ROG100

I have just replaced the stock cats with a Dave Lomas X Pipe and smaller cats on a friends 89S4.
Also removed were the air pump and associated pipework.
I forgot to weigh the X pipe and cats before I installed them.
Dave do you have a weight or anyone else please?

Stock Cats and two clamps = 23.5 Lbs
Air Pump = 8 Lbs
Pipework = 4 Lbs
Total weight = 35.5 Lbs

The weight saving plus no shaft HP to drive the pump must all add up.

the flyin' scotsman

I did the same last fall, Motorsport X in place of the cats and removed the air pump, belt and associated hoses. I didn't weigh the X but it must be apprx 5lbs if that; no cats on my system.

The biggest diff i noticed was the engines ability to freely rev; the cats were choking it.

FRporscheman

How will you pass smog next time? Or is this a track car?

Nicole

There is an upgrade available in Germany where they replace the stock ceramic cats with high flow metal cats. They use the same housing, remove the air pump, and reprogram the chips on the dyno. Costs about Euro 1200 and gains about 30hp on most cars. Best of all: This modification lifts the car into the Euro 2 emissions class, which means the VLF will be much lower. The savings in VLF pay for the upgrade in two years.

Then there is another solution where they keep the stock cats, but add two smaller high flow metal cats to the downpipes. This improves cold start emissions significantly, and lifts the 928 into the Euro 3 emissions class - which means even more savings in VLF. I believe they also disable the air pump for this one. No chip reprograming in this case, and I'm not sure about the cost.

I don't know why the air pump is no longer needed for these upgrades, but it's sure nice to have one less belt to worry about...

Earl Gillstrom

Interesting thread about removing air pumps. My wife drives a '96 Buick Roadmaster with a Chevy LT1 engine. GM says that you no longer need the air pump and will sell you a sticker that says so for emissions inspections. 928s are so rare that I don't think most emission inspectors could recognise that the air pump is missing since they never saw a 928 before.

whitefox

What you gain any horsepower by just removing the belt?

ew928

Hmmm.
So what story to fabricate to the emissions inspector that that is not an empty pulley but a spacer because the 928 oil pan forces the alternator to have to be placed so far forward.

They run the rolling road emissions test in NYC. Not sure if I can get away with not running stock emissions equipment. Think the air pump emissions dilution was much more apparent at cold engine conditions. The roller emissions test is done with engine nicely warmed up.

Ernest (NYC)
Always wondered why the "clean" running 928 needed an emissions sticker when I follow that smoke bellowing truck or clunker down the road.

the flyin' scotsman

Passing winter is the real challenge

Gary Knox

Roger,
How was the sound level of the car after changing from OE cats to the Dave Lomas ones we saw at Denver? I'm interested for the GTS, but don't want it to be significantly louder. This is my quiet - almost stealth car. I replaced the OE cats on my '89 5 speed with another aftermarket X pipe system, and it is signficantly louder. Won't use that one on the GTS.
Thanks for your input, mate.

Gary Knox

marton

Tell him it is for the belt for the optional a/c for the rear compartment of the 928

Marton

ROG100

Here in TX we run the rolling road test.
As long as it passes they are not looking for an air pump. They would not know what an air pump was anyway.
The cats that come with Daves X pipe that is fitted on my GTS passed with flying colors - very clean.

My 87 has no cats with an older X pipe and MSDS headers. I will try and pass emissions without cats for interest. If she fails I will put on Daves cats.

Gary,
My GTS sound very sweet to me - X pipe - cats and stock everything else. Very subdued with a growl when you get on it. Fitting an RMB adds a little more growl.

SteveG

Ernest: As fellow New Yorker, don't know how to address this problem (not running stock equip in NY), most shops won't look, but if you sell the car, or there is any problem with passing the test, it could be a problem for a new owner to consider. There is no way to know if high flow cats will be adequate on a car til it is in place, then the fun begins. Just know that the SLC Motorsport equip comes with metal band clamps and webbed furnace tape, it does not provide any air pump hook up and your O2 wire may have to be extended for their position on the sides. You can eliminate the hokey band clamps with welding, but then if you change anything in the rear, that has to be cut; and that is additional work for adapting air ump bung. My check list for PPI now includes examining exhaust set up visually.

Jim R.

Well, the motorsports crossover and cats will pass the rolling road dyno test in NY even with a stage 2 murf SC kit installed and fully functional/unchanged from normal trim. Will it pass the visual-no. But at least my shop feels if it runs clean enough to pass, it passes. As for when or if I ever sell it, all my saved stock components can be put back on in a weekend or two.

Jim

blown 87

Unless I am mistaken, the pump for the AIR system only works during the first few minutes of engine operation.

Its sole purpose, in most cars is to get the cat up to temp sooner.

It could be different in a 928, but I doubt it.

So unless they are doing a visual inspection or a cold start inspection you should be able to get away with out it.

PorKen

Cars with electric air pumps only run on startup, to afterburn any gas, and also heat up the cats. Our Mercedes has a electric clutched, belt driven fan - $1000 to replace!

All 928 air pumps run all the time. On decel, pumped air is diverted to the airbox, so as to avoid backfiring in the cat.
...

I just put my 3" catless single exhaust back on the '81, after a month with the factory exhaust and air pump. It runs cooler (about 2mm lower on the gauge), and there is definately more torque. When I floor it on the highway, when it kicks down, the front end lifts and she reels in the horizon a lot quicker. (Note: identical tuning, ~29°@3K ignition advance, and 4° cam advance with both systems).

The factory exhaust is nice, because you can drive hard without making a ton of noise, or looking like you're trying.