Author Topic: Dyno Speeds  (Read 19466 times)

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Offline revolutionary

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Re: Dyno Speeds
« Reply #15 on: October 31, 2007, 10:19:22 PM »
BTW the chassis dyno showed we made 518rear wheel hp (505 uncorrected) an 462 tq (really flat with the tight converter) through a TH400.  This was on a Mustang Chassis dyno at Delk Performance in TN.  There was no CD info in their book for a 59 Jag so we picked a generic mid 80's Mercedes E type as a relative comparison to input as well as the vehicle's weight of 2650 plus driver.  We pulled the car up to 190 on the dyno and it was still creeping up but slowly.  It showed peak hp at 180mph  - coincindentally basically our exit speed at Maxton - Or maybe not so coincidentally.

Anyhow, it showed us that we need to make just over 500 uncorrected hp at the wheels to run 180 at Maxton in that car.  AT least that is A data point.
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Offline SPARKY

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Re: Dyno Speeds
« Reply #16 on: November 01, 2007, 11:44:55 AM »
The amout you need to gear short can bee figured by using the tractive effort formula qnd you eng. dyno. sheets:

TQ.   eng torque
FDR  Final drive rato--Trans Ratio X Rear Axle Ratio
TC  you use one of you tires as a value of 1.00-- then use the a 1.1 for a tire that is 10% smaller and .90 for one that is 10% larger
FDR X TC==Overall Gear Ratio or Total Gearing---or what ever you wish to call it.

Tq. X FDR X (TC)= tractive effort


you can put this on a spread sheet for you eng speeds and figure your speeds in each gear "Your Dream Chart" as well as "what is being put to the ground" no driveline losses figured but they should remain almost the same. This will tell you when to change the Overall Gearearing for better speed---My lakester is at the cross over point. Right now,  It will probabally run the same speed with the 2.28 or the 2.14s---I will be cleaning up the body this winter and installing the 2.14s-- peak Hp is about 6800 and I am turning  7050+ for the last mile.
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

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Offline Sumner

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Re: Dyno Speeds
« Reply #17 on: November 01, 2007, 12:13:40 PM »
The amout you need to gear short can bee figured by using the tractive effort formula qnd you eng. dyno. sheets:

TQ.   eng torque
FDR  Final drive rato--Trans Ratio X Rear Axle Ratio
TC  you use one of you tires as a value of 1.00-- then use the a 1.1 for a tire that is 10% smaller and .90 for one that is 10% larger
FDR X TC==Overall Gear Ratio or Total Gearing---or what ever you wish to call it.

Tq. X FDR X (TC)= tractive effort


you can put this on a spread sheet for you eng speeds and figure your speeds in each gear "Your Dream Chart" as well as "what is being put to the ground" no driveline losses figured but they should remain almost the same. This will tell you when to change the Overall Gearearing for better speed---My lakester is at the cross over point. Right now,  It will probabally run the same speed with the 2.28 or the 2.14s---I will be cleaning up the body this winter and installing the 2.14s-- peak Hp is about 6800 and I am turning  7050+ for the last mile.

Hey Sparky you tried to explain this to me once and how it relates to racing, but I can't get my head around it.  When I do a google search I come up with how it applies to trains:

Quote
Tractive Effort (abbr. TE) is the pulling force exerted, normally by a locomotive, though the term could also be used for anything else that pulls a load. It is normally understood to be the actual force on the locomotive's drawbar or rear coupler. When a bare figure for tractive effort is quoted without a speed qualification, this is normally for starting tractive effort, i.e. at a dead start with the wheels not turning...................

..........................For a locomotive to accelerate from a stationary position, it must apply a force to overcome the inertia of the train, along with the frictional forces in the form of mechanical friction, and wind resistance as the train accelerates. In order for this to occur a particularly high tractive effort is required, usually the maximum tractive effort of the engine is applied. This means that the engine works to produce the highest possible force that it can exert onto the wheels to cause movement or motion. Few engines can maintain work at the maximum tractive effort for very long, but neither is it usually necessary for an engine to do this. Once the train is running at a constant velocity the train no longer needs to overcome its inertia to remain at the same velocity, and hence must only provide power to compensate for frictional forces. This leads to one potential upper limit on the speed a locomotive can haul a train at, once the force due to wind resistance becomes greater than the tractive effort the locomotive can supply (fluid drag increases with the square of velocity), the locomotive cannot accelerate the train anymore (in reality the situation is more complicated than this due to a number of mechanical considerations).

The last part sounds a lot like our problems:

"upper limit on the speed....once the force due to wind resistance becomes greater than the tractive effort the locomotive can supply (fluid drag increases with the square of velocity), the locomotive cannot accelerate the train anymore"

So how do I use your formula and this concept to figure my gearing, HP needs, traction needs???

Thanks and maybe you will have to explain it when you get to my place later this month,

Sum

Offline SPARKY

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Re: Dyno Speeds
« Reply #18 on: November 01, 2007, 02:57:02 PM »
Sum,  I think you are trying to make it too complicated---all we are trying to do is compare the force to the ground at a given speed with different gear and tire posibilites; and we need to go with combo that produces the largest TE. 

As the torque falls off past peak HP, are we better going with a 5% lower gear because at 5 % more revs. the eng torque is only down 3% so we have a net gain of 2% TE.

.. I my case I am past peak TQ to the point  that my TQ cure is really beqining to fall off pretty fast; I am going to proabably better off changing the gear which will move me 7%  back down the TQ cure so that the net result is that I am putt more TE to the ground---when we get against the Aero Wall --ever little bit helps..depending how much I can clean the car up we are only talking 3-5 MPH in my quess. 

Bototm line TE just lets you compare at a selected speed either what you have already done or what you are shooting for---does nothing to tell you how much you are going to need!!!!!!!!
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

aswracing

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Re: Dyno Speeds
« Reply #19 on: November 01, 2007, 03:37:48 PM »
As the torque falls off past peak HP, are we better going with a 5% lower gear because at 5 % more revs. the eng torque is only down 3% so we have a net gain of 2% TE.

The scenario you describe is a physical impossibility. You cannot be at a 5% higher rpm than your hp peak, with 3% less engine torque, because that combination would result in more horsepower, not less.

Horsepower is just torque times rpm. Raise rpm by 5% and reduce torque by 3% and you have more horsepower. 1.05 x .97 = 1.0185. So to be precise, your scenario has 1.85% more horsepower.

The maximum rear wheel torque at any given rear wheel speed occurs at the power peak. You can't gain rear wheel torque by revving past the power peak and then gearing deeper to get back to the same speed. You'll have less rear wheel torque if you do that.
« Last Edit: November 01, 2007, 04:08:29 PM by aswracing »

Offline tortoise

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Re: Dyno Speeds
« Reply #20 on: November 01, 2007, 05:31:31 PM »
You can't gain rear wheel torque by revving past the power peak and then gearing deeper to get back to the same speed. You'll have less rear wheel torque if you do that.
But, as you pointed out earlier, gearing it a little short makes it a lot easier to accelerate to around your peak speed, and is way better than being geared too high.

By the way, in this month's Street Rodder, their tech guru, Ron Ceridono, says "a car will accelerate the hardest when the engine is at its torque peak". (I'm not making this up.)

Offline SPARKY

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Re: Dyno Speeds
« Reply #21 on: November 01, 2007, 06:06:32 PM »
ASW---I am refering to the thrust at the rear wheel--by using the higher number ratio you get a larger number at the wheel because of the larger gear multiplier--- vs gearing for peak torgue---you have a bigger number to the trans and rear axle---but loose it by the smaller rear gear multiplier---you can multiply torque---but not HP---bottom line---its all about what you can put to the ground and hook up.---
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline SPARKY

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Re: Dyno Speeds
« Reply #22 on: November 01, 2007, 06:12:35 PM »
Tortise---the statemet you quote applies to the same overall ratio---and probabaly does not necessarily apply to LSR cars that run way over 2---because of wind resistance.
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

aswracing

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Re: Dyno Speeds
« Reply #23 on: November 01, 2007, 06:50:36 PM »
ASW---I am refering to the thrust at the rear wheel--

So am I.

Quote
by using the higher number ratio you get a larger number at the wheel because of the larger gear multiplier---

Of course. Gearing multiplies torque. The more rpm you turn at the engine, the more gear reduction you can apply for a given rear wheel rpm, hence the more you can multiply the torque. I understand all that.

Quote
vs gearing for peak torgue---you have a bigger number to the trans and rear axle---but loose it by the smaller rear gear multiplier---you can multiply torque---but not HP---bottom line---its all about what you can put to the ground and hook up.---

Here's where you lose me.

Torque and rpm are interchangeable entities. Gear taller, you give up rear wheel torque but gain rear wheel rpm, and you do so by equal factors. Gear shorter, you gain rear wheel torque but you give up rear wheel rpm, and again, you do so by equal factors.

Because they're totally interchangeable, each of these two items, torque and rpm, are weighted the same in the horsepower formula. Horsepower is literally torque times rpm. They make an equal contribution to the performance because they're totally interchangeable. And they make absolutely equivalent contributions to the performance. So horsepower describes performance.

When you're at your power peak rpm, that's the point where the total combination of torque and rpm are at their greatest. This notion that you can run your motor past it's power peak rpm, and then gear shorter such that you get back to the same rear wheel rpm you had at the power peak, and end up with a higher combination of torque and rpm at the wheel than you had before, is patently false. If you could do that, you would be raising horsepower with gearing, because your total combination of torque & rpm would be higher on the downstream side of the gearing. Gearing can't raise horsepower, it can only change the mixture of torque and rpm that makes up the horsepower.

Bottom line, the power peak rpm of the engine represents the point where the combination of engine rpm and torque are at their highest. You cannot artificially create a higher combination by revving higher and gearing deeper.

If you're still convinced there's something to be gained by revving past the power peak and gearing deeper, give me an example. I can show mathematically that it doesn't work.
« Last Edit: November 01, 2007, 06:52:56 PM by aswracing »

aswracing

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Re: Dyno Speeds
« Reply #24 on: November 01, 2007, 06:59:39 PM »
Quote
But, as you pointed out earlier, gearing it a little short makes it a lot easier to accelerate to around your peak speed, and is way better than being geared too high.

Yep.

Quote
By the way, in this month's Street Rodder, their tech guru, Ron Ceridono, says "a car will accelerate the hardest when the engine is at its torque peak". (I'm not making this up.)

Wow.

Whenever someone has tried to make that argument to me, they generally argue that the car "accelerates hardest in any given gear at it's torque peak".

Which of course, is true, but misses the point. In the real world, we're not constrained to staying the gear we're already in. We have the option of downshifting and putting the motor at it's power peak instead. And when you do that, you accelerate even harder.

A very simple example that most people can visualize is to get two identical vehicles moving side by side, both at their torque peak. On one of them, floor it. On the other one, downshift and then floor it. It won't even be close. The downshifted one will run away.

Offline SPARKY

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Re: Dyno Speeds
« Reply #25 on: November 01, 2007, 07:44:23 PM »
If you have a dyno sheet---plot your own---I have done it with two different engs the first was more head constrainted than the current one so it had a flatter torqe curve---this new eng has more HP---but falls off much faster---on the spread sheet I am at he cross over point---next year I will know for sure if it works out in the real world---the first eng I was better of staying with the lower gear.  WE are not talking about big numbers---15-30' # difference on a BBC. I shift at 8 and am pull 70-71 out the back nowI hope to work it out so that I can pull the same with more gear.
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline SPARKY

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Re: Dyno Speeds
« Reply #26 on: November 01, 2007, 07:51:58 PM »
aws---Your own example prove my point---I am just downshifting the rear gear or tires-instead of the Trans---to change the FDR
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline SPARKY

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Re: Dyno Speeds
« Reply #27 on: November 01, 2007, 08:14:02 PM »
Sum,  RPM vs. TQ   What you say is true about them being interchangable---but when you put the non linear curve of the eng. Torque x by the overall ratios vs linear speed --- get some crossover one combo vs another combo at the same speed.  I you can pull both and one is falling off faster than the other-- one should try the combo with the most Tractive effort to try to accelerate. 

But as The Mayor has pointed out---its still VERY Important--- the 2 1/4 ET---the 60' of LSR--it still is a drag race-- it just happens to be for 4 miles with a one mile trap.
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline Sumner

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Re: Dyno Speeds
« Reply #28 on: November 02, 2007, 12:57:26 AM »
Sum,  RPM vs. TQ   What you say is true about them being interchangable---but..............................

I don't think I was the one who said that.

One thing I'm not familiar with that was said above was:

Quote
the power peak rpm of the engine represents the point where the combination of engine rpm and torque are at their highest.

I've never seen combining the engine rpm and torque together before and would like to know more about that concept.

Sparky I think I'm beginning to understand a little more where you are headed with with this.  Since in the HP/Torque formula we have 5280 that is the point where they are the same. 
 

Above and below that point and even through that point they typically are on different curves (angles) and thus are rising or going down at different percentages.  I think you are trying for gains by working in the area where the torque begins to fall off rapidly in the area where the HP is peaking or just past peak.

I made a spreadsheet today, but didn't have time to play with it and want to plug in some dyno numbers to see if I can understand this better.  So with the tractive effort are you trying to maximise thrust at what you hope will be your top speed??

c ya,

Sum
   

Offline isiahstites

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Re: Dyno Speeds
« Reply #29 on: November 02, 2007, 02:19:47 AM »
.

Sparky I think I'm beginning to understand a little more where you are headed with with this.  Since in the HP/Torque formula we have 5280 that is the point where they are the same. 
   

Sumner,

                I am pretty sure that number is 5252 rpm. Hp and tq always cross at 5252 and the forumla to figure out Hp is........

torque x rpm/5252

The constant 5252 is derived from James Watt's 17th Century definition of horsepower. One horsepower is equivalent to performing 33,000 pound-feet of work in one minute. If 33,000 pound-feet per minute is divided by pi (6.2832) multiplied by 2, the result is 5252.1008 rounded to 5252.

An example using the graph you posted

That motor makes its peak torque of 425 at 3750 rpm

torque x rpm / 5252
425 x 3750 = 1593750 / 5252 = 303.45 Hp at that same rpm

Scott