Have you considered a Fridgidaire intake filter? Top notch, frost-free!

cheers,
Ray Hull

 

Well, the good news is that everyone else is affected similarly. Hopefully, our engine management systems provide us with a little edge when the weather becomes unfavorable.

 

Hi Again All:

I have posted the analysis given below before, but it is pertinent here as it addresses the effects of weather on performance. Forgive me, or ignore the analysis, if you have seen it before. I think the points made are very interesting and, thus, worth posting again in the context of this thread. In this regard, the analysis follows the one given above logically and directly addresses the effects of weather on horsepower and related 1/4-mile performance.

I consider the issue of how Tesla Pro RR g-meter horsepower values can be used in explaining the ET effects related to SAE J1349 density-altitude (DA) adjusted FWHP differences. Some background, including a discussion of J1349, is needed before beginning the analysis.

The graphs I posted in post #108 of the "straight-line performance" thread show maximum all-loss RWHP of about 250 in third gear (with about 90 MPH implied). My Pro-RR-indicated average maximum all-loss RWHP over 48 passes, for example, is 239 at an approximate average of 90 MPH. This value implies an overall average percentage loss of .26462 = 1 - .73538 (239/325) given BMW?s claimed 545i FWHP. In this regard, five types of loss are possible, engine mechanical inefficiency, power train, or parasitic, inefficiencies (all mechanical inefficiencies occurring between the flywheel and the road), aerodynamic drag, altitude, and weather. For now, note that I have no reason to change the following value: 35 FWHP = Aerodynamic-Drag FWHP-Loss (see earlier ?snapshot? of aerodynamic-drag loss calculator on the "straight-line performance" thread).

The current protocol for horsepower measurement is SAE J1349 (i.e., SAE net) (revised 8/04 and effective after 1/1/05). J1349 assumes an average 15% loss from mechanical engine inefficiency and the following standard atmospheric/altitude conditions: 77F (or 25C), 0% relative humidity, barometric pressure of 29.235 inches-Hg (or 990 mb), and altitude = sea level (0). These assumptions imply a DA of 1962' and produce FWHP values that are as though related tests were performed at this altitude.

J1349 is meant to ensure that manufacturers? FWHP claims are comparable and accurate. Thus, it applies directly to engines tested using engine dynos. To obtain comparable results for engines tested using chassis dynos, the dyno output must be adjusted. For example, dyno output may not be adjusted even for the assumed mechanical engine inefficiency of 15%. Additionally, even if such results are adjusted for this factor, they generally are not adjusted for the parasitic inefficiencies, and are not affected by aerodynamic drag as are g-meters. Finally, note that J1349 requires corrections be less than 7% (+ or -) to be certifiable.

Probably the clearest way of showing how Pro RR horsepower values can be used in explaining the ET effects related to SAE J1349 density-altitude (DA) adjusted FWHP differences is to convert ?everything? to the J1349 DA of 1962?. I proceed in this fashion below in determining whether, and to what extent, my Pro RR maximum average all-loss RWHP values (238.729 versus 241.114) can be used in explaining the difference in the average weather and altitude adjusted ETs (see below) related to the 14 DAs (average = 1890?) encompassing my best 5 weather and altitude adjusted passes and my 14 lowest DAs (average = 910?). I am counting on averaging to wash out any confounding effects of differences in starting procedures, wheel spin, and etc. I proceed using the steps given below.

1. Calculate the weather and altitude adjusted average ETs using standard adjustment procedures and the difference to be explained.

Unadjusted Higher DAs? Average ET: 13.749
Unadjusted Lower DAs? Average ET: 13.710
Difference = Unadjusted Weather Effect = .039 = 13.749 ? 13.710.

Higher DAs? Average ET of 13.749 Adjusted from Average DA of 1890? to J1349 DA of
.....1962? = 13.762
Lower DAs? Average ET of 13.710 Adjusted from Average DA of 910? to J1349 DA of
.....1962? = 13.892
ET ?Swing? to be Explained = Weather Effect Difference Adjusted for DA
.....= .13 = 13.762 ? 13.892 = Unadjusted Weather Difference (.039) ? Effect of
.....Adjusting the Unadjusted Weather Difference for DA (-.169)

The altitude effect is zero since all of my passes were made at the same actual altitude of 1600?. Regardless, DA adjustment produces an interesting and appropriate result; the higher DAs produce the lower average ET?a reversal from what is shown by the unadjusted data. An implication of the existence of any significant difference in DA-adjusted ET values (e.g., -.13) is that the 545i?s advanced engine-management system cannot adjust perfectly for changing weather conditions.

Note that the CF for the higher DAs should be larger than the one for the lower DAs since, other things equal, FWHP is greater the lower the DA. As shown below in 3a, the Pro RR implies higher uncorrected FWHP for the lower DAs, specifically, 2.89 = 327.259 - 324.369. But, as shown later in 3d, J1349 correction predictably reverses the FWHP rankings similarly to the ET reversal noted above. Thus, the higher DAs end up with the higher FWHP by 3.963.

2. Determine the J1349 CFs using average weather data (or known DAs).

Higher DAs: CF = 1.023
Lower DAs: CF = 1.005

In general, CF = 1.18[(990 / Pd)(Tk/298 raised to the .5 power)] - .18 (Pd in mb),

where: Pv = water vapor pressure;
............Pd = Dry air pressure = [Air Density (D) - (Pv / (Rv*Tk))](Rd*Tk);
............Tk = temperature in Kelvin; and
............all other values are constants.

Ultimately, CF can be shown to be a function of DA.

The correction factor for the lower DAs is much smaller because 910? is much closer to sea level than 1890?. Recall that J1349 assumes zero sea level.

3. Under J1349, the CF is applied to an adjusted FWHP reading?where the FWHP reading ideally is obtained from an engine dyno. To use a CF with the all-loss RWHP values obtained from a Pro RR, one must eliminate the effects of the parasitic inefficiencies and aerodynamic drag. To use a CF with the results from a chassis dyno, one must eliminate only the parasitic effects. In my case, the CFs of 1.023 and 1.005 and related calculations, are applied/made as follows:

3a. Estimate engine-dyno FWHP reading by eliminating the effects of parasitic inefficiencies and aerodynamic drag from Pro RR all-loss RWHP values:

Higher DAs:

238.729* + {[238.729 / (1 ? (.175 (estimated parasitic inefficiency percentage)) ? 238.729]} + 35 (aerodynamic drag from above)))]
= 238.729 + (289.369 ? 238.729) + 35)
= 238.729 + 50.64 + 35
= 324.369 (which, for all practical purposes, equals BMW?s FWHP claim of 325)

*Pro RR all-loss RWHP value

Lower DAs:

241.114* + {[241.114 / (1 ? (.175 (estimated parasitic inefficiency percentage)) ? 241.114]} + 35 (aerodynamic drag from above)))]
= 241.114 + (292.259 ? 241.114) + 35)
= 241.114 + 51.145 + 35
= 327.259 (which exceeds BMW?s FWHP claim of 325)

*Pro RR all-loss RWHP value

Original Difference* = 2.385 = 241.114 (lower DAs) ? 238.729 (higher DAs)
Difference Given the Above Adjustments = 2.89 = 327.259 (lower DAs) - 324.369 (higher DAs)

3b. Calculate the constant HP values needed to overcome the engine mechanical inefficiencies and the related adjusted-for-engine-mechanical-efficiency HP values:

Higher DAs:

324.369 / (1 - .15 (J1349 engine mechanical inefficiency percentage)) ? 324.369 = 381.611 ? 324.369 = 57.24

Adjusted HP value = 381.610 = 324.369 + 57.24

Lower DAs:

327.259 / (1 - .15 (J1349 engine mechanical inefficiency percentage)) ? 327.259 = 385.011 ? 327.259 = 57.752

Adjusted HP value = 385.011 = 327.259 + 57.752

3c. Apply CFs of 1.023 and 1.005 to the adjusted-for-engine-mechanical-efficiency HP values from 3a:

Higher DAs: 1.023(381.610) = 390.387

Lower DAs: 1.005(385.011) = 386.936

3d. Subtract the constant HP values calculated in 3b from the results of 3c to obtain the adjusted for altitude and weather J1349 FWHP value:

Higher DAs: 390.387 ? 57.24 = 333.147

Lower DAs: 386.936 ? 57.752 = 329.184

Difference = 3.963 = 333.147 (higher altitudes) ? 329.184 (lower altitudes)

One of the implications of these calculations, which reveal the FWHP ?reversal? noted earlier, is that my car produces disproportionately more FWHP, on a corrected basis (i.e., performs disproportionately better), the less favorable the relative weather conditions. I draw this conclusion very tentatively since the values I am working with are based on numerous estimates. My conclusions necessarily are restricted to the effects of weather since, as mentioned, all of my passes were made at the same altitude (1600?).

3e. Determine the J1349 DA-related corrections in FWHP and the related Pro RR FWHP difference:

Higher DAs:

333.147 ? 324.369 = 8.778 FWHP correction

Lower DAs:

329.184 ? 327.259 = 1.925 FWHP correction

Pro RR FWHP Difference = RWHP ?Swing? Pertinent in Assessing the Pro RR Data
.....= 6.853 = 8.778 ? 1.925

4. Now, we can see if the Pro RR maximum average all-loss RWHP values (238.729 versus 241.114) at least partially explain the difference in the average weather and altitude adjusted ETs related to the 14 DAs (average = 1890?) encompassing my best 5 weather and altitude adjusted passes and my 14 lowest DAs (average = 910?). Recall that the difference is: -.13 = 13.762 (higher DAs) ? 13.892 (lower DAs).

The Pro RR FWHP difference is 6.853. Using the ?standard? heuristic that a 10 FWHP increase produces a .1 second improvement (i.e., decrease) in ET, the Pro RR value implies an ET swing of -.06853 = -.01(6.853). The implication of this calculation is that the Pro RR maximum average all-loss RWHP values explain about 53% (i.e., -.06853 / -.13) of the swing in the average adjusted ETs.

I also used a variety of online calculators to estimate the FWHP difference it would take to produce the swing in ? mile terminal velocities related to the adjusted ETs of 13.762 and 13.892. The average value produced by the calculators is approximately 12 FWHP. Using this value, Pro RR maximum average all-loss RWHP values explain about 57% (i.e., 6.853 / 12) of the swing in the average adjusted ETs.

The above conclusions also are tentative because of the inherent estimates. Nevertheless, it appears that the Pro RR data are able to explain a large percent of the average adjusted ET swing. From an overall perspective, I find it somewhat surprising that my analysis is completely consistent and has this much explanatory power. For example, all signs, reversals, calculations, and implications are logically related according to theory. Nevertheless, one issue remains?whether (a) theory fails to account for all pertinent explanatory factors, (b) the numerous estimates involved interfere with a proper determination of the Pro RR?s explanatory power, or ? averaging fails to wash out any confounding effects of differences in starting procedures, wheel spin, and etc. as I assume.

 

Hmmm, I will need to take some time to thoroughly digest your analysis... On the other hand, my original question had more to do with whether or not the performance difference between winter and summer temperatures in Phoenix is perceptible, or if it is just in my head ;-)

Thanks, Jon.

 

You are welcome Jon. Check the following part of post #10 above out. It directly addresses your issue--based on what precedes it for background. To understand what's below completely, you'll need to refer to some additional values found in post #10. Sorry, there is no convincing short and sweet way to get at what your are interested in. And, check out the weather effects on HP and performance in my last post above. In sum, it is not in your head IMO (the easy short and sweet way ).

From post #10:

But now, suppose that I made another 48 passes with the average early morning, before dawn temperature being 100 F--which can happen here in August. In addition, I am going to asssume 20% relative humidity (i.e., a dew point of about 50 F) and AS of 30 Hg. Note that these conditions also are highly possible in August in Phoenix. Under these conditions, my DA is:

Density Altitude Calculation

Your results:
Air Temp 100 (?F)
Altimeter Setting 30 (in)
Dew Point 50 (?F)
Altitude 1600 (Feet)
Density Altitude 4594.5 (feet)

Next, I use this DA to convert my performance averages to zero sea level and standard weather conditions and subsequently to 1600' to rid myself of the altitude effect.

Correct 1/4 mi. Timeslip to Sea Level

Your results:
Density Altitude 4595 (feet)
Uncorrected ET 13.74 (sec)
Uncorrected MPH 102.85 (mph)
Corrected ET 12.96
Corrected MPH 109.065

Correct 1/4 mi. Timeslip to New Density Altitude

Your results:
E.T. 12.96 (sec)
Trap Speed 109.065 (mph)
Measured DA 0 (feet)
Corrected to 1600 (feet) DA
Corrected ET 13.195 (sec)
Corrected Trap Speed 107.084 (mph)

Now consider these ratios:

13.752/13.195 and 102.755/107.084,

and multiply as follows to yield:

(13.752/13.195)(13.74) = 14.32 sec.
and
(102.755/107.084)(102.85) = 98.69 mph.

Thus, my prediction is that, under the assumed weather conditions, my average unadjusted ET and TV would be 14.32 and 98.69, respectively. These values clearly show the potential effects of weather as suggested by jmdhuse.

Adjustment of the above predictions for weather and altitude to 500' yields:

Correct 1/4 mi. Timeslip to New Density Altitude

Your results:
E.T. 14.32 (sec)
Trap Speed 98.69 (mph)
Measured DA 1600 (feet)
Corrected to 500(feet) DA
Corrected ET 14.139 (sec)
Corrected Trap Speed 99.979 (mph)

--which doesn't sound quite so bad.

 

But I swear my Stock Supercharged MINI was noticably faster in cool San Diego 40-50 degree foggy air than in 90+ degree sun. It pulled much harder...

 

It did pull harder. Your senses were correct. Check out my analyses. But, still the big issue is weather and its effects on air, not engine heat. Crudely, speaking my first analysis implies that my car, running in 100 F weather, would beat my car, running in 53 F weather, by about 5.5 car lengths in the 1/4. You can feel the difference, IMO, in two cars such that one will beat the other by 5.5 car lengths in the 1/4. such a difference might something like the difference in these two cars:

Chevrolet C6 Corvette Z51 CD 9/04 4.30 12.70 113.00 and
Pontiac GTO CD 1/05 400 400 3787 4.80 13.30 107.00

 

My 550 during the day (90 degrees) feels much more sluggish than at night (67 degrees). I'm sure it makes a difference in performance. Just wanted to give my non-technical opinion

 

Thank you Professor we ca always learn sg from you

 

I seriously think Znod should work for NASA