Originally Posted by Too Many Projects
Is there enough difference in street performance between these 2 intakes to justify spending almost twice as much for an used air gap versus a non-air gap...
If this is a street driven vehicle with street gearing use either the Performer or for a little more top end emphasis the Performer RPM.
The Air-Gap is strictly a high RPM manifold, not that it delivers so much more power but rather without manifold warmth to vaporize the fuel as in the Performer/Performer RPM the Air Gap needs high port velocity to mechanically rip the fuel into a vapor state. So the Air Gap requires very rich mixtures in cool to cold weather when street driven as well as in wet humid weather has icing problems that jam the throttle butterflies and plug the intake as well as allowing breaking off ice chunks to enter the engine. The extra rich mixture alone greatly shortens engine life by washing away the upper cylinder lube.
The advertiser give you half the information you need to decide about these things, while it's true that a cold thus dense mixture packs more molecules into the cylinder, the fuel has to be vaporized and well mixed to burn. Inside a manifold there is a lot of mayhem and amazing amount for such a short distance but this is why port fuel injection is so superior in making power than a carb or TBI as this mayhem is eliminated. The finely vaporized fuel the carb or TBI puts into the airstream quickly comes out of suspension with the air and becomes streams of liquid running along the outside of every turn the mixture has to make. This stream if not remixed does not burn, it just gets pumped around the rings to enter the crankcase and gets tossed out the exhaust valve. That's lost power and lost money. The answer to this was to just richen the mixture till a good burnable mixture can be achieved to run on and just let the excess go as I describe. Modern heads put a lot of effort into wet flow in order to understand what combustion chamber shapes help re-mix the liquid flow with the air flow, this being the foundation of performance and mileage seen with the GM Vortec, Ford GT40, and Chrysler Magnum heads. This technology being driven from the EPA in its attempt to clean up the exhaust and improve mileage. The technology actually goes back to the work of Sir Harry Ricardo from the 1930's. Except for old man Henry Ford, this work was ignored by Detroit as they would not pay the royalties for these patented combustion chambers. The flat head used this technology for many years and Ford carried into the early Y Blocks, but when the wiz-kids took over they wouldn't pay the royalties so the heads got simpler and more fuel hungry. Chevy actually walked a real thin line on the new SBC for a lot of years with the double quench head, right on the edge of the Ricardo patents just short of a law suit. Everybody else took a path far away from the Ricardo chamber throughout the 1970s and 80s until finally emission and mileage mandates drove them into the Ricardo chamber. You see it coming at GM on the SBC with the L98 and the Swirl Port where double quench is reintroduced and the spark plug moves up to the valve tangent line so the burn has less distance to travel this is faster to complete. It comes in pretty fully with the LT1 and LT4 heads of the mid 90s where a bench extends from the spark plug to the exhaust valve side restoring the quench on that side while the intake feeds into a relief cut into the old quench pad on that side of the plug with sharp edges leading to the spark plug which is intended to remix the wet flow running on the long side port turn with the air flow that can and does turn in at a sharper angle than the wet flow. This is really needed with port injection above the valve but also does wonders for undoing fuel separation on conventional carb and TBI manifolds. The LT1/4 chamber shapes later in the 90's appear on the L31 Vortec and the aluminum Fastburn heads for conventionally cooled engines.
This of course has nothing to do with port efficiency; the truth is you need both excellent porting and combustion chamber configuration. So there are heads out there that breathe better but don't burn as well, and heads like the Swirl Port that burn pretty well but don't breathe. There are lots of engines that got one Oldsmobile for example rather a prototype for the SB2 port layout and not the other with big open chambers having the spark plug off in Siberia.
So the fact is that vaporized fuel burns and liquid does not, so before you worry about cold high density air you've got to worry about how to mix the fuel into it. The factory uses heat because most engines are used at low RPMs, the hot rod industry seizes this opportunity to generate big power numbers but doesn't tell you that without super high RPMs to rip the fuel into vapor you will need to run so rich that engine life is seriously degraded especially in cold wet climates.