Stock IM vs RBC IM

VitViper

VitViper

Well-Known Member
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Dyno clearly labeled. Picture is worth a 1000 words?

stockvsrbc.PNG


Keep in mind, it is 2 different cars, but the difference in power is so large when the rest of the mods are identical it can't really be thrown out to "different cars".
 
RBC gained a bit below 2500 rpm, and gained 5hp after 7100 rpm. Lost a ton of mid range.

Purple is the stock manifold.
 
VitViper said:
It's the 8th gen intake manifold.
Click to expand...
Thanks Vit. The strange thing is, looking at the torque chart, that where one IM dips the other seems to peek at the exact same spot!
I'm curious to know what the other mods are to these cars? I'm getting a new 2014 Si and I'm not sure if I should put my K&N intake on the new car or look at something else, keeping in mind that I have a budget so I don't want to go crazy.
 
The mods are listed on the dyno chart... they are identical, aside from the IM.

It's pretty clear to me that Honda tuned the 9th gen manifold for the motor -- it's a perfect fit N/A -- and the RBC throws Honda's tuning away (tuning goes beyond just the ECU -- you can "tune" the powerband on the car with parts, then the ECU does the rest).
 
Agreed, it's just like the stock air intake, PRL has been the only true intake to show gains. I won't even think about upgrading my IM until there's a proven one made specifically for our 9th's
 
VitViper said:
The mods are listed on the dyno chart... they are identical, aside from the IM.

It's pretty clear to me that Honda tuned the 9th gen manifold for the motor -- it's a perfect fit N/A -- and the RBC throws Honda's tuning away (tuning goes beyond just the ECU -- you can "tune" the powerband on the car with parts, then the ECU does the rest).
Click to expand...
Wow! That's great Vit!
SO nice to be able to see what the difference between the stock IM and the RBC are without having to spend a penny or lift a finger.
Thank you for sharing this invaluable information. :1:
 
You've tuned a ton of people with the rbc manifold, and some with the zdx throttle body as well. Are those dynos all looking like this? Because I recall quite a few users in the 220's-230's to the wheels with those setups. I just don't know what their dyno charts looked like.
 
Stock is better than RBC? Im woth webby. What about those people with 230 hp running the rbc? I was considering the rbc swap but now I have questions lol.
 
there's a whole lot more that goes into intake manifold design than most people realize. one thing that affects performance is resonance caused by the pressure waves created as the intake valves open and close. a properly designed manifold can use those waves to the engine's benefit, maximizing the intake charge at the moment the intake valve opens. For high RPM motors, the problem is finding the sweet spot. the resonance frequency at low RPM is not the same as the resonance frequency at high RPM, so traditionally, manifold design was a compromise between choosing good low RPM torque or good high RPM power. Honda's old B-series motors were designed more for the latter. One solution that some manufacturers (including Honda) have come up with is variable length intake runners (which is also one reason for the increased prevalence of plastic intake manifolds). Not sure if the Si's motor has the variable length intake runners that Honda used in some other k24s, but it could one reason why the OEM manifold seems to be better across the whole range when compared to the RBC.

King Motorsports actually had a good article that simplifies the principle of these wave dynamics on their website:

"When the valve opens, the air in the runner and port decompresses into the low-pressure region (the cylinder and combustion chamber). The air on the upstream side of the port is completely isolated and unaffected by what happens on the downstream side of it until the valve opens, allowing the compressed air at the valve to flow in, sending a wave back up the port. The air at the runner entrance does not move until that wave reaches all the way to the end. Up to that point all that happens is the higher pressure gas filling the volume of the runner/port decompresses or expands into the low-pressure region advancing up the runner. Once the low pressure wave reaches the open end of the runner it reverses direction, and the inrushing air forces a high pressure wave down the runner. Conversely the closing of the valve does not immediately stop flow at the runner entrance, which continues completely unaffected until the signal that the valve has closed reaches it. The closing valve causes a buildup of pressure which will travel up the runner as a positive wave. The runner entrance continues to flow at full speed, forcing the pressure to rise until the signal reaches the entrance. At the closing of the intake valve, pressure rises far above atmospheric. It is this phenomenon that enables the so-called "ram tuning" to occur and it is what is being "tuned" by tuned intake and exhaust systems. The speed that the signal can travel is the speed of sound in the gas inside the runner. This is why port/runner volumes are so important; the volumes of successive parts of the port/runner control the flow during all transient periods. That is, any time a change occurs in the cylinder - whether positive or negative - such as when the piston reaches maximum speed. At first glance this wave travel might seem to be blindingly fast, but calculations show the opposite is true. In an intake runner at room temperature the sonic speed is about 1,100 feet per second (340 m/s) and will traverse a 12-inch (300 mm) port/runner in 0.9 milliseconds. The engine using this system, running at 8500 rpm, takes a very considerable 46 crank degrees before any signal from the cylinder can reach the runner end. 46 degrees during which nothing but the volume of the port/runner supplies the demands of the cylinder. Why not eliminate the delay with short ports? At the end of the cycle when that big long runner now continues to flow at full speed disregarding the rising pressure in the cylinder and providing pressure to the cylinder when it is needed most. The runner length also controls the timing of the returning waves and cannot be altered (except with OEM variable runner intakes, like the Acura Integra GSR). A shorter runner would flow earlier but also would die earlier while returning the positive waves much too quickly and those waves would be weaker. The key is to find the optimum balance of all the factors for the engine requirements. When the valve closes, it causes a pile up of gas giving rise to a strong positive wave which must travel up the runner. The wave activity in the port/runner does not stop but continues to reverberate for some time. When the valve next opens, the remaining waves influence the next cycle. The goal of tuning is to arrange the runners and valve timing so that there is a high-pressure wave in the port during the opening of the intake valve to get flow going quickly and then to have a second high pressure wave arrive just before valve closing in order to fill the cylinder as much as possible. The first wave will be what is left in the runner from the previous cycle while the second will primarily be one created during the current cycle by the suction wave changing sign at the runner entrance and arriving back at the valve in time for valve closing."
 
^ Doesn't have that wild dip at 4k like the 1st post
 
I would like to know what impact the zdx has on the setup and if it benefits from the rbc or vice versa.
 
webby said:
You've tuned a ton of people with the rbc manifold, and some with the zdx throttle body as well. Are those dynos all looking like this? Because I recall quite a few users in the 220's-230's to the wheels with those setups. I just don't know what their dyno charts looked like.
Click to expand...

It always goes back to -- every dyno reads different. eDynos will vary with elevation, climate, etc. It's a great way to track the progress of *your* car where *you* live, but it's not comparable from car to car (unless you and your friend live in the same place, using the same road for the eDyno). Same can be said for "real" dynos -- comparing #'s from states 3000 miles apart may have a large margin of error -- comparing results on the same dyno, much less so.

I have a customer on the east cost -- 205whp on eDyno, downpipe only, everything else stock. Intake & exhaust will probably put him at 215-220... healthy motor, great climate for making power?

I've never had two cars so similar, in the same location, to actually do such a close comparison -- but every RBC setup I've tuned lacks all that mid range. You can look at all the dynos being posted with the RBC -- very smooth curve that seems to attest to it making power, but really it's sacrificing a lot of torque that "should" be there.

squiggy said:
I would like to know what impact the zdx has on the setup and if it benefits from the rbc or vice versa.
Click to expand...

It may net some top end -- but the TB will probably help on the stock IM. However it will never give you the mid range back -- the mid range is all from the intake manifold being tuned to the motor from the factory.
 
this was going to be my next big mod. I wonder if the reason no one with this mod has weighed in here is because they agree with Vit and the mod was a waste of time and money, or they're just shocked about these graphs.

Damn. I have the PRL RBC, PRL manifold adapter, PRL tbs, and waited all winter too. But if it sucks, I'd rather know now.
 
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I just got the RBC with PRL SRI installed few weeks ago too with my full race downpipe/exhaust, currently on the 9th calibration with vit. Kinda sad news :/
 
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