The airbox is gone. The carburetor bore area is increased 50%. The reed valve tip area has been increased 70%. It is my hope that the Jolly Moto pipes are now the restriction to breathing. I am hoping for a BMEP of somewhere between 145-160 - with torque peak in the 8000-9000 range.
I didn't believe I could greatly index torque with ignition timing, but who knows until you have a whack at it?
This first chart is of all the ignition curves I tested that day. The Zeeltronic makes it easy, as I can store up to 10 discrete curves at once. Of course the baseline curve ("Jim") is stored along with 4 more. Two advanced (approximately +2 & +4) and two retarded (approximately -2 & -4). I have neglected to mention that I have a rev limiter set at 11,000. The data point at 12,000 RPM is only to establish the downward slope of the curve past 10,000 RPM. You will also notice the the advanced curves shade back toward the Jim curve. It was suggested that under no circumstance did I want more than 16 degs of advance after 10,000 RPM.
Note: All tests are based on full throttle application. NOW - I would give you that running all the same tests at both say 1/2 and 1/3 throttle might generate some interesting results ....... I am inclined to "tune" for full throttle and _compromise_ settings to find acceptable part throttle operation.
First up was the -2 deg curve. I was under no illusion as I was pretty sure less would be less .......
..... and I was pretty much right with one exception. At about 6700 RPM the -2 shows a 1 HP advantage. Dyno aberration? Don't know. Right at the top -2 gave away about 1 HP. Not really enough to draw a firm conclusion. This run was not enough different to make much of a difference.
-4 deg curve test
OK - less advance ain't gettin' me nothin' at full throttle openings. On to ignition advance.
+2 deg test
Still really hard to see the difference in the chart, but I am clearly now heading in the right direction.
+4 degs test
Now we're slicing the bread pretty thin. Mostly a 1 HP gain between 9500 and 11,000.
I decided not to advance the curve +4 degs through the mid range. It was getting me about .5 HP. I decided instead to mostly mirror the +2 and settle at 16.5 degs at 10,000.
The next chart is a where I was at the begining of the day and where I ended up.
Final Settings Pull
I netted a gain from 6700 all the way to 11,000 - averaging something like 2.5 HP. A nice day's work considering all I did was tell electrons to do different things.
The jetting is not far off. Is there another 3-4 HP hiding in this basic set-up? I think so, but it will most likely come from jetting.
I just can't get over what those Jolly Moto's did to the 250 engine ....... The 389 doesn't seem too interested in making substantial power after 11,000. I would like to think that the Jolly's are really holding this set-up back. With the self imposed 11,000 RPM limit I've set, I will have to find a lot more torque to get anywhere near 150 BMEP.
Time to set the Jolly's aside and design a pipe to work with this set-up. The BEST part is that I now have the tools to optimize the new pipes. It will be a whole new game!
The next instalment will likely be as regards the condition of the engine at tear down. Stay tuned.