Tech topic: Advancing cam timing

[Joel87GT]

garbled said:

The point of an adjustable cam is to allow you to advance timing by very small amounts, and each cam independant of one another.

Independant from each other. Am I reading your right? You mean someone would adj each cams indifferently from stock N/A setup. Meaning, ie. Intake cam adv by 3* and Exhaust cams retarded by 5*? That would seriously F things up. Does vvti do that?

[White87GT]

V-TEC, VVTI and all those other fun things adjust cam timing as you drive. Some adjust intake and exhaust independently of one another.

[Jeremy]

ok I need to make some things clear as some ppl are getting confused.

There are 2 different types of timing when talking about a engine

1 is CAM TIMING
& the other is ignition timing

They are not the same
the cam timing has not much to do with a timing light
you use a timing light to set ignition timing not cam timing

Cam timing controls when the valves open & close & ignition timing controls when the spark plug fires.

for the purpose of this thread topic we are ignoring ignition timing all together as that's not what we are talking about.

What we are talking about is advancing the cam timing, making the valve open a little earlier in the stroke to let the fuel & air charge in so that the pistons have a longer stroke to compress the air fuel charge, therefor getting a little more power from it. Adjustable cam gears are used to fine tune engines, and also change your hp & torque bands. Like if you are producing 300hp at 6900rpms & you want it to create that hp a little earlier like 6200 you can advance the intake cam timing to try to acheive that.

VTEC & VVT'i are 2 totally different concepts all together.

VVT'i uses the ecu to calculate load, the ECU then determines when to change the intake cam timing, it changes the intake cam timing by sending a signal to a oil control valve on the head, the oil control valve opens & lets oil flow into the actual cam gear, pushing on a rotor inside the camgear it actually varies the intake cam timing. Basic VVT'i theory is that with low load situations the ECU will keep valve timing at 0 degrees & with high load it will advance the intake cam timing for more lower end torque.

VTec is variable lift which uses oil to push pins into another cam lobe that locks into place that has a higher lift. THis is a totally different design & theory. It's why hondas can create some impressive max hp & torque figures but no bottom end at all. Toyota finally designed a system that is similiar & teamed it up with VVt'i to create a more HP & torque all the way from idle to redline.

Basically VVT'i optimizes valve timing for any given situation & calculations are done in realtime.

[White87GT]

What Jeremy said, he knows better than I.