I decided to see for myself what type of gains your typical home "Free Mods" will yield on my 99 C5 A4. Everything from the Throttle Body to the Air Cleaner was removed and Flow Tested on my SuperFlow SF-400 Bench. Then the Mods began with porting and enlarging the MAF sensor and Throttle Body and installing a Z06 Airbox. The results were enlightening.



Flow Testing throttle body



Testing complete intake system



Boring out MAF Sensor half



Ported MAF



Boring Throttle Body



Finished Throttle Body

All testing was done with the following parameters:

* All flows corrected to 10" of H2O
* TB flowed without throttle blade
* No clay entry on TB when flowed

The results:

1) Stock Throttle Body = 582 CFM

2) Complete 99 Air Cleaner Assy from lid to TB = 317 CFM

Wow! That is restrictive!

3) Remove Lid and Filter = 409 CFM

4) Stock 99 Air Cleaner Assy with Z06 Lid and K&N Filter = 383 CFM

5) Same as 4) with ported MAF Sensor = 402 CFM

6) Paper air filter substituted for K&N filter = 396 CFM

7) Removed MAF and Air Cleaner Lower = 495 CFM

8) Ported TB only = 612 CFM

9) Air cleaner assy with ported TB, MAF, Z06 lid, K&N = 418 CFM

10) Same as 9) with Z06 lid and filter removed = 450 CFM

11) Enlarged opening in Z06 lid and added with filter = 439 CFM

12) Drilled extra holes in Z06 lid = 449 CFM

That's a 50% improvement in flow over stock (449 vs 317 CFM). I hope this answers some questions.

Paul

 

Paul,
Very Thanks for taking the time to do this. I found interesting the minimal (in my mind) advantage to running the K&N over the paper filter - seemingly a lot of hoopla about nothing....

 

thanks for sharing... I'm still digesting the data versus previous hot air I've read.....

 

Looks like the K&N was worth about 6 CFM over the stock paper filter. In addition, the flow did not increase when the K&N filter was removed (450 CFM). I did not have any aftermarket filters (Blackwing, etc) to compare at the time but I suspect there is some flow to be gained with a smoother coupler between the air bridge and Throttle Body. I was suprised how restrictive the stock airbox lid was since there is very little area for the air to enter the filter. GM must have done this for noise reduction and a simple way to up the HP for later models.

Paul

 

Wow, great tests!

I'm trying to understand what the airflow path is when using an airbox lid with no hole like this 99. Does air come in through the cardboard, or are there little holes on the side, or what?

Anyway, thanks again for sharing your elbow grease.

 

I believe the air enters from the bottom but is partially blocked by the ducting for the radiator. That is why I placed the cardboard under the air box to simulate the installed condition. Very restrictive.

Paul

 

Thanks for sharing all of your findings. Just curious, do you still have the MAF screen laying around, I have always wondered how much (if any) gain there is to be had by removing it. Also, curious if polishing/sanding the throttle and MAF will give any more flow. Very cool info you've provided, and once again, thanks for sharing.

 

Paul,

Really excellent post. I've looked at a lot of intake flow data/testing but as you would expect, the baseline is always different. Thanks for sharing.

 

Great post!

 

It just confirms what many have already stated in previous threads....ported T.B.'s not worth the money. Thanks for taking the time to post the data.

 

Excellent post!! From what I can determine, it makes sense that the Zip Tie Mod should give a big boost in flow, although you didn't actually test that specific mod. Your testing backs up the seat of the pants boost as being real. I have a stock 97 and just removing the stock lid really woke it up. Did you leave the MAF screen in for your testing? Chuck.

 

Thanks for all the replies. The MAF sensor was de-screened after baseline testing before porting. Unfortunately, I broke the screen during removal and chunked it. All tests performed with the ported MAF were done with the screen removed.

At a later date, I would like to compare aftermarket parts to see if they offer any increase in flow. Anyone in the Houston area can contact me if they would like to be a Guinea Pig and have parts tested at no charge for the good of C5 owners as I may want to purchase these at a later date. My flow bench is also set up to flow LS1/LS6 heads as well. Any results will be made public and posted here on this site.

Paul
713-306-1892

 

Great test!! Thanks.

I wonder what effect an aftermarket air bridge would have on flow numbers?

 

This is one of the most useful threads I have read. I'm really curious to see if one of the true CAI systems (ie vararam, honker etc) actually outflows the stock throttle body?

 

I am curious about aftermarket air bridges as well. I may purchase one and a smooth coupler to see what type of gains, if any, are possible.

The aftermarket air filters would probably flow comparable to the stock airbox with K&N filter and Lid removed. The best design would be to draw air from the area just below the filter that feeds the radiator since it supplies cool fresh air. I think there may be a manufacturer that does this by cutting a hole in the partition and mounting the airbox there. Seems to me, the biggest problem with the stock airbox is that it is shrouded top and bottom by the hood, front bumper, and partition, resulting in trouble drawing air.

Paul

 

Absoloutly awesome! Thanks you! This'll help a lot of people wanting to do changes to the intake.
Amazing work! Keep it coming!

Thanks,Matt

 

I'm always behind the curve.

My math leads me to believe that very marginal gains will occur with ANY mods which only allow for greater air flow above what is already present in a stock configuration.

346CID X 1/4 (four cycles) X 6200 rpm / 1728 Cubic Inches per Cubic foot= 310CFM

That is assuming absolute efficiency in that which is available being consumed.

It would appear to me that in order to make any intake mod worthwhile, scavenging the cylinders post combustion would be massively important.
To lend any credibility to what I'm saying would also require someone to run a motor on a stand making mods while studying flow.

Resonance in the manifold may lead to a denser charge and requisite increases of CFM flows or the converse- less, at different RPMs.

The Vararam and it's imitators claim their increases are due to added compression gains of inflow, not an actual increase in CFM but denser CFM.

Anyway unless you are running increased displacement or RPMs and making no other exhaust mods, the stock intake is OK?
Tell me it isn't so!

 

Thanks for taking the time and most of all for sharing this info !!

Matt

 

Great post

Hopefully some local guys will take you up on your offer.....I would if I was around your neck of the world.


DH

 

The basic 4 cycle engine takes in its cubic inch displacement every 2 revolutions assuming volumetric effeciency is 100%. So at 6000 RPM, a 5.7L Ls1 would draw in 347 cubic inches of air times the number of revolutions (6000) divided by two, or 347 X 3000 = 1041000 cubic inches per minute. To convert to cubic feet/min divide by 1728 which equals 602 CFM @ 100% VE.

At 10" of water, the pressure drop across the Air Cleaner assembly would be 10"/27.7" or .36 psi (Pound per square inch). Remember, the stock air cleaner flowed 319 CFM @ 10" of H2O. Since flow is proportional the square root of the pressure or DOUBLING the flow causes the pressure to increase by FOUR times, trying to flow 600 CFM through the Air Cleaner assembly would result in about 40" of pressure drop (600/319)squared X 10" = 35.4" of H2O or 1.28 PSI.

So you can see, bolting on a low restriction air cleaner assembly could result in an effective BOOST pressure of .5 to 1.0 PSI for this reason. At sea level, you have 14.7 psi of pressure trying to force the air into the cylinders in a normally aspirated application. With the stock system, you have 14.7-1.28 PSI or about 13.5 PSI. More pressure at the valve and cylinder means more oxygen and with more fuel means more POWER.

Man, was that long winded!

Paul