Re: idle speed ??

I think you are right, but for the wrong reasons. The big v-twin, longer stroke bikes which can sustain a lower idle do so because they have a heavier flywheel (not directly because of longer stroke) - that flywheel inertia is needed because the stroke is long and only two cylinders, so the explosions happen far apart from each other. Flywheel keeps things turning over. It so happens that these engines generate their power down low (because of the v-twin/long stroke), and don't do as well up high, so you have the situation you describe - low idle engines which also don't happen to be high revvers. Smaller 4-bangers have smaller pistons and strokes, and because they need to be very responsive off idle, they have lighter flywheels. Lighter flywheels mean higher idles. They are helped a little by thefact that there are twice as many explosions/rev than two cylinders (on some).

I believe the lower emissions at higher idle is a result of the cat running hotter at a higher idle. Hotter cats are more efficient, up to a point.

Dan B


-----Original Message-----
>From: Oil Guy
>Sent: Jun 21, 2006 12:25 PM
>To: Tom Heron , VFR
>Subject: idle speed ??
>
>
>----- Original Message -----
>From: "Tom Heron"
>>
>> Those of us who weren't born yesterday remember when bikes had idle
>> speeds of about 650rpm or lower. They did and still now have exactly the
>> same crankshaft inertia (alternator rotor etc). It's *emissions
>> legislation* that has bumped idle speeds up.
>>
>*** I'm not an engin-eer, but this just doesn't sound right. I wasn't born
>yesterday, and it seems to me idle speed is somehow tied to length of the
>piston's stroke. Very long stroke engines, like Harleys and diesels have
>very low idle speeds of just a few hundred rpm, and have correspondingly low
>red lines. Bikes of the 1960s and 1970s, when I started riding, had
>significantly longer strokes than the rockets of todday. The modern 16,000
>rpm engines have very short strokes and correspondingly relatively higher
>idle speeds in the 1100 to 1300 range. I know I've fiddled with idle speeds
>on my various Honda V-4 and inline 4 short-stroke engines and below about
>1100 rpm or so they just won't sustain an idle.
>
>I don't wish to challenge Heron per se, but can anyone knowledgeable about
>engine design chime in?? I don't believe *emissions legislation* is the
>reason for faster idle speeds. Thanks,
>
>Mike in Houston
>
>
>_______________________________________________
>Vfr mailing list
>Vfr@xxxxxx
>For subscription and delivery options:
>https://lists.cs.wisc.edu/mailman/listinfo/vfr

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I think you are right, but for the wrong reasons. The big v-twin, longer stroke bikes which can sustain a lower idle do so because they have a heavier flywheel (not directly because of longer stroke) - that flywheel inertia is needed because the stroke is long and only two cylinders, so the explosions happen far apart from each other. Flywheel keeps things turning over. It so happens that these engines generate their power down low (because of the v-twin/long stroke), and don't do as well up high, so you have the situation you describe - low idle engines which also don't happen to be high revvers. Smaller 4-bangers have smaller pistons and strokes, and because they need to be very responsive off idle, they have lighter flywheels. Lighter flywheels mean higher idles. They are helped a little by thefact that there are twice as many explosions/rev than two cylinders (on some).

I believe the lower emissions at higher idle is a result of the cat running hotter at a higher idle. Hotter cats are more efficient, up to a point.

Dan B


-----Original Message-----
>From: Oil Guy
>Sent: Jun 21, 2006 12:25 PM
>To: Tom Heron , VFR
>Subject: idle speed ??
>
>
>----- Original Message -----
>From: "Tom Heron"
>>
>> Those of us who weren't born yesterday remember when bikes had idle
>> speeds of about 650rpm or lower. They did and still now have exactly the
>> same crankshaft inertia (alternator rotor etc). It's *emissions
>> legislation* that has bumped idle speeds up.
>>
>*** I'm not an engin-eer, but this just doesn't sound right. I wasn't born
>yesterday, and it seems to me idle speed is somehow tied to length of the
>piston's stroke. Very long stroke engines, like Harleys and diesels have
>very low idle speeds of just a few hundred rpm, and have correspondingly low
>red lines. Bikes of the 1960s and 1970s, when I started riding, had
>significantly longer strokes than the rockets of todday. The modern 16,000
>rpm engines have very short strokes and correspondingly relatively higher
>idle speeds in the 1100 to 1300 range. I know I've fiddled with idle speeds
>on my various Honda V-4 and inline 4 short-stroke engines and below about
>1100 rpm or so they just won't sustain an idle.
>
>I don't wish to challenge Heron per se, but can anyone knowledgeable about
>engine design chime in?? I don't believe *emissions legislation* is the
>reason for faster idle speeds. Thanks,
>
>Mike in Houston
>
>
>_______________________________________________
>Vfr mailing list
>Vfr@xxxxxx
>For subscription and delivery options:
>https://lists.cs.wisc.edu/mailman/listinfo/vfr

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My TLS had very little rotating weight and was a little hard to ride because
of it. It all so would rev to 10500 rpm or so.

Kevin
----------------------------
IBA 23360

----- Original Message -----
From: "Dan Barufaldi"
To: "Oil Guy" ; "Tom Heron"
; "VFR"
Sent: Wednesday, June 21, 2006 12:07 PM
Subject: Re: idle speed ??


>I think you are right, but for the wrong reasons. The big v-twin, longer
>stroke bikes which can sustain a lower idle do so because they have a
>heavier flywheel (not directly because of longer stroke) - that flywheel
>inertia is needed because the stroke is long and only two cylinders, so the
>explosions happen far apart from each other. Flywheel keeps things turning
>over. It so happens that these engines generate their power down low
>(because of the v-twin/long stroke), and don't do as well up high, so you
>have the situation you describe - low idle engines which also don't happen
>to be high revvers. Smaller 4-bangers have smaller pistons and strokes,
>and because they need to be very responsive off idle, they have lighter
>flywheels. Lighter flywheels mean higher idles. They are helped a little
>by thefact that there are twice as many explosions/rev than two cylinders
>(on some).
>
> I believe the lower emissions at higher idle is a result of the cat
> running hotter at a higher idle. Hotter cats are more efficient, up to a
> point.
>
> Dan B
>
>
> -----Original Message-----
>>From: Oil Guy
>>Sent: Jun 21, 2006 12:25 PM
>>To: Tom Heron , VFR
>>Subject: idle speed ??
>>
>>
>>----- Original Message -----
>>From: "Tom Heron"
>>>
>>> Those of us who weren't born yesterday remember when bikes had idle
>>> speeds of about 650rpm or lower. They did and still now have exactly the
>>> same crankshaft inertia (alternator rotor etc). It's *emissions
>>> legislation* that has bumped idle speeds up.
>>>
>>*** I'm not an engin-eer, but this just doesn't sound right. I wasn't born
>>yesterday, and it seems to me idle speed is somehow tied to length of the
>>piston's stroke. Very long stroke engines, like Harleys and diesels have
>>very low idle speeds of just a few hundred rpm, and have correspondingly
>>low
>>red lines. Bikes of the 1960s and 1970s, when I started riding, had
>>significantly longer strokes than the rockets of todday. The modern 16,000
>>rpm engines have very short strokes and correspondingly relatively higher
>>idle speeds in the 1100 to 1300 range. I know I've fiddled with idle
>>speeds
>>on my various Honda V-4 and inline 4 short-stroke engines and below about
>>1100 rpm or so they just won't sustain an idle.
>>
>>I don't wish to challenge Heron per se, but can anyone knowledgeable about
>>engine design chime in?? I don't believe *emissions legislation* is the
>>reason for faster idle speeds. Thanks,
>>
>>Mike in Houston
>>
>>
>>_______________________________________________
>>Vfr mailing list
>>Vfr@xxxxxx
>>For subscription and delivery options:
>>https://lists.cs.wisc.edu/mailman/listinfo/vfr
>
> _______________________________________________
> Vfr mailing list
> Vfr@xxxxxx
> For subscription and delivery options:
> https://lists.cs.wisc.edu/mailman/listinfo/vfr


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Lots of factors. Various issues, but one of the big ones is getting a good
air fuel ratio so that combustion can occur and the engine keep turning,
hopefully steadily. Stroke is a factor because it determines how much
vacuum can be pulled; flywheel is a factor because it helps keep things
going when otherwise not stable; engine configuration because it determines
how evenly things fire (I4 better than a thumper); intake configuration
because it determines how the vacuum pulls on the available air;
carb/injection because of the atomization of fuel and how accurately it is
delivered; ignition control because it determines how accurately the spark
can be delivered to get best combustion; etc.

In the old days, idles might have been lower but so were maximum engine
speeds, and everything was tuned accordingly. Note that not all idles were
lower, some were higher, especially to get a high performance engine to run
because carburetion was terrible if the airflow was too little. New
technology has fixed this so we can have high performance engines that also
behave well at low engine speeds.


Carl

-----Original Message-----


I don't wish to challenge Heron per se, but can anyone knowledgeable about
engine design chime in?? I don't believe *emissions legislation* is the
reason for faster idle speeds. Thanks,

Mike in Houston

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<<< No Message Collected >>>

Hi Mike,

You weren't born yesterday, but it seems like you came down in the last
shower ;-)

How it *sounds* is irrelevant - especially if one has no engineering
background. I suggest you speak to an automotive engineer then - I am
and have taught in and managed a teaching centre with over 60 engineers
and auto teachers for many years.

I'd suggest there's a good reason why engineers shy away from this type
of discussion and that's exactly what I'll do now.

And of course you're welcome to believe whatever you wish (and maybe I'm
too passionate about pre-VTEC VFRs ;-)


Bye,

Tom H.

-----Original Message-----
From: Oil Guy [mailto:oilguy15w40@xxxxxx]
Sent: Thursday, 22 June 2006 2:26 AM
To: Tom Heron; VFR
Subject: idle speed ??



----- Original Message -----
From: "Tom Heron"
>
> Those of us who weren't born yesterday remember when bikes had idle
> speeds of about 650rpm or lower. They did and still now have exactly
the
> same crankshaft inertia (alternator rotor etc). It's *emissions
> legislation* that has bumped idle speeds up.
>
*** I'm not an engin-eer, but this just doesn't sound right. I wasn't
born
yesterday, and it seems to me idle speed is somehow tied to length of
the
piston's stroke. Very long stroke engines, like Harleys and diesels
have
very low idle speeds of just a few hundred rpm, and have correspondingly
low
red lines. Bikes of the 1960s and 1970s, when I started riding, had
significantly longer strokes than the rockets of todday. The modern
16,000
rpm engines have very short strokes and correspondingly relatively
higher
idle speeds in the 1100 to 1300 range. I know I've fiddled with idle
speeds
on my various Honda V-4 and inline 4 short-stroke engines and below
about
1100 rpm or so they just won't sustain an idle.

I don't wish to challenge Heron per se, but can anyone knowledgeable
about
engine design chime in?? I don't believe *emissions legislation* is the

reason for faster idle speeds. Thanks,

Mike in Houston





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----- Original Message -----
From: "Tom Heron"

I'd suggest there's a good reason why engineers shy away from this type
of discussion and that's exactly what I'll do now.

*** Sounds like a euphemism for "I was mistaken when I claimed high idle
speeds are driven by need to meet emissions legislation so I'll try and back
out graciously since I can't back up my original hip shot." I've lived long
enough to recognize that!! Mike


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Perhaps engineers shy away from this type of comment because they are sick of dealing with the
constant barrage of "barstool bullshit" you see on lists such as this. Your comments on idle
speed vs fuel economy and emissions legislation could fit neatly into this category.

Anyway, I know a lot of automotive engineers, and they sure aren't all experts on engines. And
the people I've met that make comments such as "I am and have taught in and managed a teaching
centre with over 60 engineers and auto teachers for many years." Are typically trying to "win" a
discussion by intimidation and not with knowldege or reasoning.

Have emissons legislations effected idle speeds? In many cases yes. Are legislations the only
factor in increasing idle engine speeds? No, not by a long shot.

Steve George
Carney Racing
WERA North Central EX #684
CCS EX #684


**************
Date: Thu, 22 Jun 2006 06:05:00 +1000
From: "Tom Heron"
Subject: RE: idle speed ??
To: "Oil Guy" , "VFR"


Hi Mike,

You weren't born yesterday, but it seems like you came down in the last
shower ;-)

How it *sounds* is irrelevant - especially if one has no engineering
background. I suggest you speak to an automotive engineer then - I am
and have taught in and managed a teaching centre with over 60 engineers
and auto teachers for many years.

I'd suggest there's a good reason why engineers shy away from this type
of discussion and that's exactly what I'll do now.

__________________________________________________
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Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
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Yes, lots of meaningless discussions with no end in sight.

See my earlier post on this subject for a more complete list of factors. I
am an auto engineer and have had responsibility for delivering control
systems to the industry, including strategy and calibration. Not to win an
argument, just to add a little credence. Do with it what you want.

Emissions legislation has had a huge impact on all aspects of engine
control. Typically there is a drive to minimize idle speed to improve
emissions, but this can only be lowered to the point of stable combustion.
Injection systems have the potential (not always realized) of providing
stable combustion at lower idle speeds. But emissions isn't the only
factor, nor is the flywheel mass. There are many factors that go into the
equations ... again, see the earlier post that lists some of the factors.

Oh, and from experience, many of the people teaching the technicians have no
clue of what is really happening in the control system either. If they did
then we wouldn't be getting as many perfectly good parts back in warranty
returns, followed by a later warranty hit for the real issue. Just my 2
cents.

Carl


-----Original Message-----

Perhaps engineers shy away from this type of comment because they are sick
of dealing with the
constant barrage of "barstool bullshit" you see on lists such as this. Your
comments on idle
speed vs fuel economy and emissions legislation could fit neatly into this
category.



Have emissons legislations effected idle speeds? In many cases yes. Are
legislations the only
factor in increasing idle engine speeds? No, not by a long shot.


**************


I'd suggest there's a good reason why engineers shy away from this type
of discussion and that's exactly what I'll do now.
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Yesterday I asked if anyone who knew design factors in engine idle speed
considerations, and we got some suggestions, but nothing factual. So I did
what any 21st century curious person would do, I searched the internet. I
found lots of interesting information, mostly tangential, but below are two
sites which cover what seems to be the key points. Factual information to
help silence the quacks!

First, idle speed IS a function of piston and crankshaft stroke, and
flywheel weight. Since an internal combustion engine makes power in a
series of pulses, these pulses must be averaged out and converted to
rotational power. The crankshaft and attached flywheel do this, and the
greater the rotational inertia (weight and radius), which keeps pistons
moving between pulses, the lower the optimum idle speed will be. That's why
a big, long-stroke engine like a Harley or a heavy diesel can idle so
slowly, they require comparatively heavy cranks and flywheels to average the
relatively longer time between pulses. Modern high-reving engines use
shorter strokes and lighter flywheels, with much less rotational inertia, so
have to idle faster to prevent engine stall.

Second, someone suggested that higher idle speeds are somehow associated
with meeting pollution requirements. Actually, the opposite is true.
Websites which deal with the subject specifically (engines failing to meet
pollution limits) mention "too high idle speed" as one of the
troubleshooting points. Higher idle speeds actually make it more difficult
to meet pollution requirements, and burn more fuel. (As some have correctly
pointed out, in a VFR this has to be balanced with such things as charging
system, oil flow, and engine cooling requirements. While the VFR 'may' idle
OK at 900 or 1000 rpm, that probably isn't good for it. Honda's design of
about 1200 is probably optimum.)

For those who want to read more,
www.gambelli.org/download/ ingegneria/automazione/IFAC_2005.pdf -

This site is highly technical but discusses some of the design
considerations which relate flywheel inertia and idle speed.

This site is much easier to read and discusses why light crankshafts are
impractical and how they would require idle speeds up to the 3000 rpm range.

Mike in Houston


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I think it depends on when the high idle is performed. Our new Toyota is
designed to fast idle right at the turn of the key and stay that way for
several minutes.. I cringe in cold weather because I just think it can't be
ideal for the internals to be idling so high right at the turn of the key.
Toyota's official line is the idle is necessary to bring the engine up to
operating temp as quickly as possible since that is when the vehicle is
running the richest (and polluting the most). I agree that once the engine
is up to operating temps, any fast idle is burning excess fuel and adding
pollution.

Paul Kolbo
02 VFR
94 ST1100


----- Original Message -----
From: "Oil Guy"
To: "VFR"
Sent: Thursday, June 22, 2006 2:48 PM
Subject: idle speed - some technical answers


> Second, someone suggested that higher idle speeds are somehow associated
> with meeting pollution requirements. Actually, the opposite is true.
> Websites which deal with the subject specifically (engines failing to meet
> pollution limits) mention "too high idle speed" as one of the
> troubleshooting points. Higher idle speeds actually make it more difficult
> to meet pollution requirements, and burn more fuel.

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