M275 tuned for overrun?
02-17-2021, 05:58 PM
#1
Member
Thread Starter
M275 tuned for overrun?
Just curious if anyone has tuned the M275 engine for more overrun to allow more "pops and bangs". Does this come with eurocharged or Renntech tunes? If anyone has done this and has a sound clip, I'd love to hear it.
02-18-2021, 09:00 AM
#4
Super Member
Hmm, probably like little broken chunks of turbocharger and catalytic converter rattling around in the exhaust pipes... but I'm just guessing. 
Carry on.
Edit: What causes this is a too-rich mixture during deceleration. It took me a while to tune it out of my Harley. There was one setting for adding fuel during acceleration to prevent detonation. Another setting was for leaning it out during deceleration to keep unburned gas vapors from entering the exhaust pipes. When that unburned gas combines with the oxygen in the pipes, it explodes -- giving you that pop-pop-pop on decel. In a bike it's not a big deal; there's nothing in the exhaust and it's generally not enough of an explosion to damage the mufflers. It's just a little annoying unless you like the sound of poorly tuned engines. In the Mercedes... maybe a different story here. First you have the catalytic converters, whose job it is to deal with the hopefully tiny amount of unburned hydrocarbons left over from combustion. They work, but they really can't deal with too much of it. That's one reason there's so much attention paid to preventing and detecting misfires. A misfire will dump unburned fuel into the exhaust and damage the cats. Intentionally dumping fuel into the exhaust would kill the catalytic converters pretty quickly, I believe. Of course you'd have a constant CEL that would be annoying at best.
Also consider that your turbos are right in the path of the exhaust. That popping sound is the result of a fairly violent air/fuel explosion inside the exhaust pipes. While it would likely be downstream from the turbos, I can only imagine what the shock waves from those explosions would do to the turbos. I have no experience or direct knowledge to tell me for sure, but I suspect their service life would be remarkably short under those conditions.
In a race car with no turbos, not catalytic converters, and no mufflers (or not much for mufflers) it would probably be acceptable if the race tuning required it. But I think there's more than one reason you don't hear turbo V12s doing that - aside from the fact that I'm guessing that the number of people who would want it is too small for anyone to have pursued it.
Carry on.Edit: What causes this is a too-rich mixture during deceleration. It took me a while to tune it out of my Harley. There was one setting for adding fuel during acceleration to prevent detonation. Another setting was for leaning it out during deceleration to keep unburned gas vapors from entering the exhaust pipes. When that unburned gas combines with the oxygen in the pipes, it explodes -- giving you that pop-pop-pop on decel. In a bike it's not a big deal; there's nothing in the exhaust and it's generally not enough of an explosion to damage the mufflers. It's just a little annoying unless you like the sound of poorly tuned engines. In the Mercedes... maybe a different story here. First you have the catalytic converters, whose job it is to deal with the hopefully tiny amount of unburned hydrocarbons left over from combustion. They work, but they really can't deal with too much of it. That's one reason there's so much attention paid to preventing and detecting misfires. A misfire will dump unburned fuel into the exhaust and damage the cats. Intentionally dumping fuel into the exhaust would kill the catalytic converters pretty quickly, I believe. Of course you'd have a constant CEL that would be annoying at best.
Also consider that your turbos are right in the path of the exhaust. That popping sound is the result of a fairly violent air/fuel explosion inside the exhaust pipes. While it would likely be downstream from the turbos, I can only imagine what the shock waves from those explosions would do to the turbos. I have no experience or direct knowledge to tell me for sure, but I suspect their service life would be remarkably short under those conditions.
In a race car with no turbos, not catalytic converters, and no mufflers (or not much for mufflers) it would probably be acceptable if the race tuning required it. But I think there's more than one reason you don't hear turbo V12s doing that - aside from the fact that I'm guessing that the number of people who would want it is too small for anyone to have pursued it.
Last edited by DaleB; 02-18-2021 at 09:15 AM.
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AndreasHannover (02-19-2021)
02-18-2021, 09:22 AM
#5
Member
Thread Starter
Thanks for the info. This is something I heard someone discussing when getting their C63 tuned. I had never heard of anyone tuning for that before. So I was curious to know if any V12TT guys had done this to their cars. I'm assuming this would have the same effects on the V8TT. If it causes damage, why would anyone tune for this??
