wobblywalrus


« Reply #2205 on: November 14, 2015, 01:10:35 AM » 

Tom, the carbs are well sealed and should work OK. The plan is to use them with low boost until I get the blowers installed and sorted, then to replace them with EFI.
The friction drag is calculated for all three of the 2014 runs and my target speed of 165 mph. Cooper's second equation is used. The tire pressure was increased from 37 to 42 psi for 2014 and the bike with rider continued to weigh 740 pounds. The fiction drag horsepower is 17.9 for 146.45 mph, 16.5 hp for 141.95 mph, 17.1 hp for 143.82 mph, and 25.1 hp for 165 mph.
The rear wheel horsepower at Bonneville is 86 percent of the rear wheel horsepower on the dyno at Beaverton. I did some calculations a few years ago to determine this. The rhp was 75.1 for the 7,300 rpm run at 146.45 mph, 74.3 rhp for the 6,880 rpm run at 141.95 mph, and 74.0 rhp for the 7,580 rpm run at 143.82 mph.



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wobblywalrus


« Reply #2206 on: November 14, 2015, 12:14:03 PM » 

Tom, last night I remembered how the turbos were set up back in the days when we had carbs. There was also mechanical fuel injection and no one I knew used it on a bike. The trick was to fool the fuel system to thinking the blower was not there. The carb needed to be a sealed unit with only the venturi and that breather hoses open to the atmosphere when in NA use. The fuel system was set up so the tank vent, carb breather hoses, and venturi inlet were all plugged into the plenum between the turbo and the engine. One guy had his carb in the plenum box.
The friction drag horsepower is subtracted from the rear wheel horsepower to get the aero drag horsepower. The simple equation at the bottom of the attached is used to calculate the aero drag coefficient. The equation is corrected to the typical air density at the bike speed trials on the lake. Wind direction and velocity as well as tuck all influence this calculated factor. That is why you want to calculate it for each run. The average is the best indicator of overall aerodynamic performance.
The average drag coefficient is (.43 + .47 + .45) / 3 = .45
This method is detailed. The advantage is it can be used to look at the effects on speed from these variables: frontal area, aero drag coefficient, tire pressure, bike and rider weight, and horsepower. The effects of air density can be used by altering the constant in the aero drag equation.



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wobblywalrus


« Reply #2207 on: November 14, 2015, 02:47:55 PM » 

The rolling drag horsepower was calculated for 165 mph a few posts previous. The aero drag horsepower is calculated and added to this to get the rear wheel horsepower. This is multiplied by a factor to give me engine horsepower. The flow I need to have at 28 inches water is calculated from the engine horsepower and a coefficient. It is 235 cfm at 28 inches water.
The dashed red line on the flow curve is the expected limit imposed by the diameter and geometry of the valve curtain. No amount of port work is expected to give flows above this line. In theory, fully opening the ports can give 235 cfm flow at .39 inches lift. The cams will have over .4 inches lift. This port work might do the trick, in theory at least.



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Koncretekid


« Reply #2208 on: November 14, 2015, 06:57:37 PM » 

Well Bo, that looks like the work of an engineer But if that formula for rolling resistance works, you'll save about 12 HP just by doubling your air pressure! Now just cut your weight in half and halve it again! P.S. I went back to Bradley's book to the page where these formula are posted to see that I had actually done these calculations to find out that if Mr. Cooper had increased his tire pressures from 28 psi to 60, he would have freed up 5.07 hp. I suspect he did! I subsequently increased my tire pressures to 60 to help increase my speeds. The proof is in the pudding! Tom


« Last Edit: November 14, 2015, 07:20:12 PM by Koncretekid »

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wobblywalrus


« Reply #2209 on: November 16, 2015, 02:31:08 AM » 

It says on the tire that 42 psi is the maximum cold pressure. Do you run your tires at more pressure than the maximum recommended?



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fredvance


« Reply #2210 on: November 16, 2015, 10:31:48 AM » 

I dont. I run 42 on both ends of my 1350, Bonneville and pavement. The big motor bike,1657, I run 3738m in the back and 42 front, on pavement, 42/42 at Bonneville



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Going Fast  Slowly


« Reply #2211 on: November 16, 2015, 10:32:58 AM » 

Bo...................I run BTX and Avons on my bikes..........at 50psi front and rear. I'm thinking of following Tom's lead to go a little higher. My Cub has tubes..........the Honda is tubeless.



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fredvance


« Reply #2212 on: November 16, 2015, 10:49:16 AM » 

Bo, you should look on Carpenter Racing's website. They have a 90HP kit for your bike for 2400 bucks.



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Koncretekid


« Reply #2213 on: November 16, 2015, 04:42:48 PM » 

It says on the tire that 42 psi is the maximum cold pressure. Do you run your tires at more pressure than the maximum recommended?
Bo, The short answer is that it has been done and it was recommended to me by a team member whose bikes were heavier and faster than mine. The long answer is that as a professional engineer, I cannot recommend that anyone use equipment at any other conditions than those specified by the manufacturer as it would be a breach of my professional code of ethics. My point is that Kevin Cooper's equations were derived from empiracle data from his experience, trying to determine a formula for drag due to rolling friction for his 125cc CanAm salt flat race bike and he was very successful. Therefore it may be applicable to our bikes and it does imply that rolling friction drag is inversely proportional to tire pressure and proportional to weight. If these formula are accurate (and I have no reason to believe they are not), then we should be looking at reducing weight and possibly using higher air pressure in our tires to free up some horsepower. How important is this? At the speeds I am going, my calculations indicate that I can gain about 1 mph for each 1 hp I can gain (as I increase my speed, the hp to speed ratio get steeper), so saving a few hp on rolling friction should result in proportional gains. Every little bit counts. And how often have you heard the weight is not important? Incidentally, Mr. Cooper's detailed studies of air flow drag in the wind tunnel on the CanAm are phenomenal and should be required reading for land speed racers. Keep up the good work! Tom



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joea


« Reply #2214 on: November 16, 2015, 08:15:50 PM » 

a pushrod Triumph 650 "without" streamlining ran 175 this past weekend at EM.



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wobblywalrus


« Reply #2215 on: November 16, 2015, 08:26:43 PM » 

Thanks for pointing this out, Joe. Now, back to the problem at hand. I'll use the maximum stamped on the tire, which is 42 psi. This is a big and heavy bike running tubes so it is best not to take chances.
Carpenter's engine build looks nice. Some day I will describe the best street setup for these engines. It is not a lot different than his.
The target is 111 rear wheel horsepower so I need to reach deep. This has been my goal from the beginning and I have been working toward it year by year. All of the parts are bought. All I need to do is verify the cylinders will accept the new pistons without needing to be replated, send the pistons, etc out for ceramic coating, have the port shapes optimized, break in the engine, and set the jetting. Also, maybe blend up another batch of jungle juice with a bit less nitropopane and a tad more toluene.



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Koncretekid


« Reply #2216 on: November 18, 2015, 08:09:46 AM » 

Bo, In your post # 2206 above, you show a formula to determine drag coefficient of friction that uses a constant of 175,281. I know that you have been using Bradley's Technical Guide for Constructors but his formula on page 198 uses the same formula with the constant 146,806. Are you using a different constant to allow for different air density at Bonneville? Tom
Edit: I need to go back to your earlier formula for rolling resistance above in post #2205. Once again, you have introduced another number of 1.467 into Kevin Cooper's formula to arrive at your figures. What does this additional factor represent?


« Last Edit: November 18, 2015, 10:07:44 AM by Koncretekid »

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wobblywalrus


« Reply #2217 on: November 18, 2015, 08:28:02 PM » 

Time slip data from many runs at BUB was used to figure out the air density for each run. Those were averaged to arrive at a typical expected air density for the speed trials. That average value was used to calculate the constant in my equation.
The 1.467 factor is under investigation. I did lots of figuring on the subject and I have it written down somewhere.



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wobblywalrus


« Reply #2218 on: November 19, 2015, 12:27:13 AM » 

The friction drag equation combines the rolling resistance equation on page 172 with the rolling power equation on page 173. Velocity in the rolling resistance equation is in feet per second and it is in miles per hour in the rolling power equation. The 1.467 factor converts miles per hour to feet per second. You would be entering velocities described by two different units in my combined equation if I did not have the factor.



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Koncretekid


« Reply #2219 on: November 19, 2015, 09:30:10 AM » 

Bo, I have combined both equations that you used, including your revised constant of 175,281 in place of Cooper's 146,806, and used your most recent weight (740 lbs.), tire pressure(42 psi), coefficient of friction (.45) and area (7.46) assuming that these will remain constant, at least in the near future and I came up with the following formula for total horsepower required:
Horsepower required for speed V (mph)=.012V + (.00002425) V cubed. (note this only applies to Bo's conditions)
I derived the general formula, but typing it out on the keyboard is a bit cumbersome when you can't use math symbols. I could write it out and photograph it and post it as a jpeg if anyone is interested.
For 165 mph, I get an answer of 110.9 hp at the rear wheel. I think you got 111 with your methods which is probably just rounding differences. With this equation, you should be able to determine hp for any speed. The interesting thing is that except for the first term which only adds 2 hp, the total equation can be boiled down to the following, ignoring that 2 hp:
Horsepower required for speed V (mph) = .00002425 V cubed = 109 hp for a speed of 165 mph
Although I used Bo's drag area, tire pressure, and weight for this calculation so the constant only applies to his bike, this formula allows us to see that basically horsepower required increases at the cube of the increase in speed. For anyone who has a rear wheel horsepower number which can be directly associated with a speed at Bonneville, new horsepower requirements can be calculated without knowing any other info, as long as weight, tire pressure, and shape (drag area coefficient) remains constant.
Tom


« Last Edit: November 19, 2015, 09:51:57 AM by Koncretekid »

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