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Parra 2.5

Old 03-04-2015, 01:09 PM
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telmore
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Default Parra 2.5

Here is the third run of the engine - starts easily and a real screamer.

Annette


https://m.youtube.com/watch?v=qqmwe1uLAoU

Last edited by telmore; 03-06-2015 at 01:06 PM.
Old 03-04-2015, 01:22 PM
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qazimoto
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Post deleted because it's not relevant any more

Last edited by qazimoto; 03-07-2015 at 04:14 PM.
Old 03-07-2015, 07:35 AM
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I have one of the Parra AAC diesel RC engines. They are great runners. Parra checks each engine out carefully before selling them to ensure the quality is up to their standards. They offer the engines as a steel sleeve lapped piston, ABC or AAC and glow as well.

For RC usage it might be tricky as the engine cools off fairly fast at low speed, thus it tends to be sluggish coming back up to full throttle as it has to heat up again.

I like the cute little mini-pipe that I got with the engine. It does offer a some performance improvement over just running no muffler too.

Since the engines were primarily intended for control line combat, the threaded crankshaft end is short and that can be a problem if you want to use a spinner on the engine.
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Old 03-07-2015, 07:43 AM
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Now I have a video I posted on YouTube that shows my engine running with a 8x4 Master Airscrew propeller. I was using Davis Diesel Development diesel fuel in it.

I was able to get a little over 16,000 RPMs with the engine and that propeller. But since the engine is new I didn't want to push it too hard. Many glow 2.5cc engines do not do that well with a 8x4 prop either.

https://www.youtube.com/watch?v=tl4OF2WOIak

Last edited by earlwb; 03-07-2015 at 07:46 AM. Reason: typo correction
Old 03-14-2015, 02:26 PM
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Originally Posted by earlwb
Now I have a video I posted on YouTube that shows my engine running with a 8x4 Master Airscrew propeller. I was using Davis Diesel Development diesel fuel in it.

I was able to get a little over 16,000 RPMs with the engine and that propeller. But since the engine is new I didn't want to push it too hard. Many glow 2.5cc engines do not do that well with a 8x4 prop either.
Nice running engine, what's the idle speed do you recall ?

Boo
Old 03-14-2015, 08:10 PM
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I do not recall at this time. I think it was typically under 2500 RPMs maybe 2200, hard to say.
Old 03-16-2015, 03:06 PM
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My Cox Conquest .15 spins an 8x4 at 18k on the ground, 25% nitro.
I have a Parra that has a Nelson type plug, which is claimed to be the best, but is not my choice.
Old 03-16-2015, 03:47 PM
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Originally Posted by JohnAV8R
My Cox Conquest .15 spins an 8x4 at 18k on the ground, 25% nitro.
I have a Parra that has a Nelson type plug, which is claimed to be the best, but is not my choice.
There have been some ordinary Parra's and there have been some very good one's. My early AAC Diesel version picked up about 1500 rpm on an APC 7x6, when I fitted a new ABC piston and liner. Using a 4.5mm venturi and the same prop it now turns 19K, a few hundred rpm better than my Nelson diesel. My conclusion was that they are much better at making ABC p/l than AAC.

Some of the early Parra's in the club suffered from very "wet nosed" front bearings. Thankfully this seems to have been fixed in the latest versions.

Alberto Parra actually sells a non-leaking replacement crankcase for worse case ( :-) ) engines.

The same problem may occur with a minority of the Fora Juniors diesels. Some of these leak quite badly.

They also go very well as a glow on lots of nitro.

Last edited by qazimoto; 03-16-2015 at 03:59 PM.
Old 03-18-2015, 07:13 AM
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I would expect that the nitromethane in the glow fuel would allow the glow engine to outperform a diesel engine that doesn't use it.
But those Cox Conquest .15 engines are still pretty awesome today though. You have to go with some of the more exotic glow engines to outperform it.

I didn't notice if my engine leaked too much out of the front bearing. But yes I was thinking that the AAC cylinder setup might not be as good as a ABC cylinder setup. But I tend to prefer the messier engines that do ooze oil out of the front end. It lets me know it is getting oil and being flushed out regularly like that. The bearings don't have covers on them to seal them up. But I know that nowadays many people like clean engines that have little to no oil residue coming out of them.
Old 03-20-2015, 01:19 AM
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Originally Posted by earlwb
I would expect that the nitromethane in the glow fuel would allow the glow engine to outperform a diesel engine that doesn't use it.
But those Cox Conquest .15 engines are still pretty awesome today though. You have to go with some of the more exotic glow engines to outperform it.

I didn't notice if my engine leaked too much out of the front bearing. But yes I was thinking that the AAC cylinder setup might not be as good as a ABC cylinder setup. But I tend to prefer the messier engines that do ooze oil out of the front end. It lets me know it is getting oil and being flushed out regularly like that. The bearings don't have covers on them to seal them up. But I know that nowadays many people like clean engines that have little to no oil residue coming out of them.
"Wet nosed" engines leak crankcase compression which may make it harder to hand start hot, and ruin fuel economy. Neither of these things really matter for an r/c engine. As I said above , newer versions are much better.
Old 03-31-2015, 07:25 PM
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I don't know if I can agree with that completely. In the past I used and ran a lot of engines that were quite messy and oozed a lot of oil out of the front of the engines. They started and ran just fine like that. I think it depends on the design a lot. The old plain bearing bushed crankshaft engines were very messy in that respect. The older open front bearing engines were also quite messy too. Now then a older engine that has been run a lot and has a lot of time on it may start to have problems with excessive wear. Thus they would behave like you stated and become harder to start like that.

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