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Supercharging a 944 - Why so hard?

 
Old 12-01-2017, 12:25 PM
  #91  
jderimig
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Default VE assumptions for pulley sizing

I received the MB M62 charger, it seems in excellent shape but the pulley was missing. Not a big deal because I would not be using the factory pulley as it is too large for the 944 motor. But I hoping to work the splined hub to accept new pulleys, oh well all projects have their challenges.

There is an outfit in Hungary who sells custom pulley conversions for the MB m62, but each pulley iteration will cost me $120 (including shipping) so I would like to get it close the first time.

There is a supercharging boost calculator here (http://performancetrends.com/Calcula...Calculator.php) that I would like to use to get into the ballpark with the initial pulley ratio. It needs an assumption of the engines and the blowers VE.

I think I can assume 90-95% for the engine VE, right? What about the blower. Eaton's data shows 62 ci/rev at a pressure ratio of 1 and it drops about 8% at 1.4. But this data is bare with no inlet losses. Any idea on what I should assume for the actual inlet ci/rev for this application?
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Old 12-01-2017, 12:51 PM
  #92  
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ive seen that before, just used 80 for engine and 85 for blower.
just run the numbers at 62 ci/rev, no real reason to complicate things thinking about inlet efficiencies. just build the best (airflow-wise) inlet you can fit to the back of the blower.
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Old 12-01-2017, 12:53 PM
  #93  
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Originally Posted by V2Rocket View Post
ive seen that before, just used 80 for engine and 85 for blower.
Spencer, does VEMs give you flow rate in log anywhere? IT should be available and it can be used to estimate the VE of your motor at various RPMs (at WOT of course).
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Old 12-01-2017, 01:01 PM
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dunno, never looked for it.
but VEMS is tuned with assumed/calculated VEs based on AFR data from the O2 sensor, but i dont recall how high it goes.
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Old 12-01-2017, 01:06 PM
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If it uses a MAP and IAT then an airflow calculation is done somewhere, or can be done it you can get the MAP and IAT readings.

I estimate that with a standalone I will be able to dial in the pulley ratio in 2 interations. With the first one you determine the motors VE from the ECU data. With the flow and boost pressure measured the blower VE will be known. Then you will be able to calculate the pulley ratio for the boost and flow you want. I just want to get close on the first and avoid being too high. I would rather miss low than high but don't want to miss too low.
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Old 12-01-2017, 03:58 PM
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You can calculate airflow using VE logs, in fact most popular datalogging utilities do it for you. I use megalogviewer and I believe it tells you calculated airflow based on the measured sensor outputs during the log's duration.
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Old 12-01-2017, 05:45 PM
  #97  
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Originally Posted by jderimig View Post
Darren, what compression ratio do you recommend for your level of boost?
I think 9:1 would be ideal. The turbo motor is close to 8:1. As long as you keep boost levels fairly low, run good fuel and the tune is solid, it should last and last. My brother built his motor at 9:1 so we'll see how that holds up next year.
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Old 12-01-2017, 05:49 PM
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Originally Posted by DarrenD View Post
I think 9:1 would be ideal. The turbo motor is close to 8:1. As long as you keep boost levels fairly low, run good fuel and the tune is solid, it should last and last. My brother built his motor at 9:1 so we'll see how that holds up next year.
I have an 84 motor which is 9.5 to 1. Do you think I can get a touch lower with a thicker head gasket (if there is one) or is that not recommended with a boosted engine? Or are piston mods the only way to go?
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Old 12-01-2017, 06:19 PM
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OK did a monte-carlo model which accounts for the uncertainty in the assumed VE of the engine and blower. Initially I do not want to end up over 7psi. Looks like I want to start with an 80mm pulley on the M62. Plots are the range of "what could happen"

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Old 12-01-2017, 06:21 PM
  #100  
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Originally Posted by jderimig View Post
I have an 84 motor which is 9.5 to 1. Do you think I can get a touch lower with a thicker head gasket (if there is one) or is that not recommended with a boosted engine? Or are piston mods the only way to go?
I wouldn't be afraid to run a slightly thicker head gasket as long as it's a quality brand.

I also wouldn't run your little M62 too hard. And I hope you are planning on intercooling?
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Old 12-01-2017, 06:23 PM
  #101  
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Originally Posted by DarrenD View Post
I wouldn't be afraid to run a slightly thicker head gasket as long as it's a quality brand.

I also wouldn't run your little M62 too hard. And I hope you are planning on intercooling?
I plan on water/meth injection, no intercooler.
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Old 12-06-2017, 03:24 PM
  #102  
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Spencer, can the stock alternator fit in the power steering pump place? I see you moved it there but selected a different alternator.
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Old 12-06-2017, 04:43 PM
  #103  
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Don't know, didn't try.
My arrangement as I showed off once upon a time was space-limited by an oil cooler line that is no longer there.
The GM alternator I had on there is MUCH smaller than the stock 944 unit.

I could throw it on there maybe tonight or later this week, but I doubt it'd be a good fit versus finding a more modern, more powerful, more compact unit.
Seriously, the early 944 alternator is 90 amps...modern 90 amp alternators are about 2/3 the size.
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Old 12-06-2017, 05:09 PM
  #104  
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Thanks. Have you considered an electric PS pump so we can have the SC, AC and PS?
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Old 12-06-2017, 05:33 PM
  #105  
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no, I haven't ever had functional PS on my car (12+ years) so it wasn't ever a consideration of mine.
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