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I need some advice about my engine.
The setup is a 43 mm DrEvo, a reed valve side intake and a PVL ignition working thru a Simonini Proline tube.I had expected at least 10.000 rpm´s but it won´t go over 7300 roughly, I have tried different ignition settings, from 1,0 mm pre BTC but it seems to be strongest at 1,4 mm BTC.
Yesterday I took off the cylinder and piston to see some indication and found the marks just close to the main transfers interesting, have a look at this picture:
At the ower left side the clean area is not as clean, it seems a bit more irregular.
You see the arrow in the bottom pointing at the exhaust, to the upper right you see the clean area just where the right side (looking at the cylinder the same way) transfer ports.This is a picture of the exhaust port and the left side transfer port.
Can you make any sense out of this?
The carter was ground to match the ports, both main transfers and the booster transfers but I recall the size of the carter was a little bit more narrow on the left side on the picture, can that be the reason?
I should not think so as the transfer ports are much smaller than the grinded parts of the carter.UPDATE:
I know my reeds in the side intake are not perfectly sealing but the leak seems to be quite small.
Can that be the cause to my RPM loss?There are no replacement reeds but I have 0.3 mm carbon fiber reeds but they need to be adapted to the house.
I think the carbon pattern on the piston looks fine. Because the exhaust channel is under an angle of 30dg compared to the cylinder the flow and heat is not symmetrically distributed over the piston. I’ve never had a completely symmetrical carbon deposits on any of my vespa setups.
A stock (or nearly stock) dr70evo produces max power around 7000-8000rpm. A stock DR70evo with a light pulley drive and a high revving exhaust should also be able to make 9000rpm+ however it does not give maximum power. If you want to move the max power to 9000-10000rpm you need to do some serious exhaust work.
AW50-4t | 13.13 | Gianelli Citypower | 3.2Nm@6000rpm | 3.0pk@6700rpm
Home made engine dynoThanks for the input Arvid.
What about the minor leak of the reeds, will that reduce the top end power or is it mainly affecting the low end power?
Minor leaks of the reed valves normally shows in crappy idle and poor low down torque (really low down)
At high RPM’s the seal is not that important any more due to the inertia of the gasses flowing. A friend of mine had a wrongly tuned standard engine (foto as example). It was nearly impossible to start but at high rpm’s it outperformed a mildly tuned engine with the same cylinder.
AW50-4t | 13.13 | Gianelli Citypower | 3.2Nm@6000rpm | 3.0pk@6700rpm
Home made engine dynoOK, that makes sense with the inertia.
How about the small canal from the exhaust to the compression release, is there some gain with filling it and making it blind?
I don´t use it and it just puts pressure on the head gasket.
The blind canal may create some turbulence in the exhaust like the blind canal on some new EU mopeds but this one may be so small it may not affect the gasses?
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