Breather question for you blower guys.
 

Im building my first blower (Roots) motor and I'm not sure about venting the crank pressure. I know blowers increase crank pressures. Wondering what most do and what works good. I know the best route is a crank vent. system but I'm not willing to spend that kinda money yet! I WAS planning on (and just bought) (2) -12 fitting to weld to each cover and running 2 -12 lines to a catch can with breather on it. BUT, the more I look at the hole size of -12 fitting the more I think that its looks too small. I was gonna go with the -14 but the fittings are soo big that I thought they be an eye sore! Will the -12 be too restrictive? Now Im wondering if I if I should go with (4) K&N breathers. ALL I KNOW IS I DONT WANT ANY OIL BLOWING OUT ANYWHERE!!! Thats why I would like to go with positive lock set-up. Im sick of wrapping my K&N breathers with a sock to catch the oil!

I run -8 fittings and lines in both covers to the puke tank... if you're concerned, run a - 8 line from puke tank lid/vent to bottom of air cleaner/arrestor to create a vacuum in the tank,
my engines are 1100's with 14:71's and i dont have issues with CC venting

Thanks, do you get much oil in puke tank after running hard?

nope... more condensation than anything... I don't even run the tanks anymore since I put power into the scarab... I think if you pay attention to your ring selection and pay close attention to your ring type and what you set your gaps at, you won't need the tank...

What rings do you run? I was planning on gapless rings but figured I'd call and ask total seal what they recommend but haven't ordered yet.

many variables... callme up if you want some help, Alan 905-722-6684

Same here. I ran AN-12 hoses from both valve covers to canton racing puke tanks. All I've gotten so far is water when I've drained them. I have 14-71 blowers. Some people insist on a breather system with blowers. Even if your rings are perfect, you are going to be blowing some air through the crankcase. I would expect that in rough water, running hard, the crank will whip up some oil mist and send it to the breathers.

I found a couple of solutions. I always used the KN breathers with no problem. Makes life simple.

Use at least a 6" tube under the KN.
Make sure there is a baffle under the tube (inside the valve cover) so you don't have a rocker sending a jet of oil up there.
Put fuel cell foam in the tube, that seems to catch the oil mist and let it drain back into the valve cover.

Of course non of this will work if there is a blow-by problem.

and that's all she wrote!!! :lolhit:

ring seal is critical on a blower motor, any motor for that matter, but more so in a boosted engine... gapless rings are an unecessary expense, just use a good stainless top ring and set your end gaps correctly, and have your machine shop pay extra close attention to the honing process as the correct cross hatch will allow the ring to spin properly in the ring land of the piston, if this doesn't happen, it doesn't have a snowballz chance in hell of sealing!!

I run the vintage Chevy/Mercruiser finned valve covers, with push in style moroso/K&N kind. No issues with oil blowing out of them. 6lbs of boost. speed pro plasma moly file fit rings. Nothing fancy here.

Theres a huge debate in gapless vs non gapless in the racing world. Most people simply assume a gapless style rings seals better, well, because of the no gap thing. Yes, on the engine stand it will show very low leakdown numbers because of this, compared to a traditional gapped setup. But, like big al kinda said, theres more to ring sealing than that. Traditional rings are designed to seal when the engine is running, not sitting still. It needs cylinder pressure to seal the rings up . Its how they work by design.

So if a gapless setup shows 2% leakdown on a tester, and a tradional ring shows 12%, that doesn't necessarily mean at 6000RPM the gapless seals 10% better. Ive seen blower engines have blowby with gapless rings, and traditional rings.

Im not saying gapless aren't good, I just think most people buy them based on what I said above. Still lots of racers and big engine builders running the gapped stuff. basically I think it comes down to personal preference and cost.

Here's the thing about leakdown testers, they really are not measuring percentages. They are measuring the pressure drop across a small orifice. As the flow goes up the pressure drop increases also. And as Thunder pointed out this is under static conditions. The percentage number is strictly relative to that particular flow meter.

They are great for diagnostic use to isolate a bad cylinder, or to get a baseline for a particular engine. But don't fixate on those numbers! 12% on the leakdown tester does not mean you are losing 12% of the combustion pressure.

The real test is to measure the actual flow out the breathers on a running engine. Back in the day we used a J-tec flow meter on our dyno to do just that. I cannot remember what the numbers were but they were really low on a healthy engine. I think I'll look for some of our old dyno sheets to refresh my memory.

If you can feel puffing or a breeze out the breathers there is a problem. A happy engine will just have a little vapor drifting out.

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