Exhaust Collector Position

[ahonda55]

Hi and greetings for this rich forum..
I have a Peugeot 504, it has 4-2-1 exhaust system, while the pipes length between the manifold flange and the collector are VERY short, about 20cm, then a single pipe to the end, traditional system.

My question is, what are the effects of moving the collector, down the pipe, i mean lengthening the twin pipes before the collector, will this increase or decrease high and low rpm power/torque??

Many thanks in advance.

Greetings
Ahmed

[wrench459]

Old school method would involve a can of spray paint.

[SoYank]

Found this on DirtracingForum

One thing that I don't see anymore is the addition of exhaust tubing to the headers. At one time you would see some guys with 18" to 36" extensions! Do you remember when you tuned the exhaust length by painting a stripe on the exhaust and cutting it where the stripe didn't burn off! Technology has came a longs way! This was a old way to help tune the exhaust system before header technology and extensive dyno testing was being used by (for the most part) non-professional racers. With most engines coming from reputable engine builders, they are researched out enough that this isn't necesary. However if you have the wrong headers/cam for your combo you can at times see a fair gain in torque by doing this

Things have advanced & there is definitely a science to it.
The length should be mathematically determined to maximize engine breathing but I don't know the formulas involved.
Since an engine is really an air pump anything to improve breathing volume increases output.
The best arrangement creates a pulse in the exhaust pipe where the low pressure behind each "puff" actually helps pull the next "breath" along & helps scaveng spent fuel out of combustion chambers.

Here is an depth article covering this subject by respected exhaust guru Jack Burns.

[wrench459]

What I've got to know math to increase the power output of an engine.
Yep.
Do you have an idea of the total airflow the engine is ingesting? With our Opels slightly modified 115 gps is not out of the question.
Your going to need very detailed info on the engine.
This might help HEADERDESIGN.COM - Unlock Your Engine's Potential with your endeavors.

[RallyBob]

One thing about all the programs out there that calculate header design parameters....I've yet to see one for 4-2-1 designs. They all seem to be for 4-1 designs only. Apparently there are some variables with a 4-2-1 header design that don't calculate all too well. From what I've seen/heard, the best thing is to talk to someone who has done the development hands-on.

From my (very) limited experience with 4-2-1 designs, lengthening the secondary side moves the torque down into a lower rpm range. But I've personally never seen a 4-2-1 design that makes as nice a powerband as a well-sorted 4-1 design. I emphasize the 'well-sorted' because most 4-1 designs are far from optimal and are usually pretty horrid!

[blancojp]

The exhaust manifold on my GT is connected to a dual leader pipe which then tie together about 24" down stream; which we will call the collector for now. I don't know if this is what is ment by a 4-2-1 design, but the distance is the same from the manifold flange to the collector on any one of the cylinders. The inner pipe which takes car of cyls 2&3 is slightly longer than the outer pipe, which takes care of cyls 1&4.

I was originally thinking of separating the pipes and running a dual exhaust. But I believe if I do that I will improve flow but totally kill my low end torque.

What would be the better way to go?