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01-15-2016, 10:49 AM | #23 |
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The links weren't meant to be academic sources; they only illustrate that not everyone agrees resonance tuning in the intake manifold goes out the window when you add FI. I don't think you're going to find a thorough scientific analysis online... only opinions and speculation. If what you say about N54/N55 manifolds is correct, and BMW has ditched complex manifolds in favor of simple manifolds for FI (including N63, S63, S55, etc.), then that might make me believe that it is no longer applicable (I suspect cost is a factor too). However, a centrifugal supercharger doesn't generate boost pressure down low, so a tuned manifold is still useful through part of the powerband.
Your point about the volume is sound. As the intake valve opens, and air rushes to fill the cylinder, the manifold may experience a pressure drop. At least it would in a closed system, but this is an open system where the supercharger is constantly force feeding air. The amount of pressure drop would be related to intake runner volume, and the supercharger itself. Large volume intake runners could provide a damping effect. The magnitude could be calculated fairly easily. Back to your original point - when dealing with fluid friction, velocity is squared but pressure has a power of one. So, both play a role, but velocity more so. At 400 horsepower, you're pulling in about 40 lb/min of air (general rule of thumb). Using 40 lb/min as the mass flow rate, and taking the cross sectional area of your throttle body, you can estimate the velocity of air going through it. From there, you can estimate frictional losses. You can do the same for the larger throttle body to see if it's worth pursuing.
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01-15-2016, 11:51 AM | #24 | |
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Quote:
Installing a FI system increases the mass of the air fuel mixture and actually increases pumping losses, but the effective increase in displacement from the FI is significantly greater than the increased pumping losses so there's a net gain. Installing ITBs makes the intake volume as small as possible with a throttle plate design and it also eliminates the cylinder to cylinder directional change so pumping losses are minimal. The only means to reduce pumping losses below that of ITBs is the use the intake valves as the throttle, which is what the valve-tronic system attempts to do.
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01-17-2016, 11:02 PM | #25 |
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I had some time today and made a calculator for power gains. It's VERY rough and makes a few assumptions. For one, it neglects the parasitic drag (in the form of pressure loss) due to the throttle plate (skin friction, wake drag, induced drag). It basically shows pressure loss across the throttle body due to the piping diameter and length, since this is the restriction we were discussing. It doesn't take into account resonance tuning in the intake manifold or many of the other things that can affect performance. It's difficult to exactly isolate the throttle body's impact on performance without looking at the whole picture. Take it as a grain of salt.
I don't know what the M54's throttle body diameter and length are off the top of my head. Using 2.5 inches for the diameter and 2.5 inches for the length, I calculated a 0.0738 psi and 1.2 horsepower loss at 8.5 psi of boost. On a stock car, I calculated 0.0426 psi loss for 0.65 horsepower. Increasing the TB diameter to 3 inches in diameter but 2.5 inches long resulted in a 0.0179 psi and 0.27 horsepower loss across the TB (so basically a gain of less than half a horsepower over stock). I've got a rough draft of the calculator available for anyone that wants it (preview attached). I was also exploring how to use the Apple Numbers app at the same time. PM me your email address and I'll send it over since Zpost won't let me attached Numbers or Excel files. I'll clean it up and make it pretty at some point. Constructive feedback welcome. Remember that the throttle body is like many other things - when you increase the range (flow potential), you reduce the resolution ("feel" and ability to make minute, precise throttle applications). A larger throttle body will provide less accurate response.
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Last edited by pokeybritches; 01-28-2016 at 11:25 AM.. |
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01-18-2016, 02:13 AM | #26 |
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Interesting.
but when I calculate pressure loss of a sudden contraction from 80mm t0 64mm with 16300 l/min air (30degC) going through it (that's roughly the air my engine consumes at 6800rpm at about 8,5psi of boost, I calculate a 0.14 psi pressure drop. So that's about 8 times more than your example.(which is probably the loss in a straight pipe) Also a rough calculation though. from a german site that's all about pressure loss http://www.druckverlust.de/ Interesting that you can calculate not only straight sections, but all kinds of situations. (but all these calculations are rough estimates (more accurate data obviously comes from navier-stokes CFD calculations and the sorts), but a rough estimate always gives some sort of guideline) Obviously you won't get huge gains from a bigger TB (otherwise it would be included in any FI kit), but as I said, it's a fun and really cheap mod as long as you dont spend big bucks at dinan and such. It's (I think) also possible with cheap used parts from the internet and some ingenuity and efford. Just like intakes, headers etc people somtimes attribute huge gains (10-15hp and more) to such mods, and if multiple done, add those gains being under the impression that intake-TB-headers combo alone will give +50hp or such a ridiculous number.... Psychological HP's ... (dyno guy: lets tweak the parameters a bit so that another happy customer leaves the building....) As regarding to the preciseness of the pedal: I don't think that's a real problem. These differences are still quite small, and with the sports button it's also not a huge problem. Even with the twinscrew (which adds over half the horsepower!) it's not a real issue. With that the preciseness of the pedal obviously also is compromised as you regulate huge power. So I don't worry about the accurate response. If I would, my car would have been undriveable a long time ago. About the n54 intake manifold: Very straight foreward. Just a plenum (fairly small btw) and some fairly short intake runners. No disavalving, resonance ducting etc etc whatsoever. actually looks a bit like the ESS TS2 intake manifold (but that has charge cooling obviously) The new m3/m4 also uses this manifold BTW. Easy to fit TB's and stuff, but sadly not suitable form m54 (no injectors )
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Last edited by GuidoK; 01-18-2016 at 02:55 AM.. |
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01-18-2016, 08:44 AM | #27 |
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Yes, mine is only loss in a straight pipe (really more of whether or not the diameter is a restriction for mass flow at those pressures). Sudden diameter changes obviously make a difference too so I may go back and include them.
With your setup where the throttle body is pre-supercharger, I calculated that the pressure difference across the throttle body was greater, and the calculations were closer to what you came up with... 0.117 psi good for 3.18 horsepower. Obviously that's making the assumption that the % horsepower loss directly correlates with % change in pressure ratio. If you can give me the length and diameter measurements of each throttle body, I'll throw them in the calculator. I'd be interested to see how accurate it is.
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01-18-2016, 09:07 AM | #28 |
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If I calculate the % of boost compared to the percentage of gain that's a fair assumption (obviously cams and headers are there to facilitate/compensate for the increced flow)
And in my performance book 1 horsepower per $50 ex vat is still a [s]good[/s]acceptable deal for na->fi conversions, so the allowable cost for this mod should be about $160 (about €180 where I live incl taxes). So with the TB bought for €30 I still have 150 left to tinker I have no idea if it will really make a 3hp difference, but these simple calculations show that a 15HP difference or so often claimed by parties who sell big bore TB's and whatnot is not very likely (and the calculations I did were on a boosted engine, so more flow/loss going through than NA/stock....). Somehow advertized claims are never underrated.... Dinan attributes 6hp to their TB, and I think that's also largely overrated. Certainly regarding that their TB is much much smaller than the diameter we used in the calulations in this thread, and their spec in on a NA car too.
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Last edited by GuidoK; 01-18-2016 at 10:49 AM.. |
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01-18-2016, 11:30 AM | #29 |
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I think you have to add all the pressure losses up together... so the loss from the TB restriction, plus the loss from a sudden piping diameter change, plus the friction loss over the throttle plate. The 3 hp I calculated was the loss for a 2.5" diameter, 2.5" long pipe with a mass flow rate of 40 lb/min (estimate for 400 hp). A larger TB will still have loss, and your net "horsepower gain" will be the difference between the two. I need the actual dimensions to make it a little more accurate.
With a larger TB you will have less piping restriction, less of a sudden piping diameter change, and possibly less friction loss over the throttle plate (I was incorrect about this earlier... a smaller plate has a lower coefficient of drag, but there is a higher velocity of air going over it, so an overall increase of friction loss). Here are a few more estimates for piping restriction only, with the following conditions: 14.7 psi pre-TB pressure (TB positioned before the supercharger) 40 lb/min mass flow (~400 bhp) TB is 0.5" longer than it is wide 2.5" diameter, 3" long = loss of 0.140 psi, 3.82 hp 3" diameter, 3.5" long = loss of 0.0687 psi, 1.87 hp 3.5" diameter, 4" long = loss of 0.0377 psi, 1.03 hp With the VF kit and the TB positioned post-supercharger, 8.5 psi of boost (23.2 psi pre-TB) and 40 lb/min mass flow: 2.5" diameter, 3" long = loss of 0.0886 psi, 1.53 hp 3" diameter, 3.5" long = loss of 0.0434 psi, 0.74 hp 3.5" diameter, 4" long = loss of 0.0239 psi, 0.41 hp So in terms of piping diameter losses only, this is a much better mod for an ESS TS kit. I think if you added all the losses together, an ESS kit might see 3-5 hp. Just for fun, I calculated what the TS3 would see with 50 lb/min mass flow: 2.5" diameter, 3" long = loss of 0.208 psi, 7.07 hp 3" diameter, 3.5" long = loss of 0.102 psi, 3.45 hp 3.5" diameter, 4" long = loss of 0.0557 psi, 1.90 hp So for the straight section alone, a TS3 would see more than a 5 hp loss with the a 2.5" TB versus a 3.5" TB. When you take into account less diameter changes and friction drag over the throttle plate, it looks like a gain of as much as 10 hp is possible. But yes, on a stock car, 15 hp for a throttle body mod is a pipe dream.
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Last edited by pokeybritches; 01-28-2016 at 11:24 AM.. |
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01-18-2016, 11:40 AM | #30 |
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I don't want to leave the NA guys out... stock, 22.5 lb/min (225 hp) mass flow:
2.5" diameter, 3" long = loss of 0.0511 psi, 0.78 hp 3" diameter, 3.5" long = loss of 0.0250 psi, 0.38 hp 3.5" diameter, 4" long = loss of 0.0138 psi, 0.21 hp I don't think you'll see a 0.57 hp gain on a dyno, or feel it at redline on the street. This is a peak gain, so the average gain will be less.
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Last edited by pokeybritches; 01-28-2016 at 11:23 AM.. |
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