henrik
11/25/2004 1:55:03 PM
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
Lugnut
11/26/2004 5:59:22 AM
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.
smallgun
12/8/2004 8:31:11 AM
Why go to all that trouble when you can fit a nitrous oxide kit. That'll get you going
