moroso calculator

rskrause · Post by **rskrause** » Wed Jul 09, 2008 10:10 pm

A chassis dyno is a good tuning tool. But it can't be used to compare one combo against another because the drivetrain losses are going to differ (and be unknown). Even you use engine and chassis dyno numbers for the same motor to derive a correction factor, the percentage loss will change with any significant change in the combo. IOW, do not even bother trying to convert chassis dyno to engine dyno horsepower.

Richard

greenhj · Post by **greenhj** » Wed Jul 09, 2008 10:14 pm

518 average wheel horsepower to run a flat 11. I doubt it,

Using your formula means I have 422.x at the tyres, its just not possible from the parts Ive used.

Maybe I should start selling my unsealed bonnet scoop as a 90+hp bolton and my trans/diff oil as "negative coeficient of friction oil pack"

John W · Post by **John W** » Wed Jul 09, 2008 11:41 pm

The Moroso formula only predicts the "observed" hp. If you want to know what the "corrected" # would be on the dyno, then obviously the density altitude has to be factored. And vice-versa, if you're trying to guesstimate an et/mph based on a corrected dyno #, then the actual weather conditions have to be similar to the correction standard before you see that et/mph.

steve z · Post by **steve z** » Thu Jul 10, 2008 12:04 am

my experiences in comparing the slide-rule to the dyno have been that the car usually runs very close to right-on the MPH and usually a little short on ET. just kinda figured the chassis set-ups and gearing were probably a little less than optimum. i'm at about 850' above sea level, and the correction factors are usually never higher than 1.05, and most times less.

widowmaker race engines · Thu Jul 10, 2008 4:29 am

hi again
rskrause you hit the nail on the head, we dont race dynos and drive train losses can vary so much combined with differances in drag from ane vehicle to another at racing trap speeds, that Its almost impossible to give an accurate et from hp & weight only. Heck I would bet the same vehicle with a differect ride height would et differently. Still the et & mph readings on the moroso are pretty close.
Has anyone ever found what loss would be expected when running say a powerglide & 9 inch, it would be interesting to know peoples thoughts.

Chargermal · Post by **Chargermal** » Thu Jul 10, 2008 6:38 am

mmmitch588 wrote:chargermal, how do you come up with 20% loss of H/P through drivetrain?
If a 3500lb car runs a T/H 400 trans & 9 inch rear that makes 500 hp & another
3500lb car runs exactly the same trans & rear that makes 1000hp, why would
one use 100hp for drive train & the other with the same drive train use 200hp?

The "20%" figure is an average on drivetrain losses for a street/strip car running a conventional converter, diff and gears.

Modern family hacks probably lose closer to around 17 %, older style auto trans boxes with heavy diffs and a lot of rolling inertia lose more (22%?)......if you were running a Dana 60 it might be as high as 27%.

A 1000 HP car MAY or MAY NOT lose 20% - it depends on the drivetrain, but generally stronger parts mean more inertial loss (heat through friction, and weight for strength) .

I just used 20% because it was about right for the type of car/ HP example I quoted....But which ever way you do the HP calculation....you can use 30% or 15%, the end result will still show that the Moroso is FWHP........based on accepted HP vs weight vs ET calculations, and real life track experience.

Chargermal · Post by **Chargermal** » Thu Jul 10, 2008 6:54 am

(The formula I derived from physics says average wheel hp = 197*weight/et^3 and plugging in 11 flat and 3500 lbs that gives 518 average wheel hp so if the Moroso says 520 hp it gives wheel hp, not flywheel/engine hp.)

Sorry to be blunt, but where did you get the "197" constant?

I ask because a "constant" for RWHP CANNOT BE DETERMINED, due to varying factors as Widowmaker has explained...

The accepted formulas for FWHP are:

Hale - HP = (mph/234)cubed x weight (lbs)

Fox - HP = (mph/230)cubed x weight (lbs)

Both the 'constants" (234 and 230) were arrived at by simply taking the results of counltess strip runs using the empirical data. (see link below)

The same CAN'T be done for RWHP, becuase the inertial losses vary to a FAR greater extent for every drivetrain. ITs IMPOSSIBLE to generate an accurate "constant".

Go here for a LOT more reading.

http://www.stealth316.com/2-calc-hp-et-mph.htm

Chargermal · Post by **Chargermal** » Thu Jul 10, 2008 7:29 am

asked this original question because someone on a local board has emailed moroso and claims they replied that it is RWHP being referenced.

Green HJ, a guy on a local Mopar board did the same thing , and got the same answer - I believe whoever is taking these calls has no clue...and is simply a sales rep or some such.

Moroso is based on Fox's formula...which is NET (at the fly) HP.

Why? - because the original formulas were not 'designed" to calculate HP, Rear wheel OR Fly -

Ill explain -

When the formulas were devised, FWHP was already known, from factory dyno testing, as was the weight.The idea was to calculate MILE AN HOUR from weight and KNOWN FWHP

So - AFter the MPH results were "plotted" on a graph with hours of testing with an accelerometer and track runs, the "230"constant" (which was a median position on the curve) was arrived at -

- it was simple algebra to reverse the equation to arrive at an APPROX FWHP.

Here's how -

Fox/"Moroso" - MPH = 230x (FWHP/weight)x cube root.

Reversed - we have FWHP = (mph/230)cubed x weight (lbs)

This is why the Moroso shows an appx FWHP - the calculations it was based on used FACTORY FWHP to begin with.

Mwilson72CAMARO · Post by **Mwilson72CAMARO** » Thu Jul 10, 2008 8:26 am

ijames wrote:I'm also a long-time lurker and now first time poster. Several years ago I wasn't sure myself so I went through the derivation and posted it on a turbo Regal website, www.turbobuick.com. If you assume constant acceleration (use s, v, a, t for distance, speed, acceleration, and time) then s = 1/2 * a * t^2 and a = 2 * s / t^2. Also, force = m * a (m is mass), work (W) is force times distance, and power (P) is work divided by time. That gives P = W / t = F * s / t = m * a * s / t or

P = m * 2 * s^2 / t^3

With m in kilograms, s in meters, and time in seconds, P will be in watts. Put in 1/4 mile for the distance and convert kg to pounds and watts to horsepower and I get:

P (hp) = 196.9 * weight (lbs) / (elapsed time (sec))^3

Note that that is the weight going down the track, with driver. Again, assuming constant acceleration then v=a * t, and using s = 1/2 * a * t^2 again and 1/4 mile we get speed (mph) = 1800 / elapsed time (sec). I took the 160 or so cars on the gnttype (another turbo Buick site) reader's rides page that run 13.50 or quicker and fit them to v = k / t, and got speed (mph) = 1356 / elapsed time (sec) [+/- about 2-3 mph for et's between 7 and 13.5 with no correction for tcc lockup] so the assumption of constant acceleration isn't that great here. As many people have noted, trap speed seems to be a good indicator of horsepower while et is very traction dependent, so what I do is use et=1356/speed and then use that et in the hp formula. That gives pretty consistent numbers for Regals. Cars with better aerodynamics get a few more mph for a given et so the "constant" should be different for them.

Man, Im lost! Id like to try and make my own spreadsheet but some of that math doesnt make sense to me.

67RS502 · Post by **67RS502** » Thu Jul 10, 2008 10:42 am

Chargermal wrote:
asked this original question because someone on a local board has emailed moroso and claims they replied that it is RWHP being referenced.

Green HJ, a guy on a local Mopar board did the same thing , and got the same answer - I believe whoever is taking these calls has no clue...and is simply a sales rep or some such.

Moroso is based on Fox's formula...which is NET (at the fly) HP.

Why? - because the original formulas were not 'designed" to calculate HP, Rear wheel OR Fly -

Ill explain -

When the formulas were devised, FWHP was already known, from factory dyno testing, as was the weight.The idea was to calculate MILE AN HOUR from weight and KNOWN FWHP

So - AFter the MPH results were "plotted" on a graph with hours of testing with an accelerometer and track runs, the "230"constant" (which was a median position on the curve) was arrived at -

- it was simple algebra to reverse the equation to arrive at an APPROX FWHP.

Here's how -

Fox/"Moroso" - MPH = 230x (FWHP/weight)x cube root.

Reversed - we have FWHP = (mph/230)cubed x weight (lbs)

This is why the Moroso shows an appx FWHP - the calculations it was based on used FACTORY FWHP to begin with.

So youre saying that the original for formula devised by the Mopar engineers
uses FWHP because that the only dynos they had back then.
This would be like using logic and facts and coming to a fact based conclusion from past events,
yet some still dont get it, even when a Pro Stock car runs faster then the formula using FWHP.

hsutton · Post by **hsutton** » Thu Jul 10, 2008 2:52 pm

67RS502 wrote:It has to be a well set up car for the #s to work.
Street cars with poor 60ft with tight converters and mild gears
wide powerbands (not peaky tight ones like a stocker) will
not see the et/mph the moroso calc gives because they
are not optimized.
But it does work, a good example was a stocker with a 355
making 532hp at 3150lbs running 9.90s @ 132, thats is
better (more efficient) then the moroso calc. (old Mopar hp formula),
which shows that it HAS to be a very well set up, efficient car for the
#s to work.

Another point about using the Moroso calculator is that the drag strip time slip has a speed listed that is no longer accurate. The average speed is NOT the 1320' speed. The first speed clock is 66' before the E.T. line and the second speed clock is at the ET line, making the average speed now a 1287' one, not 1320', like in the old days. To convert the new inaccurate speed use Larry Meaux's conversion factor of 1.007 to get the real 1320' speed before applying it to the Moroso Calculator which is flywheel power.

Barry Burch · Post by **Barry Burch** » Thu Jul 10, 2008 3:14 pm

.00426*mph cubed divided by weight equal hp
Damned accurate flywheel hp formula.

rustang · Post by **rustang** » Thu Jul 10, 2008 4:55 pm

Barry Burch wrote:.00426*mph cubed divided by weight equal hp
Damned accurate flywheel hp formula.

.00426 * 125mph^3 / 3100lbs = 2.68 flywheel hp

Chargermal · Post by **Chargermal** » Thu Jul 10, 2008 10:42 pm

So youre saying that the original for formula devised by the Mopar engineers uses FWHP because that the only dynos they had back then.
This would be like using logic and facts and coming to a fact based conclusion from past events,

Good point...and it should be remebered that these formulas started as an attempt to calcualte MPH........ NOT HP or ET.

This was the easiest formula to construct becuase:

- FWHP was known from Factory Dynos
- Weight was known from scales

.- ...and the "co-efficient" was calculated through plotting many many MPH results over the qtr mile on a graph,

Im not a maths student nor a physicist - but once a pretty accurate MPH formula was arrived at, reversing the equation can be used to calculate HP.

And because FLY WHEEL HP was used to arrive at MPH - FWHP is the result when its reversed using MPH and weight.

YES - the Co-efficient" is an "average" which is why Hales formula is better under 500HP and Fox's is better over, but basically it's ALL FLY WHEEL HP.

BEWARE - there are a PILE of "on line" calculators that use these formulas and then claim the to be RWHP - They are NOT

bigjoe1 · Post by **bigjoe1** » Thu Jul 10, 2008 11:19 pm

These things are only even close for stick shift cars, automatic cars are 3 to 4 MPH SLOWER that the same car with a stick. I have done this swap many times.

JOE SHERMAN RACING ENGINES