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COX .09 HOP UPS - 12/7/2012 2:23 AM   
Steve Westphal



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Status: offline 		I need some ideas on how to hop up a Cox .09 motor. We will be racing and I want the fastest motor there! I know you aero-gearheads out there will know all the secrets. .09 is the largest engine allowed in this class. I want one that will outshine all the rest. The motor is brand new. Thanks.

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RE: COX .09 HOP UPS - 12/7/2012 2:32 AM   
icerinkdad



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Status: offline 		Important to know... which Cox 09? If it is the TD just plan on 35% nitro with at least half the oil being castor and 20% oil. Something like SIG fuel... I would be very careful about the castor as the Cox engines need it and have very short lives without it. You will need a piston reset tool (check ebay for those) and an assortment of small props to try (give me a call at 402 two five zero 5025). I work in Fremont NE and have a prop you should try that was made for the Russian 15 combat models (dont worry it isnt too big) that will really let your engine wind up.
Bob Furr

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RE: COX .09 HOP UPS - 12/7/2012 2:34 AM   
icerinkdad



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RE: COX .09 HOP UPS - 12/7/2012 2:40 AM   
MJD



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Status: offline 		What racing class is limited to .09's?

IRD - those F2D combat props are typically around 6x3.5 - 6x4 aren't they?

Ooh, hop up parts: Td .09 "performance" crankshaft

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RE: COX .09 HOP UPS - 12/7/2012 3:45 AM   
combatpigg



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Status: offline 		Make an aluminum bushing that is a snug fit around the piston. Slit the bushing lengthwise so that it can clamp the piston. Now chuck this up into a lathe and take a length of wire to hold the con rod off to the side. Turn the lathe on to a slow speed at first and use the back side of a #11 Xacto blade to shave the inner wall of the piston skirt. Experiment with turning speed and blade position. This "leadloy" material shaves off pretty nicely. Go as thin as you dare, down to 1/2 of original at least.
Check the crank's fit in the case with just the prop installed. It should spin freely with just a flick. If not, chuck the crank into a drill motor or lathe and polish the journal with 800 grit paper for a few seconds, then re check the fit. It's nice to have aerosol brake cleaner for this work.
Make sure the ball socket has zero slop.
These mods don't create HP..they recover wasted HP.


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RE: COX .09 HOP UPS - 12/7/2012 3:47 AM   
ffkiwi


 

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Status: offline 		Actually-you'd pretty much on your own for this-apart from the crankshaft mentioned by MJD-that's about the limit of what's commercially available. For reasons presumably due to the market-and likely sales- there was never the range of aftermarket and tune up options for the TD09 that were available for the 049 and 020 displacements by various suppliers. These days you'd have to be prepared to buy extra parts (a bit of a mission in itself with the scarcity of TD 09 parts) and rework them.
You can bore out the venturi slightly as per the instructions if you're running pressure, and a fine thread NVA helps. This and a pressure backplate were available from KK when he was in business-but supplies would be long gone. If you have access to machining facilities you can try shimming the cylinder .010-.015-.020 and see what that does, and there are a couple of people out there who will remachine your burnt out glowhead(s) to take a Nelson plug.

Your best area of productive effort is likely-as has already been alluded to-to be in the area of props-as there are a number of sizes ideal for the TD09 on the market now that simply weren't around in the 60's 70s and 80's-the combat props of around 6x4, the 6.5x3.5 Master, the APC 6.5x2.9-which really allows the TD09 to wind up (though possibly a bit low in pitch for your likely use....)-and Master have some 3-bladed ones now that might perhaps bear investigation. Russian C/L combat props-if you can get your hands on them-would also be worth looking at-though these are invariably metric which translates in to some 'odd' sizes when converted to imperial measurement.

Finally-for a left field suggestion-if you can lay your hands on the competition PF7 ABC variant of the Cipolla 09, this is superior in every respect to the TD 09 except in availability and spares support. At the top end (18-20K), 1000-1500rpm better depending on fuel-but I didn't have the current generation of props available to me when I tested it back in the 80s. I cheerfully concede that TD09s are easier to find than Cipolla PF7s........

ChrisM
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RE: COX .09 HOP UPS - 12/7/2012 4:00 AM   
longdan



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Status: offline 		You can raise the compression a bit by sanding the sealing face of the glow head using some fine sandpaper on a flat surface. Be sure to keep the head flat and square to the threads.

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RE: COX .09 HOP UPS - 12/7/2012 6:26 AM   
lfinney


 

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Status: offline 		the novarossi .09 is available with plenty of spare parts from planet hobby planethobby..com

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RE: COX .09 HOP UPS - 12/7/2012 2:24 PM   
MJD



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Status: offline 		I dug around a bit for performance info on the TD .09. The only curve I can find indicates that on the stock engine, power starts to drop off at around 18k or so unlike the TD .049 whose power, in stock form, increases up to 22.5-23k. This makes perfect sense to me, since .09 has never been an AMA competition class that I am aware of, and pegging the engine for that kind of rpm makes it ideal for sport aircraft with the prop sizes you would associate with that displacement - 7-3.5, 7-4. If this is really where the best power is made on this engine, somewhere around a 6-5 might [I stress might] be ideal to absorb peak horsepower and deliver some pitch speed. Spinning the bejeebers out of it on a fine pitch 6" combat prop might not be productive. Could be wrong.

On a similar train of thought, I worry about the TD .09 fan conversion on another thread.. not sure what benefit that may offer unless the impeller is right for the job or the engine is modded appropriately.

As pointed out, there is probably a pretty thin database on TD .09 hop ups.

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RE: COX .09 HOP UPS - 12/7/2012 3:23 PM   
Jim Thomerson



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Status: offline 		First off, find some replacement cranks. If you are going to race TD 09s at max HP you can expect to blow cranks.

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RE: COX .09 HOP UPS - 12/7/2012 4:22 PM   
MJD



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Status: offline 		Like the lightened cranks in the link posted above?

The lightened crank, lightening the piston per CP's suggestion, opening up the intake as far as recommended and running pressure, and making sure the ball/socket joint was set right would be a good starting point. I tend to think that much less than 4" pitch would be counterproductive unless this is a combat class.

OP - what is the event?



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RE: COX .09 HOP UPS - 12/7/2012 5:24 PM   
combatpigg



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Status: offline 		Lightening the piston takes a lot of stress off the rod and the crank pin.
The skirt can also be trimmed [shortened] to produce the .010" of SPI. I believe .010" is a "not to exceed" number, so proceed cautiously.
I would try a APC 6x4 prop and also MAS 6x4 props. There is also a APC 5x5 E prop that looks very dangerous, but really produces some speed. You couldn't use it in a group setting with other people milling around the pits.


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RE: COX .09 HOP UPS - 12/7/2012 8:16 PM   
Jim Thomerson



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Status: offline 		The TD 09 is an actual 1.5 cc engine, as is the Johnson Bulldog 09. There was some discussion about changing the FAI competition engine size from 2.5 cc to 1.5 cc. I think the two engines mentioned were designed with this in mind. According the the engine review in the May 1963 Aeromodeller, the TD 09, 0n Cox racing fuel (30% nitro?) peaked at .235 HP at 19,000 RPM. A couple of 6 x 4 props were at 19,000 and 19,500 on the bench. So a 6 x 4 is not enough prop. I would guess a 6 x 5 would be close for racing. I would want a prop turning about 17,000 on the bench, with the thought it would pickup a couple thousand in the air.

So we are discussing a 50 year old design, which is still pretty darn good. I think I would start out with a pretty much stock engine and do a bunch of prop testing to find the fastest prop.

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