Here is another post that deviates a bit from car audio but may still be helpful to a lot of people. This will go over how to install a dual oil catch can setup for my 2007 STI that doesn’t break the bank as much as the higher quality custom kits from name brand manufacturers. This is not meant to take away from those companies’ sales. In fact I used to sell Mishimoto, Boomba Racing, Cusco, Beatrush, and ProSport catch cans. These kits are much higher quality, have the proper R&D behind them, and shouldn’t be completely overlooked when considering a catch can or air oil system. I am offering a cheaper alternative geared more towards DIYers that like to build things from scratch and source their own materials.

Why to use an oil catch can

First thing you should know is why a catch can is beneficial. The way the stock system is setup, air is pulled from the engine crankcase and valve covers using vacuum from the intake tract. The problem with this is that this air contains oil vapors which often condense somewhere in the intake. This is worse on turbo cars or cars that are more susceptible to blow-by which will pressurize the crankcase and push more oil out into your intake. This oil in your intake air will obviously mix with the combustion gasses and lower your effective octane rating which can lead to knock on certain engines. The oil can also pool up in the intake tract and cause air flow problems, especially on forced induction cars since pressurized air won’t hold liquid as well.

The catch can intercepts the path of this air back to the intake and condenses the oil in the can. The reason I chose the cans i did is because they have a baffle and a filter media in them to help with condensing the oil back to a liquid. Some people also put other filter media in the cans to help with this.

These pictures show what happens without catch cans.

One thing I realized while doing this was that figuring out a clean looking mounting solution was difficult. This part alone may make it worth a high quality custom fit kit. The catch cans come with a couple of self tapping screws which are probably fine for mounting, but I decided to go with a more robust solution.

Below is a diagram and parts list along with links to all of the parts I used for my kit. My total cost at the time of purchase was around $130. Price will fluctuate depending on when you’re reading this.

Click Image below for high resolution copy.

The guinea pig

How to install an oil catch can

For mounting location, I used the normal area on these cars which is the passenger side strut tower after removing the engine harness bracket. I found an old bracket from an Escort 9500ci install that worked pretty well and mounted it to the strut tower with these nutserts, these screws, and these washers (check out this awesome DIY nutsert tool. The one I put together is a variation of this. Works great). I also gave it a quick spray of undercoating to help prevent rust, but I was too lazy to jack the car up to spray the other side. Maybe next time I take that wheel off.

I used the install instructions from both Mishimoto and Radium to base my install on, but to make it easier, I just vacuum capped the little white plug that runs from the back of the PCV valve tee fitting to the turbo inlet and used the factory metal valve breather tubing that’s mounted to the intercooler.

To get the 1/2″ hose to fit on the turbo inlet, I used a heat gun and the end of a ratchet wrench to expand it. Didn’t use a hose clamp on this fitting since I put it on with the hose still warm, so it shrunk in place.

These cans come with fittings made for 1/2″ hose, so I needed two 3/8″ hose barb fittings. That’s where the brass ones came from. For my setup, I needed one 2 port and one 3 port catch can, but I liked the blue which was only available in 3 port. I used the plug that came on the bottom of one can to plug the extra inlet port for the PCV can since I put valves on the bottom of the cans to drain them. I used some thread sealant to seal the fittings on the cans.

Scroll through the pictures below to see what I’m talking about.

Oh and if you want a sweet LED hood light kit, let me know: CAAInstallations@gmail.com. It works great. I had to finish up after dark and could see most of what I needed with just that one light.

Update:

After I had this installed on the car for a bit, I would recommend upgrading to higher quality drain valves. One of mine had a very slow leak to it, but other than that, this kit worked out great. I’m not sure how it’s holding up now because I sold the car a few months after installing this.

If this helps you out, let me know with a donation. I would really appreciate it. Just select the amount and click on the “Donate” logo. I spent a lot of time on this. Also, if you need help with anything, leave a comment below or sent me an email: CarAudioAdviceBlog@gmail.com. Thanks!

Why not just shift at redline?

You might be wondering why you need to know where to shift when there’s that nice red line on the tach showing you were to shift. The answer: because redline isn’t always the most optimal shift point. The way an engine makes torque and gear ratios have a lot to do with this.

How to find optimal shift points

I made an excel spreadsheet to calculate the best shift points for your car. The trick is you need to do a little research and googling to find a few input parameters.

Download and open this spreadsheet to follow along (click here).

Everything in gray boxes on the spreadsheet is what you need to input yourself. Everything else will be calculated for you.

Step 1

First you need to find the gear ratios and redline rpm for your vehicle. Google will probably be your best bet here, or if you have a Subaru up to model year 2007 there is a link in the file to gear ratios since I used a 2006 STi for the example in the spreadsheet. Enter all of this in the gray boxes on the ‘Car Spec’ sheet of the file.

Step 2

Click on the Tire Size Calculator link either here or in the spreadsheet. This will bring you to discounttire.com’s calculator. Input your tire specs here and take the “Revs per mile” result from there and input it into the last gray box on the ‘Car Specs’ sheet of the file.

Step 3

You will need a dyno graph of your car for this step, or you can find one on google for a car with similar mods. If your car is extremely modified, chances are you already have on of these. This is the trickiest part, but once you play around with it some, you’ll get the hang of it.

Click on the Plot Dyno Using WebPlotDigitizer link either here or in the spreadsheet.

• Go to file->load image
• Upload the image of your dyno graph
• A “Choose Plot Type” box will pop up. Make sure “2D (X-Y) Plot” is selected and click “Align Axes”
• A little how-to will popup explaining how to define your axes. Click “Proceed”
• Now select one point on the X-axis (horizontal axis) close to the origin. You will notice a magnified box at the upper right of the screen. Try to get it as close on the line of the actual X-axis on your graph as possible and at a legible rpm
• Select a second point  on the X-axis using the same technique further down towards the end of your graph, again at a legible rpm
• Your third click here will be the first point of your Y-axis. Do like you did for the X-axis selecting a legible torque value
• The fourth and final click for defining the axes will be your second Y-axis point. Do the same as above
• It should look similar to this:

  

• On the right of the screen, click “Complete”
• It will pop up with a calibration screen. Remember I said pick legible points? Input those here in the correct order
  • For my example above:
    • X-Axis Point 1 = 3000
    • X-Axis Point 2 = 5500
    • Y-Axis Point 1 = 100
    • Y-Axis Point 2 = 300
  • This is why I say pick legible points
• Now on the ride side, make sure “Add Point (A)” is selected.
• Input 32 data points following along the torque curve. This is very important to input exactly 32 data points, or the excel file won’t function properly.
  • It should look similar to this: 
  • It will take a while playing around with this since you need an exact number of data points. Sorry about that. But be sure to put them all in order from low rpm to high rpm (x-axis values). You can use the “Adjust Points (S)” option to move them further apart, etc. to get them where you need them (but I think it’s just easier to “Clear Points” and restart); just keep them in order!
• Once you input 32 data points along the torque curve, click on “View Data”
• The data will pop up in a screen. Click on “Download .CSV”

Step 4

Open up the new .csv file you downloaded of your data points. Copy and paste these values in the gray “RPM” and “Tq (lb-ft)” columns on the ‘Dyno’ sheet of the Tractive Force excel file. Note: In the .csv file you downloaded, the first column will be rpm and the second will be torque, so you can copy and paste both columns at the same time into the spreadsheet

You can do the same for the horsepower curve like I did, but it’s just to make the excel sheet look pretty and give you peak hp numbers

Now look at the graph on the ‘Dyno’ sheet of my excel file and make sure it looks similar to your dyno graph. It may be off due to scaling, but make sure it follows roughly the same curve. If not, try the above steps again and make sure everything was put in properly.

Step 5

The next sheet, ‘Tractive Force Graph’ is where the magic happens. This is how you will find out what speed to shift at.

Notice in my example each curve represents a different gear. The green circle shows where 2nd gear intersects 3rd gear. This intersection occurs at around 52 mph. That means shift at 52 mph from 2nd to 3rd.

Why is this the optimal shift point? Well when the second gear curve drops below the 3rd gear curve that means your torque in 2nd is less than what your torque would be in 3rd gear.

So to find shift points for all gears using my example:

• 1st – 2nd gear shift: At redline because the first gear torque curve never drops below the 2nd gear curve. Therefore, you need all of 1st gear. 34 mph
• 2nd – 3rd gear shift: This is the example from above: 52 mph
• 3rd – 4th gear shift: 68 mph
• 4th – 5th gear shift: 93 mph
• 5th – 6th gear shift: Slow down you’re going too fast! Or 122 mph

Step 6

Now you can convert those speeds to rpm by using the ‘Tractive Effort’ sheet. For example, for 5th gear we want to shift at 122 mph. Find the 5th gear section on this sheet and look for 122 mph. You will have to do a little guessing for this part, but it will be close enough for all intents and purposes. 122 mph equates to right about 6200 rpm:

Notice that this is 300 rpm below redline. Due to the gearing on this car, it actually helps to short shift the 5-6 shift by a few hundred rpm.

Using this technique for all gears:

• 1st – 2nd gear shift: 6500 rpm (redline)
• 2nd – 3rd gear shift: 6500 rpm
• 3rd – 4th gear shift: 6300 rpm
• 4th – 5th gear shift: 6500 rpm
• 5th – 6th gear shift: 6200 rpm

Sorry these numbers aren’t calculated already for you, but that was beyond my excel expertise.

Conclusion

That’s how you find your shift points using this excel sheet. I know it’s not that straight forward but beats hand calculations any day.

Notice the gear ratios in the stage 2 2006 STi example car were pretty well designed from Subaru to let you wring out each gear to redline. You will probably notice the same for a lot of other cars. If so, great! That makes it easier for you to remember when to shift. Once you start doing some pretty crazy modifications or changing gear ratios, that is when you will probably find this of the most importance.

Again, if this helps you out, let me know with a donation. I would really appreciate it. Just select the amount and click on the “Donate” logo. I spent a lot of time on this. Also, if you need help with anything, leave a comment below or sent me an email: CarAudioAdviceBlog@gmail.com. Thanks!

Link to download “Tractive Force” spreadsheet (click here)