The 2011+ Mustang Thread

[SLOWHITE]

http://www.motortrend.com/roadtests/...rformance.html

The rusults aren't suprising. I just wanted to see what they said about previous GT500s only being in the high 12's. Now all of the sudden they have a 12.4 GT500 they are talkin about. Not doubting it can't do it, but from what I remeber all the GT500's were 12.7-12.9 or only a tenth ahead of an SS on head to head test. Oh well, f,ing motor trend.

[syr74]

After a quick glance here is a link to a guy who runs his own dyno at this bike shop, and his explanation of why bikes, cars, etc. typically dyno higher in the 1:1 gear.

http://www.bishopsperformance.com/dynoinfo.htm

Again, there are no absolutes and there are a lot of things that can change this with some consistent exceptions (older Mitsu Evo's often dyno better in third than in their 1:1 fourth gear for example). But, more often than not, a car will dyno lower in any gear lower than the 1:1 ratio we are talking about here.

I found two examples on the internet, using cars which I know typically dyno better in third, fourth, or fifth. In the first, here are some guys on a MB forum talking about their C63 Mercedes dynoing better in fifth (which is their 1:1 gear) than in the lower fourth gear (so long as the top speed limiter is removed of course, a C63 would bump into the limiter on a fifth gear dyno run otherwise)

http://www.mbworld.org/forums/c63-am...results-2.html

........and here are some Evo guys talking about how their cars dyno better in third than in fourth even though fourth is their 1:1 gear.

http://www.socalevo.net/forum/index.php?topic=86304.0

However, as I said earlier, the Mitsubishi example is more often the exception than the rule. Most cars, bikes, etc., dyno best in the 1:1 gear.

[mrray13]

Originally Posted by syr74

This is a common misconception, but it is still a misconception...I'll explain. All a dyno sees is how fast your tires are spinning the dyno roller and the information it gets from the spark-plug lead. In other words, it knows how fast the roller is spinning for a given rpm. When you dyno your car, in what gear is that dyno roller going to spin the fastest for a given rpm, fourth of fifth? Put more simply, in what gear is your car moving at the fastest speed for a given rpm? Typically that is fifth gear which, in most cars, is a 1:1 gear ratio. Since virtually no dynos are designed to account for gear multiplication they simply cannot take that variable into account if you try to dyno your car in a lower gear.

I have seen examples where a car has dynoed higher in fourth gear than in fifth, but typically something else was afoot when that happened (ie: something was wrong with the car or the dyno, fuel cutout causes a problem, etc.) or fifth gear was not a 1:1 ratio (or close to it) in that car.

Just a quick observation...if a dyno only worked by the drums speed with engine rpm, then why is it I make peak power at ~135mph, and apx 6300rpm? At 7k rpm, I'm at 155mph, yet my horsepower drops off about 14-18hp (depending upon dyno). By your definition, all cars should be making peak horsepower at max rpm in the gear that gives them top speed. Correct? That is what you are saying in the bold section of your quote above.

Yet, in my gear closest to 1:1, 4th, I lose horsepower well before I reach top speed. Yet, in a gear with a steeper ratio, 3rd, at ~ 107mph and ~6300rpm, I'm making almost 20 more horsepower, torque is about 8lb-ft higher too. So how is my car making more power at slower speeds then it is capable of? In third gear, my car tops out around 117mph or so, at 7krpm. I lose about 13 hp from 6300 to 7k in third.

[syr74]

Originally Posted by mrray13

Just a quick observation...if a dyno only worked by the drums speed with engine rpm, then why is it I make peak power at ~135mph, and apx 6300rpm? At 7k rpm, I'm at 155mph, yet my horspower drops off about 14-18hp (depending upon dyno). By your definition, all cars should be making peak horsepower at max rpm in the gear that gives them top speed. Correct? That is whay you are saying in the bolded section of your quote above.

Yet, in my gear closest to 1:1, 4th, I lose horsepower well before I reach top speed. Yet, in a gear with a steeper ratio, 3rd, at ~ 112mph and ~6300rpm, I'm making almost 20 more horsepower, torque is about 8lb-ft higher too. So how is my car making more power at slower speeds then it is capable of?

Read my other posts, including the most recent, I never said that all cars dyno higher in the 1:1 gear I said that the same is the status quo and that if that is not the case there is a variable leading to that, and there are a lot of variables that could lead to that. As for your other comments, If the dyno has more information than drum speed and the ignition readings it is getting from the sparkplug wire lead exactly where do you think it is getting this information from? (actually, to be fair, there are dynos which use software that is supposed to compensate based on more detailed info entered by the operator, but most don't)

There are a lot of reasons why what you cite as happening with your car can happen, some of those reasons pertaining to the dyno, some pertaining to the car, and some to both and there is no way to cover them all here.

[ULTRAZLS1]

This engine will be SAE certified. Any dyno showing more power than 412 (in relation to rwhp losses) is just a testament to the efficiency of the driveline in the mustang and/or user error/calibration/dyno discrepancies. Nothing more...end of story.

I have seen dynos of ls3 camaros in the 390's...I dont go around nut swinging saying that camaros are under rated. I have also seen dynos of the camaro as low as the 350's. I dont go around sayin they are dogs. Common sense people cmon now.

[syr74]

Originally Posted by ULTRAZLS1

This engine will be SAE certified. Any dyno showing more power than 412 (in relation to rwhp losses) is just a testament to the efficiency of the driveline in the mustang and/or user error/calibration/dyno discrepancies. Nothing more...end of story.

You sure about that? You do now that the 2010 Mustang was not rated under the new system but under the old SAE net standard, right?

Originally Posted by ULTRAZLS1

I have seen dynos of ls3 camaros in the 390's...I dont go around nut swinging saying that camaros are under rated. I have also seen dynos of the camaro as low as the 350's. I dont go around sayin they are dogs. Common sense people cmon now.

Seems to me that the bulk of this conversation is about how and why dynos do what they do and not about who is or is not under-rated.

[76z28]

GM must have something coming cause they havent said a thing yet...
mustang is pretty quick todays cars smoke even the old big blocks....
except the zl1

[syr74]

Originally Posted by THE EVIL TW1N

EDIT: Actually, the new 5.0 has been SAE Certified.

I know, but I can't as yet find anything saying to which SAE standard it was certified. If I am not mistaken manufacturers can still use the old SAE net standard for a while longer.

[mrray13]

Originally Posted by syr74

Read my other posts, including the most recent, I never said that all cars dyno higher in the 1:1 gear I said that the same is the status quo and that if that is not the case there is a variable leading to that, and there are a lot of variables that could lead to that. As for your other comments, If the dyno has more information than drum speed and the ignition readings it is getting from the sparkplug wire lead exactly where do you think it is getting this information from? (actually, to be fair, there are dynos which use software that is supposed to compenate, but most don't)

There are a lot of reasons why what you cite as happening with your car can happen, some of those reasons pertaining to the dyno, some pertaining to the car, and some to both and there is no way to cover them all here.

So, the answer is, you don't have the answer. Not being a smartass, so please don't take any offense. The truth is, and you said it above, there are too many variables in order for a dyno to be right. We all agree that a dyno is a tool to be used for a direct comparison mod for mod on a specific car.

I, however, take some umbrage to the fact that the new GT dyno is being spoken to as if it's the gospel. By some people who say that the numbers would be even higher in 5th, that car's 1:1 IIRC, yet will agree that in at least some cases a car will dyno higher in a lower/steeper gear then 1:1. Why not dyno the car in 5th and end the discussion? Same dyno, same car.

Also, no car is that efficient. Not one with tires on it anyway. So either it's a ringer, it's under-rated, or the car dyno'd higher in the lower gear. It's supposed to be SAE certified, so unless Ford changed the ratings, it's not 412. That leaves ringer and wrong gear. Which one do you think it is? Could also be the dyno and operator just suck. Which after reading some threads about the previous GT500 dyno there, I would agree with, or better put, wouldn't argue against.

Lastly, I'm glad Ford is making a worthy rival, both in v6 form and v8, to the Camaro. It is going to make the track a blast when they show up! It's about time Ford started dropping real powerplants in the basic Mustangs and GTs, and not just the Cobras and such.

[mrray13]

Originally Posted by syr74

I know, but I can't as yet find anything saying to which SAE standard it was certified. If I am not mistaken manufacturers can still use the old SAE net standard for a while longer.

What's the difference? In a nutshell, or a link, would be fine, lol.

[rayhawk]

Originally Posted by mrray13

Wasn't needed. No offense was taken. If I'm wrong on how it works, I'm wrong, no biggie. I'll argue the results, as I have dyno sheets in front of me that back up what I'm saying.

Besides, there's nothing wrong in learning. Again, I'll argue the horspower can't truly be measured, it's derived from torque. All my reading says this in one way or another. It's a mathmatical guess, based off torque, which can be measured. For while we have a constant to relate to getting horspower from torque/rpm, that constant is just an accepted standard, based on what a person judged the amount of force a horse could generate. I've not seen anything that says that constant was ever verified, but rather, I have seen text that states there are different opinions on just how much that force could/should be.

Then again, I could be wrong, lol.

BTW, thanks esperman

Horsepower is an exact value, not a guess, that is based off an amount of work done over a given time period.

1 HP= 746 Watts = 550 ft-lb/s

A typical chassis dyno uses a roller of known inertia, and the dyno simply has to compare how fast the rollers are accelerated and determine the power it would take to accomplish that. The final numbers are based on the calibration values for the particular dyno.

HP=torque (ft-lbs)*rpm/5250

Note that HP is a function of force (torque) and time (rpm). The higher the rpm (shorter time interval) for a given torque, the higher the hp. So a chassis dyno does not directly measure hp, it measures the rate at which the roller is accelerated.

An engine dyno uses a water brake attached to a load cell to measure the resistive braking force (lbs), then based on the distance from the center (ft) you determine how many ft-lbs of torque are output by the engine. Then you use the formula above to calculate the hp based on rpm.

[syr74]

Originally Posted by mrray13

Also, no car is that efficient. Not one with tires on it anyway. So either it's a ringer, it's under-rated, or the car dyno'd higher in the lower gear. It's supposed to be SAE certified, so unless Ford changed the ratings, it's not 412. That leaves ringer and wrong gear. Which one do you think it is? Could also be the dyno and operator just suck. Which after reading some threads about the previous GT500 dyno there, I would agree with.

All of you're reasons are plausible, but you are leaving out two other plausible reasons.

1: SAE says that cars rated on their new system cannot be 'under-rated'. Not to sound silly here, but why are we taking their word for it? They initially said more or less this same thing when the SAE net standard appeared in the early 70's and we know how that worked out.

Call me a skeptic, but I'm loathe to take the SAE's word for it that their own ratings system is infallible. Particularly since one car, the BMW 335i, has already made it through that ratings system and still managed to come out meaningfully under-rated.

2: Assuming for a moment that the new system is as infallible as they claim, are we sure the new GT is rated under the new system? I'll check into it again, but the 2010 GT was rated under the old SAE net setup and as far as I know nobody has said what system the new 2011 model is rated under, just that it is SAE rated.

The truth is that we don't know why those dyno numbers are as high as they are, it could well be an onver-inflated dyno run, but a Chevy guy blindly ruling out under-rating at this point could seem self-serving.

[syr74]

Originally Posted by mrray13

What's the difference? In a nutshell, or a link, would be fine, lol.

SAE net was the system used from the early 70's until the new system showed up recently. As for hard and fast differences, probably about a million of them. In a nutshell the high points are that the SAE claims that the under-rating that happened under the old SAE net system cannot occur under the new ratings system for several reasons including the SAE having to witness dyno runs, etc.

[mrray13]

Originally Posted by rayhawk

Horsepower is an exact value, not a guess, that is based off an amount of work done over a given time period.

1 HP= 746 Watts = 550 ft-lb/s

A typical chassis dyno uses a roller of known inertia, and the dyno simply has to compare how fast the rollers are accelerated and determine the power it would take to accomplish that. The final numbers are based on the calibration values for the particular dyno.

HP=torque (ft-lbs)*rpm/5250

Note that HP is a function of force (torque) and time (rpm). The higher the rpm (shorter time interval) for a given torque, the higher the hp. So a chassis dyno does not directly measure hp, it measures the rate at which the roller is accelerated.

An engine dyno uses a water brake attached to a load cell to measure the resistive braking force (lbs), then based on the distance from the center (ft) you determine how many ft-lbs of torque are output by the engine. Then you use the formula above to calculate the hp based on rpm.

Awww, but that's not the whole story. The constant 5250 is indeed based upon a guess, by James Watt. He estimated the force it took for the horse to turn the mill wheel. He didn't/couldn't measure it.

The latter part of your post backs me up. The engine dyno measures torque, then computes horsepower. Which is my argument, even in chassis dyno form. Torque can be measured, horsepower has to be computed. I made that part bold in your quote.

Originally Posted by syr74

All of you're reasons are plausible, but you are leaving out two other plausible reasons.

1: SAE says that cars rated on their new system cannot be 'under-rated'. Not to sound silly here, but why are we taking their word for it? They initially said more or less this same thing when the SAE net standard appeared in the early 70's and we know how that worked out.

Call me a skeptic, but I'm loathe to take the SAE's word for it that their own ratings system is infallible. Particularly since one car, the BMW 335i, has already made it through that ratings system and still managed to come out meaningfully under-rated.

2: Assuming for a moment that the new system is as infallible as they claim, are we sure the new GT is rated under the new system? I'll check into it again, but the 2010 GT was rated under the old SAE net setup and as far as I know nobody has said what system the new 2011 model is rated under, just that it is SAE rated.

The truth is that we don't know why those dyno numbers are as high as they are, it could well be an onver-inflated dyno run, but a Chevy guy blindly ruling out under-rating at this point could seem self-serving.

1: Completely agree with you here. No argument from me.

2: Good point. I don't know the difference between the standards, so I'm at a loss.

I'm not blindly ruling out under-rated, just saying that is probably not going to happen. Based upon your comments above, I'll await judgement on the SAE until one can determine if it's the old, or new, standard used.

I do find it hard they would under-rate in a time when paper numbers mean more then anything. If they advertised the car at 425hp, vs the 412hp they are advertising, which is closer to what the dyno says it is making,the 425, it would garner even greater attention then it is. Or are they after they paid for, by both sides, ewww, awwww from magazine puppets when the track numbers show impressive performance for a 412hp car, vs okay performance for a 425hp car?