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Horsepower, dynos, & why 600 crank hp isn't enough

Broncobowsher

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Are you using the HP to accelerate or to climb?
Acceleration, the heavy parts are inertia that has to be overcome.
To climb, the parts are spinning a steady state, they are already at speed. Doing a sand dune the tires are just churning through the sand. Or a boat cruising through the water. Or a generator making electricity.
 
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nvrstuk

nvrstuk

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No idea and that's why I'm inviting any & all physicists to chime in. :)
Above my head and I'm not afraid to say it. lol
 

Yeller

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Exactly and that's why I posted up again saying that to keep that larger/heavier rotating mass rotating takes more power than keeping smaller weight/diameter stuff rotating as was posted earlier.

I am interested in having someone well versed in physics, inertia, rotating mass etc skool me on it tho.
Me too lol. I understand the ideology, I’m not versed enough to explain it
 

Broncobowsher

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I'll try to explain the inertial dyno. There will be some flaws, for simplicity mostly. The biggest one is mass and diameter, i'll mainly point out mass.

Since I did point out mass and diameter I'll address those first before I dismiss them. Take a long skinny rod, baseball bat will work. Grab it in the middle and try to twirl it like a batton, you can't spin it quick. Nor can you stop it quick. But hold it by the end of the handle and spin it aling its axis and you can spin it up and stop it quick. Same mass, different radius. So if you just look at mass and ignore changes in radius (and where the mass is on the radius...

An inertia cyno has a heavy drum. Call it 2,000#. How fast it can be accelerated takes HP. Not how fast you get it up to, but the rate it is accelerated. There is very little drag. Minimal air drag, almost nothing. Bearing drag takes a tiny bit as well. It is an extremely heavy flywheel.. A lot of HP will spin it up really fast really quick. The computer figures how quickly the drum was accelerated and can figure how much HP was needed to get that rate of acceleration. Track that with engine speed and you have a HP curve. With RPM and HP you can back calculate torque. This is backwards of more normal (engine) dynos where torque and RPM is measured and HP is calculated off that.

Now I mentioned that the inertia flywheel is an extremely heavy flywheel. If you add a bunch of flywheel weight to the test vehicle, very heavy tires and wheels, lots of mass that needs to be spun up. Now that 2,000# flywheel is actually 2,500#. It spins up slower. But nobody told the computer program that you are now spinning a 2,500 worth of inertia and not 2,000 that the dyno was built with. There will be a slower rate of acceleration. The math says that less HP was made.

But all this is based on "rate of acceleration" But if HP is being used to preform work, not accelerate, wrong matrix. An airplane cruising through the air will make steady state power, a boat cruising through the water (different than accelerating). This stuff isn't playing with the rate of acceleration. Just torque at speed. Which is the definition of HP, torque (lb-ft) X RPM / 5252.
 
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nvrstuk

nvrstuk

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This simplistically explains some aspects of the dyno but not your earlier statement that I pointed out in my last post.

Without perpetual motion you need more power to continue the rotatation of an already spinning 1,000# mass than the same shaped 100# mass because of all or most of the factors that several of us have mentioned several times.

This make sense?
 

73azbronco

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Broncobowsher said... "But adding inertia (heavy tires and wheels) eats HP. How is that?"

So a large diameter, heavy wheel (shaft, ring/pinion, gears, whatever, etc) rotating doesn't take any more energy to keep it rotating than the same shape item above but it is 1/5th the diameter/mass/weight/whatever, etc, etc? Am I missing perpetual motion coming in to play here somewhere?
Uh, well, forgetting about at least one of Newtons laws for sure. More mass, longer arm or distance, yes, more energy needed in our environment. In a vacuum, sure, once spun up, no extra energy needed.

E=MC2, or also pie R squared really eats up the energy needed.
 

73azbronco

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This simplistically explains some aspects of the dyno but not your earlier statement that I pointed out in my last post.

Without perpetual motion you need more power to continue the rotatation of an already spinning 1,000# mass than the same shaped 100# mass because of all or most of the factors that several of us have mentioned several times.

This make sense?
yes....
 

Broncobowsher

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Just because you are not using the right tool to measure HP doesn't mean it isn't there. It's a faulty tool that people think is the absolute truth. No, it is the cheapest tool and it works good enough for a tuning aid. Being the cheapest form of universal dyno around, it is the most common. Doesn't make it the best. They are flawed. But if you feel like ignoring the flaws... Well you get flawed data.

Just realized I dynod my first engine 29 years ago. That wasn't taking an engine to a dyno shop, that was finding an abandoned engine dyno and bringing it back to life with no manual (and no internet either). Then seeing an early chassis dyno for motorcycles a year or so later. Some good talks with dyno manufacturers at SEMA over the years as well.

I gave the math earlier about how much heat would be generated and need to be dissipated if the drivetrain actually absorbed that much power. I've also shown that the inertia dyno cannot accuratly measure HP when the inertia values in the calibration are flawed from excessive external inertia.

So you have numbers from 2 completely different dynos that measure in completely different ways. You state the loss in HP is in the drivetrain. I used math to show it can't loose that much HP in the drivetrain without turning into a pool of molten metal and pointed why the chassis dyno has low numbers. Flawed measuring, not drivetrain losses. If you do a good chassis dyno you can get real drivetrain losses. And real chassis dynos do exist. They are more expensive, more difficult to run cars across it quickly. But they are out there http://www.dynapackusa.com/product.htm
 
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nvrstuk

nvrstuk

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Just hear to learn... never said that if we had 2,000hp at the crank that the 30% potential loss that is seen btw crank and rear wheel hp that we "see" would still be the same. Pretty obvious.

Like I think we've all agreed upon all dyno measuring is different.

Obviously an engine crank dyna'd # at 2,000 and then set on a rwhp dyno wouldn't read 1,400 due to drivetrain losses... then there could be some goo in a pile under the rig. But I'll bet if that same engine went in another vehicle with small diameter lightwt wheels, tires, axles, extra gearboxes, etc, etc like we've posted up, the #'s would be quite different.


However, I can vouch that what Steve posted earlier about almost identical parameters in different types of vehicles and no comparison when next to each other on the street.

I am still awaiting a physics guru who can explain all three sides of this. :)

I'd like to put my engine from my DD '68 with 40"s, tons, etc, etc and put it in my Shorty build and compare them on the same dyno with identical weight.

The difference will be very clear and it won't be from heat loss.

I defer to a physics guru.
 

Speedrdr

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Dang! Why y’all got to bring a bunch of SCIENCE into a discussion anyway??? At a much younger age (college age) I absorbed just enough knowledge about statics and dynamics from the engineering students in our suite at Ms State to know that I didn’t want to know anything about it. Lol

Randy
 

Yeller

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Thanks broncobowsher, Brian, myself and several others geek out on some of this stuff. Your analogy with the base ball bat was exactly what I was trying to say. The power is there, it just gets absorbed by rotating mass so it feels less responsive. That reduced responsiveness is what we’re learning about and what causes it. No denying the data is flawed. Same reason we need bigger brakes to have the same brake effectiveness as a stock vehicle.
 

broncoitis

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Dang! Why y’all got to bring a bunch of SCIENCE into a discussion anyway??? At a much younger age (college age) I absorbed just enough knowledge about statics and dynamics from the engineering students in our suite at Ms State to know that I didn’t want to know anything about it. Lol

Randy
Well Said!

Its pretty simple for me. If your not happy with the performance of your vehicle be it crawling or cruising or towing your gonna need more motor. Kinda tough to lighten the drivetrain because of the size of tires we run so with beefyness comes piece of mind that your not gonna break at the expense of weight of the drivetrain. To overcome the weight you need more Torque/Power.

As for the different dynos giving back different numbers, does it really matter? Biggest thing to me is to be consistent with the comparisons. Don't use one dyno design for one test and a different design for another because that just doesnt work. All your getting is a number and apparently the numbers can vary based on the type of dyno. However its still just a number. My .02!
 
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nvrstuk

nvrstuk

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Well Said!

Its pretty simple for me. If your not happy with the performance of your vehicle be it crawling or cruising or towing your gonna need more motor. Kinda tough to lighten the drivetrain because of the size of tires we run so with beefyness comes piece of mind that your not gonna break at the expense of weight of the drivetrain. To overcome the weight you need more Torque/Power.

As for the different dynos giving back different numbers, does it really matter? Biggest thing to me is to be consistent with the comparisons. Don't use one dyno design for one test and a different design for another because that just doesnt work. All your getting is a number and apparently the numbers can vary based on the type of dyno. However its still just a number. My .02!
Agreed again. I have very little knowledge/background with dyno's compared to broncobowsher. Just a number for comparison is right.

I am really interested in the physics tho... :)

Still early where I live & haven't had a sip of coffee so don't beat me up too bad on this next question. lol

If I run 40" tires down the road it takes a certain amount of power to roll.

If I run 40" stickies down the road it takes more power to roll me down the same road.

Is the need for more hp/torque to keep me rolling down the road due strickly to heat loss with the stickies between the tire & road or more?

Is heat the only way to measure this? Sounds like it??

Help me out someone.
Ok, reaching for the coffee sitting on my deck right now...maybe I'll have to delete this entire question once the coffee gets to work! :)
 
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.94 OR

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If I run 40" tires down the road it takes a certain amount of power to roll.

If I run 40" stickies down the road it takes more power to roll me down the same road.
I'm assuming the rolling resistance of the stickies are holding you back. If you could alter air pressure in the tires to create the same contact patch between the two types of tire, would the rolling resistance be as noticeable? This may alter the true tire radius though so that would compound the energy needed to roll the rig.
 

67sport

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Agreed again. I have very little knowledge/background with dyno's compared to broncobowsher. Just a number for comparison is right.

I am really interested in the physics tho... :)

Still early where I live & haven't had a sip of coffee so don't beat me up too bad on this next question. lol

If I run 40" tires down the road it takes a certain amount of power to roll.

If I run 40" stickies down the road it takes more power to roll me down the same road.

Is the need for more hp/torque to keep me rolling down the road due strickly to heat loss with the stickies between the tire & road or more?

Is heat the only way to measure this? Sounds like it??

Help me out someone.
Ok, reaching for the coffee sitting on my deck right now...maybe I'll have to delete this entire question once the coffee gets to work! :)
The word you're looking for is friction. When friction is increased, through tire compound, tire pattern, or air pressure, it will take more work (power) to turn them. The energy lost to friction is converted to heat.
It's that simple.
And that is also what a chassis dyno is measuring. It doesn't care how much is lost between the engine and the tire. It is only measuring the power that is being directly transferred from the tire to the dyno drum.
 
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nvrstuk

nvrstuk

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I had Toyo MT's once (never again on an EB) and it wouldn't roll worth a dang. On a 2deg slope - same one (local road) I've driven on for 5 decades I would almost come to a stop in neutral going downhill. Every other tire combo rolls down the hill and accelerates in the same spot. I drove those tires for yrs (yup still hated them) amd they never got hot/warmer than any other tire that I check at every gas station by hand ( no IR gun).

So not scientific and I really do understand friction and heat but those tires are/were crap and they even had posted on their website that the rolling resistance was "extremely high" with those. Anyway, hence my sticky tire reference from pre-coffee this am! :)
 

bmc69

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When I still had my engine dyno...I compared a 408C I built, on my engine dyno and a rear-wheel inertial dyno. The differences were in the 30% range as best I recall.

The tires on the EB on the rear-wheel dyno were 39.5 IROKs.
 

73azbronco

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Is the need for more hp/torque to keep me rolling down the road due strickly to heat loss with the stickies between the tire & road or more?
No, yes, and yes. Depends.

Think stickies, then change word to friction. More friction, more power needed. Bigger tire, more mass, more power needed.
 
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