apwhat

This is a article I'm working on for my website, i think the Honda-tech community by far has the most educated people.. so give me your input on this topic. It will be appreciated.


When most of us buy our first exhaust systems we think about the size of the tip, what other people are buying, the angle of the rear section. We focus on brand names, and pipe size.

We here today however are going to go a little deeper into the exhaust system, starting from the combustion chamber to the muffler tip. The basic idea of the exhaust system is simple, exhaust air out of the chamber.

We have two phases to learn and understand. When we understand this it changes how we look at a particle setup, or how we can further modify our own to suit the engines needs.

The first phase is when exhaust gasses are removed from the cylinder.
After the spark, the exhaust valves open and the compressed gas hits the header primary's in its given firing order. Then at a much more explosive manner we have a wave of pressure are the port throat. This happens when the port itself opens. Kinda like when you open the door on a submarine... interesting things happen.

The pressure wave is one of the most neglected subjects. Its very complicated and i don't understand much of it myself.. but basically this is the phase when we want to scavenge, collect, take all that gas out of the cylinder.

We do this so that we can fill the cylinder back up with clean, fresh, ready to be destroyed air mixed with yummy 91 or 93 octane fuel.

This second part, if you want to get super nerdy you can look into "wave tuning" Now this pressure wave is directed by the size of the header primary, that first section of tubing on a header. From that point the gases move to the midpoint of the header, the collector. Depending on your setup, tri-y(popular since the 60's) or a 4-2-1 setup, the nozzle area has to be larger than the primary area but smaller than the final collector size.

From that point on the chaos has been decided for the most part.
If you want to manipulate the exhaust gases you do it in the header.

So what is actually going on?

BOOM goes your fuel and air. Then a wave of gas hits the header at 1600 feet a second. then the hot and ever expanding gas hits your collector.. it now moving at 300 feet a second. Prize to the first person to email me that in MPH. (thanks "FlewByU352") "1090.90MPH")
From the collector on the speed of the gas is determined by the catalytic convertor, or lack of. The size of the exhaust pipe, how many bends, and last but not least how much your muffler balances out sound to flow.

Now for my point.. the first foot and a half from the port to the collector exit is what matters. We see 1600 feet a second, hit a brick wall and decline to 300 feet per second or less. Yet we see people spending $1800 dollars on an exhaust with a stock header.

This is a lack of understanding which i hope to address in education.
If you focus on what matters, you will lose focus on what doesn't.
This is a life well lived, and a car well modified

Thank you
Nicholas - apwhat.com

opc

"Now for my point.. the first foot and a half from the port to the collector exit is what matters. We see 1600 feet a second, hit a brick wall and decline to 300 feet per second or less. Yet we see people spending $1800 dollars on an exhaust with a stock header.

This is a lack of understanding which i hope to address in education.
If you focus on what matters, you will lose focus on what doesn't.
This is a life well lived, and a car well modified"

Very VERY well put. Awesome article man!

FlewByU352

messaged

apwhat

lol.. "1090.90MPH repeating"

that took less than five minutes. gotta love the internet. Thanks so much guys.

apwhat

thank you.

HdeucedeuceA

To understand header theory, you have to understand how a motor works.

apwhat

bump ttt need input

Riake

Why do you think this wave travels at 1600 ft/s?

Do you think it is always 1600 ft/s?

apwhat

"Now for my point.. the first foot and a half from the port to the collector exit is what matters. We see 1600 feet a second, hit a brick wall and decline to 300 feet per second or less. Yet we see people spending $1800 dollars on an exhaust with a stock header"

apwhat

If i missed anything or you want to add some information to the article I'm always open..

HYREV2NR

This made me chuckle. But yes I liked this read, thanks.

apwhat

haha, i try to keep things fun.. thank you

CHEETAH

iTrader: (2)

nice and simple...prolly could include some more info on correlation btwn size of engine cylinder vs primary piping, collector size, etc.

also a bit on pro/con discussion on primary tube pairing based on cylinder firing order, and the benefit of 4-2-1 vs 4-1 design vs RPM power band etc.

jsut some random thoughts.

96dxB16

And you neglect us poor E85 folk??? This is discrimination!!

apwhat

I have a thought.. lot's of very educated and knowledgeable people on the board..

If anyone wants to write up a few paragraphs on these subjects, add them to this page, we can expand further...

1. Header Design(4-2-1) vs (4-1) setups.
2. Rpm band, the effects of different setups.
3. cylinder firing order in relation to primarys design
4. header material, types of piping
5. actual dimensions,... exhaust port valve, exhaust throat/short side radius, exhaust port cfm, exhaust port entry shape, and size, gasket size, header flange size, primary tube size.
6. Fuel types, low octane, high octane, alcohol, e85,

apwhat

good point, my focus is s2000, which sadly e85 is very low in the s2000 gene pool... however since its for everyone to read.. i will enter this in for discussion as well..

thanks for pointing that out!

Riake

The wave, is a pressure wave and travels at the speed of sound.

The speed of sound relies on temperature (the other factors are constants). So no, the pressure wave does not travel at the same velocity all the time. The wave velocity is directly dependent on your EGT.

Katastrophic

Woah, you forgot about us 87 octane guys.

apwhat

you think its not safe to say about 1600, maybe say "anywhere from 900-1600 ft/s depending on a few variables such as egt, primary tube diameter, and exhaust port size."

sounds good.. what do you think?

apwhat

87 would be covered in the scope of low octane.. lol very low octane =(

HYREV2NR

I'm not a highly experienced engine builder by any means but I always want to broaden my knowledge for a future build.
The problem I (and many others) run into is asking questions to understand more and you get the old "just do a search" or the the "upity" attitude of the ones that do know more about engine theory and act as if they're superior to the ones still learning.

I said all that hoping this thread won't go that direction.

I really want to know more about how bore and stroke works with primary size and help out to achieve the goals of the build results.

Katastrophic

Sounds good.

apwhat

I hear you 100%...

we need more information...

so many positive things come from having that transparent approach to knowledge.

apwhat

exhaust valve size list..

• s2000 f20 31mm
• B16A/18C 28mm
• H22 30mm
• RSX / K20 30mm
• K20 31mm
• NSX 30mm

apwhat

primary tube size next...