Video: Marauder Doing 145 MPH !!!

[Smokie]

See for yourself: FAST (http://www.mercurygallery.net/mmnet/data/500/248Dyno_Shorter.WMV)

[merc406]

Marauder's were doing 170 41 years ago. :rasta:

[gonzo50]

Was that torque of 359 lbs ft. on a N/A Marauder ?
I heard him say "that can't be right".

[martyo]

See for yourself: FAST (http://www.mercurygallery.net/mmnet/data/500/248Dyno_Shorter.WMV)

Remember, dynos have no wind resistance, so this is not "reality"!

[TripleTransAm]

Was that torque of 359 lbs ft. on a N/A Marauder ?
I heard him say "that can't be right".


Depending on the gear selection, or if the tranny is allowed to upshift during the dyno run, it can seriously fudge the peak number. I haven't seen the video nor do I know if they show the graph, but the curve would show the real peak and not the misleading "spike".

Dynos measure acceleration against a resistance of some sort, to obtain a value for torque at the wheels, which is then mathematically converted to show horsepower (hp= torque x RPM / 5252).

As the wheels are spinning up, when the tranny upshifts there will be a momentary "jerk" in the acceleration rate of the rear wheels. In the real world on the street, the jerk isn't seen at the wheels because the motor gets dragged down in RPM by the new gear ratio... or, if it's powerful enough to overcome the tire's grip, you get a chirp or bark at the rear wheels (just a momentary bark... the tires eventually grab and the engine slows to its new speed in the new gear).

On the dyno, there's probably not the same kind of load on the wheel as that seen when on the road accelerating during the upshift. So the drum gets 'jerked' in speed and the dyno electronics go "whoa, did you see how fast the drum accelerated during that very small interval of time?". And hence you get what seems like a momentary very high peak torque output recorded by the dyno, and the ensuing high peak hp number.

And Marty's right on the money: what slows a car to a top speed is aerodynamic resistance. It's been many years but I think the formula for energy sucked up at a certain speed is something like:
1/2 x Cd x FrontalArea x velocity^2
The top speed arrives at the point where the horsepower seen at the wheels is equal to the power being lost in aerodynamic drag (lots of it) and road friction (really small in comparison).


(the above is the reason, by the way, why 6-speed F-bodies see their top speeds in 5th gear. If you accelerate to *close* to the top speed in 5th and upshift to 6th, the car will decelerate to a lower top speed, since the horsepower being delivered to the wheels in 6th gear ratio at that RPM is less than what it takes to maintain the 5th gear speed... the car slows until the formula balances once again)

[Smokie]

The video is just for entertaiment purposes. The voice that says "that can be right" is me, because I know my car does not produce that torque.

Yes there was a spike during the second run due to transmission shifting, first and third run are quite real...or as real as you wish to believe a dyno run really is. :)

About the car being able to go 145 or not, Marty are you sure that it cannot ? ;)

[sailsmen]

Thanks Steve, it's nice when an engineer can explain technical stuff in laymans terms. :rock:

[martyo]

About the car being able to go 145 or not, Marty are you sure that it cannot ? ;)

Javier: I didn't say that all. All I am saying is that the dyno would not equate to the real world in terms of acceleration/terminal velocity.

[Smokie]

Javier: I didn't say that all. All I am saying is that the dyno would not equate to the real world in terms of acceleration/terminal velocity.I know Marty, the title was meant in jest, how are feeling my friend.:D

[SergntMac]

Depending on the gear selection, or if the tranny is allowed to upshift during the dyno run, it can seriously fudge the peak number. I haven't seen the video nor do I know if they show the graph, but the curve would show the real peak and not the misleading "spike".
Yup...I believe this has more to do with how we read a dyno report, that the spike itself.

There's nothing wrong with starting a dyno pull from a dead stop and measuring the car's performance from that dead stop to the redline in 3rd (1:1) gear. Problem is, you'll have so much 411 crammed into one graph, you'll never see what you need to know about your power. Even when a "peak" spike from shifting is caputred in the graph, the real 411 isn't from the peak, or evem the SAE "rear wheel" numbers. What is happening and when in the power curve, is your 411. Knowing how to read a dyno report is the key, and "spikes" can be dealt with, unless you just wanna win a few beers at the local watering hole.

FYI...When Jerry/Dennis/Paul run dynos for power tuning, the first step is to change the shift habits of the tranny to lock out any 2nd gear downshift under WOT. That way, once in car is in 3rd gear, it stays there, and the pull can begin at 2000 RPM, producing a clean pull and data without interferrence. IMHO, this is the best way to measure power and tune to taste. Still, you need to know where to look, for the real 411 from dyno reports.

[Smokie]

Yup...I believe this has more to do with how we read a dyno report, that the spike itself.


FYI...When Jerry/Dennis/Paul run dynos for power tuning, the first step is to change the shift habits of the tranny to lock out any 2nd gear downshift under WOT. That way, once in car is in 3rd gear, it stays there, and the pull can begin at 2000 RPM, producing a clean pull and data without interferrence. IMHO, this is the best way to measure power and tune to taste. Still, you need to know where to look, for the real 411 from dyno reports.Hi Sarge ! I was the last run of a long day and there was no tuning involved just 3 pulls without a break in between.
I don't take any of it very seriously, only my 1/4 mile time slips.:D

[TripleTransAm]

FYI...When Jerry/Dennis/Paul run dynos for power tuning, the first step is to change the shift habits of the tranny to lock out any 2nd gear downshift under WOT.


What an ingenious approach... I never thought about that. Makes sense... since you're going elbow-deep into the calibrations during the dyno session, it should be just a small extra task to mess up the tranny shifts first. Really cool idea.

I've always heard you get the best (ie. more reliable) results when pulling in 3rd gear anyway. I suppose it has something to do with the 1:1 ratio in most automatics (in today's overdrive manual trannies, it's usually 4th gear that is 1:1). Because of the torque multiplication provided by the gear ratios (ie. a ratio of 2.40:1 provides 2.40 times greater torque output but 2.40 times less revolutions per minute), a non 1:1 ratio during a dyno pull will add another unknown.

I think modern dyno s/w will take into account stuff like tire size and diff ratio due to the revolutions per speed that the operator has to provide (if he's worth his salt) because the s/w will want to know the relation between engine RPM and torque (to get hp). If you're in a non 1:1 gear ratio, that screws up that relationship.

[TripleTransAm]

The video is just for entertaiment purposes. The voice that says "that can be right" is me, because I know my car does not produce that torque.


Nice disclaimer! ;)

Seriously, I hope you didn't take any offense at my analysis of the results. I was just trying to explain how some operators attempt to pass those results off as valid, or perhaps try to "enhance" them by pulling in gears other than 1:1 without paying attention to the speed / RPM data that is required by most dyno s/w. Some even go so far as to crank the heater on the car to max and 'cook' the ambient temp sensor of the dyno, so the SAE corrected values show up much higher than they really are.

One case I personally know of (in the Toronto area) got a dyno result showing some 50rwhp more than the motor actually put out (unfortunately, said dyno operator / tuner also tuned the motor over the ragged edge just to get the nice numbers that would then be bragged about on the 'net... once the owner discovered what was going on, a quick retune to a safer tune and re-testing on a dyno showed more than the 50rwhp "loss" but at least the motor wouldn't self-consume...)

[Smokie]

Nice disclaimer! ;)

Seriously, I hope you didn't take any offense at my analysis of the results.Not at all Steve, I thought the thread title might provoke some curiosity and I wanted to have a little fun with it. I did post elsewhere my actual dyno sheets and I think 2 of the runs did produce numbers that are consistent with what I have done to my car and the resulting time slips.

I do wish that I had a true run from 2000 rpm's in 3rd gear, but that would have cost more than the $75 I paid, as Sarge said that requires telling the tranny electronically not to downshift....maybe next time.:up: Javier.