"A. Types of Intake Manifolds (IM)
1. Isolated Runner
2. Single Plane
a) Open Plenum
b) Partial Divider Plate
d) Tunnel Ram
e) Cross Ram
3. Dual Plane
For a good overview of all types of intake manifolds please read:
Hondas use isolated runner IM's.
Isolated IM's " offer the absolute best idle quality, throttle response, tolerance of high-overlap cams timing, and allow accurate tuning of intake length for maximum torque. The disadvantages are higher mechanical complexity, synchronization problems, limited under-hood space..., and much higher manufacturing costs."
If you are not familiar with the some terms used for an IM:
An isolated runner IM has a cylinder or log called a plenum which has at one end the throttle body attached to it. The opposite end of the plenum from the TB has an end plate.
There are 4-8 tubes which run perpendicular to the plenum and these tubes are called runners.
Here is a homemade IM showing the plenum up top and 4 runners in the middle, and the end plates . The TB is in the bottom right corner.
Here's a website that describes how to make a homemade IM FOR A TURBO (not all motor)
B. General Rules For IM Designs and Complementary Parts
1. If you increase the plenum size (volume), the powerband is shifted up to a higher rpm.
2. Smaller plenums have lower to midrange rpm powerbands.
3. Large plenums prefer smaller diameter TB's and runners to maintain air flow velocity.
4. Small plenums prefer larger diameter TB's and runners to obtain more air flow capacity or air flow volume.
5. Tuning the runner length achieves the best air flow velocity for the powerband location you want.
a) Longer runners have, on the plus side, more flow velocity which shifts the powerband gains to a lower rpm and has less reversion than shorter runners.... but on the downside, longer runners have less air flow capacity.
b) If you need more air (capacity) to get into the engine , you must increase runner diameter .
c) If you want a higher powerband location , you shorten the runner length.
In the old Mopar Chrysler engines, Steve Magnante at Hot Rod magazine described a formula to obtain the best runner length (mind you on a carburated engine) based on your desired powerband location:
N x L = 84,000
where N represents the desired engine rpm to tune for and L is the length in inches from the opening of the runner tube to the valve head.
Here's my IM calculations article over at Team-Integra.net which includes Steve Magnante and other's methods of finding the right torque peak and boost gain from resonance tuning in N/A setups (Ram Theory explained):
Here's a good site that can calculate ideal runner length and area so that you can tune the location of your peak torque given the number of cylinders and displacement you have:
C. Honda IM's: Differences in Single Stage and Dual Stage IM Designs
1. Dual or Two Stage IM Design:
A dual stage IM design has 8 runners:
4 long runners with square small diameter ports (open all the time) &
4 short runners with larger diameter, oval ports (open after 5750 rpm only).
long runners open all the time. They provide more low to midrange rpm torque (left side of pic).
@5750 rpm, the 4 short runners' secondary butterfly valves open via a vacuum line signal to the IAB dashpot, for more upper rpm flow and power (right side of pic).
2. Single Stage IM Design
Comparison of the GSR Dual Stage IM vs ITR Single Stage IM (Skunk2 IM is also a single stage design)
The ITR IM is a good example of a single stage IM.
The ITR plenum is larger than the GSR plenum.
The ITR IM has 4 runners only (not 8).
The ITR runners are medium length (shorter than the GSR's long runners but longer than the GSR's short runners).
The Integra LS (B18B) and Civic Si (B16A) IM are single stage IM's. They have smaller plenums than the GSR plenum. Their runners are longer but smaller in diameter compared to the ITR runners. The older Prelude's (H23) had a dual stage IM with huge plenums.
Figure 2 a) . GSR dual stage IM (left) and ITR/Skunk2 IM single stage (right)
Figure 2b). GSR dual stage IM (top) and ITR/Skunk2 IM single stage IM (bottom)
Figure 2c) & d) Here is a cutaway view of the inside of the plenum of the Jun single stage IM and you can see the air horns as the openings for the runners. The view is as you would see it as the air enters through the TB and into the plenum. You don't want these air horns to be too high or the air will become turbulent as it turns down into the runner openings:
Notice the plenum tapers as it moves away from you (away from the TB) to generate flow speed so that the runner furthest away from the TB gets just a smuch flow as the runner closest to the TB.
D. Difference in Dual Stage IM vs Single Stage IM Power Curve and Powerband Locations
Here is a dyno comparing the GSR (dual stage IM) torque curve in grey and ITR (single stage IM) torque curve in red.
Notice the torque curve on a stock single stage car (red): it has 2 humps, one at 2500-4000 rpm and one at 7500-8000 rpm. Notice the dip in torque from 4000 to 7000 rpm. This is where the GSR kills the ITRs: in the midrange. The GSR dual IM gives a flat torque curve (grey). Notice that the ITR kills the GSR up top, from 7000 rpm to 8400 rpm .
Figure 3. GSR vs ITR power curves
The consequence of these IM design differences shows up on the dyno.
The GSR's dual stage IM gives more low-midrange torque. In fact, the GSR torque curve has the exact quality we want in the midrange: a flat broad torque curve. The problem with 8 runners and butterfly valves in a dual stage is that they have too much surface area which adds too much aerodynamic drag to the air flow. It slows down flow and causes turbulence or poor flow quality. The fuel droplets aren't as well suspended in the air when air flow becomes turbulent . The fuel become less atomized or begins to separate out from the air and clumps (or rains out). Flow quality is compromised with more surface area.
The consequence of a dual stage IM design problem with more area is that it sacrifices upper rpm hp. It's a compromise design to get more midrange and get some decent (but not optimal) upper rpm power.
The ITR IM is an uncompromising design that sacrifices midrange and makes no apologies for going balls out in getting higher rpm power. The powerband is shifted up to higher rpms. Notice the single stage IM design gives a characteristic double hump shaped torque curve. When a constant diameter, constant velocity CAI (AEM or Injen) is added to the single stage IM, it enhances the first torque hump called the famous "AEM hump".
The RSX's K20 dual stage IM uses a new rotary valve instead of the GSR's high aerodynamic drag butterfly valve in the shorter runners. The rotary valve has less surface area and flow drag which allows for a higher powerband and with better flow quality (keeps the fuel atomized better ).
E. Bottomline Summary
The advantage of a dual stage manifold is better midrange torque over the single stage IM. The longer primary runners of a dual stage IM provide better torque and the shorter secondary tubes allow for more flow in the higher rpms.
The single stage manifold has less midrange torque compared to a dual stage manifold.
what if you kept the dual stage's shorter runners open all the time?
The problem is when both primary and secondary runners are open, they still do NOT get the same flow as a single runner at the higher rpms. Moreover, you lose that midrange torque advantage you had if the secondaries are open all the time.
Why? More aerodynamic drag from more surface area. It just plain hinders upper rpm flow capacity and quality. You can port the dual stage IM 's short secondary runners to a larger diameter to achieve the same flow as a single stage IM. Notice Erick Aquilar's 10.71 sec. , all motor, 2.1L B18C1 still uses a Joe Alaniz-ported dual stage IM. Are the butterfly valves removed or did Erick keep them in? What is your guess?
So, if your goal is to have a high powerband and a higher peak hp, you would want a single stage manifold.
If you want a broad low-midrange powerband, then a dual stage is better. Putting on a single stage manifold would reduce your midrange."
posted by user TUAN on automotivetech.org