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[wlaukaitis]

Yes, if you had a standard SBC with 2.02" intake valves and decided to change to 4 valve (or 2 intake vs. 1 intake) with 2 1.01" valves, you would end up with .25" more surface area even though the valves are half the size.

Ever wonder whay the intake valve is bigger? I thougt so! Take a piece of paper (which is your intake charge) and crumple it up, see how much volume it has? Now burn it, now see how much volume it has now? There is less "stuff" after it is burned. Keep in mind that gas IC engines are very innefficient.

 

[BLACK6PACK]

Actually the 2.02 valve has quite a bit more surface area than 2 1.01 valves. The difference is that you can put 2 valves bigger than 1.01 in the same space within the combustion chamber by moving them closer to the cylinder wall.

 

[CTX-SLPR]

He's right Area goes up as the square of the radius so 2x 1.01" valves have 1.602 sqin of open hole for the valve while a single 2.02" valve has 3.205 sqin of open hole.

As for your crumpled paper model..... you might think it's a good one... but its not. Even if you account for both fuel and air in the crumpled paper, when you burn it you are loosing all the CO2 and water and the soot in the smoke. By the fundemental laws of physics, you can't loose stuff, you can convert it from matter to energy and back or change the moleculear structure but you can't make any of it disappear. The reason the exhauste valve is smaller is that exhauste gasses are far more entergetic and under greater pressure than the intake charge is so they get out on thier own faster. You actually have more potential volume at an equal pressure with the exhauste as it is less dense than the intake charge. Also increased exhausted velocity will help scavenge the cylinder and other cylinders as the inertia of the gas pulls more behind it as the exhauste pressure wave travels down the pipe creating a kind of suction wake behind it.

More mad scientist musings on fluid dynamics,

 

[wlaukaitis]

I guess I should get the rocket out of my garage.

 

[2quiktocare]

Someone needs to remember Pi R squared. That is 3.1416 times the radius of the valve squared (times itself). That will give you surface area. Multi valves work better for several reasons. The quench area in the head will take more smaller valves than one large valve, and the multi valves will give better combustion patterns.

 

[TUFNUF 6]

Originally posted by 2quiktocare
Someone needs to remember Pi R squared. That is 3.1416 times the radius of the valve squared (times itself). That will give you surface area. Multi valves work better for several reasons. The quench area in the head will take more smaller valves than one large valve, and the multi valves will give better combustion patterns.

Pi are not square...Pi are round...cornbread are square AHA!!!

 

[CTX-SLPR]

Originally posted by TUFNUF 6
Pi are not square...Pi are round...cornbread are square AHA!!!

Ah.... good old Southern math... I love it, mak'n me homesick there man!

 

[Nashty]

The valve doesn't move completely out of the way when it opens, airflow only moves around the circumference of it.

Circumference = Pi * D
Area = Pi * R squared

To find the open area it's valve circumference times valve lift.

Hot exhaust gases are also less dense and have more volume. You only have so much area to stick a valve in there too. Bigger intake valve = smaller exhaust valve.

 

[2QUIK6]

While computing that open area based on valve size, don't forget the area that is displaced from the valve stem needs to be subtracted back out....2 valves means double that amount to subtract out.