I have to disagree. Larger inlet valves are advantageous because a larger
port opening makes filling the cylinder easier considering the fact that you
have only the ambient air pressure outside the cylinder to induce the air to
flow.
The exhaust gases, on the other hand, are forced out of the cylinder by the
motion of the piston. Since the exhaust is being forced out the port doesn't
need to be as large. That's why the inlet valve is usually larger (sometimes
considerable larger) than the exhaust valve. Whoever enlarged the exhaust
ports while leaving the inlets alone demonstrated a basic misunderstanding
of physical principles.
The exhaust is going to leave anyway because it physically cannot stay. The
intake charge, however, needs to be romanced to enter the cylinder, Larger
ports with reduced resistance is the way it's done.
Bill Lawrence
On 5/6/05 11:19 AM, "Dave & Marlene" <rusd@velocitus.net> wrote:
> Hi Mike,
>
> It depends on the overall engine design. The in & out need to be
> somewhat balanced. What can't get out can't get in & vs. Usually the
> exhaust needs to flow about 70% to 80% of what the intake flows. Some
> folks believe that the original exhaust valves/ports are
> disproportionately restrictive. I have certainly not found any
> disadvantage to this modification.
>
> Dave Russell
> Bn2
>
> Mike MacLean wrote:
>> To all that answered my question about what size exhaust valve to
>> use in my 4 cylinder head because of the oversize seats, 3000 valves
>> fit perfectly. Some suggested just that, but I always thought if you
>> wanted more power you used bigger intake valves. What kind of a
>> performance gain do you get from bigger exhaust valves only? Mike
>> MacLean 56 BN2 60 AN5
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