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Author Topic: Quickchange horse power drain  (Read 5897 times)
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John Burk
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« Reply #15 on: December 09, 2016, 05:24:47 PM »

It's easy to calculate the efficiency of a rear by how hot it gets and converting the heat into hp . If a rear is 70# steel , 15# alum. and 4# oil and it gains 35 deg. during a 1.2 minute run that's 393 btu / minute that converts to 9.27 hp . For 600 input hp that says the rear is 98.5% efficient .
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Stan Back
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« Reply #16 on: December 09, 2016, 07:19:55 PM »

How much air flow did it have on the run?
Was the cover finned aluminum?
Did you use a pump and cooler?
. . . and whatever.

Feed those into the sliderule, too.
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John Burk
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« Reply #17 on: December 09, 2016, 07:33:36 PM »

This hypothetical car is a lakester . No air cooling .
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Frank06
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« Reply #18 on: December 09, 2016, 08:28:50 PM »

No way it is 98% efficient.... chain drive isn't even that good.
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John Burk
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« Reply #19 on: December 09, 2016, 09:28:05 PM »

Rears would be over 200 deg. after a run if the losses were 5% .
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kiwi belly tank
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« Reply #20 on: December 10, 2016, 03:29:59 AM »

No way it is 98% efficient.... chain drive isn't even that good.
Ditto on that one!
  Sid.
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John Burk
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« Reply #21 on: December 10, 2016, 03:37:11 PM »

Do the math . It takes .12 btu to heat one # of steel one deg F . Alum. is .22 btu . Oil is .45 .  42.4 btu / minute is one hp .
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Stan Back
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« Reply #22 on: December 10, 2016, 06:00:16 PM »

And nothing radiates the heat between measurements?

I'll race with a Dream Wheel, but a computer is beyond me.
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Ron Gibson
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« Reply #23 on: December 10, 2016, 06:15:42 PM »

Amazing how many people ask "what's a Dream wheel?". I tell most of them, it's a slide rule for cars. grin grin

Ron
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manta22
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« Reply #24 on: December 10, 2016, 07:10:03 PM »

Stan;

At relatively low temperatures very little heat is lost by radiation. At the temperatures John is talking about the radiant heat loss is nil.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
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« Reply #25 on: December 10, 2016, 07:40:10 PM »

While the temperature measurement method is sort of an elegant way to estimate power loss, it is, like many things, fraught with generally unmeasured variables.  And recall that the example in the beginning was just based on arbitrary quantities of the weights, time, power etc.

In addition, varying convective cooling, some radiant loss, non-constant application of input power, uneven temperature distribution within the gearbox, and so on.  It can be done but a lot of stuff needs to be carefully measured to generate a valid result.
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Frank06
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« Reply #26 on: December 10, 2016, 08:56:49 PM »

Do the math . It takes .12 btu to heat one # of steel one deg F . Alum. is .22 btu . Oil is .45 .  42.4 btu / minute is one hp .
The math seems good, but where does the 35 F degrees come from?  I would stick with the 4-6% cited in one of the tech articles. 

It is an interesting method to calculate losses though!
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ronnieroadster
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« Reply #27 on: December 10, 2016, 10:57:22 PM »

 Interesting stuff heat transfer air flow over the housing way to many variables the way I see it. Looks like a simple percentage is not an easy figure to determine. SO
   Taking into consideration something Stan said. Using the wonder wheel I have from Mark Williams the calculated speed based off tire diameter, gear ratio and RPM came out perfectly to my top speed recorded.
 Go figure.    Dead Horse
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« Reply #28 on: December 11, 2016, 12:55:48 AM »

The question was never about gearing & speed, it was about power loss through a QC & I think Dynoroom's numbers are realistic. I know your engine is at the ragged edge & you're interested in getting more of it to the wheels so I would suggest you build a 7.5 10 bolt & give it a shot, even make it a bolt in so you can switch them to see the difference. S-10 housing is probably about the right width. I think I have a 2.56 & I know I have two sets of 2.41's & I think you could use a bigger gear.
  Sid.

 
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Stan Back
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« Reply #29 on: December 11, 2016, 04:34:07 PM »

My comment was really about feeding in the data.  My old cardboard's answer is within a MPH at 200-speeds at Bonneville.  I'm thinking that all the factors fed into a computer that comes up with an unbelievable number is missing something.
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