Compression Ratio & Cams VS Advance Timing

[hammersword]

What I suppose to do when I have to tune a car with higher Compression Ratio than factory's and with bigger cams?

what should I do with Spark advance timing? I need to decrease them cause of Compression ratio or I need to increase them cause of cams?

I would appreciate any help.....

[Sasha_A80]

Hope this will be helpful

http://www.not2fast.com/NACA/

[MeOH]

"When the spark plug fires the burn starts after a short delay (kernel growth phase). This burn accelerates and builds more and more heat and therefore pressure in the cylinder. The piston in the meantime is on its way to TDC and then (initially slowly) back down. There is a point in this process where the pressure peaks. Ideally you want that point to be at about 15-20 deg ATDC. The exact location depends on engine geometry like bore/stroke ratio and rod-length/stroke ratio, but is INDEPENDENT of engine load, boost or RPM. With ign advance you move where that ppp occurs. If you achieved at a given condition the correct ppp, the engine produces the most power for the fuel you give it. Advancing more costs power, advancing less also.
The optimal ppp is achieved when you reach MBT (minimum best timing), where more advance does not make more power.
In many engines, you can't reach MBT because the engine starts to knock before you reach it." Allmendinger So I would guess CR wont change ppp but you may need to retard to control knock. If high octane is used you may keep the same ignition and enjoy the HP

[MattS00]

There are two different types of compression ratio. One is called static. It is the difference in volume between bottom dead center and top dead center. Changes in piston dome/dish and head chamber volume will affect this. Then there is also dynamic compression ratio. Cams play a role in dynamic compression ratio. A cam with more high RPM breathing ability will have a lower dynamic ratio due to more valve over lap. Big cams and high compression goes hand and hand. Bigger cam with help top end power at a cost to low end torque. Some of the low end torque can be recouped with higher compression pistons. 190 to 210 psi compression pressure is a good range for 93 octane pump gas fuel. Also, the design of the combution chamber will affect how much timing you can run without knock. The faster the charge burns the higher knock threshold the engine will have.

So, make sure your A/F ratio is on, and like the previous poster said tune for the most power and watch knock.

This is another good read.

http://www.popularhotrodding.com/tech/0 ... index.html