1991 560SEL Emissions Delete

[stephenc1984]

I have a 91 560 SEL with 160,000 miles and runs like a champ. The vehicle is smog exempt, so it no longer needs all the emissions systems that is probably decreasing power and fuel economy. What can I get rid of and what kind of power and fuel economy can I expect? Keep in mind I still want it to sound like a benz, not a muscle car like some people have made their benz' into. Thanks.

[Elektri]

If it works, don't fix it!

[Frank Reiner]

s:

If you must, the most effective change would be to install a non-US style exhaust system; separate L&R log manifolds, two down pipes, no cats.

[compu_85]

I imagine the cats take very little power, and *vastly* improve the emissions.

Leave it alone

-J

[97 SL320]

If you are set on making changes, be sure to run the car on a dyno before and after then post the results here.

A less restrictive exhaust only helps at large throttle openings / high RPM so decide how often you drive under these conditions.

A K and N air filter is pretty much just a rock stopper.

Blocking the EGR valve could lead to pinging as spark timing is calibrated counting on EGR being functional.

Changing to synthetic lube for the engine and rear end will help power slightly.

Inflate the tires on the high side of the spec.

A higher rear end ratio number would help acceleration but cut fuel economy.

The shortest route to more power / economy is to buy a 2017 S class

[sixto]

If you live in Temecula, I don't think your '91 is smog excempt. Every gasser passenger car and most trucks since '76 gets smog checked.

Sixto
83 300SD
98 E320 wagon

[stephenc1984]

Originally Posted by sixto

If you live in Temecula, I don't think your '91 is smog excempt. Every gasser passenger car and most trucks since '76 gets smog checked.

Sixto
83 300SD
98 E320 wagon

I no longer live in Temecula. I live on an "island 26 miles across the sea."

[stephenc1984]

Sounds like the consensus is to leave it alone. Just posing the question out of curiosity.

[stephenc1984]

Mercedes Unimog

[Duke2.6]

By the early nineties emission control was built into the fuel control system and the only add on devices were the EGR and the air pump, which is only active during the first few minutes of operation before the fuel control system goes into closed loop operation.

The air pump can seize and is very expensive to repair or replace, so one thing you could do is fit a shorter accessory drive belt to bypass the pump, and you could also remove it but that might generate an error code and light the CEL.

Disconnecting the EGR control system might also light the CEL, but I don't think it would be a problem to simply block the passage at the coldest point in the system that you can access, and you will need a plug that can withstand high temperature, like steel.

The OE exhaust system is actually quite efficient even with the catalyst and is not worth modifying IMO.

By far the biggest (and easiest) improvement you can make for better fuel economy and more power is to remove the R16/1 resistor. This will quicken the rate of spark advance with engine revs resulting in noticeably more low end torque/power and better around town fuel economy.

For emission testing I short the R16/1 socket and replace a short piece of rubber tube in the vacuum advance signal line that is plugged. This considerably retards the entire spark advance map, which raises EGT and lowers measured emissions. The car can barely get out of it's own way below 1500-2000 revs, but my emission test station is only a couple of miles away, so I don't have to drive it in that gutless condition very long.

You can search for posts started my me, keyword R16/1 resistor, that have all the test data. Further searches will reveal the location of your R16/1 as it varies with model.

Duke

[Hit Man X]

The catback of the exhaust system is good, the precat side is terrible. The driver to passenger crossover pipe is a whopping 1-5/8" OD. PATHETIC. This is smaller than the downpipes on my 300SEL. Frank Reiner stated the biggest jump for least hassle, I agree. I have standard Euro dual logs on mine scrounged from a 500SEL, nice jump in power for the cost. Are the four piece manifolds from the 300hp M117 better? Sure. Are they worth the price premium? Not to me as these give you most of that power at a fraction of the cost. Another benefit is removal of that precat putting all the heat into just one cylinder bank.

I did keep my main cat and obviously the O2 sensor. Car passed smog for the few years remaining before it went exempt due to age. I wish I knew of Duke's trick when I was smogging these cars with aging cats!

EGR delete did not trigger a CEL on mine (ECU too old for this, just has O2 to trip the light) and it was so caked up at the intake entrance, it was plugged shut anyway. This was at 150k when I did the top end. I left the valve on the manifold until my car was emissions exempt for the visual impact.

AIR pump only works at start up, easy enough to remove it if you have to. Mine was seized so I did...just plug all the other vacuum connections to it accordingly. I TIG'd mine shut at the intake. I think some went to the throttle body even. Been years since I had it all apart, cleaned, and sorted.