In Reply to: Ok..but isnt this the theory that GM uses on the Vortec Engines? I mean they are.. posted by Stephen (Smurf) on March 31, 1999 at 23:31:32
First, the Vortec and many other designs, are talking about swirl port or the way the air fills the combustion chamber. It is brought about by the cylinder head design and the way air flows into and out of the cylinder more so than the intake. The goal is to effectivly fill and empty the cylinder without leaving areas which are rich or lean during intake, and fully expelling during exhaust. The D cyclinder head was redesigned as well, hence the "Magnum" upgrade from the venerable Mopar smallblock. Marketing loves these terms, yet find a salesman who can tell you what they mean.
Now to clear the air on some other issues. Engines are basically air pumps. Their efficiency is often measured as "volumetric efficiency". In most cases this "effeciency" is measured at wide open throttle, other wise you are looking at the artificial constraint of the throttle butterflies. In other words an engine that pumps its displacement in two revolutions has a volumetric efficiency of 100%. Stock engines rarly are able to achieve this. ANYTHING that impedes the flow of gasses either on the intake or exhaust side reduces this efficiency. Engineers have exceeded 100% through the use of tuned intake and exhaust but is difficult to achieve, especially with the constraints of a streetable vehicle. Tony's kit IS helpfull for the simple reason that it offers more filter surface area and a minimum of bends, restrictions or flow disruptions to the incoming air. If there is a shortcoming to Tony's system is that it is drawing in warm underhood air. For Detroit engineers the concern over noise wins out over flow effeciency. Anything we can do to the engine that reduces impediment or turbulence will help the engine. Hence popular options are free flowing intake and exhaust systems. Note that in doing so we are negating one of the engineers of a street vehicle primary concerns, which is noise.
Volumetric effeciency approaching 100% and beyond is possible like I said through the use of "tuned exhaust and intake systems. In practical application for a street vehicle these practices become akin to the perverbial pissing into the wind. Unless access to a dyno and a lot of dollars and time of are no concern, the goal of simply cleaning up existing systems is the most cost effective.
I've spent more than 25 years racing both stock and modified classes and it can be amazing what can be "rung" out of a stock engine by simply getting these basics of good flow down. Rarely in a "stock" motor will "tuned" intake and exhaust bring big gains. This is especially true in a street vehicle where a wide powerband and drivability are bigger concerns than eeking out that last pony. Truly "tuned" exhaust and intake systems are done at a specific rpm or a very narrow rpm range. Those "tuning" gains that are readily available are already in effect by Detroit and are in the way of the tuned port intakes and large plenums such as the D intake manifold, though even these are a compromise of HP vs drivability vs fuel economy.
I could go on but at least I got that off my chest.
Anybody interested in this subject should read:
Scientific Design of Exhaust & Intake Systems ~ John C. Morrison(Contributor), Philip Hubert Smith / Paperback / Published 1972
Available from Amazon for about $30, or about half what one would waste on some gizzmo.
John