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Old 02-09-2006, 01:43 AM   #64
patr
Scooby Specialist
 
Member#: 97
Join Date: Jul 1999
Location: Vancouver, BC, CANADA
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Dyno Dynamics is much more accurate and better for load holding than the popular "whp" dyno (good example is the thickness of the line on their plots spans about 10hp on ours) - but it reads lower. For Mustang correction, you need to do 1.17 - 1.20. All bets are off if the Mustang pulls use 'atmospheric compensation' - which is actually invalid for turbo cars. I've been pained to not just in general insert a fixed a correction factor because it would save me a lot of headache but its against my principles to do so... but if people want we can always run it at 1.2 (trust me a lot of shops do this - many of which have 'claims to fame' in the proven power bragging forums). All of our pulls are uncorrected and do not use atmospheric compensation. The reason I try to show at least 2 semi-identical pulls in every plot on our site is to demonstrate that they aren't "best of" pulls and also that they are accurate.

You cant measure crank hp without an engine dyno - all you can use is emperical evidence from testing 'known' quantities to come up with correction factors to make 'estimates'. Gimmicks like coast-down etc. are not accurate. Nor is atmospheric compensation. Furthermore, estimates are not linear throughout a speed range or driveline friction envelope, or temperature envelope. I don't like estimating crank hp, because its meaningless (honestly). If you measure it at the wheels, before and after, the same way, that is what is important. THE SAME WAY is what is most important.

To show why it is bad to estimate, or rather, how it gets out of control:

A lot of Mustang guys are using more than 1.2 to estimate crank. But lets just say they use 1.2 to give them the benefit of doubt. 1.2, multiplied by * 1.17 (DD mustang conversion - conservative lower end again just for data purposes) is 1.416 (just for data purposes). So lets say 200 hp on DD is 234 on Mustang. 234 * 1.2 = 283.2 (typical mustang shop crank estimate). That would mean around 1.416 for a DD. But a lot of Mustang shops use more than 1.2 !! A lot of DD shops are using 1.4 (Dynocomp, APS, etc.). To say its over 500hp... 378 to get to 500 is like 1.3... you get the idea - its a very conservative estimate. I do them conservative beacuse its all BS (i.e. I am postitive its at least 500). So when your car gets dyon'd, what matters is RELATIVE not 'what some guy got on the internet'... When people get disapponted because they are expecting 300whp with their mods because that is what they think they should get, but on those same dynos the cars are starting out at 240, its a big difference to when you start out at 180. But generally speaking, for the WRX 1.35 to 1.4 on ours seems about right. BUT DONT DO IT, IT IS MEANINGLESS unless you are only really speaking to overall, ball park estimates.

There are many threads from old school here on Nasioc and at efi101.com and many other places explaining the differences, correction factors, etc. etc. Suffice to say, the inflation game is just that. Dynapack will over-read initial torque, then provide Dynojet-like numbers. Dynojet is double high because there is a Dynojet correction factor in there... twice ! Mustang reads low, but not as low as DD, but many mustang shops will say "our dyno reads soooo low". There are two well known nasioc vendors whos' claims of "210 for a stock STi on our Mustang dyno" have been corrected by management, and shown after the fact, in a seperate thread, on the low side. I can get a stock STi to pull 180 if i want to, I just have to drive it that way ! The more reputable Subaru shops with a DD are KTR performance (uses correction though), Vishnu, DynoComp, APS (internal use), etc. You can check out KTRs site (have a lot of plots up there) but keep in mind Franz uses atmos compensation (so he doesn't have to write long emails like this maybe) so his are a bit high. The only negative (if you want to call it that) about the DD is that it doesn't use any correction by default to give higher #s. None. At all. So it reads low, but accurate. You can see 3 hp easily.

Stock STi is ~210 (worst was 205, best was 215). Stock WRX is ~172 (worst was 165, best was 178). On 2WD or a FWD car its different. So we always compare before to after. But if you aren't after a number (which you shouldn't really be chasing), the best use of the dyno is for steady state tuning, which makes for a much more driveable car. You can ALWAYS make a higher pull from any customer tune I am sending out - but you want a tune that is driveable. To get the highest possible number is different than tuning it to daily drive and have most area under the curve.

(I am typing too much). Just remember we used to go down to run the Mustangs before we got ours so it isn't like we haven't used them first hand... and we bought DD even though it is almost twice the $$.

Anyways, that is a long ramble to answer the question, but i think as much information is needed out there concerning this, otherwise people jump to the wrong conclusions.

-Pat
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Last edited by patr; 02-09-2006 at 01:52 AM.
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