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01072008, 10:18 PM  #1  
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MINE'S GTR exhaust makes 501 hp at the flywheel:
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The dyno test was taken at the flywheel, so If this is the case, then the 480hp rating that Nissan is giving seems to be accurate. 

01072008, 11:39 PM  #2 
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Those numbers were at the wheel hubs. Not at the flywheel. After the transmission and differential losses. But does not include the tire / wheel losses which are seen with the Dynojets.

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01082008, 03:44 AM  #4 
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Further evidence of an underrating.
501 with exhaust  20 exhaust = 481 at the hubs. 5% higer than a dynojet = 457 at the wheels, "with dynojet". So we are back to 5% total drivetrain loss which is simply not possible on this car with the extra drive shafts. 
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01082008, 04:47 AM  #5 
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Explain why Eric Hsu, one of the many men behind XS Engineering and also a veteran of A'PEXi and Cosworth would get it wrong and say that it's at the flywheel and not the wheels, this doesn't make since to me. The guy clearly knows more about engines than almost anyone here if not everyone.

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01082008, 09:14 AM  #7  
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Here's what the article said.
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Clearly he's talking about from the flywheel. 

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01082008, 11:09 PM  #8 
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Despite the fellow being an expert there is no way he can really have flywheel results. It is simple  the only way to have that is to have complete information about entire drive train loss (less the tires since it is a hub dyno) as a function of rpm. The only way to really get that is to test the drive train in isolation or to have the actual at the flywheel dyno results and the hub results and subtract. If he doesn't have that then he is estimating drive train loss.
Of course this contradiction weakens my point above about evidence for underrating.... 
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01082008, 11:16 PM  #9 
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01092008, 12:45 AM  #10  
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I got the impression from one or more of Artpe's notes and others that this particular brand of dyno allows you to simulate engine HP thru allowances for drivetrain losses. Bruce 

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01092008, 01:48 AM  #11 
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I also saw the article. There is no mention about if the numbers were calculated or modified with coast down static drivetrain losses calculated. The article shows the car strapped to four Dynopacks at the hubs. The graphs appeared to be straight acceleration graphs with the numbers peaking at 508 ps with the exhaust and 485 ps in stock form. So, I'm assuming that drivetrain losses were not accounted for.
Unless someone has more information about how the test was done. You must assume that these numbers were at the wheel hubs. I'm guessing that Eric Hsu just mis spoke / typed. You can also get a hint from what he wrote... 5% higher than other dynos... Dynopacks in general only lose about 10% compaired to 15% from a Dynojet because there are no rotational / frictional losses from the wheel and tire. If he meant flywheel, then he would have said 15% higher than other dynos. Engine dynos... at the flywheel Dynopacks... at the wheel hubs... 10% losses Dynojet... at the tires... 15% losses Mustang / Dyno dynamics... at the tires... 1520% losses. This is all approximations for a clutched tranny. Lots of other variables. I am somewhat of a dyno expert. I arranged the distributorship of Dynojets to Korea. Last edited by InJapan; 01092008 at 02:08 AM. Reason: addition 
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01092008, 03:58 PM  #12 
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01092008, 06:07 PM  #13 
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His point is Eric Hsu is just not anyone, it's someone with a decent reputation and knowledge in that field. It's like Schumacher making a statement about driving F1 cars, most people like you and me probably would'nt question him. Not to say that he's never wrong.

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01232008, 04:07 PM  #14  
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Here's an explanation from another forum: Hello, The Dynapack measures power at the axle  one of the only machines that actually does  most machines measure what the roller did, which isn't ever the same thing. The reason we have a "flywheel" screen is because most chassis dynos for years have been incorrectly displaying measured torque. We show the measured torque, because we can  we actually measure it directly. If you have a car making 300lb/ft at the flywheel and run it through a drivetrain that has a 4:1 gear reduction, the gears will multiply the torque and divide the rpm. So your actual "wheel torque" or axle torque will be something like 1200lb/ft  minus a little bit of efficiency loss. So why do most if not all roller dynos display the torque as 300 minus a little loss? Beats me. It is completely incorrect, but those are the numbers people are used to seeing. It is probably because most roller machines are measuring the roller and back calculating everything from there  and dividing it by the engine rpm, instead of the axle RPM. Their torque numbers are calculated several steps away from the original measurement. By comparison, we measure torque at the source, and RPM at the source, so it is direct measurement. Because people aren't used to seeing 1200lb/ft of axle torque (even though it is correct) we have the "flywheel" screen. The flywheel screen takes our measured torque number and divides it by the vehicle's gear ratio to get it back to a "flywheel" torque number that people are expecting to see. True, it isn't actual flywheel torque because we aren't measuring it there  but it is much closer to being flywheel torque than wheel torque. After seeing the explanation, I think you'll see that calling 300lb/ft the "wheel torque" is ridiculous  but it has become the standard. We show you the real numbers as a default and have the Flywheel screen to show the numbers the other way if you want them. Because of all of this, most of our operators use the flywheel screen to give the torque numbers that they are expecting to see. The TCF function is there if you want to use an estimate for drivetrain loss and add it to the "flywheel" numbers. If it is at 1.0  nothing is done. If it is at 1.15, then the measurements are multiplied by 1.15 on the flywheel numbers only. Also, the flywheel screens show the TCF number  to discourage people from being sneaky about using it. Sorry it is so long winded, but I think it is important to show why we do what we do so people understand it. If you have any other questions, just let me know. Thanks, John Card Dynapack USA jcard@dynapack.com Phone (559) 2923800 Fax (559) 2924900 Sent: Sent: Tuesday, December 18, 2007 10:31 AM To: dynapackusa@earthlink.net Subject: RE: Dyno Graph Questions?? Hello John, Thank you for the detailed response to my questions. So the dyno sheet I sent shows a TCF of 1.00, does that mean that the results displayed are at the hubs, or an estimate of flywheel power with the Dynapack software adding a correction factor in? Response: RE: Dyno Graph Questions?? Date: Tue, 18 Dec 2007 10:55:11 0800 Hi, 1.0 means that no correction has been added in  so it is as measured at the hubs. Thanks, John IMHO the dyno graph shows the hub number with a 5% torque correction factor built in. So... 501HP * 5252/6515 = 403 ftlbs TQ after 5% correction factor which = 384 ftlbs MEASURED HUB TQ (@ 6515 RPM before 5% correction factor) = 476 HP actual measured at the hubs with NO drivetrain loss consideration. Last edited by sdiver68; 01232008 at 04:48 PM. 

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01242008, 03:54 AM  #15 
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I liked John's explanation, thanks for that. However, I am not following your analysis/interpretation above. Underrated, and if so by how much? Thanks.
Last edited by swamp2; 01242008 at 03:48 PM. 
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01242008, 10:23 AM  #16 
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476 = actual measured hub HP.
Times a drivetrain factor, let's use 10% because we do not have roller losses associated with a typical dyno. = 523 HP Minus 22 HP claimed for the exhaust = 501 HP stock...underrated by ~21 HP using the above assumed drivetrain loss of 10%. = 525 HP stock using 15% drivetrain loss, so ~45 HP underrated. 
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01242008, 04:18 PM  #18  
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Consistent?!
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01242008, 04:24 PM  #19  
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Thanks sdiver, good post.
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01242008, 08:16 PM  #20 
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If you would stop quoting me completely out of context you would appear at least marginally "on the ball". As you know, since you participated in the bloody discussion, I admitted "massively" was both slightly premature and too aggressive of a word choice. How many times did I say this exact same thing above in those threads, 5, 10?
And by the way 45 hp is very close to 10% and that is pretty darn large. 
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01242008, 09:38 PM  #21 
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^^^^ RIIIIIIIIIIIIIGHT. "On the ball" by what standards. The new estimates are between 21hp to 45hp underrating, your estimates are 80hp to 110hp underrating, you call that "on the ball", are you kidding me. I agree that 45hp is huge, but it could possibly be as low as 21hp as well. Either way, it is still underrated if this is correct.
Last edited by gbb357; 01252008 at 09:04 AM. 
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