Valve ?

[Taylorman]

Heres a question ive been pondering. Can someone explain the theory behind exhaust valves being smaller than intakes. In my little brain, it seems that once an engine sucks in the intake air and has gone through the combustion, the air expands which would require a larger exhaust valve. This may be a stupid question but can someone explain the theory behind this.

[Daytona100]

Intake air is pulled into the engine by atmospheric pressure (void) when the piston goes down on the intake stroke. Past several restrictions air cleaner, carb intake ports seems like you would need a properly sized path for the air fuel mixture to flow into the cylinder, The exhaust gasses are pushed past the exhaust valve when the piston comes up to tdc on the exhaust stroke.

[cruser]

Pressure diferentials are much greater during the exhaust stroke than during the intake stroke.

[EXTREMEBOATS]

Not to mention, Air mixed with fule needs more space then the burnt air leaving the exaust. Intake manifold designs combinded with cam profiles and the right CFM carb are what it adds up to. A high power engine is a efficient air pump.... The faster you get it in and out determines your combinations true output. :argue:
Mike

[FASTRAT]

A high power engine is a efficient air pump...The faster you get it in and out determines your combinations true output
with all that has been said above...then...give me a reason why u couldnt match the intake & exhaust??
fastrat

[SmokinLowriderSS]

I think you could if you were running a blown aplication, no way running NA. NA there is at the most 14+psi (atmospheric) trying to push the mixture into the cylinder as the piston makes room. There is easilly 50 to 100 psi (depending on what time in piston travel you take the measurement and how far open the valve is) pushing the gasses out. The valve restriction can be much smaller for the outbound exhaust than the inbound intake to deal with the same cylinder volume within the same time span. In fact, it isn't even the same volume but may well be 2x volume on the exhaust side.

[DaveA]

I think you could if you were running a blown aplication, no way running NA. NA there is at the most 14+psi (atmospheric) trying to push the mixture into the cylinder as the piston makes room. There is easilly 50 to 100 psi (depending on what time in piston travel you take the measurement and how far open the valve is) pushing the gasses out. The valve restriction can be much smaller for the outbound exhaust than the inbound intake to deal with the same cylinder volume within the same time span. In fact, it isn't even the same volume but may well be 2x volume on the exhaust side.
Yup.
Suck...Squeeze...Bang!...Blow....
The 4 cycles of .... of .... the internal combustion engine. Yea. That's it!
:D
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