intake pressure measurements

[mbtoloczko]

I've read quite a bit about home-made ram-air systems, so I've been interested in getting a manometer so I can have a tool to help me design a good ram-air system. So, I finally got around to buying an electronic manometer and taking some intake pressure measurements.

I pulled one of the PCV tubes from the black intake box that attaches to the throttle body and attached a vacuum line to that port. Then I ran the vacuum line through the a/c condensor tube into the cabin. (I pulled the condensor tube from the a/c drain first).



The manometer has a range of +/- 2.2 psi (+/- 150 mBar). The scale reads out in mBar, and 68 mBar = 1 psi. It also automatically records peak pressure and vacuum. Here is a picture of the manometer hooked up and reading the intake pressure at idle. -0.30 mBar = 0.00 psi.



Some of you might remember that I have a very crude ram-air system already in place on my car. All I did was cut a hole in the fender liner just in front of the front left wheel.



I decided that the best way to see if the ram-air system was working was to get the car up to 60 mph and then cruise along steadily in 5th gear on flat ground. That way, the engine will be consuming a minimum amount of air, and this gives a chance for pressure to build in the intake track. So, I took the car out for some runs at 60 mph and here are the pressure measurements I got:

ram-air hole covered up: -0.01 psi
ram-air hole opened up: -0.01 psi

So, my ram-air system ain't doing jack diddly for making pressure. I guess I shouldn't be too surprised because the fender liner is anything but air tight. I do think though that having the hole down there allows cooler air to get into the fender well. I also took a few more pressure observations.

1) The pressure never went positive.
2) Strongest vacuum generated was -0.5 psi at WOT 6000 rpm in 2nd gear. -0.5 psi is not too bad at all. Goes to show that the OEM SVX intake system is pretty good.

Next phase will be to install a real ram air system like SVXRide has and get some pressure measurements from that.

[SVXRide]

Real ram air system? What real ram air system???
-Bill

[svxfiles]

Originally Posted by mbtoloczko

Next phase will be to install a real ram air system like SVXRide has and get some pressure measurements from that.

My ram air system is 5 psi at 5000 rpm.

[CigarJohnny]

Originally Posted by svxfiles

My ram air system is 5 psi at 5000 rpm.

HAH hah! That's like calling a Colt 1911 a pellet gun.

[mbtoloczko]

Originally Posted by SVXRide

Real ram air system? What real ram air system???
-Bill

I thought you had that OEM JDM CXW S4 SVX ram-air system installed.... :-)))))

BTW, if anyone is thinking about trying to get some HP from an aftermarket air filter, these pressure measurements tell you the max HP increase that you can get. If you assume the -0.5 psi at WOT 6000 rpm is due to the air filter alone, and you assume that your aftermarket air filter removes all the pressure drop, then the most HP you can expect to gain is around 0.5/14.7*230 = 8 HP. Its more more reasonable to assume that the stock air filter is only responsible for about 1/2 of that pressure drop, so a more reasonable HP increase you could expect from an aftermarket air filter is about 4 HP.

[oab_au]

Originally Posted by mbtoloczko

I thought you had that OEM JDM CXW S4 SVX ram-air system installed.... :-)))))

BTW, if anyone is thinking about trying to get some HP from an aftermarket air filter, these pressure measurements tell you the max HP increase that you can get. If you assume the -0.5 psi at WOT 6000 rpm is due to the air filter alone, and you assume that your aftermarket air filter removes all the pressure drop, then the most HP you can expect to gain is around 0.5/14.7*230 = 8 HP. Its more more reasonable to assume that the stock air filter is only responsible for about 1/2 of that pressure drop, so a more reasonable HP increase you could expect from an aftermarket air filter is about 4 HP.

Thats very interesting Mychailo, I have allways thought that the inlet system was about the best you could get. This sort of testing is the only way to sort the real from the crap. Makes you wonder about all those blokes that could really feel the extra HP after fitting, a "Real Green, STI, All the power you need, air filter. Can,t wait for you to test the E Ram, and all the other Great power adders.

Harvey.

[SVXRide]

"jack diddly"

and yes, it is the OEM JDM CXW S4 SVX ram-air system that I have on my car

-Bill (looking forward to continuing the Mychailo-driven R&D effort on the East Coast!)

[freak customs]

thought (maybe already been tried): regarding the ram-air idea... what about attaching a sealed tube to the cutout in the filter lining and using a tube filter?

[mbtoloczko]

Originally Posted by freak customs

thought (maybe already been tried): regarding the ram-air idea... what about attaching a sealed tube to the cutout in the filter lining and using a tube filter?

My present plan is to copy SVXRide's ram-air system. He uses the stock airbox and part of the stock intake resonator. Its a very clean design. Check the "breathing" folder his locker. Look at the pics near the end.

[mbtoloczko]

Moved the manometer tube to a different port on the intake track and recorded -0.7 psi on two 2nd gear WOT to redline runs. If I can eliminate that pressure drop with a ram-air system, then I'm looking at about 0.7/14.7*230 = +10 HP on the road.

Bill, I'll put the manometer in the mail to you today.

[SVXRide]

Originally Posted by mbtoloczko

My present plan is to copy SVXRide's ram-air system. He uses the stock airbox and part of the stock intake resonator. Its a very clean design. Check the "breathing" folder his locker. Look at the pics near the end.

Look even closer and you'll see that that was my "version 1" (3 inch system). My "version 2" (4 inch system) is a much, much better design.
-Bill (hoping that manometer-based numbers prove out the "much, much better" comment )

[Myxalplyx]

Very interesting posts! Any more manometer readings? I would love to read about anyone elses experiences with this device. Read a lot about it in an article called 'Eliminating Negative Boost' in some online magazine. Good stuff! I....Need......more......Info....

I'm going through a host of intake threads and posts throughout the years to get feedback. I like this kind of data.

[mbtoloczko]

Originally Posted by Myxalplyx

Very interesting posts! Any more manometer readings? I would love to read about anyone elses experiences with this device. Read a lot about it in an article called 'Eliminating Negative Boost' in some online magazine. Good stuff! I....Need......more......Info....

I'm going through a host of intake threads and posts throughout the years to get feedback. I like this kind of data.

My latest measurements are here:

http://www.subaru-svx.net/forum/showthread.php?t=31238

It looks like you've been to that thread though. I was planning to duplicate SVXRide's latest setup, but so far, I'm pretty happy with the simple ram-air system, so I haven't gone as far yet as to cut my bumper. Plus, I haven't been very happy with the ram-air funnel that I bought to mount inside the bumper. I've been trying to find a way to form it, but it hasn't been easy.

[svxfiles]

Originally Posted by mbtoloczko

My latest measurements are here:

http://www.subaru-svx.net/forum/showthread.php?t=31238
Plus, I haven't been very happy with the ram-air funnel that I bought to mount inside the bumper.

I went drag racing with a strait 3" tube ram air system, (as shown in my avatar, if you look REAL close) and switched it out to a home made funnel, about 4" X 6" (about a foot long) and saw no gains that day on back to back runs.
So I removed it, cleared the codes and ran faster with the strait 3" tube.
I realize later it was WAY too rich, but the funnel did not help me that day.

[SVXRide]

Cut the bumper? Who said anything about cutting the bumper?
-Bill