Why a Catch can over a separator ? The differences explained.

[Modular Racing]

We have been getting alot of emails in regards to the difference between a separator and a catch can, so we decided to post so that others can make the correct decision when buying.

What most people call a catch can is actually just a separator, the type is truly defined by its location, if it is mounted inline with the PCV hose it is a separator. A separator ONLY works when the vehicle is in vacuum (NOT boost) this is because the PCV closes the moment the manifold sees any amount of boost, at this point the engine crankcase switches breathing from the PCV side to ONLY the air inlet side, the problem is on supercharged/turbocharged applications the air inlet side (from the valve cover) connects to the suction side of the supercharger/tirbocharger, meaning the supercharger is now sucking the oil vapors originally being caught by the separator and now putting it into the engine and ultimately into the combustion chamber which causes detonation and lowers the octane rating of fuel within the chamber. When the vehicle is wide open this is the most important time to keep the oil vapor out, which unfortunately the separator is no longer doing. Kits such as the MMR Breather kit allows the crankcase to vent the power robbing oil vapor into the atmosphere at WOT by way of a filtered catch can that catches the oil and separates the air -Much like the separators on the pcv side. Some tuners prefer not to vent the valve cover to atmosphere as it can cause a lean condition at cruise if the vehicle has not been tuned for it. A breather tank however DOES NOT cause a lean conditon (tuned or not) at WOT or anytime in boost if the inlet tube is properly capped off where it originally joined to the rubber inlet hose between the TB and MAF.

We hope this explains the differences! Ultimately, the best combination would be to have both, but in the realm of performance the most important for your engine is the one that works under WOT which is the breather kit.

Questions, comments - we are happy to answer anytime we are online.

MMR
www.modularmotorsportsracing.com

 

[bobster]

Is it ok to run both sides to the same breather and if so should you eliminate the PCV? (procharged supercharger)

 

[cb900f]

Is it ok to run both sides to the same breather and if so should you eliminate the PCV? (procharged supercharger)

I assume you mean both valve covers to the same breather. Yes, that's the recommended route. Especially when using FI. Just block off the ports on the intake side.

 

[Modular Racing]

As answered above - YES , in fact we suggest 1 breather per 1000HP - the more HP - the more cylinder pressure which makes more blow by.

The MMR kit below is plug and play for either side of the valve cover and is available in silver or black anodized

 

[bobster]

Does your kit have two ports for both sides (valve covers) or just one?

 

[Modular Racing]

They are available both ways but normally only one is required for 1000HP or less, dont forget the valves covers are joined by the timing cover so it is not needed to vent both (unless over 1000HP)

 

[cb900f]

They are available both ways but normally only one is required for 1000HP or less, dont forget the valves covers are joined by the timing cover so it is not needed to vent both (unless over 1000HP)

Interesting. So what do you put on the port for the valve cover that is not hooked to the catch can?

 

[GearsNBeers]

http://www.svtperformance.com/forums/showthread.php?890584-How-to-Valve-cover-breathers-for-under-30

So would doing something like this create a lean condition for N/A setups? Really wouldn't you must need the one on the passenger side?

 

[grnenvy]

This is the same setup I made for my car and its flawless except for the oil smell u get once in a while at the stop light. Since then I moved my system inside the bumper cover area and the smell is almost gone. I just pulled my blower so I could replace my lower manifold and my intercooler and lower intake had Zero oil in it. Also the blower was dry as can be that's proof that this imop is the best setup.
With out this setup u will have small puddles of oil either in the T-body, blower or lower intake manifold.

 

[Modular Racing]

Interesting. So what do you put on the port for the valve cover that is not hooked to the catch can?

We would normally suggest that this be the PCV side and that is left to operate as intended, the hole on the inlet tube coming from the air filter/mass air meter simply needs to be plugged.

 

[Modular Racing]

http://www.svtperformance.com/forums/showthread.php?890584-How-to-Valve-cover-breathers-for-under-30

So would doing something like this create a lean condition for N/A setups? Really wouldn't you must need the one on the passenger side?

A filter should never be added to a valve cover on a Modular engine, the baffles are simply not designed for it, they will saturate the filter and leak causing possible spill and fire hazards if dripped onto a hot header. You see the pics of the oil that comes out of the seperators - well - that has to go somewhere and a soaked / leaky filter is not the answer.

 

[bobster]

Even though they are connected my way of thinking is like the big ole Hi- C can of juice that you had to puncture in two spots to get it to pour right. You want to let fresh air come in and the excess fumes/pressure to go out, wouldn't that be better/easier with two openings like the Hi-C can?

 

[hand-filer]

So to summarize:
- Leave the PCV system as is or add a quality inline separator between the PCV and the supercharger.
- vent the driver side valve cover to atmosphere with a catch can and cap of the port on the intake tube.
Did I get that right?

We would normally suggest that this be the PCV side and that is left to operate as intended, the hole on the inlet tube coming from the air filter/mass air meter simply needs to be plugged.

 

[bobster]

My procharger and most kits block off the PCV and port going to intake. Why is that, Boost or something else? seems like a PCV valve would close onder boost and open under vacuum.