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Gasflow of VW engine



 
 
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  #1  
Old July 4th 03, 03:28 PM
Veeduber
external usenet poster
 
Posts: n/a
Default Gasflow of VW engine

Has anyone had any experience with the "gasflow" of VW engine to improve
horsepower at lower RPM?


-------------------------------------------------

If by 'gasflow' you mean volumetric efficiency, I've some experience in that
area.

I'll also assume your question hinges on the fact that maximum torque always
occurs at the point of maximum volumetric efficiency while maximum propeller
efficiency comes from the longest prop that amount of torque can swing at an
rpm that will keep the tip speed below about 880 feet per second.

Toward that end I believe you will find it is fairly easy to emulate the torque
& rpm curves typically found in aircraft engines by simply grinding a cam that
approximates the timing & duration found in the small Continental engines (ie,
a-65, for example). Unfortunately, following that path I found that the small
displacement (1584cc or 96cid) of the stock engine leads to a rather
unreliable powerplant unless you keep the manifold pressure fairly low, which
of course limits the output, usually to something to small to be considered
practical as an aircraft powerplant (ie, power to weight is poor). The obvious
next step (at least, for me) was to increase the displacement of the engine.
This gets you back into the A/C powerplant ballpark but the next limitation you
will encounter, if your experience matches mine, is the thermal barrier imposed
by the fin area of the VW heads. When the continuous output exceeded about
45bhp I found cylinder head temperatures in the vicinity of the exhaust valves
exceeded the safe maximum level (about 450 degrees on the Fahrenheit scale).
Operating at or above that level for any length of time lead to a drastic
shortening of the useful life of the exhaust valves (as little as ten hours, on
some experiments).

On a similar note, efforts to improve volumetric efficiency through the use of
a tuned exhaust system were more amusing than effective. At anything below
about 3200 rpm the weight of the exhaust manifolding begins to approach the
weight of the engine, since the minimum runner length is on the order of sixty
inches :-)

I found the best compromise to be alternate-pair exhaust stacks (ie, cylinder 1
coupled with cylinder 3 and 2 coupled with 4) each having a total length of 27"


As a point of interest, I began trying to improve the output of the VW engine
in the late 1950's, starting by applying all of the typical hot-rod techniques
that have been used to improve volumetric efficiency. Some of them work but
most do not, largely because of the nature of propellers; what you gain in
apparent output at the prop flange is lost in the reduced efficiency of the
propeller at high rpm.

Experiments with larger valves and ports having a mirror-like finish gave
remarkably better rates of flow on the flow-bench. But on a real engine there
was no significant improvement in output, probably because of the relatively
low flow rate of even the largest VW engine when running at prop speeds.
(Typically, the engine would have to operate at 3500 or above to see any
improvement in flow-smoothing.)

Experiments with different combustion chamber shapes proved to be an expensive
waste of time. Altering the shape of the VW's wedge-type combustion chamber
appears to upset internal flow during the process of combustion. At prop
speeds the typical result was less power, apparently do to improper combustion.
This is partially confirmed by a marked increase in hydrocarbons in the
exhaust gas, evidence of after-burning in the stacks and so forth.

I'm presently working with thermal barrier coatings, having spent a couple of
years learning how to appy them :-) Preliminary results on one-cylinder
engines have been positive although difficult to quantify due to the relatively
small scale of the improvement and lack of laboratory facilities (you have to
adjust your temperature & torque observations for the local temperature &
atmosphere, etc.).

Finally, none of the above is new information. I've previously posted this
information, including some engine modification drawings, to mailing lists
devoted to flying Volkswagens (which this Newsgroup is not). If you'd care to
provide a valid email address I'll be happy to point you toward the various
archives.

-R.S.Hoover
Ads
  #2  
Old July 5th 03, 01:42 AM
Marvin Barnard
external usenet poster
 
Posts: n/a
Default

Gordan Blair developed a formula in the early 60's for matching
exhaust pipe Length to a given RPM to achive the pulse tune effect. The
lower the RPM the more pipe needed.......

  #3  
Old July 10th 03, 07:27 PM
bob zee
external usenet poster
 
Posts: n/a
Default



"Veeduber" wrote in message
...

Finally, none of the above is new information. I've previously posted

this
information, including some engine modification drawings, to mailing lists
devoted to flying Volkswagens (which this Newsgroup is not). If you'd

care to
provide a valid email address I'll be happy to point you toward the

various
archives.

-R.S.Hoover


please point me to the various archives! i hope to build my own plane and
fly it soon. i have a couple extra vw engines lying around just waiting to
be used.

--
bob z.

"people with less brain power than you are doing more difficult things
everyday"Đ


  #4  
Old July 11th 03, 04:11 PM
Andre
external usenet poster
 
Posts: n/a
Default

Hi,
Thanx. I have sent an email as requested to ......
You refer to
"mailing lists devoted to flying Volkswagens (which this Newsgroup is not).
"
Where can I find these please?
Kind Regards
Andre


"Veeduber" wrote in message
...
Has anyone had any experience with the "gasflow" of VW engine to improve
horsepower at lower RPM?


-------------------------------------------------

If by 'gasflow' you mean volumetric efficiency, I've some experience in

that
area.

I'll also assume your question hinges on the fact that maximum torque

always
occurs at the point of maximum volumetric efficiency while maximum

propeller
efficiency comes from the longest prop that amount of torque can swing at

an
rpm that will keep the tip speed below about 880 feet per second.

Toward that end I believe you will find it is fairly easy to emulate the

torque
& rpm curves typically found in aircraft engines by simply grinding a cam

that
approximates the timing & duration found in the small Continental engines

(ie,
a-65, for example). Unfortunately, following that path I found that the

small
displacement (1584cc or 96cid) of the stock engine leads to a rather
unreliable powerplant unless you keep the manifold pressure fairly low,

which
of course limits the output, usually to something to small to be

considered
practical as an aircraft powerplant (ie, power to weight is poor). The

obvious
next step (at least, for me) was to increase the displacement of the

engine.
This gets you back into the A/C powerplant ballpark but the next

limitation you
will encounter, if your experience matches mine, is the thermal barrier

imposed
by the fin area of the VW heads. When the continuous output exceeded

about
45bhp I found cylinder head temperatures in the vicinity of the exhaust

valves
exceeded the safe maximum level (about 450 degrees on the Fahrenheit

scale).
Operating at or above that level for any length of time lead to a drastic
shortening of the useful life of the exhaust valves (as little as ten

hours, on
some experiments).

On a similar note, efforts to improve volumetric efficiency through the

use of
a tuned exhaust system were more amusing than effective. At anything

below
about 3200 rpm the weight of the exhaust manifolding begins to approach

the
weight of the engine, since the minimum runner length is on the order of

sixty
inches :-)

I found the best compromise to be alternate-pair exhaust stacks (ie,

cylinder 1
coupled with cylinder 3 and 2 coupled with 4) each having a total length

of 27"


As a point of interest, I began trying to improve the output of the VW

engine
in the late 1950's, starting by applying all of the typical hot-rod

techniques
that have been used to improve volumetric efficiency. Some of them work

but
most do not, largely because of the nature of propellers; what you gain in
apparent output at the prop flange is lost in the reduced efficiency of

the
propeller at high rpm.

Experiments with larger valves and ports having a mirror-like finish gave
remarkably better rates of flow on the flow-bench. But on a real engine

there
was no significant improvement in output, probably because of the

relatively
low flow rate of even the largest VW engine when running at prop speeds.
(Typically, the engine would have to operate at 3500 or above to see any
improvement in flow-smoothing.)

Experiments with different combustion chamber shapes proved to be an

expensive
waste of time. Altering the shape of the VW's wedge-type combustion

chamber
appears to upset internal flow during the process of combustion. At prop
speeds the typical result was less power, apparently do to improper

combustion.
This is partially confirmed by a marked increase in hydrocarbons in the
exhaust gas, evidence of after-burning in the stacks and so forth.

I'm presently working with thermal barrier coatings, having spent a couple

of
years learning how to appy them :-) Preliminary results on one-cylinder
engines have been positive although difficult to quantify due to the

relatively
small scale of the improvement and lack of laboratory facilities (you have

to
adjust your temperature & torque observations for the local temperature &
atmosphere, etc.).

Finally, none of the above is new information. I've previously posted

this
information, including some engine modification drawings, to mailing lists
devoted to flying Volkswagens (which this Newsgroup is not). If you'd

care to
provide a valid email address I'll be happy to point you toward the

various
archives.

-R.S.Hoover



  #5  
Old July 14th 03, 08:06 AM
Andre
external usenet poster
 
Posts: n/a
Default

Hi Veeduber,
Just a reminder hoping that you'll see this post and point me in the right
direction for the mailing lists devoted to flying Volkswagens and
the information you have previously posted on your VW experiments?
Thanx
Kind Regards
Andre

"Andre" wrote in message
...
Hi,
Thanx. I have sent an email as requested to ......
You refer to
"mailing lists devoted to flying Volkswagens (which this Newsgroup is

not).
"
Where can I find these please?
Kind Regards
Andre


"Veeduber" wrote in message
...
Has anyone had any experience with the "gasflow" of VW engine to

improve
horsepower at lower RPM?


-------------------------------------------------

If by 'gasflow' you mean volumetric efficiency, I've some experience in

that
area.

I'll also assume your question hinges on the fact that maximum torque

always
occurs at the point of maximum volumetric efficiency while maximum

propeller
efficiency comes from the longest prop that amount of torque can swing

at
an
rpm that will keep the tip speed below about 880 feet per second.

Toward that end I believe you will find it is fairly easy to emulate the

torque
& rpm curves typically found in aircraft engines by simply grinding a

cam
that
approximates the timing & duration found in the small Continental

engines
(ie,
a-65, for example). Unfortunately, following that path I found that the

small
displacement (1584cc or 96cid) of the stock engine leads to a rather
unreliable powerplant unless you keep the manifold pressure fairly low,

which
of course limits the output, usually to something to small to be

considered
practical as an aircraft powerplant (ie, power to weight is poor). The

obvious
next step (at least, for me) was to increase the displacement of the

engine.
This gets you back into the A/C powerplant ballpark but the next

limitation you
will encounter, if your experience matches mine, is the thermal barrier

imposed
by the fin area of the VW heads. When the continuous output exceeded

about
45bhp I found cylinder head temperatures in the vicinity of the exhaust

valves
exceeded the safe maximum level (about 450 degrees on the Fahrenheit

scale).
Operating at or above that level for any length of time lead to a

drastic
shortening of the useful life of the exhaust valves (as little as ten

hours, on
some experiments).

On a similar note, efforts to improve volumetric efficiency through the

use of
a tuned exhaust system were more amusing than effective. At anything

below
about 3200 rpm the weight of the exhaust manifolding begins to approach

the
weight of the engine, since the minimum runner length is on the order of

sixty
inches :-)

I found the best compromise to be alternate-pair exhaust stacks (ie,

cylinder 1
coupled with cylinder 3 and 2 coupled with 4) each having a total length

of 27"


As a point of interest, I began trying to improve the output of the VW

engine
in the late 1950's, starting by applying all of the typical hot-rod

techniques
that have been used to improve volumetric efficiency. Some of them work

but
most do not, largely because of the nature of propellers; what you gain

in
apparent output at the prop flange is lost in the reduced efficiency of

the
propeller at high rpm.

Experiments with larger valves and ports having a mirror-like finish

gave
remarkably better rates of flow on the flow-bench. But on a real engine

there
was no significant improvement in output, probably because of the

relatively
low flow rate of even the largest VW engine when running at prop speeds.
(Typically, the engine would have to operate at 3500 or above to see any
improvement in flow-smoothing.)

Experiments with different combustion chamber shapes proved to be an

expensive
waste of time. Altering the shape of the VW's wedge-type combustion

chamber
appears to upset internal flow during the process of combustion. At

prop
speeds the typical result was less power, apparently do to improper

combustion.
This is partially confirmed by a marked increase in hydrocarbons in the
exhaust gas, evidence of after-burning in the stacks and so forth.

I'm presently working with thermal barrier coatings, having spent a

couple
of
years learning how to appy them :-) Preliminary results on one-cylinder
engines have been positive although difficult to quantify due to the

relatively
small scale of the improvement and lack of laboratory facilities (you

have
to
adjust your temperature & torque observations for the local temperature

&
atmosphere, etc.).

Finally, none of the above is new information. I've previously posted

this
information, including some engine modification drawings, to mailing

lists
devoted to flying Volkswagens (which this Newsgroup is not). If you'd

care to
provide a valid email address I'll be happy to point you toward the

various
archives.

-R.S.Hoover





 




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