i was going through one of the older issues of scc and came across the eg civic project. the motor made pretty decent power everywhere in the power band with the edelbrock header with the 3in. downpipe. so my question is....would the b motors (b16, b17, b18) would still have the same kind of hp gains if the 3in. downpipe was cut and welded to a 3in. exhaust? is all this making sense? or did someone else already ask this question? i searched under "edelbrock header" and all i found was people asking how they work or how much they would cost....some one enlighten me.

 

a 3'' exhaust on a stock motor is not a good ideal back pressure is your friend..it may seem faster at first but a certain rpm's you actually lose power

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2001teggsr &raquo;</TD></TR><TR><TD CLASS="quote">a 3'' exhaust on a stock motor is not a good ideal back pressure is your friend..it may seem faster at first but a certain rpm's you actually lose power</TD></TR></TABLE>

thats for sure! If you plan on going turbo..then yes the 2.5-3" exhaust piping would be good.........but for a stock motor, expect to lose some hp

 

I read an article that stock N/A motors with exhausts up to 2.5" cat back exhausts will make power. Dont expect the same off the line torque numbers but you will get better top end hp.

 

Stick with 2.25, or at most 2.5. 3 is too big for your set up.

 

3.0 only if youre boosting.

 

My theory has always been:

RS,LS,GS-R's = 2.25"
ITR's = 2.5"
FI engines = 3.0"

 

RS,LS,GS-R's = 2.25"
ITR's = 2.5"
FI engines = 3.0" [/QUOTE]

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2001teggsr &raquo;</TD></TR><TR><TD CLASS="quote">a 3'' exhaust on a stock motor is not a good ideal back pressure is your friend..it may seem faster at first but a certain rpm's you actually lose power</TD></TR></TABLE>

The whole, "you need backpressure" thing is a myth.

But yea, the more freeflowing the exhaust (up to a point) the better top end you'll have. I just went from a cat-back Apexi N1 to an OEM ITR cat-back w/the bottle neck removed. The top end was better w/the N1, but the the modified OEM ITR catback gave me a better low and midrange, it's more fun driving around town now.

 

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

The whole, "you need backpressure" thing is a myth. </TD></TR></TABLE>

I wouldn't say it's a myth... Factory cars are tuned before we are able to buy them, allowing them to make the most power with factory parts.... When you change exhaust, your changing the amount of air that escapes the motor, thus throwing off the factory tune... So, in some cases those cars do acutally need that backpressure... The S2000 would probably be the best example...

But to stay on topic, 3" exhaust for an N/A car is rediculous... Not only will it lose power, but it'll sound like ***....

 

I don' think its really the back pressure affecting anything, its the flow of the exhaust gases. Basically if you have a smaller tube, the gases flow slower, bigger tube they flow faster

 

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

The whole, "you need backpressure" thing is a myth.

But yea, the more freeflowing the exhaust (up to a point) the better top end you'll have. I just went from a cat-back Apexi N1 to an OEM ITR cat-back w/the bottle neck removed. The top end was better w/the N1, but the the modified OEM ITR catback gave me a better low and midrange, it's more fun driving around town now. </TD></TR></TABLE>

Its not a myth, its the truth. Backpressure is always bad, no matter what. The more air you can flow, the more power you can make.
gmoore

 

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

Its not a myth, its the truth. Backpressure is always bad, no matter what. The more air you can flow, the more power you can make.
gmoore</TD></TR></TABLE>

This is true. The loss of power due to exhaust overkill is due to turbulence, not backpressure. There's a difference.

 

Ya backpressure doesnt make too much sense to me.

Backpressure doesnt affect the motor up until it hits the exhaust stroke (valve opens) at which point the engine is expending energy to eject the exhaust....the bigger the difference between the exhaust pressure in the cylender and teh exhaust pressure in the exhaust, the more it will flow and the less engergy that has to be expended.

I assume that the myth has been proved by dynos....at which point I wonder how you can loose power by flowing more. One possibility is that if the difference in pressure is large enough, the exhaust will flow at such speed that it will cause non laminar flow effects such as a sonic boom etc...which will take a considerable ammount of energy to overcome. I donno...thats my theory if the myth has been dyno proven.

But it seems kinda odd to me.

 

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

This is true. The loss of power due to exhaust overkill is due to turbulence, not backpressure. There's a difference. </TD></TR></TABLE>

 

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

Its not a myth, its the truth. Backpressure is always bad, no matter what. The more air you can flow, the more power you can make.
gmoore</TD></TR></TABLE>

I'm not really saying that backpressure is good, but neccesary in some cases... Take the RSX Type S for example... Honda was able to make 200 chp N/A... Now imagine that the only way to make 200 chp with that motor and it's internals would be to use a 1.75" exhaust...(Not really, just use for this example) So say they were able to make the power they wanted with a certain amount of backpressure... Now adding a more free-flowing exhaust could make more power, or could lose power... When you add aftermarket parts to a stock car, your throwing off the tune of the stock computer, possibly making the car faster or slower...

So yes velocity plays a role in exhaust giving more power, as does backpressure...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2001teggsr &raquo;</TD></TR><TR><TD CLASS="quote">a 3'' exhaust on a stock motor is not a good ideal back pressure is your friend..it may seem faster at first but a certain rpm's you actually lose power</TD></TR></TABLE>

if you need back pressure then why do people run open headers.

 

The way that I understand it is that you want as little backpressure as possible. What causes a loss of power is not an absence of backpressure but the stagnation of exhaust gasses inside the exhaust system. So running open headers is the ideal way of lowering backpressure because it just vents into the atmosphere. Add a pipe though and the gasses then have to travel at a quick enough velocity to exit the pipe without building up inside the piping and muffler causing stagnation. Correct me if any of this sounds wrong.

 

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

if you need back pressure then why do people run open headers. </TD></TR></TABLE>
this is exactly the reason why i asked this question...

 

You guys are right, back pressure is always bad.

With a smaller piping, the exhaust gas has a higher velocity, which is good. Obviously it also depends on the HP rating, because a smaller piping can't handle high HP cars without causing back pressure. That is why you need to find the correct size piping based on your HP. So you can have the least back pressure, yet highest velocity.

-Will

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Racer X &raquo;</TD></TR><TR><TD CLASS="quote">The way that I understand it is that you want as little backpressure as possible. What causes a loss of power is not an absence of backpressure but the stagnation of exhaust gasses inside the exhaust system. So running open headers is the ideal way of lowering backpressure because it just vents into the atmosphere. Add a pipe though and the gasses then have to travel at a quick enough velocity to exit the pipe without building up inside the piping and muffler causing stagnation. Correct me if any of this sounds wrong. </TD></TR></TABLE>

that would also explain side pipes; shorter piping

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by integra707 &raquo;</TD></TR><TR><TD CLASS="quote">You guys are right, back pressure is always bad.

With a smaller piping, the exhaust gas has a higher velocity, which is good. Obviously it also depends on the HP rating, because a smaller piping can't handle high HP cars without causing back pressure. That is why you need to find the correct size piping based on your HP. So you can have the least back pressure, yet highest velocity.

-Will</TD></TR></TABLE>

Exactly! Back pressure is what everyone talks about, but exhaust gas velocity is the real issue. So you put a 3" catback on an stock GSR, sure it can flow more gas volume than stock due to its larger circumference, but the velocity of the exiting gasses will decrease. Blow through a straw and then blow through a toilet paper roll and exert the same amount of force with each exhale. The velocity of the air shooting out of the straw will be much higher than that of the toilet paper roll, make sense? If you run open header, there is less turbulence, thus more velocity. Mandrel bends increase velocity over crush bends by decreasing turbulence, same deal as with shortening the pipe(open header). Cats, resonators, bends, mufflers, etc. all increase turbulence...

 

i would not reccomend it.