NefMoto > Technical > Tuning > TFSI - cam advance or ignition advance?
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Author Topic: TFSI - cam advance or ignition advance?  (Read 5770 times)
gman86
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« on: April 04, 2017, 07:00:39 AM »
Without having the luxury of a dyno, I'm not able to observe the differences between combinations of ignition and camshaft advance. I'm not a big believer of kidney dynos as they can be deceptive depending on noise etc.

Just now I have a hybrid K04 turbo and am in two minds whether fully advancing the cam timing (28 deg advance) and lowering ignition timing, or retarding the cam (to say 0 deg) and advancing ignition would yield best results.

Has anyone played with the two to see where the sweet spot is? I dare say each hardware configuration will be different but I'm not able to work out, as a rule of thumb, if I'm better with more ignition or more cam.
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turbojohan
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« Reply #1 on: April 04, 2017, 11:19:50 AM »
it's about getting as much airflow into engine as possible.
Retarding cam on higher rpm normally makes more power.
Maybe you can try some cam timings and look what gives highest MAF readings.
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nubcake
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« Reply #2 on: April 04, 2017, 11:58:56 AM »
Be very careful with cam adjustment, especially at high RPM . Wink
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prj
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« Reply #3 on: April 04, 2017, 11:01:44 PM »
Quote from: turbojohan on April 04, 2017, 11:19:50 AM
Maybe you can try some cam timings and look what gives highest MAF readings.
That is a very bad idea, because MAF readings incorporate the air that is dumped into the exhaust due to valve overlap.
Usually it will stop making higher power with overlap way before the maf readings actually drop below the level of the retarded cam.
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gman86
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« Reply #4 on: April 05, 2017, 01:27:20 AM »
Quote from: nubcake on April 04, 2017, 11:58:56 AM
Be very careful with cam adjustment, especially at high RPM . Wink

Why? Knock or potential valve/piston contact? I'm only adjusting within OEM parameters
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lepatron972
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« Reply #5 on: April 05, 2017, 02:08:04 AM »
There is no risk in uncrossing the camshafts on tfsi, it would be necessary especially to decrease the advance to the ignition to have the max of power. So log after every write
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lepatron972
prj
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« Reply #6 on: April 05, 2017, 03:40:56 AM »
Quote from: nubcake on April 04, 2017, 11:58:56 AM
Be very careful with cam adjustment, especially at high RPM . Wink
So many things wrong with this statement...

1. High RPM or low RPM makes ZERO difference to advancing the intake cam, because the cam is pushed open by the lobe AGAINST the spring. So the relationship between piston and valve is completely irrelevant here. It does not change with RPM.
2. We come to point 2 - if there is no problem at 3000 rpm, there will be no problem at 6000 rpm either.
3. The reason people install stiffer springs is not to OPEN the valve, but to CLOSE the valve, as the lobe moves away. By advancing the intake cam, you are giving the valve 20 degrees LONGER to close, so actually advancing the intake camshaft is SAFER with higher RPM. Not that you would do this for RPM constraints of course.

Why do people never use their head and regurgitate bullshit is beyond me...
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gman86
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« Reply #7 on: April 05, 2017, 04:28:43 AM »
Quote from: prj on April 05, 2017, 03:40:56 AM
So many things wrong with this statement...

1. High RPM or low RPM makes ZERO difference to advancing the intake cam, because the cam is pushed open by the lobe AGAINST the spring. So the relationship between piston and valve is completely irrelevant here. It does not change with RPM.
2. We come to point 2 - if there is no problem at 3000 rpm, there will be no problem at 6000 rpm either.
3. The reason people install stiffer springs is not to OPEN the valve, but to CLOSE the valve, as the lobe moves away. By advancing the intake cam, you are giving the valve 20 degrees LONGER to close, so actually advancing the intake camshaft is SAFER with higher RPM. Not that you would do this for RPM constraints of course.

Why do people never use their head and regurgitate bullshit is beyond me...




I was going to follow up with a similar hypothesis should the response have been around valve/piston contact. I've heard a few folk shy away from adjusting cam advance for that very reason. I suspect they'll have been bitten in the past with overzealous adjustment on vernier cam sprockets. The only thing I've noticed with advancing the cam is the engine being less tolerant to ignition timing due to increase dynamic CR.
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nubcake
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« Reply #8 on: April 05, 2017, 07:10:52 AM »
Quote from: gman86 on April 05, 2017, 04:28:43 AM
I was going to follow up with a similar hypothesis should the response have been around valve/piston contact. I've heard a few folk shy away from adjusting cam advance for that very reason. I suspect they'll have been bitten in the past with overzealous adjustment on vernier cam sprockets. The only thing I've noticed with advancing the cam is the engine being less tolerant to ignition timing due to increase dynamic CR.

You're right.
When I saw "TFSI" I immediately thought about continuous valve adjusters with 50+ degrees of travel and ignored other points about only using it for advance within stock regulations.
Actually, this doesn't make my statement less idiotic.
Even with "long-travel" continuous adjusters, they're usually in "power" position by default, and can't be adjusted in the "dangerous" direction anyway. That being said, sometimes there are exceptions. Wink
« Last Edit: January 25, 2018, 01:54:42 PM by nubcake » Logged
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