> it back to 2nd, and it'd rocket up the passing lane. It had a 200 cube 6
    >>> IIRC, and it wasn't till later, a mechanic in the mechanical service
    >>> bay,
    >>> told me its secret [the XT that is] It had a commercial ratio diff in
    >>> it,..circa 4.3 : 1. I was suitable impressed by my new-found knowledge.

    >>
    >> Perhaps.
    >>
    >> Apart from the GT there were 4 ratios in the Falcon/Fairlane range in
    >> those
    >> days, and they were 2.93, 3.23, 3.5 and 4.0:1. 4.0 was about the physical
    >> limit of what would fit in a Borg Warner "tin hat" housing at the time
    >> and
    >> there was nothing shorter than that. Ratios varied according to the
    >> model,
    >> but there were options available.
    >>
    >> The number of permutations was considerable depending on the engine and
    >> trans combination, but basically the only ratio that *wasn't*
    >> available as
    >> standard in a commercial was the 3.23, which was reserved specifically
    >> for
    >> the 221 powered manual Falcon sedans and Fairlanes.
    >>
    >> As far as commercials go, the main difference was the axle housing
    >> itself,
    >> as it had thicker tubing material to accommodate the increased load
    >> capacity. Standard "off the shelf" ratios for utes and vans were 4.0 for
    >> the188 powered base models, 3.5 for the 221 powered "Falcon 500"
    >> models, and
    >> 2.93 for the V8 jobs. Of those, the only one with an "official" option
    >> was
    >> the 221, which could be had with the 4.0 if you wanted it. Hardly anyone
    >> ever did, as a 4.0:1 rear axle in a Falcon ute or van gave it a freeway
    >> cruise of around 3500rpm @ 60 miles per hour, which would have been
    >> enough
    >> to drive anyone nuts in about 8 minutes :)
    >>
    >> Incidentally, the 200 cube engine finished it's production run in the XR
    >> Falcon range, so if that's what it had then it was an XR ute rather
    >> than an
    >> XT.

    >
    > Gotcha,..it's all too long ago now, but the Falcon did haul-arse, which
    > is why I have soft-spot for the early Ford 6s. I drove an XT Van for
    > years in the west. Reliable as the day is long. It was *always* serviced
    > on time with BP Vannelas (sp) On the long dirt roads back then, we'd
    > compare our driving expertise by seeing who could do the longest 4-wheel
    > drift around a sweeping dirt-corner. My friend along for the drive had
    > the 3 L Capri I used to adjust the rocker-clearance on.
    >
    > Mad as a cut-snake behind the wheel. He'd go back to Sydney, as did I
    > and we took turns with our cars. He'd cruise at 140kph around the back
    > roads with his 2 "Mother" spotties on. More than once I told him to slow
    > down,..but he seemed to have the magic-touch come handling,..so I'd lie
    > in the back and suck on a beer, trying to shut-out the flashing Flora
    > along the way.
    >
    > Jason
    >

    I would have preferred to drive myself than put myself at risk with a
    loose nut behind the wheel. They all meet their comeuppance eventually.
    They might know all there is to driving a car at speed but, on public
    roads, you don't have any control over the unexpected. At 140 Kph plus,
    the unexpected comes up real fast. A few of my mates were taken out that
    way.

    --

    Xeno

  17. #57
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 6:15 PM, John_H wrote:

    > Of course it will, power is the rate of work (by definition) not
    > torque.


    If you say so.

    > Their bmep figures (calculated from torque) have been widely
    > published... google should find them. The specific torque figure
    > derived from the torque value you provided (which was something
    > significantly in excess of 90Nm per litre IIRC) would've made your
    > engine a potential NASCAR winner, even if its maximum power output
    > wouldn't... the only difference being down to revs!


    I don't have the dyno sheet in front of me, but I *think* it was
    520ft/lb @4800rpm from 408 cubes. I don't know why that's considered
    anything special, as it gives a BMEP value of 192.19 which is a *long*
    way off dedicated race engine stuff.

    It's around what a good DOHC multi valve engine would be, and that in
    itself is nothing special. It may seem a big deal for a single valve
    pushrod dinosaur, and it might have been 30 years ago but today there
    are some quite spectacular heads and manifolds around that made airflow
    a shit simple deal.

    > Especially if you happen to base your belief as to the significance of
    > torque on the technical irrelevance that's often propagated by
    > motoring journos and sales droids... ie torque and power figures
    > quoted in the absence of the corresponding revs! :)


    I don't think the rpm value is significant in and of itself. An engine
    either makes X amount of power or it doesn't, and whether it makes it at
    2000rpm or 6500rpm only becomes relevant if it suits your particular needs.




    --
    --
    Regards,
    Noddy.

  18. #58
    Ext User(Noddy) Guest

    Re: Holden Captiva - Opinions?

    On 24/07/13 6:15 PM, John_H wrote:

    > Other than the power band, which is related to the revs at which
    > maximum torque occurs, power is the only significant factor affecting
    > acceleration (all other things remaining equal). You could even
    > compensate for any reduction in the width of the power band by
    > changing the gearbox ratios (ie making them closer).


    Which is what a lot of circuit racers do for different tracks. You
    mentioned previously that a lot of circuit racers changed diff ratios,
    and some did, but more often than not they changed gearbox ratios to
    suit mid range performance while still having a useful top end.



    --
    --
    Regards,
    Noddy.

  19. #59
    Ext User(Jason James) Guest

    Re: Holden Captiva - Opinions?

    John_H wrote:
    > Jason James wrote:
    >>
    >> Torque times RPM =Power. If you add another gear-set in the gear-box,
    >> with the driven gear having 1/4 the amount of teeth than the gear it's
    >> driving, revs will drop to 1/4 of what they were, but torque will
    >> quadruple bringing the formula back to the same power out.

    >
    > Except you've got it arse about. You need lower gearing to increase
    > the torque at the drive wheels... ie to increase the torque
    > multiplication the revs need to increase (at the same road speed).
    > IOW you'd normally expect to have better acceleration in a lower gear
    > but it doesn't always work that way either.


    OK,..it didnt come out right that's for sure. I often wonder about the
    human as an engine riding a bicycle thru a sprocket "gearset". Not
    really comparable I guess :-) But our "engine's" torque and power seems
    to happen within a narrow rev-range...


    >
    > The maximum acceleration in any particular gear will always be at the
    > engine's maximum torque rpm (which is what fools many into believing
    > that torque is the major factor)... however maximum acceleration is
    > achieved by keeping the engine as near as possible to its maximum
    > power rpm (as determined by the gearbox step up ratios), which kinda
    > defeats the perceived benefits of having an engine with higher maximum
    > torque and less power.


    I'd guess that an engine needs to provide max-torque and power
    reasonably close to each other in the engine's rev-range

    VN C/dore V6
    Maximum power: 125 kW @ 4800 rpm
    Maximum torque: 292 Nm @ 3200 rpm

    1600 rpm

    VN C/dore V8
    Maximum power: 165 kW @ 4400 rpm
    Maximum torque: 385 Nm @ 3600 rpm

    1800 rpm

    Falcon 6
    Power: 157kW at 4,900rpm
    Torque: 357Nm at 3,000rpm

    1900 rpm

    Mazda 6
    103kW at 7000 rpm and 157Nm at 5500 rpm

    1500 rpm

    Falcon GT [GTHO I assume]
    (428 PS; 422 hp) at 6,500 rpm and 551 N·m (406 lb·ft) of torque at
    4,750 rpm.

    1750 rpm

    Austin 1800 enhanced
    87.2 PS / 86 bhp / 64.1 kW @ 5400 rpm
    How much torque?
    137 Nm / 101 ft.lb / 14 kgm @ 3000 rpm

    2400 rpm

    Except for the 1800, the "powerband" seems generally similar for the
    other randomly selected cars.

    Jason

  20. #60
    Ext User(John_H) Guest

    Re: Holden Captiva - Opinions?

    Jason James wrote:
    >John_H wrote:
    >>
    >> The maximum acceleration in any particular gear will always be at the
    >> engine's maximum torque rpm (which is what fools many into believing
    >> that torque is the major factor)... however maximum acceleration is
    >> achieved by keeping the engine as near as possible to its maximum
    >> power rpm (as determined by the gearbox step up ratios), which kinda
    >> defeats the perceived benefits of having an engine with higher maximum
    >> torque and less power.

    >
    >I'd guess that an engine needs to provide max-torque and power
    >reasonably close to each other in the engine's rev-range


    Better wide apart, unless performance is the main objective... high
    performance engines invariably have narrower power bands (and
    appropriately matched gearing).

    >VN C/dore V6
    >Maximum power: 125 kW @ 4800 rpm
    >Maximum torque: 292 Nm @ 3200 rpm
    >
    >1600 rpm
    >
    >VN C/dore V8
    >Maximum power: 165 kW @ 4400 rpm
    >Maximum torque: 385 Nm @ 3600 rpm
    >
    >1800 rpm


    So let's look a bit closer at those figures (which I haven't checked
    but the actual numbers don't matter for the purpose of the
    exercise).....

    At first glance the V6 appears to have the wider power band, but what
    really matters are the relative ratios. On the figures you've
    quoted....
    The V6 is 4800/3200... ie 1.5.
    The V8 is 4400/3600... ie 1.2 (which sounds a bit too close).

    In fact the 5L V8 does have the narrower power band and the old T5
    manual gearboxes used in the early ones even had different step up
    ratios, with the stock V8 having the closer ratio box (final drive
    ratios were the same)... which proves that even GMH engineers know
    what they're doing. :)

    Some HSV models had higher ratio diffs... which also proves that my
    namesake also knew what he was doing. :))

    This bit might be harder to follow.... The ideal gearbox has step up
    ratios which are a geometric progression, where the 1st to second step
    up matches the power/torque ratio. This ensures that the engine will
    always be within it's power band if the correct gear is chosen... the
    geometric progression closes up the ratios in the higher gears,
    allowing the engine to operate even closer to its maximum power rpm,
    which improve acceleration times.

    I'd also add that the only gearbox I've ever owned that fully met
    those criteria was Italian (Ducati 900SS).... Italians being
    brilliant engineers, whose manufacturing practices severely compromise
    their designs. :)

    If any of that makes sense, you might apply the ratio calculation to
    the rest of your examples to separate the racehorses from the
    workhorses.

    >Falcon 6
    >Power: 157kW at 4,900rpm
    >Torque: 357Nm at 3,000rpm
    >
    >1900 rpm
    >
    >Mazda 6
    > 103kW at 7000 rpm and 157Nm at 5500 rpm
    >
    >1500 rpm
    >
    >Falcon GT [GTHO I assume]
    > (428 PS; 422 hp) at 6,500 rpm and 551 N·m (406 lb·ft) of torque at
    >4,750 rpm.
    >
    >1750 rpm
    >
    >Austin 1800 enhanced
    >87.2 PS / 86 bhp / 64.1 kW @ 5400 rpm
    >How much torque?
    >137 Nm / 101 ft.lb / 14 kgm @ 3000 rpm
    >
    >2400 rpm
    >
    >Except for the 1800, the "powerband" seems generally similar for the
    >other randomly selected cars.
    >
    >Jason



    --
    John H

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