Orifice Size

All Models and Years
User avatar
wbabst
Posts: 313
Joined: Mon Oct 27, 2014 8:03 pm
Location: Lake Elsinore, California

Orifice Size

Post by wbabst »

I rebuilt my engine on my 61, it was from California so it did not have a draft pipe, but a simple PCV valve set up. I got a later tube so it could have it feed into the equalizer tube. I didn't have a later tube with an orifice opening I had just added a fitting for the hose to attach too. Does anyone know what size is the orifice in the opening on the orifice tube?
Current owner
61(x2) Monza Cpe
55 Pontiac Chieftain Wagon


61 Progress here
https://www.facebook.com/pages/Chevrole ... 7898185672
https://www.facebook.com/pages/Goose-N6 ... 8869056897
User avatar
azdave
Corvair of the Year
Corvair of the Year
Posts: 2095
Joined: Fri Dec 11, 2009 1:27 pm
Location: Phoenix, AZ

Re: Orifice Size

Post by azdave »

1/16" or .062"
Dave W. from Gilbert, AZ

66 Corsa 140/4 Yenko Stinger Tribute
66 Corsa 140 Coupe w/factory A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5
64 Greenbrier 110/PG, Standard 6-Door
User avatar
bbodie52
Corvair of the Month
Corvair of the Month
Posts: 11872
Joined: Mon Aug 06, 2012 12:33 pm
Location: Lake Chatuge Hayesville, NC
Contact:

Re: Orifice Size

Post by bbodie52 »

:chevy: The crankcase vent specification for the fixed orifice PCV system is .089", as shown in the chart below from the 1965 Corvair Chassis Shop Manual - SECTION 6 - ENGINE TUNE-UP (Page ENGINE TUNE-UP 6-2). Note that in 1964, when the METERED ORIFICE was first introduced as a replacement for the original 1963 PCV Valve, the Orifice size was .062" for the 95 hp Turbo Air and 110 hp Super Turbo Air engines, and was increased to .089" for the 150 hp Turbo-Charged engine. (See page 7-6 of the 1964 Shop Manual Supplement). In 1965 the GM engineers changed the metered orifice specification to .089" for all engines.

The 1965 Shop Manual tune-up section and the 1964 Shop Manual Supplement are both attached below.

1965 Corvair Chassis Shop Manual
1965 Corvair Chassis Shop Manual
1964 Supplement - Chevrolet Corvair Shop Manual
1964 Supplement - Chevrolet Corvair Shop Manual
Attachments
1965 Corvair Chassis Shop Manual - SECTION 6 - ENGINE TUNE-UP.pdf
1965 Corvair Chassis Shop Manual - SECTION 6 - ENGINE TUNE-UP
(2.92 MiB) Downloaded 21 times
1964 Supplement - Chevrolet Corvair Shop Manual - Section 7 - Engine Tune-Up.pdf
1964 Supplement - Chevrolet Corvair Shop Manual - Section 7 - Engine Tune-Up
(931.65 KiB) Downloaded 18 times
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Orifice Size

Post by 66vairguy »

Some folks drill out the orifice and install a carburetor jet. Sometimes to fix a damaged orifice, sometimes just to allow for easy cleaning.

Cleaning the orifice hole is part of the normal maintenance schedule.

When engines wear out and blow-by increases the PCV tubes can become plugged with gunk.
User avatar
azdave
Corvair of the Year
Corvair of the Year
Posts: 2095
Joined: Fri Dec 11, 2009 1:27 pm
Location: Phoenix, AZ

Re: Orifice Size

Post by azdave »

I've found multiple threads on Corvair Center where the experts say that the .089" was a mistake (typo?) and that it will cause idle problems. Everyone agreed that .062 was plenty and covers all orifice tube PVC applications for Corvair except maybe the turbo applications.

Here is one thread with info by cnicol that I trust completely.
http://corvaircenter.com/phorum/read.ph ... 547,314622
Dave W. from Gilbert, AZ

66 Corsa 140/4 Yenko Stinger Tribute
66 Corsa 140 Coupe w/factory A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5
64 Greenbrier 110/PG, Standard 6-Door
User avatar
wbabst
Posts: 313
Joined: Mon Oct 27, 2014 8:03 pm
Location: Lake Elsinore, California

Re: Orifice Size

Post by wbabst »

Thanks guys for all great information. These are the first cars I have owned that had a PCV system. I am guessing from the information I am seeing here, it is an either/or situation. If you have an Orifice Tube, you don't have a PCV Valve, and vice versa, but you don't have both. Is that correct?
Current owner
61(x2) Monza Cpe
55 Pontiac Chieftain Wagon


61 Progress here
https://www.facebook.com/pages/Chevrole ... 7898185672
https://www.facebook.com/pages/Goose-N6 ... 8869056897
User avatar
azdave
Corvair of the Year
Corvair of the Year
Posts: 2095
Joined: Fri Dec 11, 2009 1:27 pm
Location: Phoenix, AZ

Re: Orifice Size

Post by azdave »

wbabst wrote: Thu Jul 27, 2017 12:01 pm I am guessing from the information I am seeing here, it is an either/or situation. If you have an Orifice Tube, you don't have a PCV Valve, and vice versa, but you don't have both. Is that correct?

I'm sure there are exceptions (certainly there are exceptions outside of the Corvair world) but that is generally the rule with Corvairs except the first few years that just had a road draft tube which vented below the passenger side of the engine.
Dave W. from Gilbert, AZ

66 Corsa 140/4 Yenko Stinger Tribute
66 Corsa 140 Coupe w/factory A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5
64 Greenbrier 110/PG, Standard 6-Door
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Orifice Size

Post by 66vairguy »

wbabst wrote: Thu Jul 27, 2017 12:01 pm Thanks guys for all great information. These are the first cars I have owned that had a PCV system. I am guessing from the information I am seeing here, it is an either/or situation. If you have an Orifice Tube, you don't have a PCV Valve, and vice versa, but you don't have both. Is that correct?
Correct - Either PCV fixed orifice, or PCV valve. I've never seen a good argument as to why the PCV valve was changed for an orifice system, but on some vehicle model years BOTH systems were used on different vehicles, just not together on the same vehicle. I could be wrong, but based on what I've read, - vehicles like the FC or wagons with low clearance above the engine stayed with the low profile air cleaner system that used the PCV valve even though the cars used the PCV fixed orifice (and taller air cleaner). Based on my ancient years with early PCV valves and their problems and replacement costs, I prefer the PCV fixed orifice system. Even without the stock air cleaner you can still route the hose to aftermarket air cleaners. NEVER vent into the engine compartment since the fumes contain carbon monoxide!!

davemotohead fixed a system dumping fumes into the engine compartment. Great pics, scroll down to 4th entry. See http://corvaircenter.com/phorum/read.ph ... msg-934298
Post Reply

Return to “Ask your Mechanical Questions here”