Hello all!

I have some questions about the various ways of tuning the SLK engine.

1. Changing the diameter of the compressor wheel and/or the crnakshaft wheel
This seems to be a common way to boost performance. Has anyone tried it? Even if I havn't tried it I argue that it will not work. If I make a quick calculation on the air consumption of the engine:
In my case the stroke is 2.3 liters. Since it is a four stroke engine it consumes roughly 1.15 liters per rotation. Acording to the compressor manufacturer the compressor produces one liter of air per rotation. The ratio between the crankshaft wheel and the compressor wheel is about 2.25. If we want 0.75 bar more then the atmosperic presure then we need about 1.15 * 1.75 liters of air which is about 2.0 liters. I therefore argue that the compressor produces alot more air then what is needed. This can also be verified by removing the air filter cover and then reving the engine a little bit. The overflow valve will then always be a little bit open. Anyone that have any other ideas?

2. Adding a small resistor/diod to the air temperature sensor
This is adivertised as a very cheap way to squeze 20 extra HP out of any mercedes. Again, has anyone tried it? I believe that this will only make the car less fuel efficient since it is almost the same as when you on old cars rich the mixture to make it start in the winters. On diesel cars it might work since the mixture of air and fuel is not as important, but on gasoline engines the mixture needs to be about 15.7:1 if you want the most out of it. Also, when you have a warm engine the rich mixture might acually damage the pistons. At least two stroke engines sometimes burn a hole straight through the piston if you run with a to big nozzle.

Does anyone have any ideas about any other way to tuning the engine? I should also say that I'm not that interested in $1000 chips, but more into "doing it myself".

Regards
Henrik from Sweden

 

I don't know enough about boost in general to help you there. I will say you can definitely increase it, both mechanically and through the engine control software, to add power.

Regarding the air temp sensor, you got some bad info. A modified sensor will never add power. Things like compression boosters and nitrous oxide add power. The sensor modification you're talking about will add no hp at all. An engine is tuned from the factory for the maximum designed performance under ideal conditions. The various sensors actually de-tune the engine from the max to protect it from being damaged and to improve emissions under other than ideal conditions. The sensors, then, cut power and restore power, but they do not add power.

The air temp sensor measures the incoming air temp as a variable in determing which ignition timing table to use. A more aggressive table is used when the air temp is cooler and therefore denser. If the air is cool AND there is no engine knock at various checkpoint RPM, then a more aggressive table is used. This continues until the most aggressive table is being used or until engine knock occurs.

The most aggressive table has predetermined upper limits. It's designed to produce the maximum performance. The modification you describe will "fool" the engine control software into thinking the air temp is cool no matter what. It can be scorching hot outside and the software will advance the ignition timing thinking the air is cool and dense.

If there weren't a fail-safe, the engine knock sensors, this modification could be very damaging to the engine. What would happen if the knock sensors should fail on a hot day? You could blow a head gasket or bend a head or worse. Without the modification, the timing would have been retarded and any damage avoided.

So, anyway. The modification does not add power. It prevents a loss of power under certain specific conditions. It can cause damage under certain conditions. It's there to protect your engine, not to slow your car. I'd leave it alone. It's not worth the risk unless you drag race your car to pay for your mortgage payments and the kids college funds.

 

Why go to all that trouble when you can fit a nitrous oxide kit. That'll get you going

 

All what trouble?

 

Yes I did many times tune up SLK with bigger kompressor wheel.(4-times)
It seriously works very well.

I really experimented a lotI tested all with brake deceleration meter, and comparisons with S2000 and NSX

When you fit it with the original chip it works up to 30 hp extra.

How it works: The kompressor delivers at a lower rpm already more turbo pressure, so the engine torque comes in earlier.
Over the whole range torque increases.

I did it ones with the chip changedin match with the bigger wheel, worked excellent , gave alltogether about 50 hp extra.

I once mounted bigger wheel to an allready genarally chipped slk, it really went off extremely fast.
But now and then the compressor pressure became to big and blow of.
So pushing the throttle completely would give often lower torque responce then with three quoter throttle.

When accelerating from 100 to 200 km/hr in 4-gear it would come up fast from 100 then at 130 it would give suddely more torque, then at 150 it seemed like acceleration would become little lower but then at 160 it would go like a rocket up to 200.
So acceleration at 180 was more then at 150 !

Together we drove with Honda NSX and this slk on a tour both machnes were very fast. Depending on the speed the rev's the gear
the throthle now and then this SLK was as fast or even little faster then the Honda NSX, wich is allready fasterthen a porsche carera!!

Generally when mounting the bigger wheel the enige responce may become now and then, depending on rev's, instable but defenitely with this it goes like a rocket, much much faster then the standard slk 230. It can come to the level of a
Porsche Carera.


Now I have onother SLK 230which is allready charply tuned withe a chip, theni added the big wheel and now responce is bad, it is faster without the bigger wheel.

So do not calculate on volume and rerv's; the air is compressed so the volume changes.


Also one can misguide the inlet temperature sensor by adding resistence.
When engine iscold resistance is high+-4 kohms; when engine is hot resistance is low = 1kohm.
So if you put exta 3 or 4 kohms between the inlet resistor, you increase pretrol injection and will get more torque.
( to my experience 10 to 20 hp ; some advertise with 25 up to 75 hp extra; thatis really false)
This simulation of inlet temperatue I did with my Honda S2000, I had mounted a microswitch on the throthle; and when I pushed
the throttle more then 3/4 it switched on and a relay to increase inlet resistance by 3 kohms, wichgave more petrol ( and changed at thge sametime v-tec switchover)
So when I wanted I had from 4000 to 9250 revs extreme torque.
I moved up with a ferrari Modena.
When driving on the low throttle I had no etra fuel consumption; Everything became as normal.

Marinus
from Holland