To Pop Off or not to Pop Off?

[Bob Kontak]

Originally Posted by Marc Bixen

WOW! Just a trans guy? Maybe you should do some research before more stupidity comes out of your mouth gomezo.....

He was just joking. He knows Peter is a God.

There are like maybe five guys. Peter is among them.

I like Johnny's posts also.

[Reiver]

Ok, you made me go look. You can see the dent in the filter screen, more obvious than the pic shows. I'm guessing you are referring to these screws.
They are all tight, none loose. So, the pop off saved me 400 or so bucks and time/labor. When I put this in I smoke tested it with a proper machine buy a gut familiar with this device...it did take some time to get properly seated.

[Reiver]

here is the filter....didn't take in the other

[proporsche]

Originally Posted by Marc Bixen

WOW! Just a trans guy? Maybe you should do some research before more stupidity comes out of your mouth gomezo..... Pete Zimmerman is a Porsche GOD when he comments, and is ALWAYS correct. If you don't know So.Cal Porsche history, here's a bit for you. Pete Z. opened Red Line Service, the oldest Porsche only repair shop in So. Cal. in 1975 after a stint at the dealer. Pete was a full fledged master of all things Porsche running Red Line until I purchased the shop at Pete's retirement in 1999. I had been working for Pete since 1995, after 13 years experience at other well known shops. One of those shops actually held the patent on, and manufactured the pop-off valves. I've built and boxed thousands of them, and installed hundreds. EVERY car that came in got one. Then I went to work for Pete at Red Line, and he explained that a properly tuned 911 didn't require this, and they cause numerous problems, so here's a short list of issues I've seen: 1) Pop-off installed backwards, first time it opens it gets stuck on the air filter and...giant vacuum leak, no start. 2) pop-off valve sticks to the o-ring, doesn't open and blows the box anyway. 3) Pop-off valve opens, the o-ring falls out, and again giant air leak, no start. 4) Epoxy gets old, pop-off falls out. and #5) MY FAVORITE, epoxy gets old, cracks, causes a lean mixture, and voila, the customer burns a piston and requires a complete engine rebuild. This actually occurred on a 74 Carrera.
Your choice, tune it right, or put on an unnecessary aftermarket part that most likely will create more AAA tows than you really want. In the 22 years plus I've been at Red Line I've seen less than 10 or 15 blown boxes, and probably only 5-10 of those were regular Red Line Clients.

Hi Marc..i do know of another Porsche God in Southern California..His name is Jack Pfluegler...he had a place in Calabasas Prestige Autoservice....back in the 1980`

Ivan

[boyt911sc]

Originally Posted by Peter Zimmermann

The original airbox on my '82 lasted 192,000 miles. I had, early on, set the Warm Up Regulator on the rich side of the scale, and simply dealt with a "hunting" idle during the first few seconds following a cold start. I discovered hairline cracks along the assembly seam, above cyl #3, when I had the engine removed to replace the cam shafts, and replaced the airbox at that time. I never even considered adding a pop-off valve, and it's been more than ten years since the replacement, without a single backfire. Jonny H and the iceman said it best, no toilet bowl for me! And, BTW, we NEVER used them at my shop either.

Peter,

I have high respect for your accomplishment and your work. Are you aware that there are more than 4 dozens spots (conservative accounting) or locations around the air CIS air box that could leak and cause a lean condition? One intake runner alone has atleast 6 locations to cause leak. Multiply it by 6 and you will have atleast 36. This is excluding the airbox and we are giving you the benefit of the doubt that you have a perfect airbox. A perfect airbox will not prevent the system from not having any leak/s. An air leak in CIS is inevitable whether you like it or not. It is during this uncertainty that you need some sort of insurance to minimize collateral damage.

If you do a lot of CIS start ups like after an engine rebuild, a “perfect air box” can not guarantee a backfire-free operation during the very initial ignition of the system. I seldom get this big backfire but it does happen when you least expected it. To say it will never backfire is not true. It may not happen today but it will happen someday unless you are on denial. This is a fact of life.

Pop off Valve has its own weaknesses. But some of the problems with the POV could be minimized and corrected with proper and timely maintenance. I have seen and experienced so many strong backfires in the course of my work that common sense must prevail. Not using a POV is like telling a skydiver not to use a back-up parachute because you have been jumping without one for a long long time. You maybe lucky but you can not depend on luck all the time. Not all good and experienced mechanics know or understand CIS very well. My two cents.

Tony

[DanielDudley]

Originally Posted by Marc Bixen

WOW! Just a trans guy? Maybe you should do some research before more stupidity comes out of your mouth gomezo..... Pete Zimmerman is a Porsche GOD

He was kidding.

No need to worship him, But I do push his book as often as possible.

[Jonny H]

Originally Posted by Reiver

Ok, you made me go look. You can see the dent in the filter screen, more obvious than the pic shows. I'm guessing you are referring to these screws.
They are all tight, none loose. So, the pop off saved me 400 or so bucks and time/labor. When I put this in I smoke tested it with a proper machine buy a gut familiar with this device...it did take some time to get properly seated.

Your picture suggests otherwise. The two brighter looking screws just happen to be right above the usual failure point for the airbox. It looks to me like they have been replaced which suggests your airbox has cracked at some point in the past.

It has been screwed back together with some longer screws I expect which is a common cheap and temporary fix. It will probably will hold smoke when the engine is not running as there is no vibration or heat to distort the crack.

(BTW, most 911 airboxes use M4 flat head slotted machine screws. Porsche did swap to crosshead self tap screws on the later airboxes but yours looks like an original ABS type).

[boyt911sc]

Originally Posted by Reiver

Ok, you made me go look. You can see the dent in the filter screen, more obvious than the pic shows. I'm guessing you are referring to these screws.
They are all tight, none loose. So, the pop off saved me 400 or so bucks and time/labor. When I put this in I smoke tested it with a proper machine buy a gut familiar with this device...it did take some time to get properly seated.

Reiver,

Are you aware that your POV is incorrectly mounted and installed on your air box? Take a closer look at the POV and it is resting on the plastic ribs instead on the flat base. This a common mistake committed by many DIYers including professional shops. While it is glued in place it is incorrectly mounted by your guy. This is easy to correct if you want to fix it.

Tony

[Reiver]

Originally Posted by Jonny H

Your picture suggests otherwise. The two brighter looking screws just happen to be right above the usual failure point for the airbox. It looks to me like they have been replaced which suggests your airbox has cracked at some point in the past.

It has been screwed back together with some longer screws I expect which is a common cheap and temporary fix. It will probably will hold smoke when the engine is not running as there is no vibration or heat to distort the crack.

(BTW, most 911 airboxes use M4 flat head slotted machine screws. Porsche did swap to crosshead self tap screws on the later airboxes but yours looks like an original ABS type).

Actually, they are the same color and the bang happened to me not to some prior (about 8 thousand miles ago and for me that's less than a year)....and, it had a top end rebuild not long ago...this is a Euro 83. IOTW, if it were a repair job and I had that backfire I wouldn't expect an already boogered box to survive....those screws were in place when the boom happened. No shop has messed with the box during my ownership.

All of them are tight, all the same color (photo light) and the car runs perfectly. How do I know the box does not leak....I have a wide band AFR in place of my clock and monitor AFR all of the time...it is very consistent and only changes a bit with elevation (I live in the foothills 2600 ft but often go above 5k etc.)

I am not saying your experience is not valid and they may not work all of the time but this one did once.....and for the investment once is good.

[Reiver]

Originally Posted by boyt911sc

Reiver,

Are you aware that your POV is incorrectly mounted and installed on your air box? Take a closer look at the POV and it is resting on the plastic ribs instead on the flat base. This a common mistake committed by many DIYers including professional shops. While it is glued in place it is incorrectly mounted by your guy. This is easy to correct if you want to fix it.

Tony

I see what you mean but no, it works and has a solid seal.

[Jonny H]

Originally Posted by Reiver

Actually, they are the same color and the bang happened to me not to some prior (about 8 thousand miles ago and for me that's less than a year)....and, it had a top end rebuild not long ago...this is a Euro 83. IOTW, if it were a repair job and I had that backfire I wouldn't expect an already boogered box to survive....those screws were in place when the boom happened. No shop has messed with the box during my ownership.

All of them are tight, all the same color (photo light) and the car runs perfectly. How do I know the box does not leak....I have a wide band AFR in place of my clock and monitor AFR all of the time...it is very consistent and only changes a bit with elevation (I live in the foothills 2600 ft but often go above 5k etc.)

I am not saying your experience is not valid and they may not work all of the time but this one did once.....and for the investment once is good.

I have a Euro '82 and the screws are not like that - they are slotted flat head M4 machine screws. I'm not certain but Porsche could have changed them just for the '83 MY. The replacement boxes DO have self tappers like you have.

Top right of your photo does it say PA6 in the stamping? ABS boxes just have a number in a circle.

[Reiver]

Originally Posted by Jonny H

I have a Euro '82 and the screws are not like that - they are slotted flat head M4 machine screws. I'm not certain but Porsche could have changed them just for the '83 MY. The replacement boxes DO have self tappers like you have.

Top right of your photo does it say PA6 in the stamping? ABS boxes just have a number in a circle.

I'll have to look (up on my lift stored above another car)...

[Reiver]

Well I was hoping you were right and it was a PA6 but the circle simply has a 2 stamp within.
All of the screws are the same color to include the ones on the drivers side exterior of the airbox (US driver side)...same style and color and extend about a few MM below the attaching points and appear to be self tappers.

[Jonny H]

Originally Posted by Reiver

Well I was hoping you were right and it was a PA6 but the circle simply has a 2 stamp within.
All of the screws are the same color to include the ones on the drivers side exterior of the airbox (US driver side)...same style and color and extend about a few MM below the attaching points and appear to be self tappers.

That’s got to be a good sign if they are all the same. They did make changes right up to the last SC.

[Reiver]

Originally Posted by Jonny H

That’s got to be a good sign if they are all the same. They did make changes right up to the last SC.

Well, if she ever blows and destroys the box I'll more than likely go a different route for injection ITB's.....the problem is the dam CIS runs so well presently and I shouldn't complain about that but it is hard to fix what ain't broke.

[RDUNCe30]

Following up to Pete Z.'s comment, I bought his 82 SC in 2014. Now at 217,000 miles with the airbox he installed. No backfires thus far; no POV.

Sam

[crashmy911]

You better pop or your gonna blow!

[Reiver]

Originally Posted by crashmy911

You better pop or your gonna blow!

Yeah, and that would suck.

[Marc Bixen]

Originally Posted by boyt911sc

Reiver,

Are you aware that your POV is incorrectly mounted and installed on your air box? Take a closer look at the POV and it is resting on the plastic ribs instead on the flat base. This a common mistake committed by many DIYers including professional shops. While it is glued in place it is incorrectly mounted by your guy. This is easy to correct if you want to fix it.

Tony

To the others, if "he's only a trans guy" was a joke, you're a putz. That is a huge insult and very rude. There are many neubies, as well as long timers who are still learning, and dissing one of the staples of this forum is just plane rude.
Also Tony, You're 100% incorrect on your install info. As I stated, I worked for the company that manufactured POV's and I can guarantee you they are suppose to be on top of the ribs. What are you doing? Grinding down the strengthening ribs?? I'd love to see a photo of that. Early air boxes, the ones identified by the slotted screws can accept this, but later boxes, phillips screw, have the cold start distribution spider inside, and my opinion is that the pop off would bottom out on the main chamber and not be as efficient. Who told you to cut the ribs???? (If I'm reading your post properly).

[Reiver]

Originally Posted by Marc Bixen

To the others, if "he's only a trans guy" was a joke, you're a putz. That is a huge insult and very rude. There are many neubies, as well as long timers who are still learning, and dissing one of the staples of this forum is just plane rude.
Also Tony, You're 100% incorrect on your install info. As I stated, I worked for the company that manufactured POV's and I can guarantee you they are suppose to be on top of the ribs. What are you doing? Grinding down the strengthening ribs?? I'd love to see a photo of that. Early air boxes, the ones identified by the slotted screws can accept this, but later boxes, phillips screw, have the cold start distribution spider inside, and my opinion is that the pop off would bottom out on the main chamber and not be as efficient. Who told you to cut the ribs???? (If I'm reading your post properly).

Marc,
Thanks...nice to know it is properly in place....the guy that did the top end and put it there has been a P wrench for 40 years....school trained and now an indy.