Never one to let things alone I purchased a Cox Hyperviper with the express purpose of modifying it into hopefully a decent performing airplane. The reports seem to range from anemic to adequate regarding the factory engine. Here are my choices for modifications: Add a Black Widow Cylinder and a high compression head to a Killer Bee backplate (all I have is the backplate) or install a TD .051 or a Norvel .061 BigMig using a Texas Timer backplate. I'm leaning towards the Black Widow just because it is probably an easier install. I was wondering what opinions/advice might be regarding this.

Thanks,

Rob

Here's a link about what the other guys are doing.

http://www.clstunt.com/htdocs/dcforu...umID9/136.html

The only thing I did with mines was tap the piston with a resetting tool and shaved the elevator with an exacto knife to free it up. Flies pretty good on 35" .08 lines.

Jay

Thanks Jay,

Rob

The factory Sure Start in my Hyper Viper was way down on compression, hence no real power. It was giving 16,000-16,500 rpm on a 5x3 black cox. It could go around and around but that was it, no stunt ability. I was also having a varnish issue with this particular engine (I ran four tanks of fuel through it to run in) and it was down on the quoted rpm. So I swapped the cylinder/head setup with a stock production engine that gives me a known 18,500 rpm. It has been too windy to fly lately but I will post what happens when I do.

I think the real issue with Hyper Vipers is the engine, not enough compression and a very loose rod socket. Once both those issues are solved they really scream. The tank can also cause problems and the elevator needs freeing as Jay said.

My personal (and therefore variable) opinion is that the Sure Start is an excellent engine and needs a little work to bring it up to scratch. Basically they are a Black Widow without the tank.

Luke.

P.S. to the above, the Killer Bee backplate needs smaller mounting screws to fit into the hyper Viper. The screw heads provided with the Hyper Viper are too large, yet they work well with the Sure Start.

Luke

Luke,

Are you using all-castor lube in that engine? Varnishing used to be quite a problem with Cox engines that were run hot. You might try fuel with 25%-50% of the lube synthetic, the rest castor. Maybe it just needs more break-in time.

George