What catch can for Road Racing?
 

I am starting to finish up a LS1 swap into a BMW chassis to run ST2 with NASA. Its been an ST5 car with the BMW engine in the past.

Its a LS1 engine, ASA cam, valve springs, LS6 intake, ported throttle body, baffled oil pan and accusump.

I have seen so many different opinions on oil catch cans. What is the bet set up to go with for a road race car that is built for the track only? I have seen some people run the stock routing to two different catch cans, a clean side and a dirty side can. Thoughts?

Run the three available outlets via full size hoses into one large catch can with a breather or two, no PCV valve. It's that simple.

I think people run a clean side can in case of reverse flow, which other people run check valves for. I run throttle body to passenger side valve cover, later ls6 valley cover to Mike Norris can to intake and I have no evidence orreverse flow or much oil going in the intake, always will be some. I also crammed a stainless steel pot scrubber in the catch can to help catch oil vapor.

Some people have gone to greater lengths but it depends on your engine. Do a basic setup and see how it performs then go back and adjust as needed, that seems to be how most have success with the pcv

I dont RR but I AX and have gone to some lengths to get a zero-oil setup. I still have PCV. IMO, RXSpeedworks and MightyMouse are good. I actually have both, run in series (from LS6 valley cover, to MM can, then to RX can, then manifold. Hose from throttle body to pass side valve cover with check valve). The biggest actual issue I think is airspeed. The tiny 3/8 hoses most run just have too much velocity and the air doesn't slow down enough in the can. One guy on FRRAX has welded a 1/2 or 3/4 hose bung to his valve cover, to get lower air speed. For RR I think you should seriously consider 2 cans if you can find the room.

Find it strange that racers find it desirable to route crank case fumes into the engine intake and so dilute and pollute the programmed fuel air mixture. Because that's what a PCV valve does so please explain.

I figure the blowby must be either exhaust (which has no effect on AFR because the air and fuel have already combusted) or intake charge (negligible effect on AFR because it's pretty much the same AFR that the computer is commanding), so I doubt it affects AFR to a measurable degree.

At low throttle openings, when the intake is pulling the most vacuum,, so it doesn't matter if it costs some power, because the driver clearly isn't trying to get full power anyway - if they did, they would open the throttle some more, and the vacuum would go away. At high throttle, I do wonder how much blow-by going into the intake tract dilutes the intake charge. Not because of the effect on AFR, but because exhaust blow-by doesn't burn and it takes up space that could have contained fresh air.

As I understand it, pulling fumes from the crankcase into the intake was originally done to mitigate pollution. So we should all be thankful that most cars are set up that way. For track cars I'm not sure it matters, but I do like the idea of drawing fumes out of the case when I'm not under power. I've not seen proof that there are bad side-effects to exhaust and fuel accumulating in there over time, but it kinda seems like it would be less than desirable.

Mighty Mouse (among others, I suspect) has their breather set up to vent pressure (at high throttle) but not draw it in (during low throttle), and that might be the best of both worlds. I still plan to set mine up without a breather though.

Because I strongly suspect that catch can routing debates are just hair-splitting that makes a negligible difference in the end. :)

Because it's beneficial to not let pressure build up in the crankcase, freash air in there helps the engine and of course pressure build up is bad. Also the PCV system typically only takes in air at low to part throttle. That's why road racers have more issues since the engine runs full tilt most of the time and not always enough cruising for the pressure to equal out.

One thing I wish someone could explain is why the MM can cost 4 times as much as a quality Mike Norris can? I put $15 eBay cans on my street cars with a little doctoring up RTV on the fittings. I don't mind putting a little more on my race car but those prices are crazy

I ended up going with the Saikou Michi dual catch can. One for the clean side one for dirty side.

Same setup I have. I mostly auto-x/road race the car. Here is my last clean-out after the 2018 season.

https://cimg8.ibsrv.net/gimg/ls1tech...23550ff6b9.jpg
https://cimg6.ibsrv.net/gimg/ls1tech...bb3fcddfbc.jpg

Do you have any pictures of it installed? How did you rote your lines?

The pcv valve is just a little spring loaded plunger and doesn't direct anything anywhere. It uses pressure and vacuum to limit airflow and nothing else. If there's lots of pressure in the inlet side or vacuum in the outlet side it opens the plunger to equalize the pressure which keeps the engine from blowing gaskets. If there's a backfire in the intake (not common since mpfi came along) the valve slams shut and prevents the flame from entering the crankcase and blowing up the block (early pcv valves were documented as "flame arrestors")

People who don't understand how the pcv system works disable it by using open air breathers. The breathers do the same thing as the pcv system, but without any control over the pressure or where any excess oil vapor gets dumped. If you're going around the banked oval at Daytona would you rather the excess oil goes into the intake or dumps on the glowing red header or just gets dumped on the ground in front of the rear tires?

As for programming, the system you're running should already be in place when you get tuned. The tune will account for the airflow and vacuum conditions since it's being seen by the sensors. It's not nearly as complex as people pretend it is.

Only pic I could find. Its older and the cracked hoses have since been replaced but it should give you a good idea. I kept the PCV valve in place.
https://cimg5.ibsrv.net/gimg/ls1tech...fe1f160012.jpg

PCV system flows in 2 directions, they depend on whether or not vacuum is present. Under vacuum, vacuum is applied to the crank case. This supposedly helps with ring seal. At WOT the other side allows the gases to escape. Where they escape to is typically upstream of the throttle body, so the suction of WOT helps evacuate the crank case. All you ever wanted to know and more below. It's based on a 4 banger, but same concept.

https://motoiq.com/crankcase-ventila...d-n-a-edition/

That's my understanding too, the PCV system was introduced as part of a car's anti pollution system, before that ordinary cars did not have it nor did race cars. The problem I have with using a PCV on a race car is the fact as you mention of introducing polluted air into the induction system.

Before the pcv showed up in the early '60s cars had something called a road draft tube. It was a tube from the intake or valve cover that ran below the engine and used the air flow under the car to suck out the crankcase vapors. It had quite a few problems, but it worked better than the system before it which was massive oil leaks and limited engine life. If you ever rebuild a road draft car don't be surprised to find the tube has become home to wasps, spiders or lizards depending on your climate.

For a performance setup I'd recommend just unplugging the last bit of pcv line that runs from the valve to the intake and running it to a catchcan with a breather. The important thing is making sure that the can is big enough to handle every drop of oil you're pushing during your race and that the breather won't drip oil on anything hot or in front of the tires if it gets saturated. People always ignore those 2 things for some reason.

The idea of running it back to the intake is twofold: one is for emissions, and two ideally would be to use the suction to keep a vacuum on the crank case for better ring seal. The latter makes it critical to increase the breather hoses to -10 or -12.

Same size on clean and dirty side? I've seen a system that was -10 clean side x2 hoses (one to each valve cover), -6 dirty side single hose to intake as normal to keep velocity on that side. I think that particular system was a problem child as I haven't had any issues that bad but curious your thoughts.

The dirty side should be large to reduce velocity. The slower the air moves the less oil vapor it'll carry. Many catchcans are useless because the velocity is too high and the flow from inlet to outlet doesn't have enough material in between for the oil to grab onto.

I use a mighty mouse race can with a big line. Works fine.

https://scontent-mia3-1.xx.fbcdn.net...eb&oe=5CBF0076

That's what I was thinking, but one elaborate setup I saw was opposite of that with larger on clean and smaller on dirty side and that seemed counter intuitive, but he said it solved his oil consumption. Maybe there were other variables at work in that case.