johns
Expert Class
Posts: 205
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posted January 26, 2003 06:07 AM
mental masturbation-BMEP
Got you to look didn't I. I can tell its really getting getting bad (winter doldrums) when I pull out the calculator and dyno charts. A question for you tech heads? BMEP (brake mean effective pressure)is a mathematical value that indicates the amount of average pressure exerted on the piston after frictional and inertia losses expressed in pounds per square inch. BMEP can be calculated in two ways. BMEP from HP and from TQ. The BMEP from TQ. will be higher because cylinder fill is greatest at peak TQ. BMEP is useful to engineers and engine builders because it is a measure of how efficent a motor is. My question is since BMEP is calculated from crankshaft HP and TQ, is a 16% driveline loss a reasonable figure to use when using dyno HP and TQ readings on a ZX-12?
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2006 ZX-14 (sold)
2012 ZX-14R (Brock's Perf. project bike Louisville Slugger)
2013 Honda VFR1200F
2003 124 C.I. H.D. Super glide
  
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zrxdean
Needs a job
Posts: 2225
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posted January 26, 2003 08:50 AM
It must be getting really cold up there, can't even futz in the garage? I don't have any real data, but I've heard slightly lower loss percentages for bikes in general, around 10-12%. I' sure it would depend on how your bike was set up- clutch slip, chain adjustment, tire psi, etc. Post your numbers... 
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johns
Expert Class
Posts: 205
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posted January 26, 2003 04:15 PM
It is really cold up here. The last dyno numbers I have are from KWS Motorsports in Charleston SC in October. With a .97 correction factor the 1270 motor made 199 HP at 11,500 and 105.6 ft/lbs at 7700. Theses numbers are within 1.5% of what the bike has run here in Louisville. If the 16% driveline loss is correct the BMEP would be 205 psi. If the more moderate 12% is correct BMEP is 198 psi using HP to calculate BMEP. With a 200 pound non proffesional rider the best numbers it has run were 154.5mph at 9.30 with a 1.78 60 ft. Not that impressive compared to some of the numbers I have seen here but we are working on improving them.
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2006 ZX-14 (sold)
2012 ZX-14R (Brock's Perf. project bike Louisville Slugger)
2013 Honda VFR1200F
2003 124 C.I. H.D. Super glide
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zrxdean
Needs a job
Posts: 2225
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posted January 26, 2003 06:22 PM
9.30 is fantastic with that short time. If you can get it down to the low 1.60s, you could scratch 8s.
Nice motor... I wonder what BMEP a Formula 1 motor makes?
Go Bucs 
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johns
Expert Class
Posts: 205
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posted January 28, 2003 02:43 PM
Thanks for the input and encouragement Dean. As for pure race engines and what BMEP figures they produce I found a few. The Corvette factory supported race engine that raced recently at LE Mans has a BMEP of 198 psi. The old Cosworth DFV V/8 had a BMEP of 195 psi at the HP peak and 203 psi at the torque peak. The newer Cosworth V/8 used in the F3000 race series has a BMEP of 241 psi at the HP peak. Before we congratulate ourselves about the relatively high BMEP figures our ZX-12's make consider a 750 cc superbike making 175 HP with a BMEP of 242 psi. Honestly I think theses engines are amazing. I am 60 years old and when I started riding in 1965 a 650 Triumph with around 50 HP was what passed for a high performance street bike.
____________
2006 ZX-14 (sold)
2012 ZX-14R (Brock's Perf. project bike Louisville Slugger)
2013 Honda VFR1200F
2003 124 C.I. H.D. Super glide
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