Stage 1 Tuning with EGR & Cats

The Engine Modifications

It sounded simple enough: “Strategically apply the engineering knowledge we’ve amassed over the years to advance the performance of this pristine, low-mileage, 1987 560SL.”  The hitch of course was that we were asked to make sure it passed California’s smog test, and that whatever changes made would be in keeping with the spirit of the R107 Roadster.  In the end, we think that were successful in doing so.

We took the client’s prompt as an opportunity to build on the already strong legacy of this marquis.  This is something we at Carobu Engineering strive to do at all levels of performance enhancements, albeit ‘bolt-on’ or highly customized.  Yet doing so with the guardrails of strict emissions, we knew would require us to think creatively.  This of course is where the art of the process met the engineering science - and so our journey began.

The reality is that this was all easier said than done. Adding horsepower to a classic that still needs to pass an emissions test is no simple job. In this case, both the cats and the EGR had to remain on the car so it would pass the visual and functional tests.

The start of any special engine modification program begins with the goal; make bolt-on power while keeping the tailpipe clean. In this case, we didn’t plan to up the compression which can affect the NOx reading. We also knew that the camshaft choice had to be right or the idle quality and emissions would flunk the test.

The plan was to increase the airflow as much as possible without going over the line. We knew from our dyno testing that our modified intake manifold would help make more power. A dual-snorkel air filter housing is essential when making more power on the SL engine. Also proven were the Euro Tri-Y headers made for HB Sport by Elbe Engineering and the stainless HB Sport exhaust system with X-pipe. The trick would be to add catalysts and the factory EGR system to those performance parts.

Based on past dyno testing, we knew our stage 1 camshafts which are similar to the Mercedes factory 300 HP cams, would be a good match to the stock 9:1 compression ratio and that the idle would be steady.

Helping things along is our HB Sport ignition system which uses a modified 560 SL distributor and a standalone controller with an MSD ignition box. Managing the spark advance is very important in making power and moderating the exhaust gases.

In tandem with the spark control, we used a CIS-E control module to adjust the fuel mixture on the CIS injection coupled to an ECU and dual wide-band O2 sensors.

Using all these electronics is essential in tuning the engine for power and a clean exhaust. The engine bay also had to look period correct so the alarm bells wouldn’t go off at the testing station. This includes having the stock injection in place (Bosch CIS K-Jetronic), etc. and ensuring that the additional electronics are all hidden away.

From past testing, we knew these parts, on a standard 560 engine, would give about 290-300 HP. We were hoping for something close to this with all the smog gear hooked up. In the end, the engine made 280 HP and a sizable torque increase compared to the original engine.

As hoped for, the difference in power was very evident when the car was later driven.  Specifically, the throttle response in the low and mid-range was satisfyingly increased.  It’s as if the car finally woke up throughout the entire power band.

After the first test drives, the big day arrived when the car was tested for emissions. This was a big deal to us as the result could make or break the project. The result was better that expected and the car passed all phases of the test with flying colors. Whew!

Check out a video of the 560 SL driving here

To see what we did to the chassis, go to this page.