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11-06-2008, 06:34 AM | #89 | |
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The most entertaining one was by the scoop manufacturer, when they claimed that the car has a poor cooling system because coolant temp went up in dyno runs. Pure BS (not the temp going up part). As if M engineers are simply incapable of measuring and tracking a vital performance parameter, and this scoop manufacturer all of a sudden discovered a significant flaw in the design when they stuck the car on their dynojet. As if the car was designed to sit on a dyno and deliver 414hp. Of course, there is nothing wrong with the cooling system of the car. I've driven it pretty hard for 45 minutes non-stop on the track 3 times in one day, and for 30 minutes non-stop several times on really hot summer days, and there were no signs of overheating. Others have reported similar experiences. Regardless, it is a street car, not a race car, and if someone wanted to do more with it, it might need an extra oil cooler, but that is beside the point.
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11-06-2008, 07:04 AM | #90 | |
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11-06-2008, 10:46 AM | #91 | |
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It is modeled, from what I've seen, exactly like the stock box but it is carbon-fiber. It should behave exactly like the stock box. Now, for the money...I wouldn't exactly buy it, although I am an old Ducati guy and carbon fiber bits took more than a pound of flesh from my finances before and that GM piece is quite beautiful, but saying he wasted his money on something that will rob him of power is not exactly true. At worst, it'll perform as the stock one does.
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11-06-2008, 10:51 AM | #92 | ||
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Now, if there was a hood scoop instead of a vent, then we would in effect be installing a stronger pump where a weak one exists (or where one does not exist) and would increase airbox pressure and thus VE. The only issue with that is...aesthetics. I'm no designer, but I've a bitch of a time trying to figure out a way to elegantly add a scoop. I think the most acceptable addition would be a NACA duct, aiming in. And for symetery's sake, a reverse NACA could be added to the other (faux) side as a draw-out/vent of engine heat/air. Will I do that?...the magic 8ball says no. But I think that would work.
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"Arcadian, I've fought countless times, yet I've never met an adversary who could offer me what we Spartans call "A Beautiful Death." I can only hope, with all the world's warriors gathered against us, there might be one down there who's up to the task."Μολὼν λαβέ!! Last edited by ace996; 11-06-2008 at 11:16 AM.. |
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11-06-2008, 11:47 AM | #93 | |
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11-06-2008, 11:50 AM | #94 | |
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I think we've now discussed this to death. The only thing left is for someone to produce some actual figures of the air intake in "real world" driving conditions. I'm afraid I can't do that due to lack of access to one of your M3s. Out of interest what do they cost in the USA and what is the present price of your fuel? |
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11-06-2008, 02:07 PM | #95 | |
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Ballpark figures are mid-sixties...fuel?...depends on the day and the location. Figure about $2.75/gal for 93octane...perhaps less...I try not to look, I need to buy it anyway. Be good, TomK
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"Arcadian, I've fought countless times, yet I've never met an adversary who could offer me what we Spartans call "A Beautiful Death." I can only hope, with all the world's warriors gathered against us, there might be one down there who's up to the task."Μολὼν λαβέ!! Last edited by ace996; 11-06-2008 at 03:59 PM.. |
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11-11-2008, 02:43 AM | #96 | ||
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I looked at this unit a bit more and really like it. Definitely a great tuners tool as exdos has shown us. Basically the unit gets around having to use an acclerometer by reading vehicle speed from the OBD. You can get from velocity to power with P = F * v = m * dv/dt * v dv/dt can come from numerically differentiating the veolcity vs. time curve. I'm not 100% sure this unit does this exact calculation but as you know by numerically integrating or differentiating can take you from a acceleration to speed to position or in the other direction. I'd pretty much be willing to bet this is the basics of the method it uses. Now what would be really cool is a function that accounted for the vehicles changing mass as the tank emptied. An empty vs. full tank in our car does give rise to a 12 hp difference. I guess the lesson of that calculation is if you want really accurate and repeatable numbers with this system (as with a Gtech or any meter that requires vehicle mass) make sure you know it accurately and/or always test at the same fuel level. |
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11-11-2008, 04:34 AM | #97 |
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Swamp2,
I think that the calculation performed by the DashDyno SPD would be simpler than that. Torque=Force x Distance In the DashDyno SPD you need to create a profile of the vehicle being tested for power and torque, which requires, gross vehicle weight (including driver/passengers), wheel diameter and gear ratio, and the "force" and "distance" in the above equation can be calculated from those two parameters when combined with the continuously monitored RPM and the time stamp. In order to standardise the results, the DashDyno SPD also uses vehicle coefficient of drag and frontal area of the vehicle, plus the environmental factors of air temperature, ambient air pressure, humidity and elevation. Therefore, if you wanted to get real accuracy, to replicate the actual weight of your vehicle then you could modify the vehicle profile before each dyno test to give the correct gross vehicle weight according to the amount of fuel in your tank. As I see it, an "at the wheels" dyno calculation using a DashDynoSPD will be just as accurate as an "at the wheels" static dyno recording, and in many instances it will be better because there will be little/no wheel slip if the dyno run is performed in the correct gear for the vehicle and all results are standardise and even account for all the losses and aerodynamic effects in real world driving conditions. |
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11-11-2008, 02:21 PM | #98 |
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Not so sure. The above works but the force is mass x acceleration and as I posted above a=dv/dt can come from numerically differentiating the velocity vs. time curve. How else can you get F?
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11-11-2008, 04:48 PM | #99 |
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I had also assumed that you would need to differentiate the vehicle velocity data to get at instantaneous acceleration, and use the mass info and add theoretical drag values at the given speed to arrive at torque at the wheels. The main piece of information one can get from the OBD tool is the vehicle velocity data. You need the RPM data to plot the obtained torque figures against the RPM range the data were collected in. If you know the gear and final drive ratios, the RPM data is linearly related to vehicle velocity data, so it is not a new piece of information. So, you can simply process the RPM data, but you'll still need to get at vehicle speed and differentiate to determine instantaneous acceleration.
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11-12-2008, 04:38 AM | #100 |
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Swamp2,
Yes you do need to calculate Force. Acceleration can be calculated from the recorded figures of RPM and the time stamp data, plus the wheel diameter and gear ratio in the vehicle profile and Pi as the constant. The mass is the vehicle weight in the vehicle profile. That's how I can do it in Excel from a multipoint.csv file recorded by the DashDynoSPD. |
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11-12-2008, 06:23 AM | #101 |
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This is simply calculating vehicle speed based on RPM and gear ratio figures and then calculating average acceleration. I am assuming you are doing a basic delta v/delta t calculation. That would not yield instantaneous acceleration, and would be somewhat inaccurate, but I guess it depends on how close your time points are exactly. Plus, why not simply use the vehicle velocity data from the OBDII? Is it not as accurate?
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11-12-2008, 04:11 PM | #102 |
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Right guys, I decided to do a simple experiment for you all. I have a runabout car in the form of a Ford Fiesta 1.4litre which is normally aspirated and has a forwards facing air intake which lies behind the front grille and below the lip of the hood. I made a simple scoop device out of a piece of black plastic guttering which I moulded into shape with a a hot air gun and fixed it close to the OEM air intake aperture. It took me about 45minutes to make it and fix it and cost me NOTHING. Here's a photo of it:
I've taken the car for a dyno run in third gear and logged it with my DashDyno and I've prepared a graph from the collected data showing the torque and HP plots of the same car, with and without the scoop fitted, as below: As can be seen there is an increase in "real world" on the road performance with this simple scoop which is an increase of an average of 5.25% (calculated from all the data points) across the full engine rev range. The speed of the car under test was from around 18mph to 68mph in the same (3rd) gear. I would therefore suggest that the RPI scoops will also show a gain although I don't know by how much. I would still want to see the on the road figures for the RPI scoop though. Last edited by exdos; 11-12-2008 at 04:58 PM.. |
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11-13-2008, 12:07 PM | #103 |
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Nice work. Thanks much. Might it also be that the gains (or the size of the gains) were realized because the entire system is so well below 100% VE? And despite beating the topic to death, I do believe the hood intake is significant. Your test only shows a gain for a closed type intake on a low VE design is possible.
Excellent car choice for testing as well :-). |
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11-13-2008, 01:07 PM | #104 |
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Swamp,
I agree totally with your comments. My experiment was offered "as is" to illustrate the general principle only. Basically, I really wanted to simply show everyone just how simple it is to test anything by on-board data-logging and that folks selling stuff, such as companies like RPI and ASR Engineering can easily produce the data if they want to. The cynic in me says that if they did use on board datalogging to prove/ disprove their products, then at the same time they would highlight the fact that static dynos are not the place to test air-intakes and show their customers that they are wasting their money on static dyno testing, and that car owners would be better off and better informed by buying and using their own datalogging kit. |
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11-14-2008, 12:14 PM | #105 | |
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11-16-2008, 02:06 PM | #106 |
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The gains from the RPi scoops are definitely noticeable from 60mph+. Also past 7k rpm I pull much harder. When my car was completely stock, I raced my friends RS4 (intake, exhaust, filter) and I slowly pulled away from him. Now with the RPi scoops, I pull away from him about twice as fast, and I pull harder the faster I go.
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11-16-2008, 02:21 PM | #108 | |
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Yep, highway speeds is where you really notice them. |
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