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Forced Induction SystemsDetailed discussions regarding cold-air intake systens, superchargers, turbo chargers, and other induction systems for your vehicle.
This is a discussion thread titled "Stock Air Flow Numbers and Mod", within the Forced Induction Systems forum, part of the Technical & Vehicle Assistance Forums category.
It is a Canadian spec regular cab 4x4 06. At 4200 lbs it is the lightest V8 Gen 1 available up here.
Besides HC filter removal, airbox mod, K&N, the only other mod is dual exhaust.
Thanks, that explains your faster ET's, you have a few more HP from the VVTI and are 1000 lbs lighter, so the numbers I get are about right. Mine is also a Canadian spec, '01 Access cab 4x4 weighing in at 5225 on the track scales. My mods are the airbox, K&N, headers and single exhaust, TRD LSD, 3.91 gears. My best ET so far is 16.318 at 1244' (corrected altitude). You certainly have the ET I want, but I think a blower is what it will take for me to get there. Glad the airbox mod helped !
It is a thin screen in the top half of the airbox. With the airbox fully closed, the HC filter is a couple inches above the main air filter, parallel to the main air filter.
The HC filter is attached to the top of the airbox lid using plastic rivets. You can use a small chisel to cut off the tops of the rivets to remove the HC filter. It should be possible to reinstall it using small self tapping screws or glue into the plastic lid if you wanted to.
I am not sure of any maintenance issues with the HC filter. Presumably it is not exposed to dirt because it is downstream of the main filter (i.e. the HC filter is only exposed to filtered air from the main air filter). Therefore replacement intervals should be long, if there are any.
I was reading on this site last night about a mod that Tundraholic did on a stock airbox. I thought this over and ran some actual tests on the flow of the stock airbox. For the engine to make full power under WOT engine vacuum should be zero or very close. Being Zero means that the engine is getting all the air it requires, if there is however vacuum, then the air intake system is causing a restriction. This is common place when chassis dynoing engines, if there is still vacuum, then you can put on a bigger carb. The same holds true for fuel injected engines. I define the air intake system as the throttle body, intake hose runner, air filter and airbox. NOTE: engines will require different amounts of air depending on mods such as exhaust.
First of all I wanted to know just how well the stock airbox supplied air to my engine. My truck has JBA headers and a custom dual in single outlet 2 1/2" cat back system, K&N drop in filter. For the tests I had a nice stretch of country road I could repeat the tests on all day long. I mounted 2 hose nipples into my stock airbox, one below the filter and one above. I also located a vacuum port right behind the throttle body. The first test was conducted with my K&N drop in filter installed. I placed a vacuum gauge on the lower nipple which would measure any restriction of flow from the inlet tube ( from the fender ). I ran at WOT to 4000 RPM and monitored the vacuum gauge (any vacuum reading would indicate a restriction). Next I did the same on the upper nipple which would measure air filter/inlet tube restriction. I finally used the engine vaccum port, this would give me throttlebody, air filter, inlet tube restriction. I did the same test with a stock toyota filter as well. I repeated the test a few times and got consistant results. To determine WOT I used the lowest spike in the vaccum readings. O.K. Here are the results:
K&N Filter
Intake 0.75" vacuum
Air Filter 0.75" vacuum
Engine 0.75" vacuum
To understand what these numbers mean we must look at the differences in vacuum along the way: No difference between the air intake and filter numbers tells us that the K&N filter flows adequately for the engine. As well, no difference between the filter and engine vacuum tells us the throttle body size is adequate for the engine. The restriction is in the air box inlet !
Now if we look at the stock filter numbers we see something a little different. We can see the throttlebody is still fine ( no restriction ) as it should be. But the stock filter has 0.75" of vacuum over the inlet tube vacuum (restriction). The reason for the inlet tube's number to be lower is that the air filter's restriction causes less draw from the airbox and the inlet tube can keep up better during the reduced flow.
These results showed that there was indeed room for improvement so I did a similar mod as described by Tundraholic. From that post I understand that the air box mod is yet someone else's idea, however I am sorry I don't know who, but hats off, good job !
I crunched some numbers and calculated that an 1 1/2" ID second inlet should be sufficient (preferred instead of trying to modify the OE inlet). I used 1 1\4 " PVC fittings which are 1.7" ID. I used a Gates # 20523 2" rad hose ( cut a section) to connect the airbox to supplemental inlet tube. I have posted some pictures to show the installation. I chose to place the inlet behind the right headlight as it is protected yet gets air. The back of the headlight was very clean after 200,000 mi so it is a good place for clean air. All the parts cost $23.00 and took me a couple of hours to do.
After the install I re-ran all the tests, here are the results:
K&N Filter
Intake 0" vacuum
Air Filter 0" vacuum
Engine 0" vacuum
As you can see, the K&N combination is just what we want to see, the stock filter, while better, only gives some improvement. The numbers show the quantitaive results, as far as my qualitative results... YES there is a noticeable improvement on my truck. Even at lower speeds it helps, here is why, when watching the vacuum gauge during a quick hit of the throttle, there is a vacuum drop to almost zero at 2400 RPM which indicates WOT as commanded by the ECU. CAI's should do the same thing, however the issue is how the intake runners affect the MAF. With this mod, the stock MAF characteristics are maintained as we are only modifying before the air filter. Well worth the $23.00 ! I may just abandon my CAI research from what I have just seen and felt.
Hope this is of some interest
Hi Volt, all I hav to say is "Brilliant"
Last edited by Tundradrenalin; 10-28-2007 at 12:17 PM.
Reason: fixed the quote brackets
well yesterday i decided to remove this mod. the way i had it ran, excessive amounts of dirt and a little bit of water would come into the air box. the filter itself was relatively clean, but the bottom of the air box had excessive dirt in it.
since i removed this yesterday, i have noticed a little bit of mpg gain. with this air box mod i would get about 100 miles from the time i filled up to 3/4 tank. i checked today and i got 112.5 miles to that same point. it seems like the stock intake box is the best for mpg! and yes i finally cleaned my MAF and throttle body, so that probably helped also.
Calculating fuel mileage should really be done over a long period. With all do respect, and if I understand your post correctly, how can you possibly look at the fuel gauge and know just how much fuel you have each time to know you went 12.5 mi further, when you don't accurately know how full your tank is each time you fill up ? ( the 3/4 point on the gauge is only one side of it ). Some will use the first click of the pump as a fill point, however the sensitivity of pumps vary greatly. I was recently on a trip and let the pump fill and stop automatically. The amount didn't seem right at all, so I kept filling... another 8 gallons ! Unless you can visually confirm a level in the tank, the best you can do is average over a long period ( not just once ). The closest I have come to a method is to fill until I hear the gurgle of the fuel hitting the base of the filler hose. Although this is not recommended on some vehicles as you can put fuel into the EVAP vent, my Tundra seems to be o.k. in this regard. This method is also not perfect but I figure the cross section of the filler hose is small enough that it will be fairly close each time. Maybe you are right, however I would try it a few more times and see if you get the same result. Your numbers add up to a change of 11 to 12 percent, if these numbers are accurate, should the mod not have dropped your economy by about 50 miles per tank when first installed ?
I however wouldn't argue that cleaning the MAF and throttle probably gave you the increases, but not removing the intake mod.
Calculating fuel mileage should really be done over a long period. With all do respect, and if I understand your post correctly, how can you possibly look at the fuel gauge and know just how much fuel you have each time to know you went 12.5 mi further, when you don't accurately know how full your tank is each time you fill up ? ( the 3/4 point on the gauge is only one side of it ). Some will use the first click of the pump as a fill point, however the sensitivity of pumps vary greatly. I was recently on a trip and let the pump fill and stop automatically. The amount didn't seem right at all, so I kept filling... another 8 gallons ! Unless you can visually confirm a level in the tank, the best you can do is average over a long period ( not just once ). The closest I have come to a method is to fill until I hear the gurgle of the fuel hitting the base of the filler hose. Although this is not recommended on some vehicles as you can put fuel into the EVAP vent, my Tundra seems to be o.k. in this regard. This method is also not perfect but I figure the cross section of the filler hose is small enough that it will be fairly close each time. Maybe you are right, however I would try it a few more times and see if you get the same result. Your numbers add up to a change of 11 to 12 percent, if these numbers are accurate, should the mod not have dropped your economy by about 50 miles per tank when first installed ?
I however wouldn't argue that cleaning the MAF and throttle probably gave you the increases, but not removing the intake mod.
i understand completely, i was just stating an estimate on what my mileage was around that same point. i will wait for another couple of weeks to see some real numbers come in. but cleaning the MAF and throttle body probably is what helped my truck a lot.
It is not unbelievable there is a small mileage difference with the mod. The guys who run dynos have noticed the engine controller tends to overly richen the air fuel mixture when bolt ons are added, which explains to a degree why some bolt ons do not offer the increases people expect. Just another reason to get a URD recalibrator and lean it down.
I wouldn't think this mod would actually alter fuel mileage anyway. Under normal cruising you are probably not running past 40 - 60% throttle, and at that point my tests never showed any airbox vacuum, so the engine was supposedly getting all the air it needed anyway. Under snap acceration where WOT would be commanded, or actual pedal to the metal operation, the stock system did have airbox vacuum, this is the point I noticed the improvement after the mod. Unlike most CAIs that alter the airflow past the MAF, this mod doesn't so I think the fuel trims should remain unaffected ( except at WOT ). Would be interesting though to actually have some repeated testing, other than the very basics I used. I am still planning to get a scanner and log fuel trims with and without the mod ( easy to plug the hose and be back to OE ). With my inlet behind the headlight, the bottom of my airbox is about the same as it looked before the mod. But to be fair, I haven't offroaded that much lately, but have had plenty of long rain soaked highway drives.
well so far my mileage is looking to be getting better, but its still too early to be certain. has anyone else had problems with extra dirt entering the air box because of this mod?
Re: Stock Air Flow Numbers and Mod
Glad the airbox mod helped !
Linear Mode
