PCV valves - hot air vs. Intercooled?

[Anthony P]

hot air and NA used Delco CV-770C (crosses to a Standard Motor Products V172)

86 and 87 IC turbo buicks used Delco CV-893C (crossed to a Standard V242)

I have both Delco versions in-hand and there is no physical difference on the outside other than part #.

Both have the letter "E" stamped on the rattle valve sealing surface. Is there any internal difference or were the 893C's created to have a "special" application to only the 86-87 intercooled engines?

EDIT: Delco CV-893C crosses to SMP V242. Typo where I originally listed SMP V272.

 

[mikestertwo]

There is a difference in air flow when the valve is open.

 

[Anthony P]

Thanks Mikestertwo. I curious so I'll bother SMP engineers tomorrow to learn if they will share the design data differences.

 

[Anthony P]

Standard Motor Products was able to provide me with some tech data for the hot air pcv valve - their part # V172 ( cross to Delco CV-770C). The flow data is at the top of the drawing.



Unfortunately, the tech rep was unable to locate a similar internal document for pcv valve V242 ( cross to Delco CV-893C) used on the 86-87 turbo buicks and the 89 TTA . I was hoping to learn the exacting difference but we'll have to accept the intercooled engine needed a higher flowing valve as Mikestertwo noted so a new design and new part was created.

 

[robertf]

Im not running one with no known issues. Big breathers on each VC. Am I missing something? I know the subjects been beaten to death for years. {Probably on most forums}

 

[Anthony P]

Robert,
No you're not missing anything. I have both NOS delco versions on the shelf in the garage. My engineering background got me curious as the difference between the two not whether the use of a pcv is needed.

EDIT ADD: GM 3.8l (3800) engine development team decided that the NA pcv valve already in production would meet the design criteria for the hot air engine producing 12 psi boost. However, that spec was determined to be inadequate for the LC2 producing 14 pounds of boost in a GN, etc, or 15 psi in a GNX or TTA, requiring the introduction of a new pcv valve design for the 86-87 turbo buicks and 89 TTA only.

It is interesting that a NA pcv valve would carry over to a forced induction application producing 12 psi boost but the operational fluid mechanics disqualify that part for an application producing an additional 2-3 psi.

I was hoping to learn the specificity of that operational difference and share that with the forum for anyone interested.

 

[No disintegrations]

The whole thing seams odd to me since the valve is slammed shut during boost or a normally aspirated engine when backfired.

 

[mikestertwo]

The pcv valve is there for a reason. It's there for emissions reasons and it keeps the blow-by (crank case pressure) from venting to atmosphere which eventually winds up in the passenger compartment. During positive boost the valve is closed so the blow-by is vented to the inlet of the turbo then back to the intake into the cylinders where it gets burned. During high vacuum conditions the valve opens and the gasses get sucked into the intake manifold into the cylinders where it gets burned. Different valves flow different amounts depending on the size of the "pintle" inside the housing. If you look in the hose connection end of the pcv valve you will see a small diameter rod. Different valves have different diameter rods or pintles, which ever term you prefer, which rises when the valve opens. This rod diameter serves as a restriction to air flow. The smaller the rod the less restriction there is so there is more air flow. The 893 pcv valve has a very small pintle as compared to a N/A pcv valve. I guess GM decided the LC2 motors needed more air flow to evacuate the crank case because they tend to boost faster creating more crank case gases.

 

[robertf]

The pcv valve is there for a reason. It's there for emissions reasons and it keeps the blow-by (crank case pressure) from venting to atmosphere which eventually winds up in the passenger compartment. During positive boost the valve is closed so the blow-by is vented to the inlet of the turbo then back to the intake into the cylinders where it gets burned. During high vacuum conditions the valve opens and the gasses get sucked into the intake manifold into the cylinders where it gets burned. Different valves flow different amounts depending on the size of the "pintle" inside the housing. If you look in the hose connection end of the pcv valve you will see a small diameter rod. Different valves have different diameter rods or pintles, which ever term you prefer, which rises when the valve opens. This rod diameter serves as a restriction to air flow. The smaller the rod the less restriction there is so there is more air flow. The 893 pcv valve has a very small pintle as compared to a N/A pcv valve. I guess GM decided the LC2 motors needed more air flow to evacuate the crank case because they tend to boost faster creating more crank case gases.

I've always hated how those little bastards gunked up inside my throttle body.