Project Triple Double Is a Test to Find a Dollar to Horsepower Ratio of a 200 Cc OHV Engine
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.
Throttle Linkage
Warmed up and engine and did three runs recording data on the second and third full throttle runs
Run #2
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
HP 7.16 7.26 7.26 7.18 7.00 6.70 6.39 6.08
Run #3
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
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
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
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”.
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
HP 8.41 8.63 8.74 8.79 8.76 8.64 8.51 8.30
Install ARC billet flywheel
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
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.
Dyno
See the overlay of the above dyno runs. Notice the two bone stock runs are very close together.
Dyno Graphs
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.
Firing point ARC
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.
Firing Point Stock
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.
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.
Indicating head
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.
Cut head
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.
Piston cc's
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.
Grinding valves
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.
Grinding seats
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.
Making shim
Checking spring force
First step on the block is to enlarge the oil return hole located between the lifters. I used a 17/64” bit.
Oil Return
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.
Head Gasket
Rod & Piston
Milling Setup
After Milling
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.
Hone
Flex Hone
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”.
End Play
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”.
Checking Cam
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.
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
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.
RPM 4000 4200 4400 4600 4800 5000 5200 5400 5600
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.
Boring carburetor
Cutting fixture
Throttle shaft
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.