So, the previous owner of my vehicle cut the mufflers out and welded pipe in place, with some nice exhaust tips. For a 4 banger, it sounds mean. My concern is, I'm sure I'm losing back pressure, which from my current understanding, means that I'm also losing HP.
Question #1 - What long-term effects, on which components, will the lack of back pressure have?
Q #2 - What are some options to add back pressure without putting mufflers back on? I know some fellow bikers I've met have welded bolts, washers, etc. inside their short exhaust to compensate for the loss of back pressure.
Whatever forum you are frequenting that perpetuates the blanket "engines need backpressure" claim is a forum where you want to log off and never return. Engines need proper breathing and an exhaust that's properly tuned and sized, i.e. tube diameter, for the amount of airflow the engine is capable of producing. And depending on the specific engine, that may mean smaller diameter piping for proper scavenging. Put huge pipes on a small engine and the airflow is going to be terrible because the exhaust velocity is going to be slow and the engine is going to have issues, usually being gutless on the bottom end.
My friend had a Dodge Ram a few years back, and towed his 25 ft boat with it. He then went all out and put a beautiful aftermarket full chrome exhaust on it, huge pipes, huge money, sounded absolutely incredible..... and now he couldn't tow his boat, it was like pulling a 30 ft camper with a Prius. He called me and said he thought he screwed something up, could I come look at it, he can barely tow his boat anymore. I took one look at it and thought these pipes belong on a Kenworth semi, not on a pickup. I said "where is your factory exhaust?" He showed it to me, I looked at the pipe size difference, and said "Put your factory exhaust back on". He reluctantly did. Then he was thrilled he did. The torque was back and he could tow again.
You can run lean, run rich, burn valves, run hot, induce detonation, and whole bunch of other undesirable things running an exhaust that is a bad match for the engine and how it is used, what cams it has, how its being fed fuel, what RPM range its running, and lots of other variables. Simply removing mufflers, putting on big pipes, welding in baffles and washers and other things just says that the person doing it doesn't really have a good understanding of exhaust tuning. Plenty of reading to be had on the web about this.
If the 4 banger has a catalytic converter it has backpressure. If it's supposed to have a cat but now your running catless then it probably has or should have a tune for the check engine light and performance. What is this 4 banger in any way?
2001 Subaru Forester S Replaced with a 2006 Forester
2004 Subaru Forester XT Death by deer. Replaced with 2003 Impreza Outback Sport (beater)
Quint nailed it on the head. If your engine has to work to push the exhaust out, like what happened when his friend put a massive pipe on his truck, the engine is now using power to push that exhaust out instead of putting it to the ground.
Unless you are getting a check engine like for something like lean conditions, you'll be fine. Fiat Abarths come without mufflers too from the factory and they sound terrific.
Being a Fiat tuner and fan from the 70's and early 80's ( Yugo GV too!)
I'm not a fan of that new abarth sound. , Also that's a turbo - which take a lot of energy from the exhaust.
I wonder if the OP car is a turbo?
If not, I would put a muffler on that pig! You will in time. Its get old fast.
Youth, hormones. Lots of testosterone, the "run through the forest gorilla" attitude dragging a branch making noise to show your station - Its actually in our DNA
To point, 4 strokes don't need "back pressure", they need proper scavenging, which means the " correct" sized pipes for the torque range.
Its resonance tuning - like organ pipes in church or ported subwoofer boxes. and its not just the primary length, the "collector" area air mass and velocity is critical too. Open headers make less power than say a header with a necked down 20" collector extension with a turnout.
The car will have a muffler soon.
Last edited by ARCOgraphite; 01/14/2008:23 AM.
2019 VW Jetta S 6MT OCI#2 7378mi-MOTUL Specific VW508.00+VW Service Filter; '17 Subaru Crosstrek CVT OC#8 60864mi-Subaru Idemitsu 0W20 + SOA Filter
Back pressure is a myth. It was most likely started decades ago when people would put bigger exhaust pipes on their car and lose a few hp. They mistakenly thought this meant the engine liked back pressure. In reality, the engine liked the higher exhaust velocity of smaller pipes while not being small enough to cause back pressure. It's a bit of a goldilocks zone.
I am considering no mufflers on my track car because 1) the class I race in doesn't require them, and 2) I have no way to run mufflers right off the headers without hacking at the frame. I would have to add intermediate pipes to extend back with a merge and put mufflers back near the rear axle. That adds weight, and this pig is already heavy enough. So... probably going sans muffler.
"He who is without oil, shall throw the first rod." - Compressions 9:1