Straight Pipe & Cold Air Intake for 300SD - PeachParts Mercedes-Benz Forum

bikpedlr · #1 04-11-2009, 10:11 AM

I've got an '84' 300SD that I've been playing with for about a year now converting it to run on both BioDiesel & WVO. It's doing really well but I've been told that I can get both performance and ecomomy benefits from giving it a cold air intake and scrapping the stock exhaust system for a striaght pipe.

I live in Houston TX so getting any kind of varried info can be a little hard. Just doing the BioDiesel & WVO conversion is like I have knelt before the Anti-Christ here in Petro-Metro ( Oil Capital of the World )

oldsinner111 · #2 04-11-2009, 10:32 AM

Check my pics.But in dusty summers I run paper filters.

VegStew · #3 04-11-2009, 11:00 AM

Some folks have done straight pipe with what sounds like minimal gains in power. Stock is already 2.25" i believe.
Cold air intake...their have been many an argument on this subject from "the stock system is already a cold air intake" too people having "seat of the pants" power gains from using a cone filter for example. If your tired of replacing air filter mounts, modify your intake. As far as the "cold air" part goes, without an intercooler it wont really matter if you draw your air from outside or from under the hood. As soon as the air passes through the turbo, it heats up due to compression.

toomany MBZ · #4 04-11-2009, 11:20 AM

The SD already has a cold air intake.
I understand diesels don't benefit from reduced back pressure.

tbomachines · #5 04-11-2009, 11:37 AM

The intake indeed, is already a true cold air intake, and flows quite well. As for the exhaust your bottleneck is the turbo, so increasing the exhaust diameter and flow post-turbo is rather pointless. The only thing I can think of would be the cali traps and perhaps the muffler. No doubt it probably sounds awesome though

pawoSD · #6 04-11-2009, 11:41 AM

The stock MB air intake is already flowing more than enough air, and it is a snorkel/cold air intake. Leave it alone!

Doing a straight exhaust does increase performance EVER so slightly, perhaps 2%....it just allows the turbo to spool a tad quicker, there will not be any actual power increase from it though.

Actros617 · #7 04-11-2009, 12:51 PM

You loose 1 psi of boost when you straight pipe, and when you straight pipe make sure u have a resonated exhaust tip, or else your car will sound like its farting...
http://www.youtube.com/watch?v=9WfpgCCcmqc
here is my video with a resonated tip installed

Simpler=Better · #8 04-11-2009, 02:33 PM

A straight pipe will increase performance and economy at the expense of more noise. It will not make you lose boost pressure-that's impossible
Low pressure post turbo means that it can spool faster and spin more freely, resulting in faster turbo response.

#9 04-11-2009, 05:37 PM

Quote:

Originally Posted by Simpler=Better

It will not make you lose boost pressure-that's impossible

It does actually. The turbine works on pressure differential so reducing exhaust system backpressure increases the pressure drop across the turbine. There is less backpressure needed in the exhaust manifold (power to drive the turbo) so less throttle and fuel is needed to make the same power to the wheels which means less boost is needed.

Basic physics.

300SD81 · #10 04-11-2009, 06:22 PM

I just put a straight pipe on my car 2 days ago, I've definitely noticed at least slightly faster turbo spooling. The sound does not increase much inside the car except under hard acceleration, outside, it sounds like a diesel truck.

MTUpower · #11 04-11-2009, 08:21 PM

Hey Forced Induction here's some good reading for you. You post as if you and only you are the authority on everything, and your word is law. You imply that removing backpressure is bad. While it may lower boost, it clearly improves perfomance, which is the goal of the original post and thread.

from Jay Kavanaugh, a turbosystems engineer at Garret.

The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible...

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.”

Larger exhaust does help performance by removing back pressure, and quite a bit on the 617 with increase over stock boost pressures, and removing the muffler does help performance with increase boost levels over stock.

tbomachines · #12 04-11-2009, 08:45 PM

I think maybe I'm reading this wrong, but you're both saying the same thing to me, difference is in spool time rather than the actual power produced by having a turbo...

#13 04-11-2009, 10:12 PM

Quote:

Originally Posted by MTUpower

You imply that removing backpressure is bad.

If you were to actually read my post instead of assuming, you would see I said exactly the opposite what you think I said.

Translation of my post: Less backpressure means better turbo efficiency and slightly more power through lower turbo drive pressure (Exhaust manifold pressure).