ORIGINAL: flywilly
Hi Johnkpap,
Have you examined the liners/pistons of both engines disassembled? Just curious as to what the porting changes were (photos would be great). I'm guessing there were changes to the exhaust timing and possibly/probably the intake timing. How about the crankshaft - any changes there? If there are changes to the intake ports on the liner were changes made to the engine casting?
Performance Specialties (Dave Shadel) sold replacement piston/sleeve sets for the OS 61VF back in the '80s (they were manufactured by Henry Nelson). The chrome plating and honing process (especially the former) are VERY specialized and only a few people (modelers) world-wide have the technical capability to do it correctly. If you have a Shadel/Nelson piston/liner then you have some top quality replacement parts.
My stock OS 61VF with 7D carb (with insert and no pump) was plenty of power for my Arrow. The pump is unnecessary in the Arrow as the tank has to be located behind the firewall - not much room in the fuselage with the pipe tunnel floor.
Thanks for the information and good luck! I'm looking forward to the flight reports!
-Will B.
flywiilly,
>>
The pump is unnecessary in the Arrow as the tank has to be located behind the firewall>>
This rule of thumb is ONE of my reasons to use controllers for fuel and tank pressure, and in the past a Webra Speed 10 ccm with pump. Show me one airplane with the tank before the firewall, and yes!
The pusher!!
And that was exactly the reason for Ed Kazmirski to use a pressure regulator for his pusher.
In the pusher the mixture can be too lean in horizontal flight when you adjust the right ratio nose up for max power.
Always you have differences in horizontal flight and nose up the same as normal or pusher only in the pusher the "wrong way".
The difference in run time of a "hopper" tank on several levels on your test bench gives you the information in difference in air fuel ratio.
If the difference is too much and you haven't much fuel left after the pattern flight and you have "
Plenty of power for an Arrow" you can think about making a restriction in the throat of the carb when un-pumped.
With that restriction is the throat the cartb generate more sucking pressure so fuel level differences (as result of the consumption and flight position) and G-Force influences are less.
Result
In horizontal flight you will have a better mixture and less consumption.
With pressure regulators (or a pump) a carb with bigger throat is possible as I use on my OS Max 61 FX now, a Moki carb with enlarged throat!
Than you will get "plenty of power" from your standard engine!
"
Plenty of power for an Arrow" is no measured value.
I do never use engines where "experts" did work on and when I read these questions I have one answer. "Measure all you can and after that use or throw away!"
If you do not want to measure, then mount the engine in the plane and test fly because then the prop can do his real job.
For that I have a data logger ïn my plane so I can measure airspeed, RPM. temperature (and know trottle position) during flight on any moment and plane position I want.
With these measurements I can select (or adjust) the right propeller.
Always first measure the important values of an engine (if possible) before disassemble.
The measured values you need in the future as reference.
BTW I also read:
>
not much room in the fuselage with the pipe tunnel floor>
It hasn't to do with tankdimensions?
With a better midrange fuel air ratio and plenty of power you maybe can use a smaller fuel tank en make the pipe tunnel floor on another level? (I do not know the Arrow, so maybe this is nonsense)
Cees