Crankcase ventilation

Peter Delaney

GT40s Supporter
In keeping with the KISS principle, my setup is as follows :

- Edelbrock rocker covers with stock open Edelbrock breathers
- Leave one breather open
- Block off the other & fit a spigot under the sealed top
- Run a 3/16" pipe from the spigot to the main vacuum line (used for power brakes)
- Stick a 1/16" orifice restricter in the above pipe (a bit of brass rod with a 1/16" hole)

This seems to allow just enough vacuum to draw any crankcase vapours into the intake manifold (fresh air drawn in thru the open breather, fumes sucked into the manifold via the closed/spigotted breather).

With both breathers open, I could see the fumes in the rear vision mirror when stopped at the lights, and then got to clean them off the rear window & rocker covers ! With the vacuum setup described above - no fumes, no crap on the rear window or rocker covers, AND, it doesn't seem to affect the tuning at all (such a tiny bleed from the crankcase).

The pic shows the LHS blocked-off breather with the rubber tube heading off to the main vacuum line.

Kind Regards,

Peter D.
 

Attachments

Markus

SPRF40
Lifetime Supporter
Hi Guys,
I have to resurrect an old thread.
In the picture you see my setup for crankcase ventilation.
20210602_150349-2.jpg

Certainly the breather on top of the left valve cover did not make too much sense from the beginning but it did not bother me much as there was little to non oil dripping out. However - the situation changed - obviously after 10k miles I have some more blowby and the breather started to drip oil. During driving I don't really recognize but after cooling down there are some drops which fall directly onto one header pipe and further down.
My idea is to put an oil cap (which seals the gap) onto the valve cover to replace the breather!? What do you think - any recommendation or reasons against?

Oil cap e.g.:

In the past I never had any oil accumulate in the puke tank.

Thanks in advance.

Markus
 
Hi Guys,
I have to resurrect an old thread.
In the picture you see my setup for crankcase ventilation.
View attachment 115662

Certainly the breather on top of the left valve cover did not make too much sense from the beginning but it did not bother me much as there was little to non oil dripping out. However - the situation changed - obviously after 10k miles I have some more blowby and the breather started to drip oil. During driving I don't really recognize but after cooling down there are some drops which fall directly onto one header pipe and further down.
My idea is to put an oil cap (which seals the gap) onto the valve cover to replace the breather!? What do you think - any recommendation or reasons against?

Oil cap e.g.:

In the past I never had any oil accumulate in the puke tank.

Thanks in advance.

Markus
Read post 2, a bit of work, but works.
 

Howard Jones

Supporter
Here's how I did my SLC. Since I took this picture I have increased the size of the two hoses from AN8 to AN12. Two AN8 lines are not enough. That's a combined hole .8 inch in diameter and that's not big enough! Since increasing to AN12 (1.2 inch combined) the oil leaks have gone away so I know that's worked. I am also in the process of redoing the baffles inside the valve covers to try and decrease the oil being pushed out of the valve covers. Why have I done all this? To keep the oil in the motor or in the catch can and nowhere else! This engine will pump out a 1/2 quart into the catch can in the course of a weekend at the track. That would be about 350 -400 miles at 50 -100% throttle @ 4000-6500 RPMs.

Jac told me a long time ago that the AN6 hoses were too small for a track motor. He was right again. I was seeing the crankcase getting pressurized to the point that it was blowing oil out of the dipstick hole. I should tell you that this is a fresh rebuild motor with very carefully set ring end gaps, new near-perfect valve seals, and a very carefully hand-done 5 angle valve job.
 

Attachments

Here's how I did my SLC. Since I took this picture I have increased the size of the two hoses from AN8 to AN12. Two AN8 lines are not enough. That's a combined hole .8 inch in diameter and that's not big enough! Since increasing to AN12 (1.2 inch combined) the oil leaks have gone away so I know that's worked. I am also in the process of redoing the baffles inside the valve covers to try and decrease the oil being pushed out of the valve covers. Why have I done all this? To keep the oil in the motor or in the catch can and nowhere else! This engine will pump out a 1/2 quart into the catch can in the course of a weekend at the track. That would be about 350 -400 miles at 50 -100% throttle @ 4000-6500 RPMs.

Jac told me a long time ago that the AN6 hoses were too small for a track motor. He was right again. I was seeing the crankcase getting pressurized to the point that it was blowing oil out of the dipstick hole. I should tell you that this is a fresh rebuild motor with very carefully set ring end gaps, new near-perfect valve seals, and a very carefully hand-done 5 angle valve job.
To add a bit of 'WHY' to Howards post... WHY do V8's often seem to be 'Heavy Breathers.. A lot is due to the layout of Rods/Pistons & Crankshaft. Close your Eyes and switch you mental vision on. As the two front pistons move down ( 1 in each bank ) the air under the pistons has to go somewhere- you would think the 4 middle cyls immediately behind would help but they are not moving much due to crank position so the air tries to get to the space under the two rear cylinders, rotate the crank a half turn and the situation is reversed. The center 4 cyls in the meantime are having a similar smaller situation happening, but not as big in terms of displacement. Add to this the larger effect of stroker cranks and larger bores plus many engine blocks having 4 bolt mains to reduce that window for the air to move back and forth is why a engine tends to leak out of the breathers especially when compression is raised along with RPM.
 

Markus

SPRF40
Lifetime Supporter
Thanks Jac Mac and Howard,

@ Jac Mac, I have to look into this - would be a winter project > it is some work > mmmhh - have to change the oil pan gasket some when soon anyway.......

@ Howard, on you pic it's hard to see... you have a sealed oil cap on your oil filler hole? is it with a thread or push on only?

Thanks

Markus
 
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