65air_coupe

For those that are using an aftermarket air cleaner, what are you doing for crankcase ventilation?

PO had punched two holes in the base of my air cleaner to clear the Holley float needle screws and given that that top needs replating, I was thinking of just going to an aftermarket, drop base air cleaner. But when looking through the selection at my FLAPS, I realized none have any provisions for crankcase ventilation.

waynec

Punched 2 holes... WTF?! The correct air GM cleaner worked with the Holley the car came with, why did he need holes? Can you patch them, or would that interfere with the filter element? If you can patch them, why not just buy a new top for yours?

lars

The purpose of the tube from the air cleaner to the valve cover is to allow the engine to draw clean, filtered air into the crankcase during normal operation, and to capture and recirculate emitted crankcase vapors when at WOT (when flow reverses through the tube due to elimination of PCV valve vacuum). You can get the same effective crankcase ventilation by retaining the PCV valve and using a standard breather in the valve cover instead of the tube. Although the breathers do not look stock, they do provide effective filtering of the air for the PCV system, and they do prevent excessive oil discharge at WOT. Of course, you need to retain the PCV valve for this to work right.

I have found that the stock PCV tube in the stock air cleaner can interfere with aftermarket carb secondary accel pump linkage, and the breather system is a good alternate method to keep the PCV system operational. K&N makes a good drop-base air cleaner with a 3" element that allows use of a pretty tall manifold on a stock C2.

TJefferson2020

But assuming I'd like to plumb a line from my valve cover to my air cleaner, what would I need?

65air_coupe

To the best of my knowledge, these cars were not equipped with PCV systems, and as such, the have neither PCV valves nor vented valve covers. They were one step better than the old down draft tube of the 50's, in that they attempted to draw crankcase vapors into the carb by routing the vented air from the lifter valley into the low pressure plenum within the air cleaner between the air horn of the carb and the filter element. A smaller tube ran from the plenum inside the air cleaner but outside of the filter element to a spigot on the side of the oil fill tube.

I suppose one could retrofit a PCV system into this vintage. Is that what is being down to run an aftermarket air filter?

65air_coupe

Not for the original Holley, but for the later models double pumpers which is similar to the BG carb I'm now running.

Vetterodder

They certainly DID have a PCV system. Later years use a vacuum accuatated valve instead of the restrictor in the carb fitting but the function is the same. If I understand your situation correctly, you have several options for using PCV with your current BG carb. L78, L72, and LT1's were factory equiped with dual feed, center hung float bowls and a replacement air cleaner base for them should solve the problem (but they're not cheap). Most aftermarket air cleaners come with PVC adapters and cost much less than the oem repro's. The after market units will typically have knockouts for the hole and an adapter.

65air_coupe

Thanks Vetterodder, I wasn't aware of what you've described. I need to look at my AIM and re-educate myself on how it was equipped originally. So far the aftermarket air cleaners I've seen have no provisions for PCV, I think I need to look at the local speed shop.

StickShiftCorvette

I found the same secondary pump interfered as well, however with a little heat one can easily modify the steel tube to provide pump linkage clearance.

chris ritchie

Look again at the aftermarket air cleaner bases. Most of the ones I've seen (about 4) do indeed have a provision to install a nipple for the PCV hose. The base should have pre-punched cutouts for it. The hole(s) won't acutally be punched out. Just pre-punched so you can do it yourself if you want. The aftermarket air cleaner package usually includes a black plastic hose connector to install. It should also include a device to prevent explosions. I can't remember the name now - vapor or explosion something. That's nothing more than some metal mesh to cover the hole. Do use that. Very important. You do not want a backfire in the carb propagating to the crankcase and causing an explosion there.

Do you have the correct valve covers? If so, then just use the correct air cleaner base for your car. Then you can buy that and the hose that connects them. Call your favorite Corvette parts vendor; give them your credit card number; and, voila, a package arrives on your doorstep with all the solution to this problem.

65air_coupe

Thanks for responding Chris. I will look again at those air cleaners, more carefully this time. I have the correct valve covers (finned cast al.), but the crankcase vent is at the rear of the block, not thru the valve cover.

I gather that I need to buy an aftermarket PCV valve and tee it into the line at the base of the carb to complete the system?

Vetterodder

The stock system used a line from the oil filler tube at the front of the intake manifold that ran to the base of the carb. The fresh air into the crankcase was from the air cleaner to the opening in the block. Are you using the stock manifold or after market? Some after market intakes have a provision for the stock filler tube, most don't.

65air_coupe

I have the stock oil filler tube with the fitting. At the moment, I'm planning on connecting a line from the carb base to this fitting with an inline PCV valve.

I did find and buy an aftermarket air cleaner with the knockout and fitting. Connecting that to the existing ventilation tube may take some doing, but I'm sure I can handle it.

chris ritchie

I'm not familiar with 65s. But it sounds like you've got a hose from the base of the carb to the oil fill tube on the front of the intake manifold. That'd be the vacuum side. The PCV valve would be plumbed somewhere in line there. Then filtered fresh air is supplied to the crankcase from a hose that goes from the base of the air cleaner to a fitting on the back of the block, just behind the distributor. And it sounds like you've found an air cleaner base with provisions for the nipple. You have the oil fill tube with the fitting for the hose. There is a hose fitting that goes in that hole on the back of the block. Check your parts catalogs if you don't have it.

With all that, you should be able to put something together that'll work. Try heater hose for the PCV hose. Heater hose usually comes in 5/8" and 3/4". One of those sizes is slightly too big, but it'll work. You'll have to rotate the air cleaner base around so that the nipple and the hose don't interfere with the carb or choke linkage. You can buy the correct hose from the parts suppliers.