camatv Posted August 26, 2014 Report Share Posted August 26, 2014 more bore = more rpm. more stroke = more tq. more cc = more power ( potentially) more size = more weight = more issues with breakage potentially done 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 Anyone who has owned or had the chance to try out a 4mil DM 72x58 or the 78x58 please let me know your thoughts on that set up. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted August 27, 2014 Report Share Posted August 27, 2014 A stock banshee is over square, not under. Oversquare means bore diameter > stroke. Please know engine sizes before you comment. Stock banshee is a 64x54 engine 4mil DM is 72x58 or 78x58. stfu... Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 27, 2014 Report Share Posted August 27, 2014 Hate to do it but I agree with sloth^ Bpb, I wasn't saying a big bore 4mm is a bad idea. I was just trying to show that an extreme sized piston could potentially be an issue, but after looking at a bunch of different cranks, it seems that the 4mm HotRods rods are about as durable as anything, so maybe I'm just putting my foot in my mouth. Idea. If you are serious about building a few race bikes, why not throw a few 421 cubs together. Just shelf stock with poor man's CPI's and used sets of 35 PWK's. Lease the bikes..... You can get fancy, but why if they're just bikes you're selling. Really you are gonna take a loss unless you start just buying used motors to toss in them or something. Building a good cub costs about the same as what guys are getting for decent complete bikes. Maybe just build a few stock stroke draggers. Send a few motors off at once and possibly get a deal. Have the cylinders done and stock heads re chambered, cranks checked and welded with new bearings, cheap used VF3's, used sets of 34mm PJ's. 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 Yes that is for sure the smartest and cheapest way to do it, I 100% agree with you. I really never thought of it, or looked at like that, I am for sure serious about it, here is the thing tho I wouldn't mind a second bike, and there is a good chance the bike will take a long time to sell or not sell?? So my thoughts were building what I want incase it doesn't sell. But a stock stroke motor built from good used parts could be built very cheap these days, build it cheap, sell it cheap, probably a much better chance of getting guys to get into it. Ummm, not to mention most r all running piped banshees around here, so a drag ported stock stroke stock cyl. Bike, would still be nothing to laugh at. The other thing is I already own the 421 cheetah, I just haven't picked it up yet. I'm seriously thinking of a 78/58 DM if nobody buys it I'm stuck with a sweet bike, and also , of coarse this would all be over winter to have ready for spring and next years season. The DM build would only be if I could get a good price on selling the 68mm pv cheetah cyl. Cause I would already have all that's needed for the DM cyl. Bore and port cases and good to go. Great idea tho and I believe it would work , if guys could get into a drag bike for less then 3grand it would be much more appealing to them. Quote Link to comment Share on other sites More sharing options...
shanYE west Posted August 27, 2014 Report Share Posted August 27, 2014 Hate to do it but I agree with sloth^ Shhh... dont say stuff like that.. He needs to know his place.. lol Quote Link to comment Share on other sites More sharing options...
m671054 Posted August 27, 2014 Report Share Posted August 27, 2014 A stock banshee is over square, not under. Oversquare means bore diameter > stroke. Please know engine sizes before you comment. Stock banshee is a 64x54 engine 4mil DM is 72x58 or 78x58. Thats what i get for rushing through a post on my break. Thanks for clearing that up thoughBtw hows that efi coming along. You done reinventing the wheel yet? 1 Quote Link to comment Share on other sites More sharing options...
shanYE west Posted August 27, 2014 Report Share Posted August 27, 2014 bahaha!! i knew that was coming! POW! Quote Link to comment Share on other sites More sharing options...
m671054 Posted August 27, 2014 Report Share Posted August 27, 2014 Square is 14 mil cub 68×68,24 mil dm 78×78 etc Stock is over square 64×54,16 cheetah 74.5×70 etc. under square is very rarely seen. I cant come up with a build combo that fits. Hope this revision clears up any confusion i have caused. Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted August 27, 2014 Report Share Posted August 27, 2014 Square is same bore and stroke ie 68×68 Stock is under square 54x64 4Mil dm 64x78 is oversquare Tradional thought is square motor runs better Also tricked what about 130,132,137 rods I know that stuff is out there, but I don't know shit about it. I've never built anything big enough to even need them. That's why I asked about it Quote Link to comment Share on other sites More sharing options...
registered user 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. Quote Link to comment Share on other sites More sharing options...
m671054 Posted August 27, 2014 Report Share Posted August 27, 2014 Larger piston would require shorter port windows due to more displacement under the piston and wider ports from larger bore diameter. The whole deto thing im not to sure about. I dont think transfer tunnel size is an issue as you are implying. lets use stock cylinder 68×54 and 66×58 as examples since cc wise they are similar 1 Quote Link to comment Share on other sites More sharing options...
registered user Posted August 27, 2014 Report Share Posted August 27, 2014 lets compare 78x58 to 71x70 both same 554cc . i know theres no such engine by why not. makes more sense than one thats redicously over sqaure Quote Link to comment Share on other sites More sharing options...
registered user Posted August 27, 2014 Report Share Posted August 27, 2014 (edited) everyone says 100hp from stokestroek and bore cylinders. dyno section has 7mil dm at only 120hp ?? 220cc more only gets you 20hp ? lame. because huge piston short stroke aint worth a fuk. if you cant see it oh well. sorry of the rant but i dont understand some of you guys and if your thinking clearly Edited August 27, 2014 by registered user Quote Link to comment Share on other sites More sharing options...
m671054 Posted August 27, 2014 Report Share Posted August 27, 2014 Its a fact that the larger the engines get the less efficient they become whats the tq in your referenced examples. Were they on same fuel type? If a big bore short stroke is not a good idea then why did calvin build a 84bore 4mil dmx to fit the 650 class when he already had 10 dms out. The dmx has even bigger transfer tunnel issues as well but it seems to work fine Quote Link to comment Share on other sites More sharing options...
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