Engine/Transmission (1998.5 - 2002) 0-60 horsepower calculations

[ptraufler]

Here is the trouble, the wheel slip is important as at the start it is the big power waster, as the speed increases drag takes over and saps power. The formulas do not account for this at all. I guess you COULD do a "decceleration" test, going from a steady 60 MPH to say 50 MPH with NO brakes or engine braking to see the drag force. (I would go to 30 MPH but that would take some distance I expect!) This would be an additional force to add to the acc. calculation and increase HP. Wheel slip, well guess at it! These are all just "back of the envelope calculations". If I had to make a guess the drag force would be about 25% of the force required to accelerate the truck.

 

[mschoenheider]

There are a few problems with any equation based on times and weights to figure hp. First, the force due to air resistance will vary with the square of your speed, if you are going twice as fast, you will have 4 times as much air resistance. Second, any formula that you use the total time divided by the total change in velocity will give you the AVERAGE hp, not the peak hp numbers which people usually quote on this site.

By adding in another piece of information to the equation like distance (1/4 mile) you can calculate a more accurate hp number, but it is still not very close. Put it on a dyno, or don't worry about it, who cares how much peak hp a truck has, it's just a number that does not tell the real story.

Mark

 

[ptraufler]

Yes we did not talk about rolling resistance, static friction, aerodynamic drag, gravity, solar/lunar affects, and other less know issues! OK the physics class is dismissed for the day! Just drive the truck and enjoy it! (BTW a dyno is only a know mass accelerated by the vehicle over a time interval to figure HP, at least the aero drag is not an issue!)

 

[THerman]

I buy the 233 number with the assumptions made... .



I would tend not to worry too much about the drag coef. 's for this problem at first.



The biggest question I see is the assumption of 30mph for the average speed. To assume this, you are assuming A is a constant. We know that this will not be the case... . play with this number just a bit and the results will vary a lot.



I would bet that much more time would be spent above 30mph than below it, making the average speed higher than 30mph.



Just raising this to 35mph will give 273hp.



That is why the instantaneous averaging computers can work as well as they do... .



Weight(lbs)*Ave. Accel(mph/sec)*Averaging Time(sec) / 375(lb-mph/hp)



You take a two measurements very close in time, ie. 0. 1secs and do the calculation... . and you have instantaneous HP...



If you also measure rpm, you can then calculate torque...



Tod

 

[ptraufler]

The avg speed is used as we know the conditions at the start and end only, we have no other data to use! Given all the assumptions and data this is as close as we can get. The gTech thing will do more as it does something like this calculation over very small time samples and then adds them up to make a closer estimate of HP. I would assume that the gTech will determine the speed also along the way so it would be interesting to have a data set over a real run and see what is going on for sure.

 

[Steve St.Laurent]

I have never seen an equation to calculate power from 0-60 times - only 1/4 mile times and et's. I have about 450 1/4 mile passes on my truck, have dyno'd on 3 dynos (all 3 were Mustang 1000's), and have done a lot of testing with a gtech. IMO by far the most accurate and repeatable numbers have been going by trap speed in the 1/4 mile, #2 behind that is 1/4 mile ET, the g-tech is third, and very last is the dyno. You can see a comparison of times at the dragstrip with what the g-tech showed on the same run at https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=12515 . My best time is 15. 784@87. 97 mph. Based on that my hp is 377 by ET, 399 by mph. My ET's vary between 15. 8 and 16. 2 depending on conditions but my mph's only vary by a mph or so. Now the dyno numbers are all over the place. My first dyno run was on Scheids Mustang 1000 and dyno'd at 313 hp (that was running an original Powermax1 and 275 injectors) and at that time I was running 17. 3's in the 1/4 mile. I later changed out the Powermax1 for a Powermax3 and dyno'd on TST's Mustang 1000 and dyno'd at 309 hp - but my 1/4 mile times went down to 15. 8 . Hmmmmm - 4 less hp but 1. 5 seconds faster in the 1/4 mile, I don't think so. I later dyno'd on another Mustang 1000 (at Thunder in Muncie 01) and only dyno'd at 290 hp. So, I don't use or believe dyno #'s any more - JMHO. I use my track times to gauge my vehicle mods now and use the formula's to calculate power - at most going by mph the #'s have varied by 2% which is much more accurate than the other solutions. BTW, the g-tech shows I have ~390 hp too - but it does swing all over the place. You definately have to do what they say which is to do 5 runs in each direction, throw out the top one and bottom ones, then average the remaining.

 

[ptraufler]

Man I never knew so many people would be so interested in this! Math was never so popular! I guess if you tie in some diesel trucks into math things will be better.

 

[THerman]

Boy! I wish I could draw a graph quickly on this.



You can go down in peak Hp and decrease ET's on the 1/4mi.



IF, you widen the Hp curve. Your time in the quarter mile is a product of lots of things... . but just looking at the engine, the higher and flatter the hp curve, the faster you times will be do the the fact that your average (over the rpm range you use, this range is itself a variable that many things affect) Hp has now increased... .



For an extreme example an engine with a flat curve making 300Hp from 500rpm to 3000rpm will stomp the same vehicle that topped out at 350Hp at 2500rpm but was below 300Hp below 2300rpm and above 2700rpm... . IF most of the run was not in this rpm range... .



Does this make sense? Hard to describe without graphs... . at least for me... .



Think of the area under the Hp curve..... the larger the area, the better overall performance will be.



Tod

 

[Steve St.Laurent]

Makes total sense - only problem is that I have the graphs and they look basically the same. Roughly the same curve - just the entire curve moved up or down.

 

[THerman]

Steve,



I don't know what to say... I don't have any experience with dyno's at all... . just alot of engineering background... .



You may be completely correct on the repeatability of the dynos...

which might explain some of the wild hp gain claims of some of the vendors... .



It would seem to me that the dynos would be subject to air density, temp variations as well as changes in the drag coef. of the bearings in the dyno, and I could go on and on...



I just got drawn into this discussion and found it interesting... . love doing the math exercises in my head...



Boy! Just realized that I AM sick!!!



I have to say this for all the non-engineers out there... .

Top Secret!!!---Just when we think we have everything defined... . it gets built and doesn't fit the model... . Almost all models are adjusted to fit what is found experimentally!



I guess what it boils down to is that we are not the Gods we tend to think we are!!!



I'm also jealous that I can't get MY wife to let me spend enough money on my truck! I sold my '69 Mustang to buy this truck... At least I should be able to bomb it 'til it will outperform the 'stang!

 

[ptraufler]

I still would think the dyno would be the most repeatable measurement. The only thing would be the poeple running the test and any changes to the machine due to wear/use. The local conditions for the atmosphere will change what the engine produces but I do not see the dyno being affected by this. (The correction factor for temp. , air pressure, density SHOULD correct the actual readings from the unit. ) I would think a direct connection to a dyno (not the wheel interface) would be the best of all. Just my $. 02 worth and yes I to am one of those engineers. (Aerospace)

 

[THerman]

I would agree that the direct connection to the dyno would be the best set up for consistant results.



On the chassis dyno I would tend to wonder about the affect of all the possible variables... especially the human ones.



The temp, density I would expect to change things some due to the drum spinning this fluid (air) up... I don't have a real feel for the extent of these variations...



I would also expect the clamp force(truck/vehicle to drum) to also affect things some.



And would different airspace change things at all? (ground clearance of the vehicle).



Let preface this by saying I have ZERO experience with these dynos... .



Just brainstorming out loud.....

 

[DiTrani]

While the math appears to be correct, what you are calculating is average HP, not peak HP, which is the number everybody uses to describe their power. The G-Tech thing is able to make the calculation more correctly because is can measure instantaneous acceleration (with an accelerometer), pick the highest value, which will indicate peak HP when the weight of the truck is know. Just knowing the an ET can't give you peak HP.

 

[ptraufler]

Yes this is an average HP, we have no other information to make any other calculations on. This is a simple only good for comparing one run to another NOT engine tuning.



The dyno's I have seen had a large steel "drum" that the wheels rolled on and the machine knew the rotating mass of the drums and measured the change in revs of the drum over some time period. Very little air would be moved and I would say that the affects of any atmosphere changes would be nil on this device. Now as for the clamping and holding the vehicle in place that would be some affect.



I'm still shocked that this thread is so popular!