Guest ozzie Posted May 17, 2009 Posted May 17, 2009 Seeing how we have a few knowledgable types here i'd thought this is a good place to start. does anyone know the length to dia ratio and appropriate bell size to dia ratio for velocity stacks?
skeptic36 Posted May 17, 2009 Posted May 17, 2009 Dunno anything about em but does this help ? Velocity Stack 60mm ID x 130mm Long - 1.6mm Gauge Ali Velocity Stack dimensions are : Overall Length of 130mm and Base to Tapered Length 50mm. Top outside diameter of 102mm and inside diameter of 74mm. Base inside diameter of 60mm. Regards Bill
Guest ozzie Posted May 17, 2009 Posted May 17, 2009 I got a feeling that i'll be wasting a bit of material doing the trial and error thing.
facthunter Posted May 18, 2009 Posted May 18, 2009 Reply Might be a bit inevitable with reed valves, It happens with poppet and rotary valves as well , in both 2 and 4 stroke engines, but extensive manifolding hides it, unless you are running something like a Bing or Amal carb. but not as much (depending on how radical the timing is) This is why there is oil dripping out of the aircleaner, sometimes. The Hirth engines are injected and may get around this. Be CAREFUL as the mixtures may be affected with your stacks. Nev.
facthunter Posted May 18, 2009 Posted May 18, 2009 Time Warp My last post "reply" has ended up before yours. Curious? Nev.
Guest ozzie Posted May 18, 2009 Posted May 18, 2009 These are only small two strokes using walbro pumper carbs. fiddely to adjust. timing is fixed. If i can stop the blowback i'll improve on the 4 lts total an hr consumption. i have to be careful with them as they are out of production and parts are as rare as. pioneer P60 or 61. only turning at 5500rpm on a good day. I have two on the Lazair and one with very low time as spare. looking for a flywheel at the moment to make up another. Any treeloppers out there? they were very popular in Tassie. Ozzie
facthunter Posted May 18, 2009 Posted May 18, 2009 Ram effect. The length depends on the RPM you are operating at. There are formulas around, but at the low RPM's that we operate at, they would be over 15 inches long, ( total intake length ). As they depend on pressure waves, they only work over a narrow range of RPM. You want your power at T/O and altitude (compensation only). Nev..
Guest ozzie Posted May 18, 2009 Posted May 18, 2009 Yes that is what i thought about the rpm. main reason i need to fit them is to stop the blow back of fuel over the wing. One home made type fitted to a spare engne i have is four inches long with a one inch throat. it has knocked a couple of hundred rpm off full throttle but has stopped the blow back. these engines are aso fitted with reed valves. Ozzie
facthunter Posted May 19, 2009 Posted May 19, 2009 Too Small. I had a look for the pioneer that I had, but it is only a P 20. Nev
Guest ozzie Posted May 19, 2009 Posted May 19, 2009 looking at the manual for the pioneers they have a plastic type V stack about an inch long in the air cleaner assembly. there are also some nice alloy machined examples for the 50cc pocket bikes/scooters that i can model mine on. looking at some chainsaw forums it seems that there are a lot of people who collect them. Pioneers seem to be a prized item especially amongst the Canucks. Then there are the competition chainsawers who hot them up, run them on nitro and put a 4 or 5 ft bar on them. that p20 may be worth a few bob. ozzie
turboplanner Posted May 19, 2009 Posted May 19, 2009 I had over 180 degrees port timing on a Mach 3 Kawasaki and it used to spit the carbies off at times, but had massive power. This timing, the chamber and the length of the intake stack between the carbie and the cylinder can all have a bearing on blow back. I built the chambers from the book "Two Stroke Tuner's Handbook by Gordon Jennings, and they worked from day 1, so I'm happy with his theory, and apparently so are many others because I see it's bringing $159.99 on Amazon.com He has a section in there on intake shape and length with formulae, so if it is feasible to build your own intake tube, and if you want to go down that road, PM me.
Guest ozzie Posted May 19, 2009 Posted May 19, 2009 I'm not really into going that far into it. i just want to stop the untidy mess with out loosing any climb rate. i had a blue model 750 wonder how much they go for now. sold it to buy a panel van and get my first skydive rig. Ozzie
farri Posted May 19, 2009 Posted May 19, 2009 does anyone know the length to dia ratio and appropriate bell size to dia ratio for velocity stacks? ozzi,I`m supprised you can speak some Chinese. Frank.
turboplanner Posted May 19, 2009 Posted May 19, 2009 I did worse than that Ozzie - sold my Vincent Comet for $38.00
Downunder Posted May 23, 2009 Posted May 23, 2009 Hello, These are for walbro carbs, 31mm bolt spacing I think. 19mm choke throat. Hobbycity Online R/C Hobby Store : FTL-26 Part # 034 $2.80 Can send you links for Alloy ones if you like? Plenty of RC engines use them. Regards, R J Mitchell
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