mark kibort

You mean "torque" at the wheels, AFTER the gear box AND at any comparitive vehicle speed.

Hey, I did have a faster time than Mark A had with the old "Estate" in our lemons races, albeit, very close though.

mark kibort

So this is where my original question on the other "Battle" came into play. Glen got it, and we were narrowing it down, and then someone brought in a hired physics Gun to try and dispell a genuine measurement of energy use over time, a Watt-second, or a Joule, or what I ended up kind of coining, a HP-second.

The HP-second is not a bad way to look at the HP curve for max performance, because it really takes all into account. averages done really do the job (integration) because the time spend in the higher rpm is longer, thus will have a weighted effect in a wheel to wheel race. plus, aero drag is greater at any higher speed too, and it goes up with the square of velocity.

So, in the end, shift points and comparing HP curves for which car will be faster, (all things being equal) is easy to do with HP curves. for shift points, get two equal points based on gear spacing. for more over all power, use HP-seconds, or take the average over the geared shift point spacing. in reality, the curves shown above all point to the higher HP engine having an advantage everywhere, but maybe for a second or so at the start of each gear, and possibly from a standing start, but that is an entirely different discussion.

acceleration = power/(mass x velocity) acceleration is proportional to power, and is inversely proportional to speed.

mk

IcemanG17

MK
I did have "FTD" (albeit a slow one) at the end of the day Saturday at our 1st race!!! Of course both "marks" were a couple seconds better on Sunday before the engine blew

However MK did have the single best lap at Sears...one of the fastest of the whole race....I think only the V8olvo with their best driver was faster... We did manage 173 laps on Sunday....only Eyesore and V8olvoi did more with 175 a piece!!! Not bad considering we had overheating problems and weren't pushing hard....

Z

"Best" depends on the application. The best is the one that has the greatest area under the curve, for the range that it's used in the most. That's also assuming that both cars are geared the same if trying to make a performance comparison based on dyno charts. Even if gearing were the same, one of the problems with trying to make comparisons using area under the curves the way that it was above, is that it only compares what would occur in first gear in a drag race. Once first gear is over with, neither car is ever back down in the low RPM area again, so what happens there is irrelevant in every gear beyond that. Here's the RPM data of the G-Tech runs of both of the cars. After about the first 2 seconds of first gear, neither one of them ever gets to below about 4,250 RPM ever again. The data also shows Andrews lower overall gearing in each of the three gears, meaning he'd have greater torque at the rear wheels due to the torque multiplication through the drivetrain, even if both engines were making the same torque at comparable points.



A more accurate assessment of the engines would be if the area under the curves for each subsequent gear was calculated, and the sum of all of them them up until the maximum speed reached was compared. Basically use the chart Andrew posted for first gear, and then a chart more like the one below for 2nd, 3rd, etc., add all of those area values together, and compare those final total area numbers.



So to compare your car to a 951, you pull off four plug wires and only use four cylinders?

Don't forget that the centrifugal car has an automatic transmission, with higher drivetrain losses than the twin screw car with it's 5-speed. The centrifugal car is also an S4, compared to the twin screw being a GT, so there are differences in the basic engines to start with as well.

Dyno results can mean a lot. When all things are considered and interpreted correctly, they can make it an awful lot easier to win an actual race. You are right about the race being the real objective though. I have yet to see the hot looking girl give the trophy and giant check to the guy who won a bench race, or who's car may have seemed to feel faster using the seat of the pants method.

Maybe the higher torque down low vs higher horsepower up high issue can be clarified a little more by showing examples of each scenario.


High low RPM torque and low high RPM horsepower:


Low low RPM torque and high high RPM horsepower:

smith 928

This is getting good

ptuomov

Out of curiosity, what's Anderson's car's average wheel hp between the shift points? With 2600 lbs he'll for sure be faster than any of these STREET cars we're discussing here, but I am just curious.

Also, since this has turned into a dyno bragging thread, I'll jump in. Anyone with a higher average hp between **** points than mine? I am eyeballing 540 axle hp between 4400 and 6600. ;-)



Of course, the above is from a tuning session with a non-standard dyno (Dynapack) with many things going on. The car will make more than 600 peak and more than 500 average axle hp no matter how I slice it, though.

I'll try to hike to Malden one of these days to get Dynojet data file just so it's comparable. Will probably have to wait until John (Speake) and Niklas deliver the new custom EZ-K software, though.

GlenL

Please use search.

(Torque!)

AO

Thanks Z, That clarified is for me. I should have looked at the RPM range we're using. Instead, the range I had choose was somewhat arbitrary.

Now it's time to up the boost.

mark kibort

Actually, its true, after 1st gear where there can be debate on actual power or torque, or really "forces" applied to the wheels for a few seconds, after that IT IS NOT GEARING that will give a unconditional advantage, it is average HP or Hp-seconds you can put to the wheels. with gearing, there is overlap, so it really depends on the range of speed you are operating at. in otherwords, just before the 1st gear shift, any two gear sets can have an advantage over another. If your top speed in a 1/4mile run might be 118mph, you might want the 2.2 :1 gear set to have better overall power to the wheels and therefore torque AT the wheels overall. if that top speed based is expected to be 100mph, then the 2.75 gear box might be best, just as it might be best if the top speed might be expected to be 140mph.

The graph above, shows a little bit of the trade offs.

If you use average power over a RPM range that will be used, you are 95% there as far as being truely correct. peak HP doesnt do it, and I have video racing examples to show why that is true. average HP over any range of speed is certainly the closest way to approximate comparitive performance in reality.

mark kibort

Yep, he was in the 490rwhp average with his last dyno run.

to your point, i was racing the 420rwhp S2000s with blowers , and with their peaky HP curve, (and flat torque curve ) I would actually not only hang with only 370rwhp, i would out pull them overall in each gear. why??? HP-seconds were greater than the peak hp would first indicate. or looking at aveage HP , I was near 360rwhp and they were only near 350rwhp AVERAGE, over the cars RPM shift point range.

want to see the drag races, the are on my videos on youtube. Sears point '08, when the stroker motor first went in. first race day with it.

mark kibort

+1 !!!!

mark kibort

There is a tremedous argument in favor of using average HP. it solves 95% of the problems here .

andy-gts

I look at it as such, I spend the majority of my driving under 5000 rpm. I would think you would need to calc just the area under the curve you really use. bench racing is just that. I would think the murphy ride would "feel the most powerful and fastest if you were always driving very high in the rpms. otherwise the twin screw, stroker etc would feel the most powerful when driven . Now adding a centrifugal to a stroker....HMMM the best of both?

I love reading everyones input because I don't know physics like you guys do and your opinions are really cool to read .

anonymousagain

Side questions to the shift points "Z" posted:

1) Murph's 1st gear shows ~6350 rpm - how did he get it to shift that high in 1st, when it seems most auto's shift much earlier than that ? Search of past posts suggests 1-2 shift somewhere around 5600rpm +/- 200rpm ??

2) 3rd to 4th is only ~6k rpm - mis-shift? or already in "D"?

3) Conversely, it looks like Andrew short-shifted to 2nd (wheel spin?), hit the rev limiter in 3rd, but overall maintained a lower rpm floor of ~4800rpm vs- Murph's 4250rpm ==> doesn't this suggest that Andrew's GT would be better suited for a CS setup? and an AT to a TS?

[not touching CS vs- TS variables like cost, install complexity, aesthetics, etc, just the data shown here]

ArthurPE

the only way to anaylze this is the convert rev/min to rev/sec and integrate torque over a given range...
this will yeild W/t or P

HP-sec, etc., are useless

but as someone said, run them side by side and all doubt is removed...

btw: you don't need a calculator to integrate an exponential
int(x^n) = 1(n+1) x^(n+1)
example:
int(3 x^3) = 3/(3+1) x^(3+1) = 3/4 x^4
check: deriv(3/4 x^4) = 4 3/4 x^(4-1) = 3 x^3