Optimal Performance Setting

[CT911SCDriver]

I have an 81 SC and had the throttle linkage and engine setup (CO adjustment) performed a while back by a shop into racing... and my car was a rocket. At the time it had a cracked air box and still ran great but then got slow again as the air box got worse.

After I replaced the air box (with pop-off)by a different shop the car still did not run as fast. Come to find out they also adjusted the CO level to pass emissions (at I think roughly 1.75%?)... I went back and they reset it at 2.5% and it's still at between 2.3 and 2.5%

Here's my question, when I first had the setup done and it was really fast I was hanging with my friend's new Vette, and kicked an M3's butt. Today, my friend's BMW 330 beat me! So, what could be the problem??? Too lean? If so, what is the best CO mixture level without running the risk of hunting idle? By the way, I have B&B headers and no O2 censor connected. Will the CO adjustment make that big of a difference?

Any other engine setup/adjustments (that the first shop could have done) to help give me back the hotrod I once had???

Thanks in advance.

Cy
81 911SC

[This message has been edited by CT911SCDriver (edited 05-30-2001).]

[adamnitti]

cy-

yes, the co adjustment will certainly influence performance... search the posts here for co settings and you'll find a lot of information instructing you how to adjust the richness yourself. (realize you'll be tampering with emissions, of course).

there are many different factors that will influence the performance of your car: the accuracy of your valve adjustment, whether or not you have vacuum leaks, co settings, condition/operation of your fuel injectors, a clogged fuel filter, etc. i'm sure others will chime in and offer some others.

by the way, i believe a bmw 330 will do 0-60 in the mid sixes without a problem... i wouldn't be too suprised if you aren't able to edge out your buddy on an acceleration run. last i read, most sc's do the same in closer to 7 seconds, fwiw...

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Adam Nitti
ajnitti@mindspring.com
www.adamnitti.com
'85 911 Carrera Coupe
PCA member, Peachstate region

[john walker's workshop]

3.5% works well on SCs. the lamda system is still on the car isn't it? regardless if the oxy sensor is unplugged, the system that works the frequency valve MUST function or the car will be a dog. the computer that works the valve is under the passenger seat. there is a small relay next to it that turns it on. it may be dead. with the engine hot, unplug the relay. if the engine immediately runs differently, then the system works. if not, check power to the relay which comes thru the domelight fuse, or replace the relay. then reset the mixture because it will be way off if it was set with the system inoperative.

[Doug Zielke]

Originally posted by john walker's workshop:
..... regardless if the oxy sensor is unplugged, the system that works the frequency valve MUST function or the car will be a dog.....

John,
Why is this so? I'm reading the Bentley manual trying to understand the function of these parts. I thought the frequency valve just defaults to a fixed value if the o2 sensor is unplugged. Can you explain a bit more, please?


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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

[CT911SCDriver]

John,

Thanks for the advice. What does that valve do and how does that affect performance? What made you think that could be the problem? It should still be in the car as I never removed it, only disconnected the sensor. Should I remove the relay while the car is running and reconnect it while running? Also, you suggest 3.5% CO huh? The car won't hunt at that level?

By the way, I'm telling you the car flew when the setup was done by a Porsche tech. I don't know if it was the throttle position (set to full throttle when pedal mid way... and since then it went back to full throttle when pushed to the floor)... or if he really made it rich... but the thing really flew, it was amazing... I guess I'm chasing that high now! Lol.

I was always under the impression that lean was better but runs hotter, and rich fouls out plugs and slows you down... I don't know why I thought that.

Thanks again. Your response is appreciated.

Cy

[Nickshu]

I have recently been fiddling with my mixture. I set it with an EGA, but was still not totally happy with it. I systematically used the highly accurate "guess and check" method to achieve the best "feeling" mixture.

I used the EGA setting as a baseline and bumped it around from there until I was happy with its performance. I am very happy with how I have it set now, bumped up about 1/8 of a turn from the EGA setting.

Just tried that unplug the relay thing. John's right...it runs different even with no O2 sensor connected.

Good Luck.
Nick.

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_ _ __ _ _
Nick Shumaker
1982 911SC Coupe
nickshu@yahoo.com
PCA -- Rocky Mtn. Region

[This message has been edited by Nickshu (edited 05-30-2001).]