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I got to thinking why the HR doesn't respond to intakes other than increased noise output. It was obvious the rubber tube part following the MAF was fairly efficient, but it seemed pretty questionable as to why a open element air filter wouldn't outperform the stock air boxes, or that removing the air filter from the air boxes for a dyno, resulted in no improvement of numbers. So I looked up some basic theoretical calculations based on the displacement and redline of the VQ35HR:
Bore x Stroke = 95.5mm x 81.4mm = 9.55cm x 8.14cm
Volume of Cylinder = ~583 cm^3
Volume of engine = ~3498 cm^3 = ~213.5 in^3
Now to get the theoretical maximum air flow rate of the engine. Where 1.0 represents 100% volumetric efficency, 2.0 represents revolutions per power cycle, and the 12^3 represents the conversion factor from in^3 to ft^3, and TAF represents Theoretical Air Flow.
At 100% volumetric efficiency, at redline the VQ35HR needs 463.3 CFM. Since most engines aren't 100% efficient, and most production engines range from 70-90% VE. We'll assume the VQ falls around 80% or higher.
463.3 CFM x .80 = ~370.6 CFM
Now since the HR has 2 throttle bodies, and 2 intakes, 1 for each set of 3 cylinders, we can further divide this number by 2.
370.6 CFM / 2 = 185.3 CFM.
What the 185.3 CFM represents is the volume of air the VQ needs at 7500rpm per side. Maybe the reason that aftermarket intakes are so ineffective are because, at this lower flow rate, the stock filter plus air box design doesn't restrict much if anything. Also once the car starts rolling the scoops in front of the box aid in increasing airflow, so even if the stock design at redline, wasn't flowing the theoretical amount of air the VQ needs, once its rolling, it very well might be?
Dayum bro! Most of that was well over my head, but your thinking seems to be correct IMO. Do you know if there are any numbers out there on the aftermarket intakes to suggest how much more air they are supposed to be letting the HR's get vs. the stock air boxes??
I think the intakes could benifit from some pulse tuning. But I have to agree on the 185.3 cfm that is pretty low. I would like to see a chambered long tube intake that runs infront of the Rad. support. I think it would help with tq.
__________________ NISMOFO -05 Silverstone = 254whp SOLD 07Redline - 285whp SOLD 08 A4 ti 2.0t = 269whp 306wtq
I have an 07 with drop in K&N filters, I just ordered the nismo intakes...
Which is better for the car? From what ive read in this post and others, if I were to put the nismo intake on I would NOT be gaining any more than the setup I have now. aside from the "sound" of the nismo intake itself.
I have an 07 with drop in K&N filters, I just ordered the nismo intakes...
Which is better for the car? From what ive read in this post and others, if I were to put the nismo intake on I would NOT be gaining any more than the setup I have now. aside from the "sound" of the nismo intake itself.
Save your money and cancel that order. It would be better spent on test pipes or HFCs or even the reflash when it comes out.
__________________
Silver Alloy 07 base - Best Time-13.21 - Best Trap 108.16 -
I got to thinking why the HR doesn't respond to intakes other than increased noise output. It was obvious the rubber tube part following the MAF was fairly efficient, but it seemed pretty questionable as to why a open element air filter wouldn't outperform the stock air boxes, or that removing the air filter from the air boxes for a dyno, resulted in no improvement of numbers. So I looked up some basic theoretical calculations based on the displacement and redline of the VQ35HR:
Bore x Stroke = 95.5mm x 81.4mm = 9.55cm x 8.14cm
Volume of Cylinder = ~583 cm^3
Volume of engine = ~3498 cm^3 = ~213.5 in^3
Now to get the theoretical maximum air flow rate of the engine. Where 1.0 represents 100% volumetric efficency, 2.0 represents revolutions per power cycle, and the 12^3 represents the conversion factor from in^3 to ft^3, and TAF represents Theoretical Air Flow.
At 100% volumetric efficiency, at redline the VQ35HR needs 463.3 CFM. Since most engines aren't 100% efficient, and most production engines range from 70-90% VE. We'll assume the VQ falls around 80% or higher.
463.3 CFM x .80 = ~370.6 CFM
Now since the HR has 2 throttle bodies, and 2 intakes, 1 for each set of 3 cylinders, we can further divide this number by 2.
370.6 CFM / 2 = 185.3 CFM.
What the 185.3 CFM represents is the volume of air the VQ needs at 7500rpm per side. Maybe the reason that aftermarket intakes are so ineffective are because, at this lower flow rate, the stock filter plus air box design doesn't restrict much if anything. Also once the car starts rolling the scoops in front of the box aid in increasing airflow, so even if the stock design at redline, wasn't flowing the theoretical amount of air the VQ needs, once its rolling, it very well might be?
TK
That is a good calculation. I am looking to the same on my car. I only have one intake so my CFM 370.6.
It would be interesting where the flow is Laminar or Turbulent with different air intake setups. More the bends will most probably the higher the frication coefficient. Guess that has to be figured that out with the Reynold number...Good old Reynold!!
Also, it would be interesting to see whether or not the front after market opening is effective in increasing mass air flow rate. I think it is a good idea but the opening will cause water/dirt to be sucked into the engine. NOT GOOD!!
I currently have a Nismo CAI and I am thinking it is not the best design. The bypass valve leaks as the alignment is not optimal. The air intake area is defined by the opening were it sits and may have issues if greater amounts of air is needed. It is for this reason I am thinking about changing it up.
The cold air has an excellent advantage though; the other intakes have these crappy shields which give people the false illusion that hot air is not being sucked into the engine. Well it is…go figure heh?
hummm.....decisions I tell you... perhaps the stock intake is the best one?
Such low air volume would explain why we dont get any gains. And since both are the short platic tubes, i dont think its wise to replace it with aluminum pipes (such as AEM or Fuijta) because that would heat up faster. i mean, at the rate the air is flowing in times the distance it travels, it doesnt have much room to heat up anyway to affect daily driving at such high levels. thats why someone suggested heat wrapping only at the track to prevent heat from coming in at idle rpms.
and for the air amount coming in, at that much volume per second, i dont think the stock airbox would be able to restrict it.
Nice to see someone actually worked the whole thing out. It puts it into perspective.
The only real way to put all this paper analysis to the test would probably be to put the airbox on a flow bench. Set up the flow bench to flow 200 CFM in its open state, and then attach the airbox with filter and see how much flow restriction there is.
But, since you dyno the car with the stock setup the same way (without the car rolling) shouldn't you notice SOME hp increase with the new intakes??? I mean a baseline is a baseline???
That is a good calculation. I am looking to the same on my car. I only have one intake so my CFM 370.6.
It would be interesting where the flow is Laminar or Turbulent with different air intake setups. More the bends will most probably the higher the frication coefficient. Guess that has to be figured that out with the Reynold number...Good old Reynold!!
Also, it would be interesting to see whether or not the front after market opening is effective in increasing mass air flow rate. I think it is a good idea but the opening will cause water/dirt to be sucked into the engine. NOT GOOD!!
I currently have a Nismo CAI and I am thinking it is not the best design. The bypass valve leaks as the alignment is not optimal. The air intake area is defined by the opening were it sits and may have issues if greater amounts of air is needed. It is for this reason I am thinking about changing it up.
The cold air has an excellent advantage though; the other intakes have these crappy shields which give people the false illusion that hot air is not being sucked into the engine. Well it is…go figure heh?
hummm.....decisions I tell you... perhaps the stock intake is the best one?
I need a translator to read this thread...
__________________
Silver Alloy 07 base - Best Time-13.21 - Best Trap 108.16 -
But, since you dyno the car with the stock setup the same way (without the car rolling) shouldn't you notice SOME hp increase with the new intakes??? I mean a baseline is a baseline???
I don't think a flow bench will do the trick.
Best way is to set up 1 car and replace the intakes during Dyno Tests (2 tests in total).
This way you minimize the variation between samples and obtain more uniformity.
Like Chipdin said, baseline is the key!!!
__________________
Black 350z
Last edited by optimumarc; 02-13-2008 at 08:54 AM.
Dyno results vary from run to run, even on the same day, and even when run back to back. If the aftermarket intake was adding 1-2hp, it would be hard label it as a power gain rather than a dyno fluctuation, without doing a very large number of runs and taking the averages, while keeping the variables from each run as consistent as possible.
Flow benching would just be easier. Set it for 200 CFM on an open bench, which would be a little under 90% VE, which is probably higher than the VQ actually is. Test with stock air box, and then the filter from an intake system, or even test without the filter in the stock air box.
Some intakes claim to provide you with a 6.5hp gain.
Even with 1 - 2hp gain variability, it would definitely show you if it (the intake) has any effect at all.
The only issue with the simulation is how would you determine the required volume of air for a CAI (i.e. Nismo). Would your testing assumption be that the encapsulated area provides sufficient volume of air?
would it be impossible to make actual Cold Air Intakes for the HR?
If the flow of air needed by each bank of the engine, is low enough that the stock air box provides little restriction, then replacing it with anything more free flowing would have little to no results. In that case, the only way to truly gain any power from an intake set up on the HR, would indeed have to be a real cold air intake, that locates the filter outside the engine bay.
Some theoretical calculations for HR intakes.
