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N54 MHI Turbo Data


04302009, 12:12 PM  #46  
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Good info, thank you.
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04302009, 12:48 PM  #47 
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We need to know VE, and I am almost sure that most tuners if not all don't know the actual VE numbers for this motor.
The motor by design should have a VE of higher than 90% though. Until we know VE, everything about HP, turbo choke, etc. is just speculation. Efficiency alone will dictate how much power at a relative amount of boost pressure. A highly effecient system can make 400 HP at 10 PSI, while a more parasitic system could produce 370 HP at 14 PSI on the same turbo's. (these are just arbitrary numbers by the way, not actual numbers)
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04302009, 03:45 PM  #48 
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+1 to make this a sticky.
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04302009, 04:07 PM  #49  
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As far as turbo rpm going "through the roof" at higher boost levels, small turbos run much more rpm than larger framed ones. Yes, at 1718 psi, the compressors are sitting at around 190200k at max power, which is actually mapped on the flow chart. High rpm? Yes. But within the feasibility of system to actually have it mapped and before the (theoretical) choke line of the map. Many times turbos are pushed well beyond charted flow and RPM. Mitsu turbos in the 4G63 world have been doing this for decades. Finally, looking at the map you put together, it's also fairly obvious why 15 psi on pump fuel is the magic number for that octane. Efficiency stays relatively high at a PR of 2, with peak flow at around ~38 lb40/min, it stays within the 65% range. Compressor RPM also stays relatively in check as well.
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'14 991 GT3, Sapphire Blue / Black, 11.30 @ 124 '07 997TT 6MT, Arctic Silver/Sea Blue: FBO E85, stock turbos: 5.9 60130 (now with 656 whp, 700 wtq) Last edited by A418t81; 04302009 at 10:05 PM. 

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04302009, 08:23 PM  #51 
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04302009, 10:13 PM  #52 
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smd, I have one other request, could you please convert your compressor map to have the flow rate in lb/min on the x axis? It would be helpful from a quick and dirty glance perspective instead of having to calculate points along the way for reference.
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04302009, 11:18 PM  #53 
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this is a great site that explains everything relating to compressor maps
http://www.enginelogics.com/cmaps.html 
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05012009, 08:36 AM  #54  
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Mike
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05012009, 10:08 AM  #55 
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i understand 2% of whats going on here, none the less fun to read

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05022009, 12:09 PM  #56 
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It seems that a lot of people are ignoring the effect of the pressure drop from turbo to intake manifold. This value plays a HUGE role in how much power/boost/flow these turbos can provide. I'll run through an example to show how important this data can be.
First, we need to state our 'conditions', and make some estimates of the N54: sample RPM: 6500rpm VE @ sample RPM: 90% stock boost @ the intake manifold: 8psi (ie, PR = pressure ratio = 1.55) N54: 3.0L = ~182cu. in. stock IC pressure drop @ 825kg/hr airflow = ~2psi (this spec is according to BMW; 825kg/hr = ~412cfm) With the above sample points, the N54 needs 478cfm in total @ 8psi intake manifold pressure and 6500rpm. Each turbo would thus need to provide 239cfm (or .113 m^3/sec). This .113m^3/sec value gives us our xaxis lookup on the compressor map. Now, with 478cfm required @ 6500rpm, the pressure drop from turbo to intake will be slightly higher than 2psi. Theoretically, it would be (478/412)^2 * 2psi = 2.7psi. Thus, if we have 8psi in the intake manifold, the pressure right after the TURBO will be 10.7psi (= 8 + 2.7), for a PR of 1.74. This now gives us the yaxis lookup value for our compressor map. So, with a PR of 1.74, and a flow of .113 m^3/s, we see that the stock turbo has an efficiency of ~67% (which is not the greatest). Next, let's do the example of 13psi of boost in the intake manifold. Our new numbers would be: 3.0L @ 6500rpm w/13psi = 584cfm (ie, .138m^3/s per turbo) Pressure drop through stock IC = ~3.8psi Pressure at turbo outlet = 16.8psi (ie, PR = 2.16) So with .138m^3/s and PR=2.16, the turbo is operating with an efficiency of <60% (basically, not even on the chart, but close enough to estimate). Now, let's take the example of 17psi of boost in the intake manifold. Our new numbers would be: 3.0L @ 6500rpm w/17psi = 669cfm (ie, .16m^3/s per turbo) Pressure drop through intercooler with 669cfm = ~5.3psi. Pressure at turbo outlet therefore = ~22.3psi (ie, PR = 2.54). So with .16m^3/s of airflow, and a PR of 2.54, the turbo is operating OFF THE CHART. It's not even rated for that flow and pressure. Hopefully, these calculations can give people an idea of what's reasonable to expect from these stock turbos, and what scenarios are just looking for trouble. 
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05022009, 03:28 PM  #58 
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Couple issues with above:
1. Your calculations make some assumptions that aren't true. The main one being that N54s run anything more than about 1011 psi at 6500 rpm. Boost ramp down after 6k is precipitous regardless of what it was prior to 6k. Figure 17 psi at 6k, but even that is pushing it. Most 17 psi power runs tend to make peak power at around 5500 rpm, if on 100+ octane and basic supporting mods = ~410 whp, give or take 10 whp. 2. Most running that amount of boost are going to aftermarket intercoolers that are looking at 11.5 psi of pressure drop at MOST at those flow values (~42 lb/min). That's hardly the ~5 psi you are using. Frankly, I don't agree with the nearly 3 psi pressure drop across the IC at stock boost pressures that you are figuring either, and neither does the pressure testing data that has been carried out on the stock IC vs. upgraded ones as far as before and after comparisons.
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05042009, 11:11 AM  #59 
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Would anyone with the time and appropriate skills be able to plot these exact demand lines at each pressure on this 10T compressor map?
The demand lines are the straight (nearly vertical) colored lines, and the boost per RPM are the little color'd circles. Please include the little keys on the upper left side of the map if at all possible. These demand lines were derived from a 3.0L V6 at the VE's shown per 1k RPM and are probably reasonably similar to the N54... or at least better than nothing. Credits for this map belong to Jeff L. and http://www.stealth316.com/ . Ive read that to convert the cfm to m 3/s, divide 2119 into cfm. I have also read that .1 m 3/s is equal to 211.888cfm. I dont know how to calculate either derivation myself. Both dont seem to be exact, but they are close enough to just get an idea of how far off the map we get at x,y,z PR's. Thanks in advance to whoever is able to pull this off. Rob 
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05042009, 04:27 PM  #60 
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You really dont want anyone to do that, because someone will come along and say thats not right and throw out some incorrect explanation as to why.
Lets just say, I've plotted it and have zero reason to post it here. I have no desire to argue with anyone. 
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05042009, 05:03 PM  #61 
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You have already plotted it just as that 2nd chart is shown? Please post and disclaim it as informational. Or worse case PM it to me so I can use it. IMO its better than what we have now (nothing) and I have reason to believe its "close enough"; and until someone has the time to prove it wrong it will do.
Thanks! 
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05042009, 05:08 PM  #62  
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05042009, 05:13 PM  #63 
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The graph you posted doesnt make a lot of sense to me.
What does boost taper off to on a stock V3 car at redline? And what is the max boost at where? I am too lazy to search, don't want to invest any more time in this than I need to. 
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05042009, 05:20 PM  #64  
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Max boost is 15.4psi at 5600rpm and drops to 13.5psi at 6500rpm (before throttle valve). Btw, it is not so important to know if the Procede or Jb3 boost curves are safe, but the safe limit for our engine so that we can adjust our tunes in order to fit it. 

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05042009, 06:25 PM  #65 
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Isnt the redline 7000RPM? What are the boost levels there?
I'm working on a new chart now... making a lot of assumptions that are going to get a lot of criticism. Pretty much I need to know what the PSIg is at right at the rev limiter. 
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05042009, 07:13 PM  #66  
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Compressor maps are all about the turbos. 

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