Daviboy

Guys,
So when I bought the car 82 sc the airbox had a minor crack along the seam where the phillips head screws are. The car runs fine which seems contrary to everything I have read re cracked airboxes however I have opted to replace it with a new one. I was originally going to get one and a pop off valve from Pelican at around $570 but managed to find one with pop off installed on e-bay for $460 inclusive shipping. Question is now I would like to replace it myself as I am pretty handy mechanically however I do not know whats involved in setting up the CIS after installation and dont know if special tools etc are required. Would I be better letting my mechanic do this or what?

Davy

Peter Zimmermann

Where do I start? First, you must remove the engine to do the job. Then you want to put your airbox back on eBay and sell it. Then buy a new airbox and plan to install it without a pop-off valve. If you're ready for this let me know and I'll list the parts that you'll need! Set up after the job is done requires a CIS pressure gauge (to measure/set cold control pressure), and a CO machine to set the mixture.

Houpty GT

What is wrong with pop-off valves? I have used mine alot. :/

Peter Zimmermann

It's well-documented how I feel about pop-off valves. Here's a rerun of one of my earlier posts...

I think that it's well documented that I don't approve of the aftermarket pop-off valve. My shop had as many tow-ins with blown airboxes fitted with valves as without a valve. Add to that the tow-ins that had a problem caused by a pop-off valve, well...

I have conceeded that a pop-off valve may be viable if:
1. The car is not professionally serviced (I realize that some areas do not have competent service available, especially now that the newest CIS 911 is just about 25 years old), and there is little possibility that the car's owner can obtain the test/tune equipment to maintain the car to factory specs.
2. The car is a '73.5 - 75, in other words, a 911 fitted with a hand throttle that is required for starting. The hand throttle system is difficult for even some mechanics to understand, for some reason it's not taken seriously. A specific adjustment must be done periodically to insure that it operates correctly.

In all other cases, I don't feel that a pop-off valve is a good thing, quite the opposite actually. In many cases its reaction time to an internal explosion is too slow to save the box. In addition, all internal explosions happen for a reason; some are:
1. Application of the gas pedal during starting, which causes mass confusion in the injection system.
2. CO% (fuel mixture) not maintained.
3. Cold control pressure not set to the optimum.
4. Air/vacuum leaks, sensor plate problems, improper tuning, etc., can all contribute.

The original airbox fitted to my 1982 SC lasted 192K miles, and was replaced because the plastic had deteriorated and hairline cracks along its assembly seams were visible.

theiceman

Daviboy search for posts by me about blown air box project. I deatialed all the steps with photos when I blew mine
It was a very rewarding project.
I borrowed an AFR meter from a rennlister to set the CO and it has run terrific ever since.

PS I got a great deal on a genuine Porsche airbox, I also got the rubber sleeves, throtle body gasket, air meter gasket, small and large cold start injector oring, throttle bushings, air, breather cover gasket, thermostat gasket and oil pressure switch from a dealer in oregon. my air bosx is larger but I payed 3 soemthing.
want any more info after reading my posts PM me.

theiceman

Just go to advanced search put " air box " in the keyword area , and threads started by me. Tonnes of reading and pics.

Daviboy

To anyone who is thinking of doing this be prepared for about 3-4 days of work. It is not the easiest thing to do but with some patience (not one of my greatest virtues) it can be done. Hardest part was actually kneeling bent over for that length of time the back and knees take a beating. I have posted a lot of pics of the tear down and re-build here http://www.flickr.com/photos/30575902@N03/ if it helps in any way.

theiceman

Congrats Daviboy sounds like you are up and running.
Took me 90 minutes to remove the CIS from the car. But admitedly I have the older flexible injector lines which makes working on it a piece of cake, no wories about bending. The rest was just cleaning , inspecting and replacing pars.
did you get a AFRmeter and trim out your CO ?

good pics too.

Daviboy

Hi theiceman no not had a chance yet to tune the CO. I have just tweaked the timing at the dizzy as it was out about 2-3° at idle, adjusted idle to +/-900 rpm and then adjusted mixture using the old sniff method. When I got the car back together she fired right up but man was she running rich ( I swear there was fuel spitting out the exhausts, obviously PO had set mix rich due to huge amounts of unmetered air getting in due to airbox being split, I am frankly surprised she ran at all. Anyway still need to set timing at high rpms. She is running so much stronger but does stumble a bit at about 4000 rpm me thinks timing and mix need tweaking again. I will need to do this and a valve adjust but right now she is in mothballs for 3 months as I am overseas working again for a month off to Australia for a vacation then back to work for a month. So it will be end of Jan 09 before I get to see my baby again. Thanks for all your help it was you who made me dive into this project and it all worked out to the good.

theiceman

Great news, keep us up to date on your project.
Incidentally when mine went i never touched the timing at all. You will be amazed how it all smooths out after the CO adjustment. it is like magic