RD 350 31K hits wall at top power - melt down

[RDrocket]

Hi to all.
Finally logged to the forum I have been reading so much.
It's been a long ride with my RD bought her in boxes 9 yrs ago, 6 yrs to build her up and now 3 years tuning and riding
The tuning was like this:
1. all stock, custom pipes and boos ports from intake to transfers ->revved 12000RPM+ no power in 5. and 6. gear (pipes to short, bad math)
2.pipes got extra length on belly for temp. fix, head o-ringed, squish 0.9 - 1mm with 11° -> max 11000RPM but pulls 5. near top RPM, 6. no power
3. pwk 28mm carbs with power jet, honed cylinders new prox pistons, clean up porting with slight transfer reorder of opening (boost, main, secondary), reed valve moded for single petal carbon 0.4mm -> massive improvement in lower revs, pulls harder all the way top speed slightly higher
4. new set of pipes, this time with better math and more knowledge, remapped pv controller, rejeted carbs -> holy s... 1. front wheel up, 2. harder throttle -> front wheel up, 3. slight bump on road at 130kmh front wheel up all the way, pulls 6. gear like it's 4.
and this is where problems start, with old pipes pilot 32, main 142, needle middle position, new pipes with a lot more volume 38 pilot, main 155, needle second from top because around half throttle there was sputtering now clean and harder pull.
But on wot lean the same color with 142 and 155 main (power jet is around 20) The main problem is a wall at 9800RPM it pulls from 4000rpm on 7000rpm starts ripping and hits a wall at 9800rpm like I pressed a brake. The pipe was designed for 9200RPM max power and wide power band transfers and exhaust also for 9200RPM and it should rev to 10000RPM. The wall scares me because it hits it so hard and constantly lean on wot in top rpm. Checked floats, fuel flows great, tank clean, no air leaks. The carbs are knokoff but first thing i did was disassemble them and reassemble and they are very good. I think it's the 11° squish and I have to much squish velocity... i fear to blow the engine so need to sort it fast.
If I remember correctly the head volume is 20cc with br8es - piston head volume gives 16.7cc. with 26mm exhaust from tdc 6.09 cr
pistons are 64.5mm
The PV opens from 3657rpm to 7676rpm.
Ignition standard (homemade programmable digital CDI in progress)
I was thinking that the bigger pipes make more compression and because of that correcting the squish to 0.9mm and 15° (with 11° I don't know what I was thinking)

[MK]

For my experience the PV actuation rpms are not optimal. If the pipes peak at 9200-9800, I'd try 9000 for fully open. Usually I start opening at 5-6 k.

If you have a high compression, high resonance engine it's prone to the ignition curve on overrev.
A programmable ignition curve is mandatory here with a steep decline short before the "wall" region.
(What makes me a bit suspicious here is that the stock ignition curve already has the required shape in that region and should work)

[RDrocket]

With my porting best acceleration (but dyno) is like this but this isn't final..
if I start opening the pv later it will lose power from cca 3500rpm to the point of opening
also with the pv fully open bike starts to pull from 6500 -7000 rpm (had a test with pv fully open at 8940 and i will say that I did lose some power from 7500rpm - 9000rpm)
but firs i need to sort out the jetting / squish
pv is a easy job

[JanBros]

it's almost impossible to have too high squish velocity.
but as it speeds up combustion, you need to retard your ignition.

[RDrocket]

On original 29K CDI the timing is 16° at 9000RPM and falls to just 9° at 9800RPM
One more thing, needle that I have is JJY.

[RDrocket]

Here post from speed-talk forum:

https://www.speed-talk.com/forum/viewtopic.php?t=39725

"I think that if the MSV is to high the flame front can be to fast and the max pressure is reached at the wrong time, of course this depends on the rpm, fuel, timing, compression ratio and squish ratio. The function of squish is to increase the turbulent intensity in the combustion chamber. Without turbulence in the combustion chamber it would burn the mixture at the laminar burning rate which is ten to twenty times slower than the turbulent rate. On some engines the increased turbulent intensity can shorten the burn times after max power so much that it kills over-rev. On others where the burn time was too long it can improve over-rev.
A lot of the time the squish is measured wrong, I use to have some hollow core solder and would snake that in the spark plug hole until it touched the cyl wall and then bring the piston to TDC plus a few degrees and then pull it out and measure it. The dyno is the only way to tell what works best without riding the bike."

[JanBros]

the MSV is not the problem, the ignition timing is.
you have invested already a lot in your engine to make if faster.
but without a programable ignition you will not be able to extract the most of it.

not even that expensive.

[RDrocket]

I did make my digital CDI with 2 timing curves and PC software for programing. Still need to test it. Some calculations and I got MSV of over 40m/s and some say that ideal is 20 - 23m/s, the squish area is 50%
OEM cdi gives 9° advace at about 9800RPM you sugest going even lower? I see that without a custom timing and dyno I will go nowhere. I just want to be sure that the head design is fine.

[JanBros]

double

[JanBros]

How did you calculate your MSV ? there are several ways of doing it and that's fine, as long as you compare with the same calculations. The only "universal" is Blair's method. if you use your calculation with Blair's data given in his book and get the same result, you can compare. But it's not easy to do it correctly.

Aprilia RSA125 had a max squish velocity of 37.

my excel gives exactly the same result as Blair : viewtopic.php?f=1&t=16273

edit : just entered the data you've given in your first post, and I get 29.58 m/s. I used 9200 rpm, 26mm from TDC (gives 198.8° duration exhaust timing), comb. chamber vol 16.7 (gives trapped compression of 6.1, trapped of 11.6), tangent squish (I suppose, or is it paralel to piston dome ?) of 0.9 at 11.3° and 50% area and with a piston dome height of 3mm ?

[RDrocket]

I recalculated MSV and now I get MSV of 38,7m/s at top RPM (10000RPM) and at 9000RPM it is 34,9m/s
Maybe i entered some data first time wrong.. But again it isn't near your results ?
The squish is parallel to piston dome and the dome is about 4mm.

[JanBros]

I know some of Dragonfly's excel's, and they are all his own theory. whether his theory's are any good is ??? reading some stuff of him certainly makes my eybrows take on weird shapes. did he ever built a well-performing state-of-the-art 2stroke engine ? why is there no dyno of his KDX showing the massive gains he should have found with all his calculator's ? I wouldn't pay a penny for any of them.
Don't know about this one, but you can test it using Blair's data.
Comparing the "hot" engine's data with Blair's cold is useless anyway.
Download mine and enter your data and see what result's you get.

[RDrocket]

And I'm back here and not on the road... Went to MOT last weak and she died on the half way..
The wall she was hitting at 9000RPM is the OEM ignition timing, i sorted the jetting with new power jet and new jet needle. Was running like a beast maybe bit rich but safe. Then one day she started to bog middle on the ride. I stopped opened the fuel tank and it made ssssss. Ok I have a faulty fuel tank vent. Sometimes i could ride no problem sometimes it just died (should sort immediately) and then I fixed it vent is working but the bike still bogs and only when the engine is hot. I start it cold runs like a charm, could idle forever. Runs strong without any sputter. Gets a bit warmer and starts to bog. When the engine is fully hot (The fan starts at about 70°C) It will only idle if I touch the throttle it will die. Pull the chocke on bouth carbs and I can ride home with max 2500RPM. Any more throttle and it stalls.
The carbs are PWK 28mm, pilot 32, air screw half turn out, JJM needle middle clip position, main 145, power jet 35.
I checked:
1. Reed valves
2. Ignition timing
3. Pushed the bike to die and checked float high
4. Checked stator output cold and hot engine
5. Replaced the ignition coil
6. New spark plugs NGK BR8ES R
7. Cleaned air filter
8. Checked fuel flow
9. Checked float high when it bogs again because it seams lean
10. Checked timing with timing gun cold, hot, when bog
11. Checked stator resistance

If I let the bike a few min it will run again normal
It was running great and just started to "run lean"

[RDrocket]

Went to 38 pilot and 155 main. Runs rich definately but again WOT 6 gears when hot and it bogs..
Idles perfect still..

[JanBros]

BR8 seems a hot plug for a tuned engine, i'de use at least 9's and probably even 10's.