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Author Topic: Cam Switching on 2.7t  (Read 9731 times)
turboskipper
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« on: November 15, 2010, 08:49:01 AM »

Anybody play with the cam switching for the 2.7t? Rather than go to a dyno and find where to switch the cam some been there, done that advice would be nice.

Thanks
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turboskipper
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« Reply #1 on: November 15, 2010, 01:12:20 PM »

I looked up the air charge calculations that depend on the cam position. Seems it would make sense to switch the cam everywhere except at idle and maybe light cruise. See attached for a compare of the KFNW, KFPBRK and KFPBRKNW. The KFPBRK maps are cylinder pressure correction factors, one for parked cams and one for phased cams. Looks like I'll change up KFNW to run the cam's switched more often. I was noticing a slight RL change at 3800 or so when it seems the cam was switching off. Thoughts?


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Rick
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« Reply #2 on: November 15, 2010, 02:28:51 PM »

I would think this would already be pretty optimum from the factory.

It's not just the combustion chamber/cylinder pressure that is important, it's also fuel economy at partial loads.

At idle and low rpm it should be retarded for smoothness and economy. Then as load and rpm increases the timing should advance.  Finally as rpm builds the timing should retard again.  I've looked at the map before and this is exactly what it does. 

Don't think there is much to be gained with changing anything if i'm honest - it would be the last think i'd look at once i'd got everything else how i wanted.

Rick
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turboskipper
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« Reply #3 on: November 15, 2010, 02:44:02 PM »

Ya, you are right Rick. I talked with a friend and if there is no turbine backpressure you'd want the valve overlap to nmax like the map shows above but with the backpressure you want to phase it back at some point to avoid too much EGR. With a larger turbo and/or better flowing exhaust there might be gains to keep the overlap a bit longer.
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spen
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« Reply #4 on: November 15, 2010, 04:06:41 PM »

any sense in looking here if you have rs4 inlet cams, NA cylinder heads etc?
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M007
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« Reply #5 on: March 04, 2011, 04:48:32 PM »

About 4 years ago, the tuner, who was tuning my Stage 3 2000 Audi S4 with RS4 inlet cams and RS4 ECU, made some changes to the cam switch over point.  The results were that it did not help to improve performance, and this was verified while tuning on a load chasis dyno.
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