Modified 911SC - Dead CIS Looking for Options and Advice

[karle911]

Hello all,

Consider this a Newb post... I have a 82SC with some modifications: 98mm Mahle Pistons (9.8CR - CIS "Shape"), 964 Grind Cams, SSIs (stock heads). Car runs fantastic... up until lately. Blew my CIS Airbox. I had not driven the car for a while so it could be many reasons. Just spent a bunch of money getting a new airbox. Just got the car back and it runs like crap. Surging etc etc. Really I have been looking for an excuse to go with another induction. I am sure that based on my mods CIS is robbing some of my horsepower. So: PMOs, Fuel Injection? What really are the best options here? I will spend for PMOs if that is the WAY to go but some exotic FI option costing 10 Grand is not an option.

Looking for some help here. I love this car. With 2 kids under 3 years of age it has helped me keep my sanity.

Thanks All.

[MotoSook]

Originally Posted by karle911

Car runs fantastic... up until lately. Blew my CIS Airbox.

If you like the way the car ran after the rebuild and running the CIS, why spend the $3600+ to go PMO. From the sound of it you just need your CIS adjusted. You new box, did it come with the air meter on it or did you have to move everything from your old box to the new box.

First thing to do is to get the air meter set correctly, then adjust your idle fuel to match the air. You'll want to do this at operating temperature after some driving...a few laps around the block should do it if it's not abosolutely cold out where you are.

When you say it runs like crap...explain what that crap means? Start-up behavior? Idle condition? Warm operating? Warm start-up?

I'm sure you know it, but you can't just bolt a CIS together and have it run right without adjusting it. The act of bolting your parts to the new box may have changed your setting, so getting the settings back to good operating points is what's needed.

[ruf-porsche]

You might have a vacuum leak. Who replace the airbox, you or a mechanic? If you paid someone to install a new airbox bring the car back to him and tell him it runs like crap.

[karle911]

My mechanic of close to 10 years replaced the airbox. He indicated that it could be bad gas for both the airbox blowing and the running condition afterwards. He topped of the gas with some super and techron and told me to drive it. It surges. I was looking to get the car warm but under load it was almost jarring my teeth loose, so I just parked it back in the garage. Before I blew the airbox it had been sitting for a couple of months.

Really, I have been looking for an excuse to replace the system anyway. Unless there are NO power gains to be had. I know that if I would have done carbs/FI when the motor was rebuilt I would have opened up the heads more and gone with a more aggressive cam. We all know how it works, you can never have enough horsepower. The other consideration is the quality of gas in CA. With the alcohol being added to the fuel I have heard it can create problems for the CIS system. This crappy gas has a very high propensity to "separate" and also, due to the alcohol, becomes very likely to "absorb dirt".

I know that carbs (PMOs) are one option. I also have read posts about "tbitz". Read the articles in Excellence about this issue. Also, I have read Bruce's book and he is obviously not a fan of CIS. So for a car with my mods there has to be some power gains to be had by switching.

This is why I am reaching out to the real "unbiased" community to determine the best course of action. I know there are other FI options but I have no idea of the cost. The car is not my daily driver. Thanks again.

[Deschodt]

The PMOs are a) beautiful b) sound fantastic c) "feel" like extra hp d) kill your gas mileage e) are carburators... I think it's more of the carbs throttle response improvement thing than you feel versus actual hp... nothing wrong with that...

The problem with e) is manyfold. Carbs are less efficient (some might say wasteful), will sometimes run like crap depending on changing conditions (CIs too, some might say), jets can get clogged, starting can be more difficult, tuning is a pain in the butt if you need to do it, you know the drill... Also depends if your state will require some emission control, you could not do that in california for instance.

CIS is a much maligned system that IMHO does not deserve its reputation. Mine's run 26 years and 185000 miles without a single hickup (got a pop off valve). I'm sure it robs you of a *little* performance but it's dead reliable once tuned up.

PMOs sure are pretty and sound glorious, depends what you want... Fix you car for $xxx or upgrade for $xxxx ! You probably should have decided on it before you bought a new airbox at any rate ;-)