EFI = eliminated airbox incident risk?

[70SWT]

As I contemplate how to best employ the neat aluminum airbox the PO fabricated for my 1980 911SC EFI project, it occurred to me:

When using an airbox set-up with EFI on a previously-CIS car, does the better tuning capability of EFI effectively eliminate the risk of an explosive event like we see with CIS cars with plastic airboxes? Is CIS the main culprit, or is the physical layout in a CIS-generation 911 somehow increase the risk? (I believe it's the former).

This concern came to mind when I saw the discussion elsewhere on aftermarket aluminum CIS airboxes with built-in pop-off valves that used to be for sale.

So I wonder (but doubt) if I should install a pop-off valve just in case on the AL airbox I plan to use on my SC with EFI. This AL box will physically function much as the plastic airbox on a CIS car, serving as a junction space sitting in the middle of the intake runners.

Any car can backfire - but manufacturers don't routinely fit EFI cars with pop-off valves...I'm just trying not to miss an avoidable failure mode when putting this car back together.

[911obgyn]

What kind of efi? What are you using for an air flow sensor? Where is it located? Sequential fuel injection? Type and location of injectors?

[70SWT]

Originally Posted by 911obgyn

What kind of efi? What are you using for an air flow sensor? Where is it located? Sequential fuel injection? Type and location of injectors?

This will be the Bitz Racing setup, which has the injectors mounted into the stock CIS injectors' locations, but with an AL airbox instead of either the full or cut-down plastic CIS airbox. I understand Tony's system uses a MAP sensor and is batch-fired, per his FAQs at https://www.bitzracing.com/FAQ/

[colingreene]

really depends on a lot of factors, if its a fully modern really actually good system then i wont say it eliminates the risk but almost eliminates it.
however if its say a microsquirt and the crank sensor moves or something then no it wont eliminate your problems.

[70SWT]

Perhaps the alternative question is, has anyone seen catastrophic intake tract failures from backfires on 911s retrofitted with EFI and aluminum intakes? I suspect that the rarity of the configuration combined with the stronger material means the answer is no by default...

[rwest]

Keep in mind, that the EFI doesn’t use the cold start injector, so there isn’t any fuel being directly injected into the airbox and therefore a lot less chance for fuel exploding in the box, although you can still have backfiring through the intake valves.

For what it is worth, I didn’t install one in my Bitz setup.

[patkeefe]

Short answer, you can blow up a CIS airbox with EFI. I did it...lost a magnet on the pulley.
I have also blown up a Webb stainless steel airbox when I still had CIS. Just takes one backfire to do it.