Project triple double is a
test to find a dollar to horsepower ratio of a 200 cc OHV engine, specifically
a Chinese made clone of a Honda GX200. The name of the project comes from the
question can I double the horsepower of this engine for triple the cost of the
initial engine? So if my dyno finds the engine to have it’s rated 6.5
horsepower right out the box can I produce 13 HP for $540? The $540 is $159 for
the engine plus $21 shipping multiplied by three.
The dyno test will
be run on an inertia type dyno equipped with Performance Trends pro version
software. Four test will be run as follows, bone stock out of the box,
aftermarket air filter adaptor and header with modified jets, complete
blueprint job and new internals for the block and head, and the final test will
be conducted after modifying the carburetor.
Here is the list of
parts.
Billet filter
adaptor
Paper filter
Foam pre-filter
Kwik link throttle
linkage
RLV header
Dynocams valve
springs
Lash cap
Exhaust valve
retainer
ARC billet flywheel
ARC billet
connecting rod with bearing
Dynocams modified
clone cam
Flat top piston
GX 160 head gasket
High strength bolt
kit
Heavy duty chain
guard
Total price is
$530.28 including all shipping charges and 7% Indiana sales tax. Now that the
budget seems to be met it’s up to me to see if I can find the power using
basics learned in Small Engines 101. I know the task would be simple given some
more money and I will make notes of that along the way. By the same token the
power could be made with less money but this would sacrifice safety and the
durability and reliability of the engine. The tests will be conducted using
87-octane gasoline (for now).
For now the document
will have to be in this form. Doing a web layout is simply too time consuming
for me to do at this time. Click on the links to view the photos.
The only thing
needed to get the engine ready for it’s first run is to add fuel and oil and
over ride the governor. I will completely remove the governor during
disassembly of the engine. After removal of the air cleaner, blower housing,
and fuel tank the first piece of the Kwik link is installed. The return springs
will go toward the front of the engine.
Warmed up and engine
and did three runs recording data on the second and third full throttle
runs
Run #2
HP 7.16 7.26 7.26 7.18 7.00 6.70 6.39 6.08
Run #3
HP 7.13 7.23 7.25 7.17 6.98 6.66 6.35 6.07
Remove stock exhaust
and install RLV 5438C header
HP 7.92 8.04 8.09 8.05 7.93 7.47 7.05 6.79
Install billet
filter adaptor, drill low side jet .024” and main jet .036”.
HP 8.41 8.63 8.74 8.79 8.76 8.64 8.51 8.30
Install ARC billet
flywheel
HP 8.87 9.09 9.19 9.28 9.35 9.24 8.96 8.69
Here is a view of
the engine at end of initial tests.
See the overlay of
the above dyno runs. Notice the two bone stock runs are very close together.
I am going to call
my baseline peak horsepower 7.29 at 4300 RPM. Letting the software find averages
for horsepower between 4300 and 4600 yields 7.27 HP for run number 2 and 7.30
for run number 3. Keep in mind that the 200 RPM increments of the small charts
hide some of the details. So now the challenge is to achieve a solid peak of
14.58 HP over a 500 RPM range.
This is a little
more than I expected given the small amount of experience I have with the blue
clone engines. Honestly, I was thinking the power would be less than 6.5 HP.
Perhaps this engines carburetor had a larger main jet than the last blue clone
I tested. I measured this one at .028” diameter and if I recall I drilled the
main on a blue one to .028”, tested, and then drilled it bigger.
Three very simple
bolt on pieces along with a jet swap made a two horsepower increase. How will these
combine with the internals to increase the performance?
When I removed the
bower housing to exchange flywheels I used a timing light to find the firing
points of each of the flywheels. Here is a photo of the ARC flywheel firing
point. Notice the mark on the magnet in reference to the front leg of the coil.
I placed a line on the coil to mark that point. Keep in mind the engine is
running at 2000 RPM in this photo.
This shows the
position of the stock flywheel firing point. The engine is not running in this
photo. Both of the flywheels were firing at 24 degrees BTDC.
With the engine
disassembled it is time to look things over and come up with a plan. The first
order of business it to determine how much material will be cut from the block
and head. The base circle of the stock cam is .870” and the ground cam is
.755”. The difference is the radii of those is .057”, this lowers the pushrod
that amount and removal of that much material will put the rocker arms right
back at the stock position. Deviation from that height will most likely not
cause a problem and may actually help a bit.
Using an indicator
setup I measured the piston to be .007” in the hole.
I need to be mindful
of piston to head clearance when setting this up. I am going to try to stay
around .030”. Given the .017” or so existing clearance I am going to need to go
to a thicker head gasket. The block will get milled to zero deck height with a
flat top piston and the head gasket will be sized for the clearance.
I arbitrarily had
picked .050” to be milled from the cylinder head. At this point that sounds
like a good starting point.
After the head is
bolted down I checked to see that there would be an even amount taken off all
sides.
I measured the depth
of the head between the valve seats to be .291” stock. This gives a reference
to how much material has been removed.
Using a CD case with
a couple of holes drill in it and a syringe I cam up with a crude way to check
some volumes. I used a dial caliper to measure the movement of the plunger in
the syringe rather that try to read from the graduations on the cylinder. Put a
bead of grease around the edge to seal in the water.
Using the CD case
and some other unscientific methods I came up with the following volumes
.010” head
gasket .025 cc
.040” head
gasket 3.69 cc
piston dish 3.5cc
top of ring to top
of piston .43cc
.007” in the
hole 4.28 cc
cylinder head 20.0 cc
milled cylinder
head 15.5 cc
Combustion chamber
volumes for some combinations are
Stock 27.8 cc
Flat piston, 0 deck,
thick gasket 24.12 cc
Flat piston, .007
popup, .040” gasket 19.84 cc
Flat piston,
cut head, .040” gasket 19.62 cc
Flat piston, cut
head, .007 popup, .040” gasket 15.34 cc
Using a swept volume
of 196 cc will put the compression ratios respectively at 7.1, 8.1, 9.9, 10.0,
12.8. These are some pretty rough guesses but it gives me some idea of which
way to go.
The zero deck height
piston, milled head, and thicker gasket seems to be in the area that I am
looking for.
Using a ¼” die
grinder with an egg shape cutter I did what I could with the ports. Basically
blend the edges into the bowl and make the best short side radius possible.
There really are not a lot of choices with the given port.
There is not going
to be any fancy work on the valves and seats at this time. After I get some
test it will be easy to remove the head and get a separate test on the effects
of extra work in this area.
Both valves will get
refaced at 45 degrees just to freshen them up a bit.
The seats will just
get trued up. I really can’t work on addition angle right now because I need to
save the material to match the valves up at the next testing session.
With the seats and
valves mated up it is time to find the valve spring installed height. Put a
spacer of known size in place of the valve spring and use an indicator to
measure the travel of the valve until the spacer stops the movement. Add that
measurement to the thickness of the spacer. I will be using exhaust retainers
because they allow the use of lash caps. I found the heights to be .909” intake
and .868” exhaust. Checking the intake valve with the intake retainer yielded
.857” height.
Checking the springs
that I have with those heights gives me seat pressures of 4 pounds intake and
11 pounds exhaust. Seams that .825” will give 18 pounds of seat pressure so
shims will be needed to get to that point.
First step on the
block is to enlarge the oil return hole located between the lifters. I used a
17/64” bit.
With the rod and
piston installed it is time to remove the necessary material from the top of
the block. I should say at this point that the flat top piston and gasket was
not in the original budget. I had to add the shipping on the engine to get that
to fit. I don’t know how necessary it was but wanted to get it in there for
future modifications to the engine. The plan was to go for zero deck height.
After taking measurement and finding head gasket to be around .046” I decided
to go with .005” pop up.
After the milling I
used a 45-degree sanding cone to knock the sharp edge off of the top of the
cylinder. Just to help prevent damage to the rings during final piston
installation. Measuring with a bore gauge if found the bore to be with .0005”
at all locations. The clearance is in the .001” to .0015” range. This is
typical as the block has been heat cycled a few times and the dyno runs. A very
few strokes with the hone should even out the cylinder wall and give a nice
fresh crosshatch. After honing a couple of passes with a flex hone will knock
off any sharp peaks left by the stone hone. If I continue to work on the Honda
style engines I will make a torque plate for use when honing.
The final
preparations now include prepping a new set of piston rings, cleaning all part
thoroughly, and finish up the crankshaft by lapping the flywheel and cleaning
the crankpin with crocus cloth and lapping oil.
With the bottom end
assembled the crankshaft endplay is checked. I noticed earlier that the endplay
was small to non-existent. After removing and cleaning both of the bearings and
using a new gasket the endplay checked to .005”.
With the engine
assembled a degree wheel is installed to accurately set the ignition timing to
the stock 24 degrees and to check the cam timing. I couldn’t come up with a
convenient holder to keep the indicator over the rocker so I clamped the engine
to the milling table and used a magnetic holder. Seemed to work well enough.
There was no card with the cam. DynoCams advertises 236 degrees duration, I was
coming up very close to that and measuring .265” lift. I didn’t think there
would be an issue with valve to piston clearance and checking it proved there
was more than .120”.
With the final
assembly completed and 14 ounces Cool Power Light oil in the crankcase it is
time for another round of dyno testing. After a short warm-up and break in
period here are some more results.
HP 9.20 9.58 9.88 10.12 10.19 10.03 9.76 9.59 9.48
Adding 2 degrees of
ignition timing and .039” main jet.
HP 9.30 9.67 9.98 10.19 10.25 10.22 10.17 10.16 10.22
On the initial run
the engine just did not pull well through the entire RPM range. I did not try
to re-jet or adjust at that time. I knew the engine would run better with more
ignition timing and time would be better spent tuning at that point.
With both the 24 and
26 degree timing the peak horsepower still occurred at 4800 RPM, but with the
higher timing the power stayed up better after that point.
If I had another
header this would be a good time to try it. At some point I will try the header
with it’s intended RLV muffler.
Now it is time to
remove and disassemble the carburetor. I measured the smallest diameter in the
venturi area to be about .612”. Once the cutter was centered I cut .005” per
pass. At around .675” the cutter broke through the wall into the low speed jet
passage. A bit of Magnum Steel two part epoxy remedied that issue. A flex hone
was used to smooth things up a little bit.
The choke is
removed, the throttle shaft and plate are thinned, and the screw has extra
material removed. I checked this carb on my flow bench against a PZ 22, I can’t
give exact CFM numbers because my bench only compares, and let’s just say there
is no comparison. In the end this engine will be wearing a Walbro.
The carb work
certainly helped. The engine accelerates very well up to about 7500 RPM’s were
it seems to just be done. I tried main jets from .030” to .042” and the largest
was the best. Would some more help? I think there may be some power left to tune
out of this engine but not enough to make the ultimate goal of fourteen and a
half horsepower. I don’t have a spare emulsion tube at the time but there may
be a bit a power there.
At this point the
best 500-rpm average is 11.43 HP. The final run peaked at 6000 rpm compared to
the previous high peak rpm of 4800. Quite simply there is not enough
carburetor.
The results with the
modified carb are shown below. Notice the scale of rpm’s is different than the
previous test.
HP 10.82 10.91
11.10 11.29 11.31 11.23
11.09 10.97 10.84
Here is an overlay
of the primary test. In ascending order they are:
BOX stock
Filter adaptor,
header, billet flywheel
Millwork, piston,
and cam swap
Increase ignition
timing +2 degrees over stock
Bored and worked
carb
One point that needs
to be made is the use of the fuel pump. While waiting for some parts to arrive
I had modified an Animal intake to for this engine. I put a hose barb in the
intake for pulsing the fuel pump. I have billet oil fill hole adaptors to pulse
from the crankcase but the Briggs threads are not the same. I pulsed the fuel
pump from the valve cover for the stock carb, from the existing hole above the
baffle. With the baffle in the cover
the fuel was very slow to come out of the fuel container. With the baffle
removed it pumped quite fast. I wanted to come up with a better way because
this method was keeping the engine from being vented. It was pushing out a bit
of oil from around the valve cover. The cover and the gasket are not the
highest quality but the point is there was pressure in there. And yes, it most
likely was robbing some power. I now realize there is enough space to get a
hose barb in the valve cover beneath the baffle. I will set the pump up in that
fashion when I convert the stock carburetor to methanol in the future.
Really at this point
I just can’t believe that ignition timing, valve springs, carb jetting, or any
other tuning will gain what I set out to test. The initial power of the engine
just made to goal too lofty. Still this is a great improvement as the overlay
graph indicates and would be one heck of a fun ride on a kart or mini bike!!!
If the engine would have produced the six or six and a half that I expected I
would continue the experiment to get into the 12 hp range.
Well, actually I
will continue the experiment, just without the budget in mind. I have already
modified an Animal intake to fit the head and set up a new PZ 22 for methanol.
The engine will also be getting 1.3:1 rocker arms, +1 mm intake valve,
replacement exhaust valve, new valve springs and retainers, chrome moly push
rods, two angle valve job, the timing will go up to 30 degrees, and the
sparkplug will be an Autolite 3910.
The first thing I
notice after removing the head is the nice color left in the head by the fire
ring on the head gasket. This makes a very nice guide to blend the combusting
chamber walls from the seat to the block-mating surface to help unshrould the
valves a bit.
Step one will be to
widen the inside diameter of the intake seat 1 millimeter. I ran the cutter to
about the top of the valve guide. After the seat inside diameter was cut to
.933” a die mini grinder was used to blend the edge where the cutter stopped
and the short radius back into the bottom of the seat.
The boring left the
45 degree cut very thin. With a bit of 600 lapping compound on the valve I
check the contact point of the valve and seat. It is near the inside edge of
the valve but the seat is sufficiently large. I wanted to go with a three angle
valve but experimenting showed it would be difficult to get the 60 degree cut
in the bottom with the stones I have right now. Sure I could have redressed the
30 or 45 stone to 60 degrees then back to its original angle.
I cut the top 30
degree of each seat with a 1 1/8” stone until the stone was getting into
aluminum on the chamber wall. I then made the 45 degree cut until it was the
width I wanted. On both sides the 30 degree cut extends past the outside
diameter of the valve. Using Dykem layout fluid helps to show the relations of
the angles. One can see in the photo where the valves meet the seat. In the
future I can reduce the size of the 30 degree cut, move the seat further out,
and put the 60 degree cut on the bottom. At this time I do not have the means
to install 5.5 mm valve guides. Since the valve seats need to be trued after
installation of guides that would be a good time to complete the seat work.
History with kart racing has proved to me that good valve guides are worth
power.
The valve springs
and shims that came with the ratio rocker kit measure about two pounds lighter
than the spring setup already installed. For now I will stay with the 18 pound
springs and shims. I do think the retainers are nice and I like the lash caps.
The rocker arms are noticeably shorter.
With everything
assembled I thought that tuning the stock carburetor for methanol would be
worth the time. After the pilot jet was adjusted so that the idle was good and
the engine would accelerate crisply from idle it was time to work on the main
jet. About the time I thought I had found the correct main jet the methanol
took its toll on the epoxy and let raw fuel seep through. I was just
accelerating the engine against the dyno flywheel to about 5000 rpm to see how
it responded without recording so there are no results. I do have a good idea
on where to start with the jets (and the limits of boring) on the next carb
though. After purchasing a new carburetor I may return to gasoline for a bit as
hindsight says there may be a better way to go about gas tuning by adjusting
the jets and timing together.
With the new
carburetor reworked and set up with the jets from the failed first carburetor
it is time to try again. The original carburetor was a good experiment on where
the fuel passages are located and how NOT to set a brazing torch to patch a
hole. I must mention that I went through the casting in two places with the
second carb while grinding but they were repaired quite nicely with a brazing
torch and aluminum brazing rod. I must add the replacement carb was a different
manufacturer than the first and in my opinion may not have the performance
potential of the original carb.
Here is a view of
both end of the new carburetor and one of the patches. The other patch was at
the low side jet area. These views represent just about as much material that
can practically be removed from the venturi area. I could possibly have the
ceiling raised a small bit after the addition of the aluminum on the top. The
two limiting factors are is the wall at the pilot jet area and the ledge that
holds down the emulsion tube on the bottom.
The fuel metering
circuits on these carb are a bit unique and there are endless possibilities to
modify the relationships within the carburetor. Here is one thought to ponder,
ALL of the fuel enters below the main jet through two holes in the side of the
casting. The pilot jet is fed from the outside of the emulsion tube. It’s no
far off now as the engine runs VERY well. If I had a choice though I would like
to try to richen below 6000 rpm and lean out a bit from there on to a peak rpm
of about 7400.
This test exceeds
the original test goals in horsepower but I cannot say that the actual goal was
met because the engine has the ratio rockers and the +1 mm intake valve. The
rockers could be easily changed but there is no going back on to the stock
intake valve.
Keep in mind that
the stock appearing methanol carb was conducted after the following PZ-22 test.
A RLV modified “square hole” muffler was used which would have increased the
performance of the Walbro carburetor. Also the valve cover was modified to
pulse the fuel pump from beneath the baffle. With some experimenting with the
fuel circuits there can be some improvements with the modified stock carb.
The final test will
involve testing a Walbro PZ-22 on methanol. This is a new carburetor with only
the fuel nozzle, pilot jet, main jet, and float height set for methanol. I do
not want to modify the casting as don’t want to make the carb out of spec for
stock class Animal racing if this engine prefers a Tillotson.
The Animal intake
can be made to fit the bolt holes and line up with the port quite well by
elongating the mounting holes. The problem being that this placed the carb at a
fairly steep angle. The testing was done with the carb in that position but I
have since went back and cut the flange from the intake and welded it back at
so that the carb will be level when on an angled engine mount.
With the PZ hooked
up I did a pull up to 7000 RPM. After seeing the graph still going up at 7000
it was time to see some more. One more run to 7500 + showed it was still
holding. Now install the RLV WKA stock class muffler for the final pull. The
muffler showed better power all around. This engine sounded impressive, never
skipped a beat, and asked no questions about going to a clean 8000+!!!!!
As a final test the
ignition timing was increased to 34 degrees and the main jet increased by
.004”. This seemed to help across the entire rpm range
Below are the
results of the last runs and an overlay of the final run verses the best
results of the modified original carburetor running gas and the original box
stock test.
30 degrees timing
.050” Main jet
HP 14.70 14.86
14.91 14.90 14.94 14.93 14.82
14.01 13.58
34 degrees timing
.054” Main Jet
HP 15.11 15.32
15.45 15.52 15.61 15.60 15.41
14.61 14.26
Keep in mind there
is some room for improvement with modification to the casting of this carb.
Also this was my only attempt at jetting the PZ based on my experience with WKA
stock class Briggs Animals. I simply removed a carburetor from a new Animal and
reamed the nozzle, pilot & main jet, and swapped needles to my initial tune
for those engines.
A post runs
inspection showed the lash caps to have a bit of wear directly in the center.
No real signs of heavy swiping. Head bolts and studs did not budge when checked
with a torque wrench. The lash was reset using some blue Loctite on the stud.
At this point I am
going to order a new clone carb and head. Hindsight is 20/20. Both will be only
for the use of going back to revisit the original test.
In conclusion, is
this a do it yourself project, probably not? This was my first attempt at
blueprinting a Honda style engine. I have completed somewhere in the mid 200’s
of engine new builds and/or rebuilds but only for 5 horse flathead and Animal
stock class kart engines. That finances the tools, equipment, and projects like
this, plus I will make a few bucks on this engine.
As for the original
question, can the power be doubled? Honestly, maybe it can!!
I hope you enjoyed
and check back later to see if there are any updates.
Thank you,
Travis Atwood
atwoodracing@tds.net
