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Post  TheotherGeoff Sat Apr 20, 2013 9:58 am

I'm putting a Sure Start into a 1950s design control line racer, and would like to make the engine as potent as possible without making it fussy. The original design used an Atwood, if I'm not mistaken, but I don't have one. I sawed off the flange on the back of the SS, substituted a BabeBee prop driver for the thick hex driver, and the SS is now just the right length to fit the original cowl design. Would using a TD piston/cylinder do what I want to do power-wise?

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Post  pkrankow Sat Apr 20, 2013 10:31 am

The TD piston assembly is an SPI piston. That's about all the benefit. It is otherwise the same as what you already have, just with the exhaust port bar milled out and lowered to induce SPI.

Drilling out the back plate orifice (press out the spray bar, open it up to ??? (I don't know the dimension) and reassemble) OR use a Killer Bee red back plate which is already opened up.

Lightening the piston and shortening the piston by wrapping the piston in paper, chucking it into a drill press or lathe and using an exacto knife to scrape out some metal (there is a thread on it) will allow you to get SPI and the performance increase from a lighter piston.

https://www.coxengineforum.com/t4279-lightening-a-piston-using-common-tools?highlight=lightening+piston

Check your SPI first, you may have SPI to start with. (SPI is sub-piston induction, an air space under the piston skirt at top dead center.)

Last going to a high performance clamp-on glow head can boost performance further.

Phil
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Post  John Goddard Sat Apr 20, 2013 1:38 pm

Depends how much you want to spend Geoff.
Cos I'm lazy I'd buy one of Bernies TD top ends, a teedee head, a killer bee crank and one of his yellow 5x3
props you'll see 20k+ with decent fuel.
Very Happy

In my experience lightening pistons does work but engine longevity goes out the window,

sunny
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Post  anm2 Sat Apr 20, 2013 4:09 pm

I find the easiest thing to do is replace the Sure Start Piston and cylinder assembly with a Number 1 cylinder and piston. I have achieved 20K+ RPM with a No 1 Cylinder/Piston assembly, a 5X3 Prop, and a Sure Start backplate (Stainless Steel Reed) using 25% Sig Champion Fuel. You may accomplish the same thing with a Tee Dee cylinder (#4), however, I find the older #1 cylinders better for the reed valve carburetor. Additionally, the cylinder and pistons on the older engines Pre-80 seem to be better. I believe this is because the tooling was newer. I do not know when they stopped upgrading/maintaining the tooling but I read a article once that said the aftermarket companies came into business because they QC at cox started slipping. I imagine that was sometime in the late 70s or maybe early 80s. I have purchased shaved/lightened pistons and they work OK, but I have never gotten over 17K on those. Also the stainless steel reeds work great. I have used them all, and the Stainless Steel reed is really good. I hope this is helpful. Andy
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Post  TheotherGeoff Thu Apr 25, 2013 8:32 pm

Thanks for the input. The mention of SPI got me wondering if they're thirstier than non-SPI engines. More air in means more fuel too, thus a richer setting.

Another question: Does anyone sell "blank" cylinders, i.e. without ports cut in them, so one could experiment with different configurations?
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Post  Jason_WI Thu Apr 25, 2013 10:13 pm

uncut cylinders are out there. Might have to pry them out of cold dead fingers to get them. Most dont want to sell them.
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Post  Cribbs74 Thu Apr 25, 2013 10:31 pm

Good luck finding an uncut one, but I hope you do. For horseshoe backplates just drill out the venturi hole as large as possible and still allow the reed to seat. Also when you press the spray bar in go slightly offset from center so the fuel will atomize better.

Ron
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Post  JPvelo Thu Apr 25, 2013 10:45 pm

TheotherGeoff wrote:Thanks for the input. The mention of SPI got me wondering if they're thirstier than non-SPI engines. More air in means more fuel too, thus a richer setting.

Another question: Does anyone sell "blank" cylinders, i.e. without ports cut in them, so one could experiment with different configurations?
If you want to experiment with your own porting you might try an older single port cylinder. One small port you will enlarge and one "blank" side.
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Post  RknRusty Thu Apr 25, 2013 10:53 pm

As for the spraybar angle, I always heard what Cribbs said, set it at about a 15 degree angle off center. However I had two backplates for my tach race engine, one centered and one offset. The centered one ran 300 RPM faster. So try it both ways, you never know what will make a sweet spot for these fickle engines.

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Post  Paulgibeault Fri Apr 26, 2013 10:16 am


Another question: Does anyone sell "blank" cylinders, i.e. without ports cut in them, so one could experiment with different configurations?[/quote]

YES, I have one for sale. Comes with piston.$35.00+ post if you're interested. Contact me further at: pgibeault@shaw.ca

Cheers, Paul
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