Topic: TWINgles and Twumpers..

[754]

Geez that talk about torque reminded me,

 Back in the day, a few dudes got the idea of sprecially grinding cams so that cylinders would fire in pairs, instead of alternately,  this on CB750s

 Was supposed to be torquier..
 Anyone ever heard one run, or seen a cam for sale for one of these..??

[Hondell]

Yup- I too am an old timer. I saw a 750 "Twingled" (Fwingled??") for flat tracking. sounded wierd but worked pretty good as a flat tracking weapon. Can't remember where he got the motor work done. You might try vintage flat trackers for more info.

[mlinder]

Some modern GP bikes are flirting with a similar concept.

twingles were, generally speaking, different, though. Twingles were 2 cylinder bikes that shared a combustion chamber.

My guess is that you could just have megacycle weld and grind mirrored lobes for 1/4 and 2/3.

[MRieck]

 I've seen it done on a CB750 engine used for hillclimbing.

[754]

Yup i know they tried it for hill climg.supposed to be more torque, more vibes, and a bit less HP.

 Lots of cams are built up and ground, both for repair and high performance.

For a mild cam you can use the stock profile and grind off the heel of the cam..

[Bodi]

The theory, for dirt track or hillclimb (basically a near-vertical dirt track) is that a single or V-twin gets more power to the ground than a four because there's more time between power pulses for the rear wheel to stop spinning, getting a "new grip" for the next torque blast. I don't know about the validity of this theory but dirt track folks really believe it. Any even firing (360 degree crank) parallel twin can be "twingled" by modifying the cam so both cylinders just fire simultaneously. I've seen twingle British and Japanese engines.
I spoke to John Williams last year about a few things, he was world hillclimb champion for a while. He never accepted the wheelspin theory and won using multicylinder engines, the Honda SOHC 750 was his most successful. He also tried a Benneli 500cc six. Always burning 100% nitromethane.
The "twingle" name is also used for some oddball 2-stroke moped engines that use two pistons side by side and one combustion chamber bridging them.. one cylinder has the intake port and the other has the exhaust port. There are some minor advantages and some big disadvantages to this design. The word isn't specifically "owned" by either meaning but the dirt-track 4-stroke meaning is the one I think of: those moped engines haven't been made for a decade or three but I will be seeing a few twingles racing this weekend (unless their owners retired from dirt track over the winter).

[754]

I am aware whar a Twingle was, and it is not a moped BTW.

However I was searching for words to convey a meaning, & I believe that is what they actually called them..

[Jay B]

Harley also did this sometimes with their XR750 race bikes. While not a true Twingle, they set them up to fire just 45* apart, giving almost 2 revolutions of the motor between firing pulses. Gave the tire more time to hook up between hits.

[MRieck]

I've seen it done on a CB750 engine used for hillclimbing.

This was done by a fella named Bill White (an AMA Champion too) from Massachusetts. Rick Stetson did the engine work. Bill went as far as you could go with the CB engine and finally switched to the GS 1100 platform. I have to take some pics of the swingarms to these bikes...they're fun to look at.

[scadaman29325]

I thought you were going for 'threesomes and foursomes'...

Later, Phil

[JLeather]

A guy on the HondaChop board purchased a cam for this not too long ago.  I forget who did it, but I suspect it was MegaCycle.  Anyway, the engine did have a really unique sound, and lots of torque, but it ran really rough at higher revs.  He was scared to take it much past 4,500 or so.  He took it back out and sold it to go back to a standard setup.  I suspect that you could gear the bike to take advantage of low-end power, but you're going to sacrifice topend.  Not what you want for a road-race bike, but for a hillclimber I suppose it'd be alright.

[mlinder]

except you'd have to shift a lot more...