First,I'm emisssions exempt on this car,so...

What's the downside to venting the PCV to the atmosphere via a valve cover breather instead of into the plenum? Both valve covers too.

It's a speed density 305 TPI

 

it is a very good idea to keep the PCV, its "positive crankcase ventilation", it does exactly what is sounds like, it help to pull the bad gasses from the engine and burns them in the cylinders. Without it, the gasses will never leave and it could degrade engine fluids and components

 

So there's no chance of blowby gases coming out of the breathers?

 

some will, not all.

and also, you will tend to get an oily mist coming out of the breathers and onto your engine without the pcv, messy

 

Your carburetor's idle circuit was designed with the PCV in mind. If you eliminate the PCV you throw off the calibration of the carbs idle and off idle fuel curve.
Can really mess with the idle quality and off idle throttle response.
You'll also have to increase the carb idle speed (throttle opening) to compensate for the loss of engine airflow at idle if you eliminate the PCV. The carb is designed to idle correctly with the throttles set in a critical "sweet spot" throttle opening/idle transfer slot exposure under the throttle edge at idle. If you deviate from that narrow "sweet spot" too far, the whole idle/off idle calibration thing gets thrown way off. (you usually get a big off idle flat spot in the throttle response.)

You're best to keep the PCV valve functional. The engine will idle better (especially with a hi perf cam) and the oil will last a lot longer.
Functional PCV prevents the engine oil from forming acids and other corrosive compounds which can eat at your soft engine bearings and seals.
If you drive your car on the street you are much, much further ahead keeping the PCV fully functional.
Some people want to clean up the appearance of the engine by eliminating the PCV hose from the top of their custom valve covers. There is nothing stopping someone custom connecting the PCV valve on the intake manifold valley cover or back of the block like a Ford V8. As long as the PCV valve does not pick up engine oil, (proper oil baffling) its fine.

 

Thanks for the replies. It's a Tuned port car and I was specifically wondering if it would indeed mess up the fueling map. The big problem I'm trying to address is how gunked up the TB/upper plenum and runners were with an oily carbon residue. I'm putting valve seals in it and threw in some new injectors as well. It's part of the 100K mile tune up I was doing over the winter. I just didn't see the need to introduce those fumes back into the intake side if I didn't have to. It's a 1K mile a year car at best.

thoughts?

 

Best case scenario: nothing much changes, it's how it used to be done.

Worst case scenario: You build up explosive gasses in the crankcase while driving around and blow your pan off; big mess, fire, embarassment, gotta get towed etc etc etc.

Most likely scenario IMO: You start leaking oil all over the place from the increased pressure in the crankcase. You throw away a few HP.

 

The PCV is not causing you issues no need to eliminate it.
Any motors intake manifold plenum will be gummed up after 100,000 miles.
If the motor is starting to age with increased blowby and you think the PCV is now drawing oil, install a generic paper element type clear in-line fuel filter in the PCV hose to help trap any oil migrating up the PCV hose. If it gets full of oil, replace it when ever you do an oil change, $2.
I'll bet you'll find the PCV is not an issue. Unless the motor has crappy non stock valve covers without PCV/breather oil deflection baffles or is really huffin serious blowby (cause its worn out).
Check the PCV hose to see if it is clogged with oil.