911SC track optimization.

[Porsche 2]

Have now decided my 1983 SC will be exclusively a track car, so no more smog testing! Already has racing exhaust with no oxygen sensor. Questions: what parts, if any, can be electrically decommissioned to gain engine performance; 1) frequency valve, 2) oxygen sensor control unit, 3) oxygen sensor power relay, 4) cold acceleration control unit. If all of these, disconnect engine fuel injection harness connection?
Will welcome any expert advice.

[flat6pilot]

Originally Posted by Porsche 2

Have now decided my 1983 SC will be exclusively a track car, so no more smog testing! Already has racing exhaust with no oxygen sensor. Questions: what parts, if any, can be electrically decommissioned to gain engine performance; 1) frequency valve, 2) oxygen sensor control unit, 3) oxygen sensor power relay, 4) cold acceleration control unit. If all of these, disconnect engine fuel injection harness connection?
Will welcome any expert advice.

Easiest performance gain is to go to headers, remove the CAT and get a good exhaust like M&K 2 in 2 out or something similar. Maybe 15hp?

I don't think decommissioning any of the above you listed will get you much of gain... Not sure what the "frequency valve' is..??

[Dave at Pelican Parts]

The "frequency valve" is the CIS part that varies the control pressure (and therefore the mixture) according to the output of the O2 sensor.

.... Have you just considered going with a good set of carbs? That is supposed to uncork even more HP in an SC...

--DD

[Porsche 2]

Thanks for your comments. Carbs will require changing racing class which I don't plan on.

[Dave at Pelican Parts]

Ah, yes--I forgot Step Zero. (RTFRB.)

--DD

[Dan J]

If you remove any of this in a haphazard fashion the car will run very poorly
If you want to keep the CIS the best thing to do would be to install a 78-79 US
or 78-83 euro fuel distributor and warm up regulator with a correctly recurved distributor
with a correctly sized set of headers

[Porsche 2]

Thanks Dan, where can I get more info on your comments re distributor curving and correct header size? This all sounds "do-able".

[SCOTITUDE]

gut it, add fg , add lightness

[Dan J]

Barry Hershon will recurve the dist He does wonders on that distributor
IAE Inc.

Jim Buckley makes the best headers for SC's
Buckley Racing - 911 Racing Headers

[Dan J]

Jim Buckley may also have the Fuel distributor and warm up regulator that you need

[Walt Fricke]

the answer to your question is none of the above.

You won't gain anything by futzing around. Leave the stock stuff so your engine is easy to start. You can disconnect the 02 sensor, though. Or leave it off when you get a trick set of headers (which will gain you a lot).

At WOT, the frequency valve/O2 system are bypassed anyway - which is why disconnecting them is a waste of time and effort. Plus, it may not be legal to do this in your race class. Lots of race class rules for street based cars say "if the rules don't specifically say you can do it, you can't."

If you don't believe me about hard starting, just disconnect the huge plug at the mini-brain under the passenger seat, and pull the relay next to it. Then see how it starts.

[Porsche 2]

Great advice, thanks to all. I will go with Walt's recommendation.

[fredmeister]

78-79 CIS has bigger diameter intake runners and not sure if the head ports are larger too. These are supposed to offer better high end flow and thus more hp at WOT.

Also, you might be able to advance or retard cam timing to gain hp.

Switching to 964 cams is nice but might violate the rules for your racing class.

Fred

[Walt Fricke]

Fredmeister:

The '78-9 US SCs had the "big" 39mm intake ports, and runners to match. Also compression of about 8.6/1. The 1980-83 US SCs had the "small" 34mm intake ports, and runners to match, but had 9.3/1 CR.

The early Euro SCs were same as US, but never changed to the small intake ports/runners. And the later Euro SCs got the 9.8/1 CR pistons. With better breathing and more squeeze, the late Euro SC is the peak performer for CIS intake cars. Racing organizations which know Porsches take this into account in classification.

[euro911sc]

Pretty sure the Euro SC's get bumped a class. Still a competitive car

[Walt Fricke]

The later Euro SCs, with their more potent motors, do run a class up from the '78-9 Euros and all the US SCs in PCA Club Racing. Don't know about SCCA Autox, POC, etc. They run well enough with the 3.2s that the latter have been heard, on occasion, to complain. It is a very good choice for an older race car which one can work on himself.

[euro911sc]

In SCCA, last I looked, the oil fed tensioner 'upgrade' is considered an 'Engine Modification' and therefore bumps the SC into territory far beyond its capabilities... this, of course, is strictly by the book last I checked. That was the reason for my departure from the SCCA... that and a stubborn refusal to reconsider the rule. *shrug*

Air cooled 911s are great choices for cars you can work on and have a good amount of community support. However... some of the parts are getting pricey!

And to keep the thread on subject... I run all my OEM CIS electronics that were on the Euro cars like mine. Runs like a champ!

[Walt Fricke]

Lots of Euro SCs will be racing at Sebring next weekend. The most potent Euro SCs did not have the oxygen sensor, frequency valve, and mini-brain that the US models have. But none of that affects HP on a race track one way or the other, so leaving it all hooked up and working makes a lot of sense.