The Dreaded SC Backfire

[RarlyL8]

Just about every time I crank my '78SC over I think about all the blown airboxes I have seen.
My motor is in a good state of tune and has never even hickupped - until a couple of days ago.
The scenerio was probably perfect. The weather was cool and very humid, misting rain. I went to pick up the car after having bigger torsion bars installed (this could be another post in itself). My mechanic had put the car in his garage the night before. He had started it bone cold and moved it only a few feet then turned it off. Condensation was covering everything.
I got in and hit the key, it took longer to fire than normal. I got a concerned look on my face and then POP! The mechanic said "OH *****".
He hasn't done any engine work on the car so he didn't know I had an aluminum air box with a built in pop off valve. I told him about the mod and hit the key again. With some throttle play the motor came to life, obviously running on less than 6 cylinders. I figure she was flooded as well as wet. I slowly took off and warmed her up. Hit an interstate on ramp, ran 'er up to 4500 and blew the cobs out. She ran fine from there on home.
The moral to this story is that if you don't already have a pop off valve in your SC airbox please get one - now. Vevy cheap insurance.

[epbrown]

I like the idea of the aluminum airboxes - more durable but not much more expensive. Are there any downsides to them?

Emanuel

------------------
Everybody wants a normal life and a cool car;
most people settle for the car." Chris Titus
1966 Rolls-Royce Silver Shadow
1983 Porsche 911 SC Targa

[Wayne 962]

Tech Article:

http://www.pelicanparts.com/techarticles/911_pop_off_valve/911_pop_off_valve.htm

-Wayne

[83 sc euro cab]

I learned the hard way.

before I installed the pop-off valve, one mechanic told me that the chances of my SC airbox exploding were "one in a million"

guess what? I got very unlucky one day and it cost me $1200 for a new airbox with a new pop-off valve (went to a different mechanic).... Since then, the car has backfired once more and the valve saved me.

This addition is almost as important as getting the hydraulic chain tensioners.

[JAE]

My car backfires intermittently- like maybe once per month. Mostly low level stuff, but about once a quarter I get a 12 gauge report. I have an aluminum airbox and don't regret the extra expense. I'm still in the dark as to why this happens, there is no common prelude.

The only downside I have noticed is that the aluminum model has a very large square relief valve. I think you need to occasionally put some lubricant on the seal to make sure it does not leak.

Joe
'80 SC Targa