What valve for exhaust EVAC?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

What valve for exhaust EVAC?

Post by ELS »

What valve do I use for exhaust crankcase evacuation?
I have a 1/2" tapered bung welded into the header, I checked with a vacuum/boost gauge hooked up and I definetly need a valve there since the pressure equalizes around 0, and at low rpm it bounces between -0.4bar and 0.3bar.

What kind of valve is even able to respond fast enough? it's a 4 cylinder engine so at 6k rpm so it would have to be able to respond above 200 times per second... right?
I was thinking of getting a water valve, if the plate there melted I would try to replace it with a light aluminum piece, and rolled up teflon for the gasket probably.
In-Tech
Vendor
Posts: 2812
Joined: Wed Apr 21, 2010 4:35 am
Location: Fresno, CA

Re: What valve for exhaust EVAC?

Post by In-Tech »

Anything wrong with this? https://www.moroso.com/crankcase-evacua ... stem25900/
At rpm with any kind of mass flow, the pulses will be minimal. Hook up a vacuum gauge to your evac points and make a quick blast to check if your evac is doing anything.
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: What valve for exhaust EVAC?

Post by ELS »

In-Tech wrote: Sun May 21, 2023 2:15 pm Anything wrong with this? https://www.moroso.com/crankcase-evacua ... stem25900/
At rpm with any kind of mass flow, the pulses will be minimal. Hook up a vacuum gauge to your evac points and make a quick blast to check if your evac is doing anything.
I already said, it equalizes at 0 at high rpm, I assume because the analog gauge cannot respond fast enough
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: What valve for exhaust EVAC?

Post by ELS »

ooh, I see what the problem is. Im not using the venturi effect, instead just the scavenging vacuum.
but wouldnt I get even higher vacuum if I find a fast enough valve? So like the venturi vacuum + scavenging pulse = more vacuum?
In-Tech
Vendor
Posts: 2812
Joined: Wed Apr 21, 2010 4:35 am
Location: Fresno, CA

Re: What valve for exhaust EVAC?

Post by In-Tech »

Hiya,
Not to be rude, it sounds like you have more crankcase vent than evac. Zero isn't a bad number -.5 bar would be nice though :) Analog gauges can be a bit slow, but will show trends, if you don't have at least 25hz data acquisition on the digital, it's not worth the effort.

A fast moving valve will always help, I don't think that is the issue though. It would take a huge diaphragm with minimal spring seat pressure and a ton of rate to make any kind of difference, if at all.

p.s.
I appreciate you are chasing a couple hp at a time. Try changing the angle of your scavenge pipe, place it before a merge collector and think ~60 degrees instead of 45. It's weird that it seems to work better sometimes than the 30 degree.
Heat is energy, energy is horsepower...but you gotta control the heat.
-Carl
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: What valve for exhaust EVAC?

Post by ELS »

In-Tech wrote: Sun May 21, 2023 2:48 pm Hiya,
Not to be rude, it sounds like you have more crankcase vent than evac. Zero isn't a bad number -.5 bar would be nice though :) Analog gauges can be a bit slow, but will show trends, if you don't have at least 25hz data acquisition on the digital, it's not worth the effort.

A fast moving valve will always help, I don't think that is the issue though. It would take a huge diaphragm with minimal spring seat pressure and a ton of rate to make any kind of difference, if at all.

p.s.
I appreciate you are chasing a couple hp at a time. Try changing the angle of your scavenge pipe, place it before a merge collector and think ~60 degrees instead of 45. It's weird that it seems to work better sometimes than the 30 degree.
Read my latest comment before yours if you didn't.

I measured the vacuum without it connected to the crankcase, straight to the manometer.
I'll get a steel tapered thread pipe or fitting and weld the pipe that goes inside the collector so I get the venturi vacuum instead of mainly just the scavenging pulses.
BLSTIC
Expert
Expert
Posts: 870
Joined: Wed Dec 05, 2018 7:14 pm
Location:

Re: What valve for exhaust EVAC?

Post by BLSTIC »

It sounds like your evac pipe is in the wrong spot.

Is this the subaru? What headers have you got and where is the valve?
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: What valve for exhaust EVAC?

Post by ELS »

BLSTIC wrote: Sun May 21, 2023 6:10 pm It sounds like your evac pipe is in the wrong spot.

Is this the subaru? What headers have you got and where is the valve?
4-1 EL headers, The bung is welded at a ~45 degree angle towards the exit in the collector. right where it merges.
I already said, I'll add the venturi tube which probably is the problem.
I did not test it under full load since it was obvious it also had positive pressure pulses.
BLSTIC
Expert
Expert
Posts: 870
Joined: Wed Dec 05, 2018 7:14 pm
Location:

Re: What valve for exhaust EVAC?

Post by BLSTIC »

Best location I've seen for a pan evac so far was the middle of a "merge spike" in the centre of the collector. It likely lined up with the start of the "choke" of the collector. Largely restriction free too, but not if you are inserting from the side, only really doable on construction of the header.

Probably much easier to make on a 4-2-1 y joint
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: What valve for exhaust EVAC?

Post by ELS »

BLSTIC wrote: Sun May 21, 2023 9:47 pm Best location I've seen for a pan evac so far was the middle of a "merge spike" in the centre of the collector. It likely lined up with the start of the "choke" of the collector. Largely restriction free too, but not if you are inserting from the side, only really doable on construction of the header.

Probably much easier to make on a 4-2-1 y joint
Drilling into the part-hardenned welds was a pain. I used a less powerful drill so my wrists weren't ground into powder, and surprisingly I broke 0 drill bits.
I welded a cast bung in there, cut from a regular T pipe fitting, It welded really great for cast iron but it may crack from the vibrations
nxtruck
Pro
Pro
Posts: 251
Joined: Wed Dec 20, 2006 5:12 pm
Location: S.E. Mo.

Re: What valve for exhaust EVAC?

Post by nxtruck »

Try an Echlin# 229000 from your local NAPA store.
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: What valve for exhaust EVAC?

Post by ELS »

I could not get a sufficient vacuum from the header, there was BARELY anything there.
I suspect it's beacause of the oversized header; 2.5" exit on a worn 1.6L...

Afterwards I connected the evac line to the intake, where it was connected from the factory but I plugged the rocker cover air inlets so air didn't just leak back in, and I got -0.65bar of vacuum in the crankcase at idle, The same pressure as the intake, so it's apparent that there's not that much blowby.
It would slowly drop when I went full throttle of course, but only after like a good 10 seconds would it be pretty much back to atmospheric pressure.

After turning the engine off it held crankcase vacuum for around 15 seconds.
It's odd since the engine has really low compression in all but one cylinder, yet it still has high manifold vacuum, and holds crankcase vacuum just fine so where is that compression going??
I did have a theory that the heads are cracked around the spark plug, quite common on subaru engines it seems. I've had the spark plug cable just pop off 3 times now, but I haven't spotted any cracks in the spark plug bore so idk.
BLSTIC
Expert
Expert
Posts: 870
Joined: Wed Dec 05, 2018 7:14 pm
Location:

Re: What valve for exhaust EVAC?

Post by BLSTIC »

Ignoring the health concerns of your engine... Exactly what headers are you running? And do you have a pic of them or just the collector region, preferably with a dodgy paint drawing showing where you have mounted the evac tube on the collector and how far it pokes in at what orientation.

And if it's a 2.5" choke, yes it's too big. My simulations say that a cross plane v8 can fit 250-ish hp through each 2.25" choke if it's a good merge and a 4-2-1 design. So your 100hp even fire collector would need a choke somewhere in the region of 1.5-1.75" (and as a result of that math, pipes that are definitely not larger than the merge coming into them).

EJ engines come in up to 2.5L and 125kw in basically identical looking motors that bolt up exactly the same. If you have to take the engine out and don't have rules that stop you, you'd be crazy not to swap.
Post Reply