CAI Pressure: Stock Vs Stillen
Joined: Jul 2004
Posts: 3,054
Likes: 85
From: Los Angeles California
CAI Pressure: Stock Vs Stillen
Hello all,
In the quest for real data I just measured the pressure difference between the Stillen and Stock intake @ 5.5K RPM. The pressure measurement was taken from the oil vapor return port behind the MAF and silencer. I wasn't about to drill holes in anything for a pressure tap so that is why I used the oil vapor return.
I knew any CAI delta P would be low so I used an aerospace quality pressure guage to measure it. I found that the delta pressure in the duct at 5.5K RPM was so low it didn't even register on the very sensitive guage.
Determined to take a measurement I resorted to a home made bordone water column to take a measurement. Even then it wasn't easy but I was able to measure a difference between the Stillen and Stock intake.
Results:
Stillen Intake Delta P= 0.236" water as measured from the intake duct. (0.0087 PSID)
Stock Intake Delta P = 0.394" water as measured from the intake duct. (0.0146 PSID)
The Stillen intake produces .006 psi or 40% less pressure drop than the stock intake.
But as they say "Twice the value of a really small number is still a small number" Adding 0.006 psi at the plenum won't produce anything for HP.
But before the Stillen CAI can be can be blown off as pure marketing BS, I can say for a fact that it does affect engine performance.
When I first installed the Stillen CAI the engine would stall after letting go of the gas from WOT. _This is not a subjective observation or speculation._
Since then the ECU has adjusted and the engine works just fine. But if the Stillen intake only decreases pressure drop by a miniscule 0.006 psi, how could it possibly cause the engine to stall?...
Now for some speculation. (Let me know yours)
I believe the difference lies in the flow charecteristics between the Stock and Stillen intake. Namely flow detachment and the resultant torroidal vortex generated by the sharp radius inlet of the stock box are eliminated by Stillens smooth velocity stack.
Flow detachment can occur when a fluid flows around a sharp radius or corner. This is almost certaintly occuring on the stock box inlet just aft of the filter. As air flows around the sharp inlet and detaches, it creates a doughnut shaped annular recirculation zone or torroidal vortex. Although the air in the vortex is rapidly spinning inwardly upon itself, its effective axial velocity is zero. The thickness and legnth of the recirulating vortex will change slightly as the axial air flow rate changes, but the discharge coefficent will be significantly reduced.
This means the only effective flow area is through the doughnut hole area of the vortex. The air behaves like it is now flowing through a 2" diameter duct rather than a 3" diameter duct.
Also notice the MAF sensor is immediatly behind the inlet where it will be right in the middle of the vortex. Dead center of the doughnut hole flow area. Keep in mind that that the MAF is in a region of the vortex where the air is behaving like it is in a duct much smaller than it really is. IE the axial air velocity in the center of the duct is much higher than it is towards the duct outer circumference.
Conversely, the Stillen inlet uses a large/smooth velocity stack. This does not create flow detachment or a vortex. The axial air flow velocity is smooth and uniform throughout the MAF inlet cross section.
Because the engine will draw the same amount of air from either CAI, the MAF is now no longer calibrated for the Stillen CAI. The engine runs lean with the Stillen intake because the MAF was calibrated for the vortex with higher air velocities towards the center of the intake. Both the stock and Stillen intakes flow the same amount of air but the MAF thinks the Stillen is flowing less.
Consequently the Stillen fooled MAF tells the ECU the air flow rate is low. At high RPM this can produce additional HP because the engine is already running so rich. At low RPM it can run too lean and cause a power loss.
Other than the pressure measurements and stalling observations, the rest is speculation. No napalm or phosphorus please. If you don't agree with any part of it you are 100%right. ;-)
Tony
2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust<P ID="edit"><FONT class="small"><EM>Edited by Hydrazine on 07/25/04 10:12 PM.</EM></FONT></P>
In the quest for real data I just measured the pressure difference between the Stillen and Stock intake @ 5.5K RPM. The pressure measurement was taken from the oil vapor return port behind the MAF and silencer. I wasn't about to drill holes in anything for a pressure tap so that is why I used the oil vapor return.
I knew any CAI delta P would be low so I used an aerospace quality pressure guage to measure it. I found that the delta pressure in the duct at 5.5K RPM was so low it didn't even register on the very sensitive guage.
Determined to take a measurement I resorted to a home made bordone water column to take a measurement. Even then it wasn't easy but I was able to measure a difference between the Stillen and Stock intake.
Results:
Stillen Intake Delta P= 0.236" water as measured from the intake duct. (0.0087 PSID)
Stock Intake Delta P = 0.394" water as measured from the intake duct. (0.0146 PSID)
The Stillen intake produces .006 psi or 40% less pressure drop than the stock intake.
But as they say "Twice the value of a really small number is still a small number" Adding 0.006 psi at the plenum won't produce anything for HP.
But before the Stillen CAI can be can be blown off as pure marketing BS, I can say for a fact that it does affect engine performance.
When I first installed the Stillen CAI the engine would stall after letting go of the gas from WOT. _This is not a subjective observation or speculation._
Since then the ECU has adjusted and the engine works just fine. But if the Stillen intake only decreases pressure drop by a miniscule 0.006 psi, how could it possibly cause the engine to stall?...
Now for some speculation. (Let me know yours)
I believe the difference lies in the flow charecteristics between the Stock and Stillen intake. Namely flow detachment and the resultant torroidal vortex generated by the sharp radius inlet of the stock box are eliminated by Stillens smooth velocity stack.
Flow detachment can occur when a fluid flows around a sharp radius or corner. This is almost certaintly occuring on the stock box inlet just aft of the filter. As air flows around the sharp inlet and detaches, it creates a doughnut shaped annular recirculation zone or torroidal vortex. Although the air in the vortex is rapidly spinning inwardly upon itself, its effective axial velocity is zero. The thickness and legnth of the recirulating vortex will change slightly as the axial air flow rate changes, but the discharge coefficent will be significantly reduced.
This means the only effective flow area is through the doughnut hole area of the vortex. The air behaves like it is now flowing through a 2" diameter duct rather than a 3" diameter duct.
Also notice the MAF sensor is immediatly behind the inlet where it will be right in the middle of the vortex. Dead center of the doughnut hole flow area. Keep in mind that that the MAF is in a region of the vortex where the air is behaving like it is in a duct much smaller than it really is. IE the axial air velocity in the center of the duct is much higher than it is towards the duct outer circumference.
Conversely, the Stillen inlet uses a large/smooth velocity stack. This does not create flow detachment or a vortex. The axial air flow velocity is smooth and uniform throughout the MAF inlet cross section.
Because the engine will draw the same amount of air from either CAI, the MAF is now no longer calibrated for the Stillen CAI. The engine runs lean with the Stillen intake because the MAF was calibrated for the vortex with higher air velocities towards the center of the intake. Both the stock and Stillen intakes flow the same amount of air but the MAF thinks the Stillen is flowing less.
Consequently the Stillen fooled MAF tells the ECU the air flow rate is low. At high RPM this can produce additional HP because the engine is already running so rich. At low RPM it can run too lean and cause a power loss.
Other than the pressure measurements and stalling observations, the rest is speculation. No napalm or phosphorus please. If you don't agree with any part of it you are 100%right. ;-)
Tony
2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust<P ID="edit"><FONT class="small"><EM>Edited by Hydrazine on 07/25/04 10:12 PM.</EM></FONT></P>
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Joined: Dec 2003
Posts: 2,514
Likes: 5
From: Marietta, Georgia
Re: CAI Pressure: Stock Vs Stillen
I do this all the time [on other cars] with Dwyer Manometers.
My gauge accuracy is 1% of 3" FS or 0.03"WC.
5500 rpm is too low as the bulk of restriction starts at HP peak rpm and increases to max at redline.
What was the Total Worst Case restriction, not differential at the measurement point.
On a 90 Q the numbers are roughly 12.3" WC [H2O] just after the MAF [which is 7.3" WC alone]. So everything [filter, air box, convoluted air piping] forward of that is 5.0"WC.
Another interesting number is that the Q plenum drops to ~~17" WC at 7,000 rpm WOT. [Hard to measure since the plenum can be 280" WC at cruise and 250" WC at idle].
Differentials between no filter, K&N drop in, and oem paper filter are less than 1.0" WC at 7,000 rpm.........the G35 filter is larger and the Q requires 28% more air, so one would expect less restriction on G35.
Study KARMAN Vortex technology.
The error you described in MAF calibration is REAL and varies with temperature and humidity.
Why overall it is best to stick with oem for drivability and give up the 1-2 HP max gain aftermarkets might create.
One would need to data log the MAF voltage [not the calculated grams per second [too slow] vs rpm to zero in on errors caused by air deflection changes.
When the software finally gets decompiled, we should learn what temperature is the pivot point for changing the equation to SUMMER protection. The AIR temperature WHEN 10% extra fuel is used. Normally one would expect 1% leaner per 11F but at a certain AIR temperature [85F, 90F, 95F, 100F?????] the equation changes reducing advance and enrichening the WOT mixture..........knowing it is Summer.
On the 90Q it is 85-90F [as read from ambient temp sensor] with AC on signal required. Also the coolant temp starts a progressive ignition advance decline at 195F, since the G35 uses a 4F hotter stablized point [180F instead of 176F].
All these things are critical in determining the accuracy of Feeling the difference between two air intake systems.
Would be nice to know the lower runner air temp just before injector spray........
My gauge accuracy is 1% of 3" FS or 0.03"WC.
5500 rpm is too low as the bulk of restriction starts at HP peak rpm and increases to max at redline.
What was the Total Worst Case restriction, not differential at the measurement point.
On a 90 Q the numbers are roughly 12.3" WC [H2O] just after the MAF [which is 7.3" WC alone]. So everything [filter, air box, convoluted air piping] forward of that is 5.0"WC.
Another interesting number is that the Q plenum drops to ~~17" WC at 7,000 rpm WOT. [Hard to measure since the plenum can be 280" WC at cruise and 250" WC at idle].
Differentials between no filter, K&N drop in, and oem paper filter are less than 1.0" WC at 7,000 rpm.........the G35 filter is larger and the Q requires 28% more air, so one would expect less restriction on G35.
Study KARMAN Vortex technology.
The error you described in MAF calibration is REAL and varies with temperature and humidity.
Why overall it is best to stick with oem for drivability and give up the 1-2 HP max gain aftermarkets might create.
One would need to data log the MAF voltage [not the calculated grams per second [too slow] vs rpm to zero in on errors caused by air deflection changes.
When the software finally gets decompiled, we should learn what temperature is the pivot point for changing the equation to SUMMER protection. The AIR temperature WHEN 10% extra fuel is used. Normally one would expect 1% leaner per 11F but at a certain AIR temperature [85F, 90F, 95F, 100F?????] the equation changes reducing advance and enrichening the WOT mixture..........knowing it is Summer.
On the 90Q it is 85-90F [as read from ambient temp sensor] with AC on signal required. Also the coolant temp starts a progressive ignition advance decline at 195F, since the G35 uses a 4F hotter stablized point [180F instead of 176F].
All these things are critical in determining the accuracy of Feeling the difference between two air intake systems.
Would be nice to know the lower runner air temp just before injector spray........
Registered User
Joined: Dec 2003
Posts: 2,514
Likes: 5
From: Marietta, Georgia
Re: CAI Pressure: Stock Vs Stillen
When factory dyno's engines they are extremely careful to make sure ALL the air injested is low enough in temperature so that the MAF air temp sensor reads the SAE STANDARD 60F temperature.........this partially explains the serious Summer drop in power as 55F ambient would probably be required to meet oem numbers.
Members have measured 110F and 138F in heat soak traffic ~~5-7 even 8% power drop due to temperature alone, PLUS who knows how much from richness and reduced advance.
Probably another 5% under worst case conditions [10-13%].
Thus the 0.2-0.3 or even 0.4 second differences in quarter mile vs temperature times.
Members have measured 110F and 138F in heat soak traffic ~~5-7 even 8% power drop due to temperature alone, PLUS who knows how much from richness and reduced advance.
Probably another 5% under worst case conditions [10-13%].
Thus the 0.2-0.3 or even 0.4 second differences in quarter mile vs temperature times.
Re: CAI Pressure: Stock Vs Stillen
wow. thats a lot of info there...that i dont understand.
so whats the bottom line? <----dumb question i know
G35s6mt/TSecu/350Z Springs&Struts/K&Nfilter+Z-tube/StillenDualExhaust /6WireGroundKit/KinetixHighFlow
so whats the bottom line? <----dumb question i know
G35s6mt/TSecu/350Z Springs&Struts/K&Nfilter+Z-tube/StillenDualExhaust /6WireGroundKit/KinetixHighFlow
Registered User
Joined: Dec 2003
Posts: 2,514
Likes: 5
From: Marietta, Georgia
Re: CAI Pressure: Stock Vs Stillen
When you go munking around with air flow [by changing things] the MAF won't be accurate.
When the air is hotter than 55F outside, power starts dropping at least 1% per 11F warmer.
When the coolant temp goes above 195F the power starts dropping.
When the AC is on the power starts dropping more than just the power consummed by the compression.
Learn to live with the power drop in Summer.
When the air is hotter than 55F outside, power starts dropping at least 1% per 11F warmer.
When the coolant temp goes above 195F the power starts dropping.
When the AC is on the power starts dropping more than just the power consummed by the compression.
Learn to live with the power drop in Summer.
Re: CAI Pressure: Stock Vs Stillen
so the bottom line is that all the data that has been collected may be inaccurate and inconclusive? oh man. im glad i stuck with my stock airbox. tried others and they just didnt cut it for me. but i do miss the sound.
G35s6mt/TSecu/350Z Springs&Struts/K&Nfilter+Z-tube/StillenDualExhaust /6WireGroundKit/KinetixHighFlow
G35s6mt/TSecu/350Z Springs&Struts/K&Nfilter+Z-tube/StillenDualExhaust /6WireGroundKit/KinetixHighFlow
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Re: CAI Pressure: Stock Vs Stillen
I have seen it proven time and time again that some of the aftermarket cone filters come over oiled from the factory. This oil lightly coats the MAS giving the ECU low airflow readings and stalling the car. Clean the MAS and throttle body with a electrical contact cleaner and it cures the problem.
Registered User
Joined: Dec 2003
Posts: 2,514
Likes: 5
From: Marietta, Georgia
Re: CAI Pressure: Stock Vs Stillen
The ecu expects [demands] a certain minimum coolant temp before going into closed loop.
Playing with a thermostat 170F vs 180 F might help a tiny tiny bit in Los Vegas Summers but the minute it turns cooler you could have serious problems if the coolant doesn't warm up enough.
From a fuel efficiency stand point warmer is better to a point say 190F.
Old American badly designed engines [from a balanced cooling standpoint] use to improve at tiny bit with colder thermostat but this was when they had carbs.
Don't know the exact answer as this kind of tweaking was abandoned [as nonproductive] 10 years ago with modern emission regulations.
No I didn't say his vacuum readings were wrong, just that they should be taken at redline to get the real WORST CASE numbers. 5500 vs 6600 might be 2-3 times worse.......the spread will enlarge.
Playing with a thermostat 170F vs 180 F might help a tiny tiny bit in Los Vegas Summers but the minute it turns cooler you could have serious problems if the coolant doesn't warm up enough.
From a fuel efficiency stand point warmer is better to a point say 190F.
Old American badly designed engines [from a balanced cooling standpoint] use to improve at tiny bit with colder thermostat but this was when they had carbs.
Don't know the exact answer as this kind of tweaking was abandoned [as nonproductive] 10 years ago with modern emission regulations.
No I didn't say his vacuum readings were wrong, just that they should be taken at redline to get the real WORST CASE numbers. 5500 vs 6600 might be 2-3 times worse.......the spread will enlarge.
Joined: Jul 2004
Posts: 3,054
Likes: 85
From: Los Angeles California
Re: CAI Pressure: Stock Vs Stillen
What I learned from this is that the Stillen intake does not alter engine performance in the way I initially assumed. The assumption being that it either lowers air inlet temperature and/or increases air mass flow rate.
Even if the pressure drop spread increased by the square of the flow rate by increasing RPM from 5.5K to 6.6K, the total pressure drop would still be insignificant.
This measurement tells me the Stock box is quite efficent. It also shows that any change found with the Stillen is due to the modified MAF calibration.
Unfortunatly, even if the Stillen box gives 10hp, it's not done in the way I would prefer. Running the engine on the lean side might be OK for a few 1/4 mile runs, but it's generally not the way to go for continuous use.
Heck, For $200 I could have bought a fully computerized F/A map controller. Fully variable at any load or RPM and readily adjusted for daily driving or hard racing.
Oh well. That's the way it goes. You won't know untill you try.
Tony
2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust
Even if the pressure drop spread increased by the square of the flow rate by increasing RPM from 5.5K to 6.6K, the total pressure drop would still be insignificant.
This measurement tells me the Stock box is quite efficent. It also shows that any change found with the Stillen is due to the modified MAF calibration.
Unfortunatly, even if the Stillen box gives 10hp, it's not done in the way I would prefer. Running the engine on the lean side might be OK for a few 1/4 mile runs, but it's generally not the way to go for continuous use.
Heck, For $200 I could have bought a fully computerized F/A map controller. Fully variable at any load or RPM and readily adjusted for daily driving or hard racing.
Oh well. That's the way it goes. You won't know untill you try.
Tony
2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust
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Joined: Dec 2003
Posts: 2,514
Likes: 5
From: Marietta, Georgia
Re: CAI Pressure: Stock Vs Stillen
Regenerate [recreate the slope] of the MAF output voltage/ temp sensor curves to finely tweak the fuel injector timing.
Within +10 to -20% of expected normal the OBD2 will not throw a fit......afterall you could be at sealevel in -20F conditions.[+8%] or 110F in the Denver mountains [-20%]..........pretty wide fuel injection range for the MAF to correct.
Within +10 to -20% of expected normal the OBD2 will not throw a fit......afterall you could be at sealevel in -20F conditions.[+8%] or 110F in the Denver mountains [-20%]..........pretty wide fuel injection range for the MAF to correct.
