How much boost pressure in airbox?

[Dr J]

For those that have done a turbo or supercharge conversion on an SC, and kept the plastic airbox: how much boost pressure are you running? I am trying to find out how much pressure the plastic airbox can take.

[patkeefe]

I did some tests on mine. Box can take around 30 PSI static, probably more. A short pressure wave, like a backfire will blow the box up. I have also found that all airboxes leak to some degree.

I put a plumbers plug in mine, set it to hold 15 PSI steady, but if I induce a quick blast of air over that pressure, the plug pops out. I did this all in a big vat of water with my air compressor and some gauges. A regular pop off valve will be held open by even small amounts of positive pressure. I run under 6 PSI in my turbo. Finally bought a Webb airbox, and blew that up also with a backfire. The backfire wave is pretty ferocious.

I found an epoxy that seals them well, but it needs to be oven cured. Problem is the oven curing at 350F kills whatever epoxy was on it from the factory. I am going to try at the lowest cure temperature the manufacturer recommends, and see what that does.

[Dr J]

Great info Pat! I was already thinking about doing the experiment in my pool. Just didn't want to risk blowing a perfectly good box up.

I once did a low pressure test on another airbox and did find minor leaking as you say. I put JB weld all around the perimeter and where the screws are. This worked for me.

[patkeefe]

Do you use the stock airbox configuration with the supercharger?

[Dr J]

Yes. In stock configuration. However, I am going EFI which gives me the option of running higher boost, but also, of cutting the airbox for the cleaner look.

[copbait73]

I have experience with the plastic box when turbing my '73. 2.4 CIS however my pressure testing was to confirm 10# my self imposed limit. I discovered that pop-off valve leaks were probably a significant issue in many naturally aspirated cars running them to prevent backfire. The leaks I saw were probably the root cause of additional issues after their installation. I think pop-off valves are marketed by people wanting to sell replacement EFI and carbs.

Anyway, I write to suggest a product I have found to be stand out in plastic bonding and it is Locktite Epoxy for Plastic Bonding. It has that caustic aggressive smell of vinyl adhesive. It cuts into the parent plastic much better than JB weld or any typical Epoxy.

The CSI spider manifold has excellent air distribution characteristics. Certainly superior to the factory 930 Turbo log and quite prossibly better than the 3.2. Good luck with your project, I'll be following along.

[Dr J]

Thanks for the info copbait. People have been wondering for a while what to use to repair/seal/bond the airbox.

[RarlyL8]

We used to make SC intake spiders out of aluminum for turbo conversions. Eliminates everything, you bolt the throttle body on the plenum just like a carburetor.

[copbait73]

Originally Posted by RarlyL8

We used to make SC intake spiders out of aluminum for turbo conversions. Eliminates everything, you bolt the throttle body on the plenum just like a carburetor.

Lots of these manifolds around and the getting is cheaper than TURBO stuff.

[flat6pilot]

If you can find a Carrera manifold they're not hard to convert if you're already running EFI.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/601643-3-2-carrera-manifold-sc.html