longer stroke, Longer cylinder life?
Cale Fraser
I am just about to put my 1641 together, but am now thinking of going with a
74 or a 76mm crank, actually, I know i am going with a stroker.
My question is, With the longer stroke, Will you get longer cylinder life? I
figure more is getting used, More even wear?
Really it makes no diff to me, I am running the 87mm untill the burn
oil..then doing a tear down, replacing bearings, and cutting for 94mm.
What is the longest stroke you can use with a stock style pistion and stock
rods?
I know you can run 74mm, With little case work and stock rods, but what
about 76mm?
And is a cast crank REALLY that bad for a baja motor? i know they flex more.
but i am not doing any drag race starts so i dont really think i will be
stressing the crank much. as of now i am planning on going welded forged.
but just thinking if cast is an option.
Thanx
Cale
PEPPE
stroke.
many people recommends using 78 stroke as maximum for a stock rod
PEPPE
Eric Allred
P's and C's, im not sure what the limit is.
Then again, for the low price of around $300, you can get some NICE 4340
chromoly 'H' beam rods. For the price, they're AWSOME!
Check em out:
http://www.aircooled.net/cgi-bin/s1.cgi?cmd=I&keyword2=ECR0005&cartid=52744.969108615
Eric
59 bug
http://www.geocities.com/eaallred
Cale Fraser
work, Not a problem, But can i use Non stroker pistions?
Thats the big issue here..i already own brand new non stroker 87mm
thanx
Cale
Searoy
this.
Longer stroke with stock length rods means lower rod/stroke ratio, means
higher side load on the piston, means more wear on the cylinder not less.
> I am just about to put my 1641 together, but am now thinking of going with
a
> 74 or a 76mm crank, actually, I know i am going with a stroker.
I wouldn't bother wasting money on the 1641. If you're going to stroke it
why use the slip in pistons at all?
> My question is, With the longer stroke, Will you get longer cylinder life?
I
> figure more is getting used, More even wear?
See my first statement.
> Really it makes no diff to me, I am running the 87mm untill the burn
> oil..then doing a tear down, replacing bearings, and cutting for 94mm.
Why bother? Run the 85.5s until THEY burn oil. It'll take longer and
you're less liely to fk something up. Or bite the bullet now and cut for
94s.
> What is the longest stroke you can use with a stock style pistion and
stock
> rods?
> I know you can run 74mm, With little case work and stock rods, but what
> about 76mm?
Far as I know you can run 76 and even 78 with no machining, if you use
I-beam or better rods.
> And is a cast crank REALLY that bad for a baja motor? i know they flex
more.
> but i am not doing any drag race starts so i dont really think i will be
> stressing the crank much. as of now i am planning on going welded forged.
> but just thinking if cast is an option.
If you are going to rev the engine past 4000 I would insist upon a forged
crank, and 4k isn't very high.
--
*** Teach a Man to Fish ***
Searoy
66 bug (daily driver project)
T4 CIS-T powered imagination
Searoy
news:fCMC5.2130$Tf.4...@newscontent-01.sprint.ca...
Your best investment would be to throw the 87s as hard as you can into an
open field.
If you're going to do it, do it right. Why do it more than once ever?
85.5x69 or 90.5x78 or 94x78. Period.
(unless you want to move up to the 84mm crank...94x84=2332 smiles!)
Ian Plain
Another thing to think about is a longer stroke means lower max rpm and shorter
rod and bearing life..
Ian
Cale Fraser wrote:
> Hey ppl
>
> I am just about to put my 1641 together, but am now thinking of going with a
> 74 or a 76mm crank, actually, I know i am going with a stroker.
>
> My question is, With the longer stroke, Will you get longer cylinder life? I
> figure more is getting used, More even wear?
>
> Really it makes no diff to me, I am running the 87mm untill the burn
> oil..then doing a tear down, replacing bearings, and cutting for 94mm.
>
> What is the longest stroke you can use with a stock style pistion and stock
> rods?
> I know you can run 74mm, With little case work and stock rods, but what
> about 76mm?
>
> And is a cast crank REALLY that bad for a baja motor? i know they flex more.
> but i am not doing any drag race starts so i dont really think i will be
> stressing the crank much. as of now i am planning on going welded forged.
> but just thinking if cast is an option.
>
> Thanx
> Cale
TQuan
its just me but if I'm building an engine with a stroke and bore I'm
going to stress it. How could you not?
-Terry
Mike Fritz
moving up then down in one crankshaft rotation, regardless of rod length.
Mike
Cale Fraser wrote:
> Hey ppl
>
> I am just about to put my 1641 together, but am now thinking of going with a
> 74 or a 76mm crank, actually, I know i am going with a stroker.
>
> My question is, With the longer stroke, Will you get longer cylinder life? I
> figure more is getting used, More even wear?
>
> Really it makes no diff to me, I am running the 87mm untill the burn
> oil..then doing a tear down, replacing bearings, and cutting for 94mm.
>
> What is the longest stroke you can use with a stock style pistion and stock
> rods?
> I know you can run 74mm, With little case work and stock rods, but what
> about 76mm?
>
> And is a cast crank REALLY that bad for a baja motor? i know they flex more.
> but i am not doing any drag race starts so i dont really think i will be
> stressing the crank much. as of now i am planning on going welded forged.
> but just thinking if cast is an option.
>
> Thanx
> Cale
--
The content of this messages contain my ideas, experiences, and general
information I've heard or read. I will usually specify whether the information
was heard, read, my idea, or from experience. It is up to you to be the judge of
how valid the content of my messages are. Remove NOSPAM to email me privately.
Mike Fritz
Mike
TQuan wrote:
> The problem with a cast crank is that the flywheel will fall off. Maybe
> its just me but if I'm building an engine with a stroke and bore I'm
> going to stress it. How could you not?
>
> -Terry
>
TQuan
-Terry
Searoy
news:39DBD948...@psn.net...
> What? Please, elaborate "the flywheel will fall off".
> Mike
>
> TQuan wrote:
>
> > The problem with a cast crank is that the flywheel will fall off. Maybe
> > its just me but if I'm building an engine with a stroke and bore I'm
> > going to stress it. How could you not?
> >
> > -Terry
> >
The force of gravity causes the mass of the flywheel to be pulled towards
the center of the Earth when no other force is acting upon the flywheel to
prevent it, or when that resisting force is insufficient to prevent it.
:)
--
*** Teach a Man to Fish ***
Searoy
66 bug (daily driver project)
T4 CIS-T powered imagination
Ramjam1
However if longer rods are used with a stroked engine the piston speed will be
reduced, in that, the piston spends more time at the top and the bottom, and so
a slower speed along with less side preassure means less cylinder wear.
currently i'm using a 78 forged crack, 5.5"
i-beam rods and 90.5 "b" pistons.
Shad Laws
Now, unless you're putting a "low RPM" condition on there (claiming that
your stroker will be revved proportionately less than your stocker), that
means that the average speed is higher, no matter how you cut it...
The shorter the stroke, the less time spent at TDC (read as dead torque
point) and the quicker it moves away from TDC, which is why they give more
power and (if you think about the dynamics a bit...) why they need more
advance.
Shad
Ramjam1 <ram...@aol.com> wrote in message
news:20001005235944...@ng-da1.aol.com...
James W. Lindsay
> true, the cylinder is moving the same amount no matter what the stroke.
> However if longer rods are used with a stroked engine the piston speed will be
> reduced, in that, the piston spends more time at the top and the bottom, and so
> a slower speed along with less side preassure means less cylinder wear.
There are pros and cons regarding running stock rods on a long stroke
motor.
As you've already pointed out, running longer rods with a long stroke
creates a situation where the piston spends a few more milliseconds at TDC
or BDC than it would with shorter rods (all else being equal). This
provides slightly more burn time for the ignited air/fuel mixture, which
can create more power. The drawback is that longer rods with long stroke
crankshafts move the peak horsepower further up the RPM scale-- sometimes
by quite a bit.
Running short rods with a long stroke creates slightly more sideload on the
rod bearings midway between TDC and BDC, and faster piston speeds at this
point too. This has the advantage of improved scavenging of the combustion
chamber through the intake valve, drawing the incoming air/fuel mixture
more efficiently (ie: drawing more in per intake stroke). Power is down
due to the fact that the piston doesn't spend as much time at TDC, but more
power is arguably created by the increased efficiency of the intake stroke.
Higher piston speeds will result in somewhat greater wear, however, even
though the piston is still covering the same distance per stroke.
> currently i'm using a 78 forged crack, 5.5"
> i-beam rods and 90.5 "b" pistons.
84mm Tony Manz welded stroker, 5.432" Carrillo rods, 90.5mm "b" P&Cs :)
----------------------------------------------------------------
James W. Lindsay Vancouver, British Columbia, Canada
Website: http://members.home.net/jlindsay ICQ: #7521644
----------------------------------------------------------------
Impropriety is the soul of wit.
----------------------------------------------------------------
James W. Lindsay
> putting spacers under and in top of cylinder it is not a problem also a 78
> stroke.
I disagree. The cylinders that come with non-stroker P&Cs don't reach far
enough into the case. When a long stroke crankshaft such as a 78mm pulls a
non-stroker piston down towards BDC, the cylinder will not properly support
the piston. The piston will cock slightly in the bore of the cylinder and
excessive cylinder and piston skirt wear will take place.
ANT The Monarch of Menace
>Now, unless you're putting a "low RPM" condition on there (claiming that
>your stroker will be revved proportionately less than your stocker), that
>means that the average speed is higher, no matter how you cut it...
>
>The shorter the stroke, the less time spent at TDC (read as dead torque
>point) and the quicker it moves away from TDC, which is why they give more
>power and (if you think about the dynamics a bit...) why they need more
>advance.
The longer the stroke the more feet per mile the piston travels, hence more
wear--but the argument can be made that you can raise the rear end ratio
because you now have a higher torque at a lower RPM, so all things may be
equal.
The longer stroke limits the high speed potential of the engine for many
reasons, including the added mass.
General rule of thumb is that short stroke engines are high revvers, both
becasue they can buzz, and that they need to buzz to make their power
(Horsepower)
Long strokes can't as easily rev, but don't really need to as they produce more
low RPM poer (Torque). These are more friendly street engines. If you can keep
the revs down your durability and longevity go up exponentially. At least this
is how it is in the V8 world. And unles the laws of physics are different in
Professor Porsche's design studio all this should apply to.
-ANT
Shad Laws
more
> wear--but the argument can be made that you can raise the rear end ratio
> because you now have a higher torque at a lower RPM, so all things may be
> equal.
>
I know. However, we're talking about someone here who I'd wager isn't going
to change his gear ratio, probably has a high RPM camshaft for more kick,
and wants to rev the hell out of it. Have you read about how many times
he's changed the configuration of his baja? This isn't going to be
strolling, calm, street car...
> Long strokes can't as easily rev, but don't really need to as they produce
more
> low RPM poer (Torque). These are more friendly street engines. If you can
keep
> the revs down your durability and longevity go up exponentially. At least
this
> is how it is in the V8 world. And unles the laws of physics are different
in
> Professor Porsche's design studio all this should apply to.
Aye, tis true. However, when one "builds up" a VW engine, they typically go
with a hotter cam designed for a higher RPM band, not a lower one. Heck,
even VW did this when they made the 914 2.0 engine!
Shad
Shad Laws
getting away from TDC as quickly as possible was an advantage. TDC is a
zero torque point... isn't it?
Shad
James W. Lindsay <jlin...@home.com> wrote in message
news:h4oqtsos7vr3fv5rf...@4ax.com...
ANT The Monarch of Menace
>getting away from TDC as quickly as possible was an advantage. TDC is a
>zero torque point... isn't it?
Nope, the longer you can stay at TDC the higher the developed combustion
charge. In other words, the longer the dwell at TDC (in crank degrees) allows
for more time for the combustion process to build pressure.
Put yet another way---most long guns (rifles) develop more projectile velocity
than a typical handgun. Why? You'd think with the extra barrel length it would
be slower due to all the friction encountered as the bullet travels that
distance. Turns out that this length allows the explosion to build a bigger and
longer duration "head of steam" and the gasses are contained along a longer
path, exerting more of their force against the bullet. See?
Longer stroke means more leverage against the crank which equals more torque.
Longer connecting rods allow for even more TDC dwell (this can be a real
geometry brain twister). Then there's the offset wristpin to consider (at least
in a V type engine) This makes for easier revving as there's less of the
overcenter "locking" at TDC. There IS a slight side loading to the cylinder in
this scenario, but may be worth it anyway.
Now who REALLY wants to get esoteric? <G>
-ANT
ANT The Monarch of Menace
Jim Adney
>My question is, With the longer stroke, Will you get longer cylinder life? I
>figure more is getting used, More even wear?
I think that there is every reason to expect a longer stroke to reduce
cylinder life. Longer stroke increases the side forces on the piston
and the area swept by the rings, as well as the piston velocity at a
given RPM.
-
-----------------------------------------------
Jim Adney jad...@vwtype3.org
Madison,Wisconsin USA
-----------------------------------------------
ANT The Monarch of Menace
>cylinder life. Longer stroke increases the side forces on the piston
>and the area swept by the rings, as well as the piston velocity at a
>given RPM.
This is true, but as I pointed out earlier, a long stroke engine has more
torque, and subsequently can be geared higher so that you will lower the revs.
So it may end up being a wash.
-ANT
Shad Laws
make power lower...
Shad
ANT The Monarch of Menace <s2...@aol.computer> wrote in message
news:20001007012623...@ng-cg1.aol.com...
James W. Lindsay
> Correct me if I'm wrong, which I may very well be, but I always thought that
> getting away from TDC as quickly as possible was an advantage. TDC is a
> zero torque point... isn't it?
The piston doesn't "get away from TDC" during the power stroke; it is
*pushed away*. Big difference. The piston will only move as fast as the
expanding gases from the ignited air/fuel mixture. Forcing the piston to
remain at TDC a bit longer (which happens with longer rods) allows the
pressure from those burning gases to rise higher than they would normally.
Those extra few milliseconds also allow for a few more milliseconds of burn
time. Both produce more power.
On the intake stroke, things are different. The piston isn't being
directly propelled by expanding gases. Rather, it is being moved by a
crankshaft that happens to be connected to at least one other piston that
happens to be in the middle of *its* power stoke. The piston on the intake
stroke is literally coasting. In this regard, you could say that an engine
with longer rods allows the piston to "get away from TDC" faster... but
only on the intake stroke. I suppose an engine with shorter rods also
exhausts more efficiently of exhaust system back pressure is kept to a
minimum.
Engines running shorter rods produce higher piston velocities halfway
between TDC and BDC, as well as shorter stationary periods at TDC. Since
longer rods allow greater time at TDC during the power stroke, it only goes
to say that shorter rods allow slightly less time at TDC. However, the
faster coasting piston speed during the intake stroke promotes faster
intake charge entry, making for a more tightly packed intake charge.
Theoretically, this fact also produces more power. Is it enough to offset
the lost power from the decreased burn times and less delay at TDC? I
don't know.
The added delay at TDC during the beginning of the intake stroke on engines
with longer rods will produce a result a bit different than on an engine
with shorter rods-- with respect to airflow and valve overlap. It is my
opinion that longer rods produce more horsepower, but at the price of poor
gas flow during valve overlap (due to the extended pause at TDC). Engines
that have poor flow during valve overlap-- or simply have radical cams with
very large overlap periods-- need to rev higher in order for the physics of
air flow to work in the engine's favour. It is a proven fact that longer
rods move the HP peak further up the RPM scale, and this may be why.
----------------------------------------------------------------
James W. Lindsay Vancouver, British Columbia, Canada
Website: http://members.home.net/jlindsay ICQ: #7521644
----------------------------------------------------------------
DEFINE: De ting you get for breaking de law.
----------------------------------------------------------------
ANT The Monarch of Menace
>make power lower...
Of course a specific cam would optimize this to take advantage of complete
cylinder filling, but you could cheat by putting a higher ratio rocker arm on
just the intakes. This will increase both the lift and the duration slightly.
Here's a rule of thumb---a cam "appears" larger in a smaller displacement
engine. While a lumpy cam gets tamer in a larger engine. Let the cubes do the
work, big cubes, high compression, relatively mild cam timing---you CANNOT use
a torque cam (mild or RV flavor) in a high comp engine as the static comp will
blow the heads right off the sucker. A radical cam reduces the static comp due
to the overlap.
This has been fun talking engine theory, has anyone been bothering to read this
nonsense? <G>
-ANT
Gerry
related) subjects mixeed up here, and going to confuse those trying to
learn. We are discussing stroke and rod length, at the same time. Untill I
re-read a couple of the posts, to clarify what they were saying, it seemed
as if the two terms were being used interchangably. The original topic was
if the longer stroke gives longer cylinder life. the answer is NO. One
reason being extra side load, or rocking of the piston. Also, for a given
RPM, the piston speed increases. Now, when we talk about rods, the longer
rod decreases side load (or rocking) of the piston, due to a lesser angle
between the centerline of the rod, and the centerline of the piston. This is
why you will find most stroker kits offer the longer rods. The longer rod
also will make more power due to the fact that the piston will remain at top
dead center a lil longer, and give the flame front longer to get moving. We
are talking about milli-seconds, but a four cylinder at 5000 RPM, everything
is in milli-seconds.......
--
GERRY... They come and they go, but theres always one around...
"ANT The Monarch of Menace " <s2...@aol.computer> wrote in message
news:20001007043612...@ng-ch1.aol.com...
Cale Fraser
ratio..but with the 5.38RP and a close 3rd gear..Possibly 4th..
My cam Is actually more low end then stock. the smallest bug pack cam you
can get.
I am only chaning my baja for the better, just went to 3X3 rear amrs..Looks
sweet. Its actually getting to be a class 5 unlimited Race car now.
High RPM is bad..I want LOW end power.
Dont worry, I know what im doing :-)
Cale
Shad Laws <s-l...@nwu.edu> wrote in message
news:8rlgk3$ibq3r$1...@ID-35662.news.cis.dfn.de...
> > The longer the stroke the more feet per mile the piston travels, hence
> more
> > wear--but the argument can be made that you can raise the rear end ratio
> > because you now have a higher torque at a lower RPM, so all things may
be
> > equal.
> >
>
> I know. However, we're talking about someone here who I'd wager isn't
going
> to change his gear ratio, probably has a high RPM camshaft for more kick,
> and wants to rev the hell out of it. Have you read about how many times
> he's changed the configuration of his baja? This isn't going to be
> strolling, calm, street car...
>
>
> > Long strokes can't as easily rev, but don't really need to as they
produce
> more
> > low RPM poer (Torque). These are more friendly street engines. If you
can
> keep
> > the revs down your durability and longevity go up exponentially. At
least
> this
> > is how it is in the V8 world. And unles the laws of physics are
different
> in
> > Professor Porsche's design studio all this should apply to.
>
ANT The Monarch of Menace
>related) subjects mixeed up here, and going to confuse those trying to
>learn.
If you can't dazzle 'em with brilliance, then baffle 'em with bull kaa kaa.
-ANT
Dr. Bob
Dr. Bob
----------------------
|A long stroke will not extend engine life. You are still having the piston
|moving up then down in one crankshaft rotation, regardless of rod length.
| Mike
|
|Cale Fraser wrote:
|
|> Hey ppl
|>
|> I am just about to put my 1641 together, but am now thinking of going with a
|> 74 or a 76mm crank, actually, I know i am going with a stroker.
|>
|> My question is, With the longer stroke, Will you get longer cylinder life? I
|> figure more is getting used, More even wear?
|>
Dr. Bob
force * distance regardless of the path, all other things being equal.
Note that larger displacement is inherently less efficient as a result of
pumping losses.
Dr. Bob
----------------------------
In article <8rlgpl$i15nt$1...@ID-35662.news.cis.dfn.de>, "Shad Laws"
<s-l...@nwu.edu> wrote:
|Correct me if I'm wrong, which I may very well be, but I always thought that
|getting away from TDC as quickly as possible was an advantage. TDC is a
|zero torque point... isn't it?
|
|Shad
|
|
|James W. Lindsay <jlin...@home.com> wrote in message
|news:h4oqtsos7vr3fv5rf...@4ax.com...
Dr. Bob
rotate up to 14,000 rpm. 150 hp from a 1 liter engine is not
extraordinary.
Dr. Bob
------------------------
In article <8efttsknd4s8jvst9...@4ax.com>, James W. Lindsay
<jlin...@home.com> wrote:
|On Fri, 6 Oct 2000 16:48:12 -0500, Shad Laws wrote:
|
|> Correct me if I'm wrong, which I may very well be, but I always thought that
|> getting away from TDC as quickly as possible was an advantage. TDC is a
|> zero torque point... isn't it?
|
|----------------------------------------------------------------
|James W. Lindsay Vancouver, British Columbia, Canada
|Website: http://members.home.net/jlindsay ICQ: #7521644
|----------------------------------------------------------------
ANT The Monarch of Menace
Yes, but in many engines this is not that critical. Use a piston with an offset
pin.
-ANT
ANT The Monarch of Menace
>force * distance regardless of the path, all other things being equal.
NOT true. You are not accounting for the combustion proccess which is enhanced
by longer piston TDC dwell. See my previous posting on this.
>Note that larger displacement is inherently less efficient as a result of
>pumping losses.
Efficient in what sense? Fuel consumption or power output? Yes, a larger
displacement engine consumes more fuel (all things being equal). The fact that
it pumps more air obviously means it requires more fuel.
Another thing to consider is that you can have too smal an engine for a given
application. In in instance a larger engine will give better economy as it
would require a smaller throttle opening which will keep the vacuum up--hence
better fuel economy.
But as the axiom says, there's no replacement for displacement. Sure you can
add a huffer of laffing gas, but you can add those to a larger engine as well.
-ANT
Veeduber
>Doesn't longer stroke produce more side load on the piston skirt?
>
Dear Dr. Bob (and the Newsgroup)
No. Stroke length has no immediate effect on piston side load.
What effects side load is the length of the connecting rod. For example,
imagine an engine with a 3" bore, 3" stroke and connecting rods five feet long.
Not much side load, right? :-)
The side-loading problem was defined and resolved by a British fellow named
Ricardo back in the 1930's. The 'Ricardo Rule' defines the ratio of stroke to
rod-length that provides the best compromise between rod length and side load.
For a stock VW rod (137mm), according to the Ricardo rule the maximum crank
stroke should be approximately 73.8mm. The small Chevy rod (ie, about 145mm in
length) or 'stroker' rods of similar length, are okay for cranks having strokes
up to about 90mm.. a bit much to stuff into a Type I crankcase.
-Bob Hoover
ANT The Monarch of Menace
>Ricardo back in the 1930's. The 'Ricardo Rule' defines the ratio of stroke
>to
>rod-length that provides the best compromise between rod length and side
>load.
I wasn't aware of Ricardo's work regarding the recip assembly. I do know of his
vast research and finding in cylinder heads (promarily combustion chambers and
turbulence).
-ANT
Searoy
news:Dr.Bob-1110...@et212pc113.et.anl.gov...
> Note that some motorcycle engines have bores almost twice the stroke, and
> rotate up to 14,000 rpm. 150 hp from a 1 liter engine is not
> extraordinary.
> Dr. Bob
The differences there are in the engineering. We are discussing a VW engine
as was engineered, not an engine designed from the ground up to rev to
oblivion. Therefore, if we concentrate on the capabilities of this engine
as engineered, then RPMs above 7000 are out of the question. Beyond that
some re-engineering is required, not patches or fixes.
--
*** Teach a Man to Fish ***
Searoy
66 bug (daily driver project)
T4 CIS-T powered imagination
> ------------------------
> |----------------------------------------------------------------
> |James W. Lindsay Vancouver, British Columbia, Canada
> |Website: http://members.home.net/jlindsay ICQ: #7521644
> |----------------------------------------------------------------
Searoy
> >Doesn't longer stroke produce more side load on the piston skirt?
> >
> ---------------------------------------
>
> Dear Dr. Bob (and the Newsgroup)
>
> No. Stroke length has no immediate effect on piston side load.
>
> What effects side load is the length of the connecting rod. For example,
> imagine an engine with a 3" bore, 3" stroke and connecting rods five feet
long.
> Not much side load, right? :-)
>
named
> Ricardo back in the 1930's. The 'Ricardo Rule' defines the ratio of
stroke to
> rod-length that provides the best compromise between rod length and side
load.
>
crank
> stroke should be approximately 73.8mm. The small Chevy rod (ie, about
145mm in
> length) or 'stroker' rods of similar length, are okay for cranks having
strokes
> up to about 90mm.. a bit much to stuff into a Type I crankcase.
>
> -Bob Hoover
Wouldn't a more accurate statement be that stroke in itself does not effect
side load, but rather its ratio to the length of connecting rod? Therefore,
taken at face value, a longer stroke in itself WOULD increase the side load
of the skirt, since a longer connecting rod was not specified.
I realize you gave an example of that in your post, but I feel your first
statement of stroke having no immediate effect on piston side load was
vague, and perhaps easily misinterpreted.
Shad Laws
the brake mean effective pressure acting on the rotating assembly.
Remember - you are nowhere even near 100% efficient in your combustion
(even 15% is pretty high, actually).
What is brake mean effective pressure? That is the average cylinder
pressure over the "down" cycles minus the average cylinder pressure over the
"up" cycles. Exhaust, Intake, and Compression all reduce it. How
combustion occurs GREATLY effects it. I won't go into gross technicalities
of combustion dynamics (partially because I only have a thumbnail's grip on
the stuff), but certainly this does greatly effect how things happen.
Here's a simple idealization of how the rod ratio effects power output: The
longer the rods, the more time per revolution the piston spends VERY near
TDC, and vice versa. In other words, short rods cause the piston to move
faster at the top of the stroke (a couple of easy diffeq's will show
this...). Now, very roughly speaking, to build up the pressure we'd "like"
to have, we need a certain amount of time for combustion to occur before the
piston really starts moving away from TDC. Let's assume (haha! simple
idealization...) that the amount of time is roughly constant, or at least
increases with engine speed less than proportionately (i.e. amount for
2000rpm is not 1/2 that for 4000rpm). Now, we can see that a lower RPM
would "desire" less time at/around TDC, so shorter rods prevail. At higher
RPM, they would "desire" more time at/around TDC, so longer rods prevail.
Again, this is a simplification, but nevertheless one that should kinda get
the point across...
And, yes, a larger displacement is typically (all other things equal) less
efficient than a smaller displacement because the things weigh more to move
around... although there really are about 2 billion other factors to
consider...
Shad
"Dr. Bob" <Dr....@anl.gov> wrote in message
news:Dr.Bob-1110...@et212pc113.et.anl.gov...
> It doesn't make any difference how long you are at or near TDC. Work =
> force * distance regardless of the path, all other things being equal.
>
> Note that larger displacement is inherently less efficient as a result of
> pumping losses.
>
> Dr. Bob
> ----------------------------
> In article <8rlgpl$i15nt$1...@ID-35662.news.cis.dfn.de>, "Shad Laws"
> <s-l...@nwu.edu> wrote:
>
> |Correct me if I'm wrong, which I may very well be, but I always thought
that
> |getting away from TDC as quickly as possible was an advantage. TDC is a
> |zero torque point... isn't it?
> |
> |Shad
> |
> |
> |James W. Lindsay <jlin...@home.com> wrote in message
> |news:h4oqtsos7vr3fv5rf...@4ax.com...
Jan Andersson
>
> Dr. Bob <Dr....@anl.gov> wrote in message
> news:Dr.Bob-1110...@et212pc113.et.anl.gov...
> > rotate up to 14,000 rpm. 150 hp from a 1 liter engine is not
> > extraordinary.
> > Dr. Bob
>
> The differences there are in the engineering. We are discussing a VW engine
> as was engineered, not an engine designed from the ground up to rev to
> oblivion. Therefore, if we concentrate on the capabilities of this engine
> as engineered, then RPMs above 7000 are out of the question. Beyond that
> some re-engineering is required, not patches or fixes.
1649cc, heavily ported dual port heads with stronger springs, Kadron
type carbs, and very aggressively lightened rotating parts.... gets you
10000 rpms and about 140hp. I see them at every race (once every two
weeks) plus a friend of mine builds and races them, as does his father.
Both are certified mechanics, both specialized in Mitsubishi and Skoda.
these beetle engines don't last very long. They don't need to. It would
be nice, but not necessary.
Jan
Dr. Bob
engine? Is the side loading on the pistons large and do you get scoring?
Do the main bearings wear out? Do the valves wear out the seats? It
would be fascinating to find out.
Dr. Bob
---------------------
In article <39E60594...@rocketmail.com>, Jan Andersson
Dr. Bob
small (in terms of fuel/work?) Large displacement suffers less flame
quenching at the walls? Fewer big cylinders have inherently less friction
than more numerous small cylinders? The power density is not so good
though.
Dr. Bob
-------------------
In article <8s4nd9$jhusi$1...@ID-35662.news.cis.dfn.de>, "Shad Laws"
<s-l...@nwu.edu> wrote:
|[...]
ANT The Monarch of Menace
>small (in terms of fuel/work?) Large displacement suffers less flame
>quenching at the walls? Fewer big cylinders have inherently less friction
>than more numerous small cylinders? The power density is not so good
>though.
>Dr. Bob
Large bore tends to have a cooler combustion charge. This causes higher
emissions and is one of the reasons why Chrysler killed the old 440. The V10
while having a similar displacement has smaller pistons (diameter).
You ever see how small the slugs are in a JagWire V12? The main reason for
these multi multi cylinder engines is to increase the overlap of the power
pulses to make as smooth a rotation of the crank as possible (at least this was
the intent back in the 30's--that, and the snob appeal).
-ANT
ANT The Monarch of Menace
>engine? Is the side loading on the pistons large and do you get scoring?
>Do the main bearings wear out? Do the valves wear out the seats? It
>would be fascinating to find out.
>Dr. Bob
Race engines are usually built with different clearences than a normal street
engine--loose bearings to reduce drag--they obviously won't last too long, but
the objective is to win at almost any cost.
-ANT
Searoy
Like the good ol' V16?
Searoy
-- Loose bearings reduce friction, but increase wear.
-- Lightened parts reduce weight but reduce strength.
-- More RPMs mean wear is faster in absolute time, more turns more often
mean more wear.
-- Higher compressions mean more stress on parts already stressed.
-- Running near-max over the entire life of the engine leaves little room
for error, so parts are replaced before they "might" go bad, even though
only half the life is out of them.
-- High compression and high RPM usually mean high heat, reducing oil's
ability to lubricate, breaking it down faster, reduces oil pressure so less
oil gets to overheating overstressed parts. Synthetic's can begin to deal
with these problems, but the problems still exist. High heat also weakens
stressed parts.
--
*** Teach a Man to Fish ***
Searoy
66 bug (daily driver project)
T4 CIS-T powered imagination
Dr. Bob <Dr....@anl.gov> wrote in message
news:Dr.Bob-1210...@et212pc113.et.anl.gov...
> That raises an interesting question: what exactly goes bad in such an
> engine? Is the side loading on the pistons large and do you get scoring?
> Do the main bearings wear out? Do the valves wear out the seats? It
> would be fascinating to find out.
> Dr. Bob
ANT The Monarch of Menace
>
>Like the good ol' V16?
Below is a list of Amurican car makers that offered multi cylinder injuns
This is from memory so pardon any boo boos----
Packard made 2 automotive V12's (but never a V16)
Cadillac made 2 V16's and one V12, they also developed a V12 in the mid/late
60's, but this never went into production
Marmon made a V12
Lincoln made 2 V12's but never a V16
Stutz and Dusenberg both made multi valved straight 8's
Pierce Arrow made a narrow angle V12
I think that's about it, if you don't count Ford in the equation (Lincoln's
Zephyr use a small V12 that was based on the Ford V8)
-ANT (isn't VW now working on a V10 or V12?)
Gerry
Point 1) By the piston remaining at TDC longer, you get a more eficient
flame front, and a more complete burn... more burn = More power.
Point2) More displacement less efficient? If you maintain same rotating
mass, and put a more powerful explosion over the piston, it makes more
power...period!
--
GERRY... They come and they go, but theres always one around...
"Dr. Bob" <Dr....@anl.gov> wrote in message
news:Dr.Bob-1110...@et212pc113.et.anl.gov...
| It doesn't make any difference how long you are at or near TDC. Work =
| force * distance regardless of the path, all other things being equal.
|
| Note that larger displacement is inherently less efficient as a result of
| pumping losses.
|
| Dr. Bob
| ----------------------------
| In article <8rlgpl$i15nt$1...@ID-35662.news.cis.dfn.de>, "Shad Laws"
Gerry
--
GERRY... They come and they go, but theres always one around...
"ANT The Monarch of Menace " <s2...@aol.computer> wrote in message
news:20001011184120...@ng-fi1.aol.com...
| >Doesn't longer stroke produce more side load on the piston skirt?
|
Shad Laws
> small (in terms of fuel/work?)
No - for example, more mass, more valves, more things to move to get the
same power (like at cruising speed) means a lower mechanical efficiency.
Large displacement suffers less flame
> quenching at the walls? Fewer big cylinders have inherently less friction
> than more numerous small cylinders? The power density is not so good
> though.
Aye - more power comes from engines with many small cylinders, which is why
Ferrari was making a V-12 Testarossa with a meager displacement of 3 liters.
See, it's kinda hard to generalize many cylinders versus a few when it comes
to efficiency. There are about a billion other factors that'd be changed in
the process greatly altering the results. However, in general, a little
4-banger still eats less gas than a V8. But, when you start climbing the
power chain, then a 6-cylinder engine is a good thing due to natural
harmonic balancing. Getting the same results from a 4-cylinder engine may
actually be worse... or it may be better depending on the other jillion
factors involved.
Shad
> Dr. Bob
> -------------------
> In article <8s4nd9$jhusi$1...@ID-35662.news.cis.dfn.de>, "Shad Laws"
Jim Adney
>No. Stroke length has no immediate effect on piston side load.
Huh??? I think I could prove otherwise. It's a pretty straightforward
vector problem.
>What effects side load is the length of the connecting rod. For example,
>imagine an engine with a 3" bore, 3" stroke and connecting rods five feet long.
> Not much side load, right? :-)
Right, but it's the RATIO that matters, not just the rod length.
>The side-loading problem was defined and resolved by a British fellow named
>Ricardo back in the 1930's. The 'Ricardo Rule' defines the ratio of stroke to
>rod-length that provides the best compromise between rod length and side load.
Now this sounds exactly right, and brings us back to: Yes, the stroke
DOES make a difference, because it changes this ratio.
-
-----------------------------------------------
Jim Adney jad...@vwtype3.org
Madison,Wisconsin USA
-----------------------------------------------
Tony W,
Jim Adney <jad...@vwtype3.org> wrote in message
news:m8qcus0itf4ueu5ec...@4ax.com...
> veed...@aol.com (Veeduber) wrote:
>
>
> >No. Stroke length has no immediate effect on piston side load.
>
> Huh??? I think I could prove otherwise. It's a pretty straightforward
> vector problem
Don't you know, size doesn't matter. ;-)
Tony
Jens-Eike Jesau
Fri, 13 Oct 2000 22:14:05 -0700:
TW> Jim Adney <jad...@vwtype3.org> wrote in message
TW> news:m8qcus0itf4ueu5ec...@4ax.com...
>>veed...@aol.com (Veeduber) wrote:
>>>No. Stroke length has no immediate effect on piston side load.
>>
>>Huh??? I think I could prove otherwise. It's a pretty straightforward
>>vector problem
TW> Don't you know, size doesn't matter. ;-)
I resisted to jump in this thread ( to be honest, didn't understand
enough..), but let me add some words ( maybe this is clear to you,
but i was fascinated when i found it out..)
If the radial pressure the piston pushes onto the cylinder
wall is so high that it breaks the oil film -- then it's too late
anyway. The piston should glide in the cylinder without metallical
contact.
This is why one sometimes finds engines that ran a lot but have no
wear at the cylinder sides, these are the engines that were only
running long distances and were not often started up.
Bye !
--
Regards,
Jens-Eike <je...@gmx.net> http://www.jesau.de
*** '72 1.6l Super Reliability rulez ! ***
ANT The Monarch of Menace
>wall is so high that it breaks the oil film -- then it's too late
>anyway. The piston should glide in the cylinder without metallical
>contact.
Ummm, what? Oil is designed to have a certain film strength--the idea is to
have it fill the clearance between moving metal parts at all times (duh!).
When oil get diluted (as by say gas) then the film strength disappears and when
a load is placed against the oil it'll squirt out from between the metal like a
watermelon seed from between your fingertips.
>This is why one sometimes finds engines that ran a lot but have no
>wear at the cylinder sides, these are the engines that were only
>running long distances and were not often started up.
Not sure what you mean by the first part of that sentence, but the second part
is true. It's generally accepted that something on the order of 75-90% of all
wear takes place during initial start up--before oil is pressurized and splash
lubrication has begun.
-ANT
Jan Andersson
>
> That raises an interesting question: what exactly goes bad in such an
> engine? Is the side loading on the pistons large and do you get scoring?
> Do the main bearings wear out? Do the valves wear out the seats? It
> would be fascinating to find out.
> Dr. Bob
My friend's last engine failure was due to broken (as in broken in two
pieces) counterweighed crank. It broke at about 9000rpm, going downhill.
It was aggressively lightened, and made from a stock 69mm crank.
(counterweights welded on by a pro, crank well balanced).
This engine was not built by him.
I always thought the rods were the first to go (lightened stock rods)
but they last pretty well. Sometimes it's as simple as an oil hose
connection coming loose....
Usually it is caused by worn bearings, and the case being too far gone
to hold the stresses.
Crank and rod bearings would be the #1 reason. They take everything out
of that engine, as long as it can possibly be used and rebuilt.
Jan
Jan Andersson
>
> >That raises an interesting question: what exactly goes bad in such an
> >engine? Is the side loading on the pistons large and do you get scoring?
> >Do the main bearings wear out? Do the valves wear out the seats? It
> >would be fascinating to find out.
> >Dr. Bob
>
> engine--loose bearings to reduce drag--they obviously won't last too long, but
> the objective is to win at almost any cost.
> -ANT
These engines have std bearing clearances, but just about everything
else is "looser" than normal just like ANT said.
WIN at any cost is the key here..:-) Without spending much money.
(dangerous combination).
The rules dictate that if anyone makes an offer on the race car after
the race, the car has to be sold. At a fixed price, same price for all
cars. If there are several offers, the "lucky winner" will be decided by
lottery of some kind.
The fixed price for the whole car (minus 5-point belts and bucket seat
which you get to keep)
is about 700 dollars, (Youo read that right), so there's no point in
investing thousands of dollars on the engine... someone will buy it from
you and you have to start over.. OR buy someone else's car! The engines
normally cost around 1500USD to build, in the national finals they can
cost twice, if not three times that. Win at any cost.. even if you lose
the car..
There is one way you can try to "protect" your car, and that is by
bidding on your OWN car. And asking your team members to do so too.
Bidding costs 20 bucks per bid.
With luck, you "win" your own car back, and only have to pay the 700 to
yourself. :-)
Jan
Jan Andersson
>
> >
> >
W12 is already out. (been for a while). Not sure if it's being fitted to
any production models yet. It's two VR6 engines baked into one.
Jan
--
r.a.m.v.a. Index
http://www.bug-bits.freeserve.co.uk/ramva/index.htm
r.a.m.v.a. readers around the world
http://www.geocities.com/bugfuel/ramvaworld.html
r.a.m.v.a. Virtual Aircooled Volkswagen Show
http://www.geocities.com/VWCreature
My Animated GIFs
http://www.geocities.com/jantoon.geo/anitest.html