American Dynos

Virtually no comparison.
Drags are loaded with variables with few, if any corrections.
Dynos are loaded with corrections with few variables.

E

 

Well that settles that then. Just the answer I was gunning for.
Bad launch, crap tyres, missed gear, IAT's and air pressures (as well as many other factors) can lead to different outcomes at the drags.
Different dynamometers, operators, IAT's and air pressures, corrections (as well as many other factors) can lead to different dyno results.

Definitely apples and oranges- not all people want to know how a car behaves at WOT on a straight road, as this is one measure of one aspect of a car's performance. WOT power is irrelevant when exiting a slow corner on a circuit. Likewise a dyno readout does not give any allusion to 'real world' driving - think of your 1400HP Big single supras which have a dyno readout which is top RPM peaked- almost exponential looking. Definately not a grocery getter, and no use on the drag strip either, as you want area under the curve for 'usable power'.

TL;DR Each 'measure' is open to its own shortcomings in accuracy and repeatability, and each method is best suited for testing different aspects of a vehicles performance.

 

Some drag strips are built below sea level and some are built above sea level and obviously the weather changes all the time so comparing results from one strip and even one run to another is unreliable.

A calibrated dyno with an accurate weather station and the correct power correction applied will allow you to compare the dyno results of engines tested at different altitudes and weather conditions. Tampering with the weather station readings and/or applying the wrong power correction will allow the dyno operator to manipulate the results.

Comparing peak HP figures just tells you which engine makes the most HP and nothing else about the engine. If you are building an engine just for peak HP dyno competition then the only figure that is important is peak HP. If you are building an engine for any other purpose then you will be more concerned with the average HP/torque throughout the working rpm range than the peak HP. In most cases you will have to sacrifice peak HP for higher average HP/Torque.

The Engine Masters competition uses the average torque between 3000 and 7000 rpm to determine the winning engine.

 

Ok, I know **** all about dynos or about drag racing, but I'll ask a couple of questions...

It's obvious that a car NEEDS a certain amount of HP if it weighs X amount and crosses the line at a given speed, but surely if the launch is ****ed up, tyres are crappy, gears are missed etc, the car won't reach it's potential at the other end...

So wouldn't it be safer to say that the car ran 100mph, so therefore it has AT LEAST a certain amount of power, because no run is flawless and it's possible that the car has more in it?

Nem, how is it possible that a dodgy start and a missed gear will result in the same MPH over a 400m stretch? It doesn't make sense to me.

What Nem is saying about 1/4 times being a good indication of power does, though. A car needs a certain amount of power to be propelled to a certain speed over a certain distance, so the strip doesn't lie. If anything, it perhaps result in a lower HP calculation than the car actually has.

 

Because mph is measured in the last 50 meters of the track. I can start scanning and posting timeslips if you like. The only time the car trapped lower was when it ran on 5 cylinders it lost 5-7 mph as a coilpack connector came off mid track.

 

I too am no expert, but think about it laterally: Any car will reach its limit sooner or later, but one of the questions to ask is whan this 'limit' might be reached?
This could be aerodynamic limits such as 'drag', engine torque to overcome drag, gearing to allow useful engine RPM to achieve speed at desired peak power RPM, vehicle weight etc etc etc.
I don't think a TT would reach its trap speed 'limit' on a 1/4 mile track. Nor would a NA. Nor would a ferrarri Enzo. Likewise a public bus with perhaps 400HP would not show a representative 1/4 mile time die to the fact that is its, ... well... a bus. You may get accuracy between busses, but not between a bus and another make of vehicle.
Limit of the vehicle may be reached on an air strip, or long, flat desolate stretch of outback road. Underpowered cars may very well reach their limit on a 1/4 mile track.

So, IMO, linking HP to trap speed seems like it hasn't eliminated enough variables to be a valid measure.

 

That's what I am saying, surely a car can't reach it's top speed in 400m, so if the start is bodged, surely the finish would be?

Not doubting your time slips, Nem, I just don't understand it.

 

If you screw up the first 10 meters of the start then you only have 390 meters left to get your good run in and put the power on the ground therefore the speed achieved at the end only represents ~390 meters of acceleration.

If you miss a gear along the way that's another few meters of ground lost.

It's basic school level physics & we ALL should know enough to know there is no way in hell anyone can say a car will reach the same speed at the end of a given distance regardless of how it is operated along the way.

I have slips to show on the same day my own trap speeds varied by more than 10kph & there was nothing altered on the car.

Post as many time slips as you like grasshopper it's not going to change the laws of physics, a messed up run nets a lower trap speed END OF STORY.

If you only have tyres capable of transferring ~400HP to the ground then you get a result worthy of that regardless of the fact you might have a ~2000HP engine. seems to make sense to most of us, I feel sorry for those that can't see this.

 

Fact of the matter is you can stall off the line, restart the car and run a 40 second pass but still have within 2-3mph trap speed of your best run, go out and try it. Trap speed is measured by sensors 50m(or thereabouts) from the finish line to the line itself. It is not a radar gun measuring your speed like some people like to think.

Until you realise that an engine will make different power at different altitudes, so yes it is a fair comparison.


My dads R33 went from 13.0 @ 127MPH wheelspinning all of first,second and third at the drags, then on MT Streets ran 11.30 @ 128MPH. Wheelspin, bog, etc MEANS NOTHING TO YOUR FINAL TRAP SPEED. The only time my trap speeds were affected as i said, was when my car dropped a cylinder(and therefore lost a lot of power) mid track. Before you try and act like you know it all mungyz go out and read up how MPH is measured and how it works because to me it sounds like you have no clue.

To everyone reading this, i couldn't care less if you don't believe what i write, it means nothing to me really. All i'm saying is go out and try it for yourselves you will then see who is right.

People can wank on about how their cars have "11tybillion rwkw" but when a car with less power on the dyno out traps and tears you a new a'hole down the 1/4 they always have some ricer excuse to make themselves feel better. Leave the "theory" at home because it means jack shit when you are lined up at the xmas tree

 

IS that altitude or attitude ?

 

That means nothing. The analogy is pointless.
You still doing a 400 meter pass arent you!!! All that means is youll have a rather shitty reaction time on the slip eh!!!

E

 

Would be exactly the same 10m down too, i've seen it more than once. 180SX tried to get on the 2step and stalled 3 car lengths off the start line. Still ran 115MPH which was the same as his best run.

 

Give it away man :rofl:

What you are trying to say is physically IMPOSSIBLE

Quit trying to have a go at me personally because I disagree with something you are saying that simply is not true or even remotely plausible.

I know where & how the trap speed is measured so please do us a favour and put that one aside.

I've done just as many if not more runs at the strip than the typical keyboard hero so put that one aside also.

Seems to me like your posts towards me are loaded with attitude about the power output of my car not being what I claim it is - tell me what the power output of my car is then please - just so we all know what YOU are so cranky about

Would you like for me to invite some of the best drag racers from Australasia to make comment on your posts here or would you like to concede that a drag strip can not possibly ever be as accurate in measuring actual power as a decent dyno?

Any fool can see what you are saying so forget that we are ALL well aware of your points - it's just that you are wrong & can't see it & can't see where exactly you are going wrong :zlove:

Cliff notes:

A car needs a certain amount of power to cover the qtr mile in x time at y speed = true 100% accurate statement.

The amount of power a car has can be calculated by using the trap speed at the end of a qtr mile run & the weight of the car = BULLSHIT you will only get a rough idea of the power it managed to throw down for that particular run on the day. It may be FAR LESS than the power the car actually has but NOT MORE (unless it' a munted calculation).

None of this is an excuse for any lack of penis size for my own car as I actually prefer circuit work & do just fine overtaking people on the straights lap after lap.

Physically impossible to have the same trap speed if you have consistent power output but loose acceleration due to wheel spin or missed gears etc.
Sitting at the start line of a few seconds wont effect trap speed, wasting ground rolling along while fumbling for another gear will.

Same day, same track, same car with no adjustments made I had 174kph & various in between up to 183kph - any fool can see that is NOT the same trap speed :rofl::rofl::rofl::rofl::rofl::rofl::rofl::rofl:

 

So at how many metres did he reach his terminal velocity of 115mph.?
That must be the max acceleration he can achieve. From then on its wind out.
If we extend that scenario to him starting at 50m down the track he would still get the same trap speed of 115mph.?
Take that to a further extreme to get a clearer view, 100m starting point. would he still get the same trap speed?

Inertia mass of the drive train to the tyres will give a constant acceleration for constant variables. eg fuel, air, tyre type and gear ratios.
A car does not have unlimited acceleration and therefore has a peak performance.

I wish I could remember my physics formulas from high school for acceleration, speed, and velocity, and then be able to calculate approx. HP from a given mass.(inc driver and his lunch)

 

If we start adding more to it say 50-60 metres out then that is a lot off the total track length. Never seen a car stall or anything that far down. 100m down no chance iy would tun the same trap its 1/4th of its total length taken away.

Also mungyz you mentioned getting drag racers to sign up and prove me wrong ? Do it.

 

Brace yourself for a hard landing cowboy, that's a pretty tall horse you're sitting on there.

Look up Arthur Coles on Facebook - he won the nightspeed dragwars 2WD turbo class this year & was laughing his ass off at your logic this morning when I was talking to him. Don't get all cry baby if he is very short with you.

Robbie Ward from RIPS will also tell you straight off the bat with no mucking around trap speed is significantly effected by the quality of the run.

Some of the guys here have already tried to tell you but you refuse to pay attention and learn.



Let me make it clearer for you:

Two cars exactly the same side by side on qtr mile, one misses 1st to second change and takes two seconds to recover. In that two seconds the other car continues to accelerate & gains another 25mph.

The car that did not miss a gear will trap a higher speed, why? because the car that missed the gear is still moving along the track decelerating & chewing up the distance it has left to accelerate.

If the two cars are the same it is IMPOSSIBLE for the one that missed out on that period of acceleration to achieve the trap speed the other has.

Harry Potter IS NOT REAL! there is no magic fix for screwing a run IT WILL net a slower trap speed.

It makes no difference how many runs you have done if you do not understand the basics of what is going on you have no business telling others fairy tails about magic numbers that don't change even if you mess up the run.
That's why they have the MPH measured dude!!! to show how you went in both time and speed.

Gearing: If you change the diff from say 3.7:1 to 4.1:1 you increase the amount of torque available at the wheels, torque is force times distance.
Therefore more force at the same radius for the same mass over the same distance gives you a faster speed at the end of the distance.
That's why your car pulls harder in first gear than it does in second (wheel spin aside) YOU CAN NOT CHANGE THESE LAWS MAN!!
People a thousand times brighter than you will ever be figured all this stuff out for us, all we have to do is read & understand.
Try doing that rather than having a go at those who point it out to you.

Or would you rather swing cocks about? my cars faster than yours, my car has more power than yours, your cars ugly............. come on man honestly

 

Ha i knew it would end up like this. As the person that made the drag strip comment to begin with i meant:

If you have a time slip and a dyno chart together, you can get fair idea of what the car can output. It will be obvious if either of the methods are making far fetch claims. This was in relation to street cars too as per the spirit of the thread (or how i interpreted it).

In reality both methods have variables that will effect an engine's performance, but this kind of gives you an average right?

 

Out of curiosity, tell me, what did you run ET and trap wise. Then what power did you make? If you have a time slip even better

 

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