wacko2000 Posted January 20, 2010 Report Share Posted January 20, 2010 Very interesting, thanks Brandon Basically you guys get screwed out of hp, the higher the elevation Quote Link to comment Share on other sites More sharing options...
FireHead Posted January 20, 2010 Report Share Posted January 20, 2010 Very interesting, thanks Brandon Basically you guys get screwed out of hp, the higher the elevation Not necessarily.......... It just means you have to run higher compression and/or some of artificial aspiration device. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted January 20, 2010 Report Share Posted January 20, 2010 (edited) He stated in his first post that he runs 91, which would be even more impressive. I believe Snop says that only a crank dyno give true #'s This! Rear wheel dynos aren't that accurate. I have seen 74.75 hp on a crank dyno from a low-mid ported stock cylinder 4mill/long rod with a set of pro circuit pipes, 180 psi compression, dyna cdi, carbon tech mid reed petals on stock cages, nology coil, wiseco pistons, and dual 28mm mikuni flat slide carbs. It also made that peak hp with a peak of 8,750 rpm on a dynomite crank dyno at a 700 ft elevation. Edited January 20, 2010 by Snopczynski Quote Link to comment Share on other sites More sharing options...
BigRed350x Posted January 20, 2010 Report Share Posted January 20, 2010 Very interesting, thanks Brandon Basically you guys get screwed out of hp, the higher the elevation Yeah, try riding at 8500ft elevation. Walden dunes is at 8500 and KP dunes are at 7200ft. Just means we have to build harder running bikes. haha! My dune bikes are up around 180lbs compression at 8000ft, when we go to sand mountain UT or St Anthony we have to swap out domes. Quote Link to comment Share on other sites More sharing options...
Badasshee Posted January 20, 2010 Author Report Share Posted January 20, 2010 theyre drag ported but from wat brandon told me the first time he ported my cylinders it took away my ability to do a full drag port with the tripple exhaust ports or whatever the f it is but my transfers wouldve been off so yeah. and shes only on pump. i dont care wat anyone says. im pretty excited to race her! Quote Link to comment Share on other sites More sharing options...
bigborebanshee Posted January 20, 2010 Report Share Posted January 20, 2010 Rear wheel dynos aren't that accurate. No but a rear wheel dyno is a great tuning tool if you have already run a crank dyno.its good to know how much your losing through the drivetrain. Quote Link to comment Share on other sites More sharing options...
RagunCajun Posted January 20, 2010 Report Share Posted January 20, 2010 Someone finally said it. A dyno is a tool. Used to tune. Either way i plan to get mine dynoed this year. Not concerned with the outcome because my bike is so much more fun to ride now. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted January 20, 2010 Report Share Posted January 20, 2010 (edited) No but a rear wheel dyno is a great tuning tool if you have already run a crank dyno.its good to know how much your losing through the drivetrain. A rear wheel dyno is good for measuring the difference in power when swapping out parts. Its not a good tuning tool because they don't have an engine brake. It's not very accurate when your trying to set needles, and basically anything other than main jets in a carb. Its not even good for measuring hp to compare to a crank dyno. They are not accurate dynos because of the correction factor formulas they use and all the inconsistencies of the drivetrain. Edited January 20, 2010 by Snopczynski Quote Link to comment Share on other sites More sharing options...
bigborebanshee Posted January 20, 2010 Report Share Posted January 20, 2010 A rear wheel dyno is good for measuring the difference in power when swapping out parts. Its not a good tuning tool because they don't have an engine brake. It's not very accurate when your trying to set needles, and basically anything other than main jets in a carb. Its not even good for measuring hp to compare to a crank dyno. They are not accurate dynos because of the correction factor formulas they use and all the inconsistencies of the drivetrain. How do you gauge power lost through the drivetrain? Effects of billet axle,oring vs non oring,clutch slippage? We only use an crank dyno when changing out parts,Once its dialed in,its dialed in.After that we use a chassis dyno, the drivetrain is very inconsistent,but its a better gauge of whats getting to the ground and how to harness it. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted January 20, 2010 Report Share Posted January 20, 2010 (edited) You baseline the rear wheel dyno with your starting axle, then you put the new axle on and test it again. Your usually better off using the time scale on the run to see the difference, rather than actually measuring the power. Crank dyno's have a more accurate testing method because they measure hp off the crank. Rear wheel dynos have correction factor formulas that they use. The Rear wheel Dyno has other variables you have to take into account: internal transmission ratios, swingarm length, tire size, gearing, chain length, chain weight, the clutch, even rolling resistance of your bearing carrier can make a difference in the measurement at the rear wheels. You can't correlate rear wheel numbers to crank numbers because of the hypothesized correction factors they use. A few years ago, Dynojet was forced by court order to disclaim that their correction ratios can be inaccurate from within 15% of what the actual displacement power may be. A rear wheel dyno is meant to be used as a parts swapping tool to measure power difference, not a baseline actual measurement of power output. Edited January 20, 2010 by Snopczynski Quote Link to comment Share on other sites More sharing options...
treybird Posted January 20, 2010 Report Share Posted January 20, 2010 thats great numbers brother im here in kansas 1300 ft above sea level and i have a 4 miil cub and i made 72 hp with stock carbs and reeds with pc pipes Quote Link to comment Share on other sites More sharing options...
RagunCajun Posted January 21, 2010 Report Share Posted January 21, 2010 Props for using stock carbs^^ So many think you NEED bigger carbs^^. Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted January 21, 2010 Report Share Posted January 21, 2010 Yeah, its pretty nuts when you see some of these guys with 35mm pwk's on dune bikes that are ported pulling like 9,900 peak rpm. Way Overkill! Quote Link to comment Share on other sites More sharing options...
SonOfSand Posted January 21, 2010 Report Share Posted January 21, 2010 Yeah, its pretty nuts when you see some of these guys with 35mm pwk's on dune bikes that are ported pulling like 9,900 peak rpm. Way Overkill! Snop, do you think the 35's are overkill in my situation? If so, why? Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted January 21, 2010 Report Share Posted January 21, 2010 This! Rear wheel dynos aren't that accurate. I have seen 74.75 hp on a crank dyno from a low-mid ported stock cylinder 4mill/long rod with a set of pro circuit pipes, 180 psi compression, dyna cdi, carbon tech mid reed petals on stock cages, nology coil, wiseco pistons, and dual 28mm mikuni flat slide carbs. It also made that peak hp with a peak of 8,750 rpm on a dynomite crank dyno at a 700 ft elevation. I'm quite sure the engine described in this thread will make more "impressive" numbers on a crank dyno at 700' with 180psi compression as compared to his pump gas 5000' rear wheel pull. Apples to oranges. Quote Link to comment Share on other sites More sharing options...
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