82 911SC CIS switch to earlier CIS

82SC · 03-28-2002, 12:02 AM

Well Rich in SD, CA has been gracious to give me his earlier CIS system for a great price...and I will be picking it up this fri

I know I 've been thinking about selling my car...but his price is too good to pass up and I can see if the euro CIS (intake runners and FD really make a change...)

But what do I do about the O2 sensor? And since the DME is expecting an O2 signal how does this work??

I am guessing that with the earlier CIS system...you set the CO and it stays that way??? Where my current system reads the O2 sensor and adjust accordingly???

I think the CIS system bolts off as one unit???

any suggestions???

Wayne 962 · Wayne 962's Garage

The closed-loop CIS system with the O2 sensor is a better system. The earlier system has bigger ports, but I doubt that you will see any difference...

-Wayne

82SC · 03-28-2002, 12:22 AM

well alex wong told me the FD is worth some ponies...
also Steve alcron and jeff at aase motors who built Steve's SC said the FD is a good upgrade...

I have heard yes and no about the late FD vs early FD....
Logically I can't figure out why there would be a difference...

also the larger intake runner will probably not make a huge difference since I am running the later SC heads anyways...

But since I plan to drop the engine for some other fixes...and the rock bottom price I am getting the intake system for...I guess it is worth a try

MJ

StuttgartDavid · 03-28-2002, 09:14 AM

If you are club racing and have the $ and dyno time to optimize everything about the motor, it may be worth the marginal benefit.
If not, the gain will be incremental at best, and a setback at worst, because that later closed loop system can compensate for a multitude of sins, whereas you will need everything spot-on and dialed in to get any benefit from the ealier open system. The real limitation on power with that engine is the cam, not the intake.
I suspect you will get much more bang for your buck putting the $ and time elsewhere. Do you have SSIs or the early exhaust? Do that first. Have you upgraded the suspension and tires/rims? Have you upgraded yourself as a driver via DE, Time Trials or autocross? These last two are the real way to make your car faster in the real sense of the word - the ability to cover a fixed distance in a shorter period of time.

Jim T · 03-28-2002, 09:18 AM

Quote:

Originally posted by 82SC
Well Rich in SD, CA has been gracious to give me his earlier CIS system for a great price...and I will be picking it up this fri

I know I 've been thinking about selling my car...but his price is too good to pass up and I can see if the euro CIS (intake runners and FD really make a change...)

But what do I do about the O2 sensor? And since the DME is expecting an O2 signal how does this work??

I am guessing that with the earlier CIS system...you set the CO and it stays that way??? Where my current system reads the O2 sensor and adjust accordingly???

I think the CIS system bolts off as one unit???

any suggestions???

There is no DME on a CIS system.

If you install an earlier, non-O2 CIS system on your car, you don't have to do anything with the O2 sensor. Just leave it in place and unplugged, or take it out and plug the hole with a bolt.

82SC · 03-28-2002, 10:11 AM

right right...there is no DME...but there is that simple computer under the pass seat...I was wondering if it has anything to do with the CIS....

hmmm...sounds like it may not be the greatest upgrade...

but I am getting it for 100...and I have a guy who has 964 cams for 200....so I am thinking this is a pretty cheap upgrade...even for a couple of ponies....

hmmm...

Jim T · 03-28-2002, 10:36 AM

The simple computer under the seat only controls the O2 sensor, but if you installed a complete earlier CIS system, you would not need that part any more.

I do agree with the others that you may want to reconsider your plot, though.

82SC · 03-28-2002, 01:38 PM

hmmm yeah sounds like a hassle for the return...

what about the 964 cam change...noah...what do you think?

200 for a pair of 964...worth all the trouble to install them??/

thanks

MJ

911nut · 911nut's Garage

Pre-lambda (O2 sensor) CIS has one advantage over Lambda CIS: the ability to run a richer mixture.

The lambda computer gets a voltage from the O2 sensor which is analogous to the amount of CO in the exhaust. The lambda computer varies the duty cycle of the frequency valve which affects the control pressure in the fuel distributor which affects the mixture (still with me?). The lambda system strategy is to run the engine at an air-fuel ratio of 14.7:1. This is the best compromise between low emissions, driveability and fuel economy. However, engines make more power at an A-F ratio of 12.5:1. If you go and play with the idle mixture the lambda computer will lean it back out when you drive so you can never get that rich mixture.

Backdating the CIS to pre-lambda will net you a few hp. I know of one guy who did it and said that it made a difference and that he had no driveability issues. You will also need the backdated intake runners, too.

The one drawback is that the bigger diameter intake runners will cost you some torque in the low end of the rpm range due to sluggish air flow.

A while back John Walker recommended disconnecting the O2 sensor (the lambda system will then run in open loop mode) and setting the idle mixture to 3.5% CO. You might try that before you do the swap.

Wayne 962 · Wayne 962's Garage

Noah's right - the heads will limit the effectiveness of the early system. I would still buy it - as these are highly sought after for people who want to place them on bigger displacement engines.

I have not heard of anyone who had to smog their 964 CIS motor - this is a relatively new upgrade, and may be an issue. Mike Zois's 914 is old enough to be exempt, and Noah's car is a Euro import registered in Vermont, so I still don't have any data points...

-Wayne