i am going to make an a stright pipe for my b18b1 all motor for the drag strip anb the after market n1 for the street, what i am asking is will the straight pipe hurt my eninge any and or horspower , since ther is not back pressior.

 

Why would you want back pressior [sic]?

Hint: don't believe everything you read... Think about it and maybe read up a bit before you go jumping to conclusions.

 

the less restricion the easier it is to get rid of exhaust gasses, but to some extent too straight could be bad

 

back pressure is what pushes your car forward. Although too much is a bad thing, not enough will make you lose hp. I read in superstreet a long time ago that they put a big catback on a stock GS-r and it actually lost about 8 hp at the wheels (which is a ton when you only have about 150 to start with). Eventhough it is one of the first things (or only thing for that matter) that most people do to their cars, you really have to build your motor up a lot before a bigger exhaust is needed or will make an improvement. Here's a test, run your car with the stock exhaust, the catback, and the straight pipe, and see which way is the fastest. I may be wrong, but I think you will be surprised at the result.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BigBoulda &raquo;</TD></TR><TR><TD CLASS="quote">back pressure is what pushes your car forward.</TD></TR></TABLE>

No! This might be the wrongest thing I have ever read. Please go learn something and try again.

 

I KNOW that backpressure does not ACTUALLY push your car forward, but the point I was trying to make is that your engine DOES NEED backpressure. Like I said, too much back pressure is not good, but no backpressure is not any better. Why not look at the overall point instead of just looking for one little piece of the whole point to discredit. Take a small displacement engine that is not heavily worked and slap on a huge straight pipe, and tell me that I am wrong about the horsepower dropping. LOOK AT THE WHOLE PICTURE BEFORE MAKING STATEMENTS LIKE THAT.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote">

This might be the wrongest thing I have ever read. Please go learn something and try again.</TD></TR></TABLE>

Actually this IS the MOST WRONG thing I have ever read. Wrongest is not even a word, so why don't you please go and learn something, like basic English and grammer skills, and then try again. You must like 5 inch exhaust tips because the sound they make reminds you of your own *** wind.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BigBoulda &raquo;</TD></TR><TR><TD CLASS="quote">LOOK AT THE WHOLE PICTURE BEFORE MAKING STATEMENTS LIKE THAT. </TD></TR></TABLE>

I suggest you take your own advice. Think about the exhaust system, and the concept of pressure. Try to determine what you associate with back pressure. Is it small exhaust piping? Could it be that this piping isn't creating back pressure, as much as velocity in the exhaust flow? Examining the pulses of the exhaust and the positive and negative pressure waves they create will give an insight into what is actually occuring in the exhaust. Some suggested reading:

http://www.team-integra.net/se...ID=47
http://www.team-integra.net/se...ID=48
http://www.team-integra.net/se...D=355
http://www.google.com/search?s...+myth

I don't make this **** up, I just study it. I dislike writing as much as the next engineer, although we tend to play fast and loose with the English language. My exhaust tip is actually from a TSX, I like it because it isn't fugly:

 

Myth Busters should do a show on this.

 

MY MAD TITE VTECH B26 MAKES MAAD POWER WITH 1" CRX HF EXHAUST BECUASE OF TEH BACKPRESSURE!!!

BACKPRESSURE = HORSEPOWERS!12

 

Interesting articles, but they are repeatedly making the same point that I was trying to make, that it is UNTRUE that a big exhaust will automatically make more power, and that you have to have considerably more power than stock to ever require a larger exhaust. And more often than not you see cars that have nothing done to them other than an exhaust system, or worse yet, just a muffler, or worse yet, just a tip. Here is a quote from one of those articles that describes where I think the misunderstanding came from. Referring to the term "Back pressure":

"It would be more correct to say, 'a perfectly stock engine that cannot adjust its fuel delivery needs back pressure to work correctly.' This idea is a myth. As with all myths, however, there is a hint of fact with this one."

I think my problem was using (misusing) the term back pressure, when talking about getting the right sized exhaust. This seems to be something that occurs because the term is used so often. It is like referring to an anti-roll bar as a sway bar. The suspension piece isn't designed to make the car "sway", infact it does the exact opposite. Sway-bar is just the commonly used slang term for an anti-roll bar, but people still understand the point you are trying to make about the "anti-roll" bar when you refer to it as a "sway-bar". The point I was trying to make is to not assume that a big, loud exhaust = big horsepower, because that is completely untrue; as was stated over and over again in those articles.
And I apologize about the "tip" comment. Your tip is very respectable and much better than 99% of all the tips I see on CRX's. Since you really didn't expand on your original post on this thread, I assumed that you were one of those guys who spends a bunch of money getting a big "Cat-Back" system on their otherwise stock Hondas, and destroying any hope of having even the original hp, but just assume that it was faster because it is loud as hell. But after you went into more detail I realized that you did know what you were talking about.

Ferraris have a flap in their exhaust piping that opens up a certain RPM. Could this possibly be for this reason? (quoting from one of your articles):

"In the lower RPMs, pulses are smaller, and further apart. When you rev up into the high RPMs, pulses get bigger and closer together. So we want to keep the small, spread out exhaust pulses in line in the low RPMs but we also want to accommodate the larger, quicker pulses in the high RPMs."

Ferrari does this so it doesn't have to:
"... decide what pipe size will give us the best trade-off of low-end vs. high-end power so we can get the highest total HP increase possible throughout the RPM range. "

So again, I think we are both making the same point, that: coffee cans are just that and shouldn't be slapped onto a car. It sounds like a fart, not the engine.

 

Good to see we are on the same wavelength. You're also obviously a level-headed, intellegent person, not a knuckle dragging "I'm right" kinda guy.

Many people confuse backpressure with velocity, and it's easy to see why. The same conditions that promote velocity also seem to generate back pressure under the right conditions. Like you quoted from Ferrari, it's a tradeoff. The same piping diameter that gives excellent velocity at 2500rpm will be too small for the same engine at 7500rpm. And likewise, a pipe that gives good flow and velocity at 7500rpm will be way too big at 2500rpm, and velocity will go down the tubes, pun intended.

The idea of designing a good exhaust is to look at the application. You'll notice that a Geo Metro has an exhaust that would make a mosquito suffocate. This provides exhaust pulse tuning and velocty at the rpm range most often used by a driver of a Metro. Removing the 1/8" crush bent piping and replacing it with a 1.75" system and a decent header would show great gains in the higher rpm range, while very low rpm right suffer a bit.

The same can be said for any motor, be it a Metro or a Ford F250 carrying a Metro. You design the exhaust around the rpm range where you want the most velocity to time the exhaust pulses just right. When this is achieved, what might be percieved as back pressure is actually exhaust scavenging. As one exhaust pulse travels down the exhaust, a rarefaction, or low pressure zone, travels back up the pipe at a speed approaching the speed of sound, as it is an accoustical wave after all. When everything is just right, and all the planets are alighned, the low pressure wave reaches the exhaust port of the cylinders just as one of them is in the exhaust cycle, preferably near the end so as to pull more air out and promote cylinder filling under the valve overlap conditions most of these cars see.

Since there is a different amount of airflow at all ranges of the rpm band, it's not possible to create this effect everywhere, from idle to redline. But we can concentrate on the range we are most interested in, and for most of us, it is the upper range. Since there is obviously more airflow, a larger exhaust is needed to accomodate the flow and get the desired scavenging effect. This also make one realize that the "right" exhaust for a 2.1L 13:1 all motor race car is not the "right" exhaust for a stock B16. You would have to reduce the size of the piping to create the same effect. And that is where the confusion is. People mistakenly connect a smaller exhaust pipe with backpressure, not realizing that it probably creates even less pressure due to the effects mentioned above. Remember that the pressure in the pipe at a given time isn't neccessarily what matters. What matters is what the exhaust valves see when they are open, and if a low pressure wave is reaching them at that point, then you can't really say anything about backpressure 3 feet down the pipe.

I may be a little biased, as he is a faculty member here at school and I see him usually every day, but David Vizard has an excellent article that talks about the right sizing of an exhaust, and choosing the right components. He addresses the backpressure issue, and explains (probably better than I did) the relationship between flow and backpressure. I don't remember where I got it from, but I uploaded the article to my server. It's 5.8mb, so dial-up: take a lunch break.

http://www.coe.uncc.edu/~mdkee...e.pdf

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spoonEG9civichatch &raquo;</TD></TR><TR><TD CLASS="quote">i am going to make an a stright pipe for my b18b1 all motor for the drag strip anb the after market n1 for the street, what i am asking is will the straight pipe hurt my eninge any and or horspower , since ther is not back pressior.</TD></TR></TABLE>

The real question is what do you call all-motor... Whats done to your b18b1? FYI, A stock engine with boltons isnt really refered to as all-motor at the strip..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">Myth Busters should do a show on this.</TD></TR></TABLE>

x2 Im gonna email the show.
Yes, I am very bored.