That velocity stuff is an urban myth. The record for NA HP at
6000 RPM is with these huge pipes. 240 HP. None of these after market
tuning weenies have come even close to this number. If that were the
case why would bridge ports combined with side ports develop more power
than side ports alone? That velocity crap keeps coming up over and
over again.

The reason the RX8 engine has more power at any RPM you wish to
choose is.... it has 30% more intake port area.

That is not to say there is not an optimum diameter at a specific
RPM. Perhaps you are thinking of low RPM torque.

BTW carbs need high velocity to get good mixture signals and IMHO
that is fooling some people about runner area who should
know better.

EFI has no such problems

Joe and Paul,
Paul has got it right for a greater portion of what we are talking about. 
If the factory chose around a 2" inlet for the LeMans engine inlet 
volume isn't as critical as we might think. Vacuum signal is VERY 
important to carb users though.  Velocity is not unimportant though. 
Paul. The Variable Length Inlet on the LeMans engine shows that in 
spades. This is a VERY complex inlet system to put on a endurance 
racing car. The only reason to do it is to improve driveability 
with those large inlets. This was WITH FI too.

 That said is this important in an airplane? Not really. The only 
thing we need to worry about is if the engine stops when throttled 
back or accellerating from idle. Both of these conditions are a 
very real possibility with a poorly designed carburreted manifold. 
Having the engine stall when you push the throttle WFO for a 
go-around could ruin your whole day.
Bill Jepson

Drive ability is a very general term that applies to a lot of factors.
One of which is throttle response. That is not what we are talking
about here. We need to be more specific.

Obviously the Lemans engine had no problems with drive ability.

The reason they  used the variable length intake was to broaden the torque 
curve. That results in better acceleration. It is the same reason Mazda went
to all that mickey mouse stuff on the RX8 intake manifold.

Compared to the Leman engine intake system the RX8 system is a compromise.
The RX8 engine would have more torque & HP through out the RPM
range with a system like the Leman engine had. Unfortunately it
would take up too much room in a street car. And the emissions and fuel
consumption  problems with low RPM low HP peripheral ports and 
valve over lap. 

What would be even better is a variable diameter and variable length 
system. In a way that is what is going on with the six port RX8 system. 
When just the center ports are used you have one intake port area number. 
When the center and the end housing lower ports are used you have double 
the area. When all six are used you have more area yet. The down side 
for peak power is six ports and runners have more skin area & friction than 
only two runners of the same total port area.

None of this nonsense would be necessary if there were such as thing
as a 98% efficient infinite variable transmission. Then the engine
could run at near peak power RPM most of the time much like it
does in an aircraft.

Paul Lamar
 
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