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Tuning variable valve cam timing

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Does this needs to be re tuned everytime when turbo is changed or just when someone changes the camshaft?

If you're changing the turbocharger then this will affect the back pressure in the exhaust manifold which in turn can affect the amount of overlap the engine wants to run. So short answer - Yes.

At a minimum I'd always recommend testing to see if the cam timing offers any improvement any time you've made changes that will affect the engine's VE.

When running a upgraded turbo what kind of changes happens to the cam timing?

Do we get to use more intake advance in the areas where the turbo is still not hitting full boost and what about like the high rpm ?

I noticed on stock turbo Subaru 5200 RPM and above is always zero advance does this change if we have bigger turbo?

Also when testing variable cams on stock engine internal Can I safely advance them to 50 degrees just to see torque is gaining or loosing

will I suffer any mechanical damage from advancing too high ? i usually stop at 30 degrees but i would like to push more and see but always scared i might damage piston or valve.

Most of the Subaru engines that I have done will only advance up to around 35 degrees, typically the OEM will not have allowed for more movement of the cams than is safe for the standard engine, so if you have stock cams, valve and piston dimensions, then you should not have an interference issue, modified engines may need to have other physical testing done for clearance.

Thanks

As in general, when you increase the Variable Vavle intake cam timing by 10 degrees how much are you suppose to compensate on VE table?

you'd really have to check that on the dyno in regards to ignition timing and with your wideband in regards to your main fuel table.

there's no rule, as it depends ;)

Is it ok i just adjust the difference from main fuel map, or i have to compensate ve table? Is there a wrong way to do this or anyway is fine as long as target fuel is achiebed~

When you make a change to the cam timing that is positive, this will result in the VE increasing as airflow into the engine is improved. There is no rule as to how much to change the VE table though - It depends on how much airflow is increased. You can modify the VE table using the 'Desired AFR / Measured AFR = Correction Factor' equation.