Bedeone

Been reading through this thread and I'm seeing alot of love towards the 17x6 props.

billdow

just put my os 120. on a aeropet 90 pattern plane. not much prop clearance with 15x? will a 14x14 work?

airraptor

My Feedback: (66)

on the 14x14 prop will only get about 8,000 on the stock muffler. you would be better off with a 14x12n for your plane. i run a apc 13x11 or the 13x13n on revolver. both of these props turn about 11,400 for the 13x11 and 11,000 for the 13x13n. This is with a modded stock muffler. i do have a jett muffler and full tuned pipe for it but havent ran it with these smaller props. I also got 11,500 on a APC 11x14 prop.

The Jett 120 size muffer for the 120AX is best suited for 10,000 or less. If going for more rpm with a Jett muffler then need to run the 90 size muffler.

billdow

thank you. i have full tune pipe and  with 15x 8 i will cut the grass. it might work if not i will try a 14x14. when i get some tach readings i will post them

Slats!

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I am going with the MAC tuned pipe system. Is anyone using this. If so what length did you cut the header approximately for the best RPM output. Thanks

airraptor

My Feedback: (66)

Slats i have that one. i cut about 1.75-2.00 inches off for the 11,500-12,000 range. i need to cut some more though.

Just set it up on a test bench with the fuel and prop you plan to use or the rpm range. then cut 1/2 inch off pipe and retest keep doing this till no more gain. this is the simple way you can so deep into tuning these pipes and fuels.

I think on the stock length i got 9,800 on a 16x8 prop

Slats!

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Thanks Airraptor. So you saw an increase from 9500 up into the 11,000 range??? Thats insane... Can this engine handle those RPMs

airraptor

My Feedback: (66)

lol no sorry didnt go from 9,500-11,000 just ran the header that short in the 11,000 rpm range. Use the stock length for larger lower rpm props. yes the engine will handle it.

The rear bearing will not last long no matter what rpm. they need replaced very often. i just ordered my second set of bearings and now went with boca SS bearings. If i was you I would change the rear bearing every 3 gallons of fuel. the use of after run oil had no effect on the bearings life.

airraptor

My Feedback: (66)

some more readings from the other day. bone stock 120 on bone stock muffler with APC 16x8 8,400, removed baffler and got 8,600. switch to Jett 120 muffler and got 9,600. The jett 120 muffler works very well in the 8,500-9,500 range any higher and it acts like a rpm limiting device lol.

Ran it today with a Apc 14.5X14.5 and got 9,100 good speed on the .46 size revolver also.

Slats!

My Feedback: (1)

Wondering if any one is having the same issue. My OS 120 AX is eating glow plugs to the point where it is getting ridiculous. I am having to switch plugs after about 1/2 gal of fuel. A couple of things.

-I am running a MACS header with a tuned pipe.
-Currently using an APC 14X12 and getting about 10,300 RPM,
-Using the standard OS #8 plug.
-Omega 15%
-I know it is not too lean. The only time it would be too lean is when tuning and looking for peak RPM but I can't imagine this would be the cause.

Just wondering:

-Could the pipe be causing this because of the RPMs I am turning.
-Is there another OS plug I could try besides the #8

Any comments or suggestions would be great. I dead sticked today and almost lost a plane because of it. Maybe I am used to Saitos where I only had to change them once a year but this is getting costly.

Thanks

w8ye

My Feedback: (16)

You pipe is on the short side and causing detonation and taking out the plugs

Slats!

My Feedback: (1)

Hey W8ye. Sorry what do you mean short side?

w8ye

My Feedback: (16)

On the short end of the stick the engine tries to go leaner on you as it gets on the pipe. You can have the mixture right on the ground but in the air, the engine unloads more and goes lean.

Your combustion temperatures are soaring. Might even sound like shaking a plastic pop bottle with a few small stones in it.

The high temperatures are eating up your plugs.

Try pulling your pipe out a quarter inch or more and resetting your needle valve?

Slats!

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Good suggestion thanks.

airraptor

My Feedback: (66)

or your rear bearing is going and bits of metal are getting on the plug.....

Slats!

My Feedback: (1)

Are you guys replacing your bearings with after market stuff. If I spin the prop with the plug out it is loud (does not sound all that smooth). Don't know if this is how it should be or not.

airraptor

My Feedback: (66)

get the Boca bearing stainless steel one. it will last about 5-6 times the stock OS bearing.

Mustang Fever

My Feedback: (2)

I think mine is still loosening up, but at present I've got it on a BUSA 1/4 scale DR-1. I use a 17x5 Zinger, and I'm getting a touch over 9100 on 10%. Perfect engine/prop combination for that airplane.