registered user Posted August 27, 2014 Report Share Posted August 27, 2014 calvin made these cylinders to make you guys happy and keep this sport going. if he were to make a engine from the ground up it would be different im quit sure of that Quote Link to comment Share on other sites More sharing options...
m671054 Posted August 27, 2014 Report Share Posted August 27, 2014 Good examples. Both are close in power and tq. Now people will only argue different builders and dynos. So much for bigger bore aint worth a fuk. I dont understand some of you guys and if your thinking clearly Quote Link to comment Share on other sites More sharing options...
B.b.p builders Posted August 27, 2014 Author Report Share Posted August 27, 2014 I wish I had the knowledge that u guys seem to have. I sure enjoy reading and learning about this stuff, u guys seem to be making some very good points, and stating some good opinions. I still can't find much on 4 mill big bore motors, not worth doing? or is it a dick thing, everyone wants the biggest crank?? So not as popular to build. Please jump in if u have personal experience with a 4mil big bore DM, cheetah or cub. Also this is for a drag motor, again I'm not even half as knowledgable as u guys, but going on what I'm reAding here, wouldn't the less torque in the 4 mill big bore be great for starting, and the higher rev good for the 300' race? Especially a guy who has no exp. setting up his lock up clutch. Or am I way out in left field? Quote Link to comment Share on other sites More sharing options...
B.b.p builders Posted August 27, 2014 Author Report Share Posted August 27, 2014 BBP... bikes around here are over priced... if I where you id be planning to gather a few engine parts together and taking a drive to the US to pick them up at 1 location....probably could buy 2 decent motors in the US for the price of one here. carefull with the market in the drag scene... you dont have that much of a market in the area just yet... There is no market here period. All parts would be bought from the US. I buy everything from our neighbours in the US. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 27, 2014 Report Share Posted August 27, 2014 lets think about all this for a minute. you should be striving for the most port surface area you can. large piston with short stroke does not lend it self well to that, not as well as a long stroke. large piston generally is heavier and surely is more prone to deto because its dome is hotter from the increased surface area not being able to transfer heat as well to the walls and water jackets. combustion flame will have farther to travel with large piston diameter. other stuff nobody ever thinks about with the short stroke is how much lower on the cases does that put the cylinder. it matters because it can shorten your transfer tunnels and reduce their volume. neither are a good thing really. On board. Go on... Only thing that's not totally kosher in that is the stroke relating to transfers. That wouldn't apply to stroking stock cyls, but the taller aftermarket cylinders it definitely is a factor as they're cast per stroke. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 27, 2014 Report Share Posted August 27, 2014 Go to the dyno section. Look at a 10mil Cub vs a 4mil Super cub This is a dyno of a super cub (72x58) http://bansheehq.com/forums/index.php?showtopic=142752 Here is a 10mil cub (68x64) http://bansheehq.com/forums/index.php?showtopic=148104 Both are alky. Teuche' Quote Link to comment Share on other sites More sharing options...
registered user Posted August 28, 2014 Report Share Posted August 28, 2014 (edited) this may help explain better what i was saying. these are my beliefs. everyone is entitled to think otherwise. like i was saying about keeping the cylinder high. if you have a cylinder of say 250cc, how much mixture volume can you pack in there ? perhaps allitle less than 250cc, maybe even more than 250cc. i guess it depends on how well the engine was designed and its state of tune. now remember crankcase volume is usually many times larger than cylinder volume so only a partial amount of the case volume will make it to the cylinder each cycle. so if we have a real good running engine and can fill the cylinder with say 300cc volume then we want it as close as possible to the cylinder because it only has a very short time to make it there. if we try to get the 300cc of volume in the transfer tunell area, that would make for a short ride to the cylinder and a better chance that all of it will make it. 100cc transfer tunells doesnt do much good because then it will just try to pull any more mixture that it needs from other areas that are farther away, which takes more time and time isnt on your side. not to mention if this volume is located in the tunells it doesnt have to go through piston windows or around corners or other obstacles etc. so this is one reason why i like longer strokes and long rod. it lifts the cylinder and increases the trans volume. heres some photos of a old honda cylinder. its not right down to the nats ass but it will give us a close approximation what these tunells hold for volume. 500cc cylinder volume but the tunells only hold about 150cc x 2 which eqauls 300cc for all 4 tunells. i didnt factor in the boost port but i think that port is far less important and its steep upward angle doesnt flow nearly as much volume as the side transfers. so i have a 500cc engine with only 300cc of volume readily available in the tunells. maybe this engine wouldnt benefit from more trans volume, i really dont know. it is a large engine and its port design is far from ideal. but on a smaller better designed engine, if you only had 1/2 to 2/3 of your cylinder volume sitting in the tunells, i think you might be cutting yourself short. so flame on if you want but it makes sense to me. theres something else to point out about the longer stroke stuff. i like picking the brain of kart guys. one dude has a cr250 with upper mid 60hp (67hp was the dyno i seen) on race gas and its power peak around 11k rpm. this is 72 stroke engine. some of that rpm can be attributed to the pipe and probly the custom design ign curve, head design etc etc but i think alot of its rpm is because the undersqaure engine has more port surface area which has alot to do with where the engine runs out of breath and cant make any more power. not knocking anybody but some people say the short stroke stuff can rev, well all the short stroke stuff ive seen around here drops off before 11k, sometimes well before 11k. Edited August 28, 2014 by registered user Quote Link to comment Share on other sites More sharing options...
shanYE west Posted August 28, 2014 Report Share Posted August 28, 2014 It might lift the cylinders and increase transfer volume.. but your also increasing combustion volume. I would think the ratio of displacement increase from stroke would be more then transfer volume increase. By adding 4mm of stroke.. Wouldn't that increase engine displacement by more cc's then the transfers would increase and put the engine even further behind? Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 28, 2014 Report Share Posted August 28, 2014 (edited) I see where you're going RU but doesn't that theory only apply if you are using different aftermarket cylinders? With a stock cyl motor you can change the transfer volume but not it's distance from the crank. So I'm not quite sure I'm following the point you're making Couple quick questions? Have you CC'd the transfers on a set of stock and well ported banshee cylinders? Just been curious if people even did that and your the first guy I've seen actually photograph it so I figured I'd ask the outcome. Also, you mentioned stock stroke rev VS. Stroked and their rev capabilities and the stuff you see around here? Are we comparing apples to apples or cr250 and 250r RPM vs what banshees produce RPM wise? There are banshees that rev to 11K but the ones I've seen are shorter stroke. Almost every banshee I've seen, the more you stroke it there is a little peak RPM loss. I'm just trying to see if your comparing yzf350's to yzf350's and not something else. Every motor has it's limitations, unfortunately the banshee has a ton and is archaic by today's standards. Edited August 28, 2014 by trickedcarbine Quote Link to comment Share on other sites More sharing options...
registered user Posted August 28, 2014 Report Share Posted August 28, 2014 (edited) we not comparing honda vs yamaha. the manufacturer is irrelevant. we are comparing short stroke big bore to smaller bore longer stroke. how can the engine rev and make power if its running out of breath because the transfer area is smaller ? i only mentioned the 72stroke x 66 bore because thats pretty impressive to hit that kind of rpm. i believe its partly (maybe mostly) because its longer stroke in relation to the piston and no i never cc banshee trans volume. maybe someone else has. be interesting to see what it is Edited August 28, 2014 by registered user Quote Link to comment Share on other sites More sharing options...
shanYE west Posted August 28, 2014 Report Share Posted August 28, 2014 I thought I heard something about a problem with the way the fuel charge is burned over the crown of the piston or something like that? anyone else hear of that? Quote Link to comment Share on other sites More sharing options...
registered user Posted August 28, 2014 Report Share Posted August 28, 2014 what are you talking about. are you referencing the straight up and turn style of trans ports or something else ? Quote Link to comment Share on other sites More sharing options...
shanYE west Posted August 28, 2014 Report Share Posted August 28, 2014 I was talking about another problem that I heard of.. though they may be related. It was a while ago when we were discussing it and I forgot the details of the conversation.. which in this case probably would be helpful. But some reason twin spark plugs was mentioned?? Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 28, 2014 Report Share Posted August 28, 2014 BIG bore and flame travel Quote Link to comment Share on other sites More sharing options...
registered user Posted August 28, 2014 Report Share Posted August 28, 2014 if there was a 10mil 64bore cylinder it would be interesting to see what happened if you put a 14mil crank in it with fairly long rod Quote Link to comment Share on other sites More sharing options...
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