**VOTE-ON-THE-NEXT-COX-ENGINE-OF-THE-MONTH** (June 2017)

Yea Hi !! Re Bump!!

WE HAVE A WINNER!!! Congratulations to mmischni and his "Cox 0.049 Black Widow Powered Pinewood Derby Top Fuel Car"



I'll have the picture up shortly, and the Ex Model Engines Black Lynx .049 drawing started!

Very good job Mr. mmischni, congratulations! Meritorious recognition!
Thanks to those who trusted my work too!

Thanks very much all! You can't see it in my photo, but I ran with a trimmed-down "COX powered" sticker on the back of the rear wing. One of the better video clips shows it.
"The Black Widow team ran a great race today. The number 18 car was in top form. I'd like to thank my sponsors Cox International for supplying the replacement parts, Rustoleum for the paints, Tower Hobbies for the fuel..."    
I will try to compile some of my better run vids and put them on youtube for better viewing than the photobucket clips I tried in my other thread.



Thanks again for the advice getting it running/not eating itself alive as well. A fine group of enthusiasts here!

Matt

Congrats Matt !!! Great job with the Dragster Bee looking for the Videos.

Congrats to the winner

Great looking model, I am glad you got the technical problems sorted out

PRET-TY COOL!!!
Looking forward to videos, this would be a great g.pa-g.son project.

WTG MMischni, and the crowd chants vid vid vid

Congrats and greal looking little car there!

Congratulations Matt! What a great powered project-model! I enjoyed assisting my nephew with a Pinewood-Derby car back in the day. It's simulated 8cyl. engine had eight simulated carbs.. made from small wooden screw-plugs drilled-out for a flared alloy-tube.. (Perfect-brand brass lead-out guides).. to resemble x8 1bbl. carbs sticking-up out of the cowl.

Yours is ultra-cool to me. The posi-traction rear-axle is nice.. Did you mention it being a friction-drive? They can make good-use of the engine's power-band. Engine-cooling is probably a non-issue on a scale drag-strip?

It would be interesting if your design spurred some interest for a CEF drag-race contest.. I'm pretty sure I'd be up for that...

Thanks fellows,

Roddie, if you have a pic of that derby car, I would love to see it! The carbs sound pretty fabulous. I built a velocity stack for the Widow just for looks, and I had dreams of a sweet set of open header pipes for it, but I ran out of time and the rapid-proto guys at my company weren't interested in sponsoring a pinewood derby car :-)



Yes, mine is friction drive. the thing I was most unsure about was what a good drive ratio would be. I found some info online about torque and RPM values for a Black Widow, but don't know much about how they run unloaded, how they like sudden loads!!, or how many rpms, I was even running. So the additional benefit of being able to make some ratio adjustments also appeared to be a great benefit. Ultimately I just ran it at the absolute lowest ratio I could manage because I was occasionally stalling the engine and was running out of my 3 runs! I wondered about cooling as well, but I figured runs of 30-60 seconds to get it running, on the track, leaned out, and released, that there shouldn't be any problem. And honestly, if it melted down after the race, I probably would have still have called it a win! It would be just like the real top fuellies. New parts and full re-build after every race.

Matt

mmischni wrote:I built a velocity stack for the Widow just for looks, and I had dreams of a sweet set of open header pipes for it, but I ran out of time

If the Black Widow has an original style cylinder with SPI then the exhaust header you mention may well reduce performance of the engine.
SPI meaning Sub Piston Induction.  With an exhaust of any sort on an SPI engine then the engine will ingest spent exhaust gases back into the crankcase, causing a dilution of the air/fuel mixture.  The only way a Cox SPI engine can overcome this is to install shims under the base of the cylinder to close up the gap under the piston skirt.  This will also have the effect of lowering compression which may need to be rectified by using a Tee Dee head.  Still, it would take some experimenting to find out whether the power loss caused by not having SPI as compared to having the engine draw-in exhaust is greater or lesser.  Then you also need to see how much removal of SPI and incresing compression as suggested impacts on power.  Header pipes may look cool but will potentially take the edge off of performance.  If you want header pipes, get a Gilbert.

Yup, I gleaned that particular caution from this very forum, not combining SPI and a muffler! Luckily I did not have SPI to deal with. I was going to run something regardless to control castor oil discharge (not directed on my friction surfaces). A muffler worked out well because working next to that thing while starting it and leaning it out was brutal. I didn't think people would appreciate that inside our cafeteria :-) The headers were solely to look cool, as you mentioned, and may even have been less restrictive than the stock muffler I used. This year was mostly about "getting something that ran down the track." Maybe next year, since I have a running chassis, I can mess around with squeezing more power out of it!

mmischni wrote:Thanks fellows,

Roddie, if you have a pic of that derby car, I would love to see it! The carbs sound pretty fabulous. I built a velocity stack for the Widow just for looks, and I had dreams of a sweet set of open header pipes for it, but I ran out of time and the rapid-proto guys at my company weren't interested in sponsoring a pinewood derby car :-)



Yes, mine is friction drive. the thing I was most unsure about was what a good drive ratio would be. I found some info online about torque and RPM values for a Black Widow, but don't know much about how they run unloaded, how they like sudden loads!!, or how many rpms, I was even running. So the additional benefit of being able to make some ratio adjustments also appeared to be a great benefit. Ultimately I just ran it at the absolute lowest ratio I could manage because I was occasionally stalling the engine and was running out of my 3 runs! I wondered about cooling as well, but I figured runs of 30-60 seconds to get it running, on the track, leaned out, and released, that there shouldn't be any problem. And honestly, if it melted down after the race, I probably would have still have called it a win! It would be just like the real top fuellies. New parts and full re-build after every race.

Matt

Hi Matt, Unfortunately I don't have any photos of that Pinewood car. It was just a simple "wedge-shape" painted gloss-red. The eight wooden plugs (carburetors) were painted silver and placed in two side-by-side rows of four pre-drilled holes. It had a little "driver's head" mounted in a rear cockpit and had a clear-plastic windscreen.. if my memory serves me.

I'm very curious about how you designed the drive on your car and also how you manage to start the engine? Does either your engine or the rear-axle slide or pivot to make contact for the friction-drive to function as a clutch? Is there a type of spring-clip used for tension? There appears to be a standard rubber O-ring fitted to a custom flywheel. I had an old lawn-tractor that used a friction-drive that was very similar... except it didn't spin at 18K!! It all looks to be very nicely engineered.. and an O-ring would be a cheap/simple/easy to replace sacrificial-element of the drive.

Knowing now; that you're running the engine for longer than a few seconds.. it would be a good idea to provide an extra measure of cooling. There are heat-sinks made by Cox, which clip-onto the glow-head.

Here's a photo of one of my proposed/prototype marine-engines with one installed.



The muffler shown, is my own design.. but it's been mentioned that running a muffler/expansion-chamber can negate the positive effects of sub-piston induction when running an SPI cylinder on the engine.

I'd love to see a video of your car in action! Have you posted one here?

Hi again Matt.. I can be a haunt.. but I just read your last post which you made while I was writing my last post..

So.. if you're engine is muffler-friendly.. you could try making a muffler like mine. It's minimally-restrictive.. and can be made in several configurations. You mentioned the problem with exhaust-oil wastes fouling your drive.. and making a mess when operated indoors (a cafeteria..) So.. my design offers the option of running a single header-pipe with a 90 degree elbow, turned-downward facing into a cloth (absorbent) pad placed in the floor-pan of the chassis..

See the link below for more info. Be sure to skim through the entire thread.. because there were advances in the materials used.. and their possible applications.

https://www.coxengineforum.com/t5505-a-cheap-sport-muffler?highlight=a+cheap

This could easily turn into a CEF proxy drag racing event.....

I also think this drive train could be adapted to tether circle for Outlaw sprint type cars

Matt
We need more details of the Track, chassis, and some one to set a very broad range of simple rules

My contribution to the rules...You Must enlist a boy or girl under the age of 18 to help you

Finally got around to putting together some of the videos from the races. Enjoy!

https://youtu.be/j1ZbApqToRw

Matt

mmischni wrote:Finally got around to putting together some of the videos from the races. Enjoy!

https://youtu.be/j1ZbApqToRw

Matt

Excellent !, beautiful the video, thanks for sharing!

Thank you for sharing my father and I did pine wood derby back when i was in the cub scouts.
You could set it up on a tether line and do some continuous laps on some good fresh flat asphalt.