Secondary air injectors - effects on turbo if removed?

[Spenny_b]

Hi guys,

I was wondering the other evening...if the secondary air pump and injector assy is removed, is there an effect on the boost function of the engine?

Reason for asking is that my new car (964T, 3.3) was in for some work with my tech last week, to fix a few little issues that I knew about, and a few I didn't.

One prob was that the air injector feeds had rusted through, as had one of the injectors itself (and had been bodge "fixed" by a previous owner). The car retains a cat built into the Hayward & Scott stainless system, and here in the UK, emissions tests are only done on warm engines, and nowhere near as vigorously as I understand you guys have in some States over there.....so we removed it (ca.£350+VAT for new pipework and £60+VAT per injector) and saved a whole load of weight, plugging the holes in the heads to seal everything.

But....does anyone know what the effect of the air pump is on keeping the turbo spooling when shifting and thus off-boost? If it's working all the time, then logic says that this air pump will keep the turbo spinning to some degree?

Or, once the engine is up to temp and running leaner on idle, is the air injector system disabled, venting air to atmosphere, and therefore having no effect?...or is it the case that this secondary air injection is so minimal that it's insufficient to have any effect on turbine speed?

I have to say, since getting the car back it doesn't seem to be quite as punchy, but maybe that's just the butt-dyno....now it's a whole load smoother, it may be fooling me with a smoother/more linear power delivery.

Thanks in advance,
Spencer.

ETA: appreciate this is a 964 question in the 930 forum, but there's more turbo talk here than in 964-land ;o)

[tj930]

Have to confess that I'm a little more expert in 930-related items..

Standard procedure to rip off the air-pump assembly, lighten the car, and not be the slightest concerned about emissions - because the thing doesn't make that much of a difference..

However, in answer to your question, I remember seeing a graph from a 1970s Porsche Workshop Manual posted up (it was in a thread late 2009 / early 2010) where the air-pump system did look to improve acceleration / performance.

At the time, I kinda scoffed and thought the image must be wrong, but I don't know. (When I bought the thing, my car didn't have the air-pump system.)

..Perhaps somebody else can chime in?

[RarlyL8]

The C2T 3.3T has a K27 where the 930 3.3T uses the 3LDZ. Given that and the different ignition systems, gearing, etc. I cannot imagine the air injection being a noticeable improvement in performance.

[TurboKraft]

The air injection pump will not help spool up - its contribution to exhaust flow volume is negligible.
Turbochargers like heat energy and exhaust velocity, and the air injection does not contribute positively to either of these: injecting cooler fresh air into the exhaust, and nozzles jutting out into the exhaust port's flow.

[Spenny_b]

Okay thanks guys for all your thoughts, very reassuring!

The other reason we decided to ditch it, was that I've just bought a Zeitronix AFR which we were installing the sensors and running wires for at the same time (EGT, boost and lambda)...it dawned on me that having the air injectors operating is likely to completely cock-up the lambda readings.

Cheers!
Spencer.

[911nut]

The air injection has a two way valve. At start-up, air is injected into the exhaust ports for 60 seconds. Then the valve re-routes the air to the cat.
If you remove the system you save 10 lb. and the engine won't know it's missing.

[oilonly]

I ditched the air injection system when I modded up my car. Just because I didn't like the looks of it.

[Spenny_b]

Originally Posted by oilonly

I ditched the air injection system when I modded up my car. Just because I didn't like the looks of it.

Haha...I did the same with the (ex) Wife!

[66cal912]

Does anybody have a stock 930 air pump part number 930 113 114 01, that they will sell me please? I have mine appart in about 25 pieces and I need a donor for the graphite guides the blades ride on.. One fell out during disassembly while I am rebuilding it and broke today..:-(.. Doesnt need to be great just turn. If you have a spare air injection spider that bolts to the nozzles I d get that from you too. Thanks Ben. Unfortunately we need this stuff in california...