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There seems to be a lot of controversy about the CAI design. On the one hand, flow is supposed to be improved. On the other hand, people say that the design actually draws more hot air in. Is there a net performance benefit? One way to test this would be via a dyno. However, the only dyno results I've seen are manufacturer-conducted, and there has been a question about what conditions were used for each run. The dyno also does not really replicate real world air flow.
To settle this matter (for myself), I tested a Fabspeed CAI, purchased a from an online retailer. I have no affiliation with Fabspeed or that retailer. I then took tracings of MAF vs. RPM. MAF is measured in grams of air per second and already factors in temperature and air density. By comparing MAF readings for the CAI vs. Stock airbox, assuming no change in AFR or engine efficiency at a given RPM (just by changing intake pipes, which there shouldn't be), and assuming no change in MAF accuracy between intakes, the % difference in MAF should = the % difference in HP. I realize this isn't a perfect assumption, but here it is anyway.
One caveat is that the Stock airbox filters were not new and had some visible dirt accumulation.
Vehicle: 997.2S PDK Existing Mods:sharkwerks bypass, IPD plenum Measurement: OBDII data (~19 samples/sec) via OBDLink LX, and OBDAutoDoctor software Data Collected: includes MAF Mass Air Flow (grams/sec air) and RPM Test: same freeway onramp (done safely, no traffic laws broken) Repetitions:4 consecutive runs with STOCK airbox, followed by 3 with Fabspeed CAI, done on same day, similar ambient temps
Results: +2.5% to +4% in MAF between 4000-7500 RPM in 1st Gear +5% in MAF between 4500-7000 RPM in 2nd Gear +19HP (ballpark), assuming the relationships above and stock HP of 385 @ (+5%). My data did not show a difference < 4000RPM in 1st Gear
Subjective Observation (Updated: 6-14-16)
- Now that I've driven the car for a month, I'll share some subjective impressions. In my craziness, I also swapped in/out the stock airbox twice during this time just to be sure.
- I think there's definitely more "pull" from 4000-redline with the Fabspeed. To me, it's very noticeable in sport or sport+ mode. Plus the sound is just amazing in this rpm range.
- HOWEVER, during "normal" driving around (sport mode), between idle and 4000rpm, I THINK the car might feel just a bit more sluggish in terms of pull and throttle response. I'm not sure though.
One thing to know is that I have consistently observed (and recorded) the Intake temp and Ambient temp under various conditions. Here's what I can share:
- The stock airbox is not a 100% cold air intake (there are mesh panels that draw in engine air), but it does seem to draw in more ambient air than the Fabspeed (obviously).
- The "delta" temp (Intake temp minus Ambient temp) appears to be greater on the Fabspeed. - At freeway speeds (65+MPH), the Fabspeed and Stock intake delta temps are basically equivalent (about 3-5*F).
- At lower speeds, the Fabspeed deltas are typically between +20-30*F, whereas the Stock deltas are more 10-15*F.
Mean MAF values within each RPM range:
These graphs are scatter plots of MAF vs. RPM. Again, MAF should be directly related to HP, given the above assumptions. Each line represents the 2-point moving average of a single run - this was done to smooth out the data points.
Last edited by gasongasoff; 06-30-2016 at 02:07 AM.
This is some very well put together research and info. Thanks for taking the time out to do this and sharing. Looks like there are plenty of benefits from a CAI after all.
I would like to see how this compares on a 997.1 with the single air intake. I imagine the 997.2 air box is quite a bit more efficient in comparison. I would expect higher MAF gains on the gen 1 cars. Great analysis and testing idea
I agree with Scott, the .1 and 996 cars would see even greater benefit. Thank you for to the OP for taking the time to run these tests for the betterment of the community.
That is great research. If the air temps and baro pressure were not much different, then that is impressive. Did you also have a way to log intake air temperature.
One good tool that allows you to diddle temperature, pressure, dew point, and altitude and see the effects on engine output is here-
Start off with 0 feet elevation, 80 deg ambient temp, air pressure at 29.92 inches of Hg, and a dew point of 60 F. That is about a 100.3% baseline, with 50% relative humidity.
So you are saying the FS CAI results in an increase of 19HP for a 997.2
Couple of questions: one, is this across all gears? you said it was inconclusive below 4000 rpm so it has no effect below this level? how does 19HP have no effect below 4000 rpm
two, what effect does temp have? all the arguments I have heard say that the CAI is really a HOT AI and there robs power once the engine is hot?
So you are saying the FS CAI results in an increase of 19HP for a 997.2
Couple of questions: one, is this across all gears? you said it was inconclusive below 4000 rpm so it has no effect below this level? how does 19HP have no effect below 4000 rpm
The +19HP was a "back of the envelope calculation" using figures for 6500-7000 RPM, where the stock 997.2S would have 385HP. It requires a lot of assumptions, and honestly seems too high of a gain to me considering I already have existing "flow mods" (although Fabspeed does claims +16 HP). At lower RPM's of 4000-6500 RPM, the HP gain should be less, since the motor has less HP in this range, and the % MAF increase was only 2.5-5%.
The only gears tested were 1 and 2 (see labels in the original post), but my guess is that it would apply to higher RPM's of the higher gears too.
two, what effect does temp have? all the arguments I have heard say that the CAI is really a HOT AI and there robs power once the engine is hot? you said it was inconclusive below 4000 rpm so it has no effect below this level?
The MAF readings for 1st gear < 4000rpm had quite a bit of variability and overlap between stock and CAI, so if there truly was a difference, it would require a lot more samples to be able to show it.
BTW, any differences in intake temperature (and, therefore, air density) are already accounted for in the units of "grams/sec." So the differences in MAF are AFTER taking into account the loss of density from hotter air.
Last edited by gasongasoff; 05-16-2016 at 11:20 PM.
But then how much of those gains are due to the sharkwerks bypass and the ipd plenum? Do they not also claim some performance improvement? Maybe they add 19hp and the cai nothing?
Still have no idea what Ericsson is talking about even after he modified his post
But then how much of those gains are due to the sharkwerks bypass and the ipd plenum? Do they not also claim some performance improvement? Maybe they add 19hp and the cai nothing?
Still have no idea what Ericsson is talking about even after he modified his post
To be clear, the sharkwerks bypass and IPD plenum were present in both test conditions. The only thing I changed was the intake (Fabspeed vs. Stock). The filters, were also different (of course).
Very nicely done! And a great observation on the MAF results and temperature.
Not trying to barge in on your great post, but from the information you have provided, you can now calculate the volume efficiency of our engines. For those not familiar with this, volumetric efficiency is a great way to determine how "high performance" an engine is. A number of 100% represents the amount of air a car can move through the cylinders if each intake pull breathes in just as much air as the piston stroke displaces. Most cars end up with a vacuum effect and get less than 100% numbers. Forced induction (turbos and superchargers) are the easy way to get beyond 100%. However, our naturally aspirated engines can exceed 100% as well due to modern high performance tuning methods such as variable valve timing and careful tuning of the intake pulses and careful overlap of the intake and exhaust valve openings.
Most "normal" modern cars have efficiencies in the 80-90% range, while some sporty cars have efficiencies in the 90-100% range, highly tuned performance cars can exceed 100%, and force induction cars can hit VEs of 135% or more.
Running your numbers into the equations here (http://installuniversity.com/install...n_9.012000.htm), the VE calculation shows that your engine was hitting a volumetric efficiency of 113% at 6500 RPMs. This is a very good number for a NA engine indeed! I guess that is part of what we pay Porsche the premium for.
Not specifically mentioned in your testing, but throttle was wide open for this data, correct ? PDK shifting allowed you to keep your foot in it the whole time, so that you don't have to remove data taken during shifting.
Throttle plate will have greater affect on air flow at any RPM than air box will, of course.
Great job here OP. Sure beats the hell out of guessing!
Speaking of that.. a good point by StormRune..
Originally Posted by StormRune
However, our naturally aspirated engines can exceed 100% as well due to modern high performance tuning methods such as variable valve timing and careful tuning of the intake pulses and careful overlap of the intake and exhaust valve openings.
I understand that this is good evidence of the viability of this intake for 997.2 (besides x51) But based on the above valid point specifically regarding the tuning of the intake I wonder if there are gains at all on x51.
Just installed Fabspeed intake on my 997.2 last night - car feels slower with decreased throttle response - thoughts on this? I want to like it but car just seems heavier!!?
QUOTE=gasongasoff;13291089]There seems to be a lot of controversy about the CAI design. On the one hand, flow is supposed to be improved. On the other hand, people say that the design actually draws more hot air in. Is there a net performance benefit? One way to test this would be via a dyno. However, the only dyno results I've seen are manufacturer-conducted, and there has been a question about what conditions were used for each run. The dyno also does not really replicate real world air flow.
To settle this matter (for myself), I tested a Fabspeed CAI, purchased a from an online retailer. I have no affiliation with Fabspeed or that retailer. I then took tracings of MAF vs. RPM. MAF is measured in grams of air per second and already factors in temperature and air density. By comparing MAF readings for the CAI vs. Stock airbox, assuming no change in AFR or engine efficiency at a given RPM (just by changing intake pipes, which there shouldn't be), and assuming no change in MAF accuracy between intakes, the % difference in MAF should = the % difference in HP. I realize this isn't a perfect assumption, but here it is anyway.
One caveat is that the Stock airbox filters were not new and had some visible dirt accumulation.
Vehicle: 997.2S PDK Existing Mods:sharkwerks bypass, IPD plenum Measurement: OBDII data (~19 samples/sec) via OBDLink LX, and OBDAutoDoctor software Data Collected: includes MAF Mass Air Flow (grams/sec air) and RPM Test: same freeway onramp (done safely, no traffic laws broken) Repetitions:4 consecutive runs with STOCK airbox, followed by 3 with Fabspeed CAI, done on same day, similar ambient temps
Results: +2.5% to +4% in MAF between 4000-7500 RPM in 1st Gear +5% in MAF between 4500-7000 RPM in 2nd Gear +19HP (ballpark), assuming the relationships above and stock HP of 385 @ (+5%). My data did not show a difference < 4000RPM in 1st Gear
Mean MAF values within each RPM range:
These graphs are scatter plots of MAF vs. RPM. Again, MAF should be directly related to HP, given the above assumptions. Each line represents the 2-point moving average of a single run - this was done to smooth out the data points.
05-16-2016, 04:19 AM
Fabspeed CAI vs. Stock (MAF measurements)
even after he modified his post
