3in exhaust

[ArmyFocus]

Will a 3in exhaust do anything for me with a supercharger? Someone had mentioned on a thread a week or so ago that I'd need bigger than my current 2.25in Magnaflow exhaust to get over the 300whp mark with the ProCharger. What do you guys think?

Jason

[OrangeSVT03]

An engine is basically an air pump.. the more effecient it is the more power you will make.

A larger exhaust will help to get the exhaust out faster... but boy will it be loud.

[IslandFocus]

Wouldn't the 3" kill alot of his low end power with his supercharger tho?

[gobstopper]

Originally Posted by IslandFocus

Wouldn't the 3" kill alot of his low end power with his supercharger tho?

No, but it's not like a centrifugal blower makes a lot of low end power, either.

[pocus]

army just make sure your going to be ready for how load it may be. I got the trubendz 3" magnaflow with resonator going onto my car right now and hopefully it won't be much loader than my car alread was but if it is I don't really care. The 3" with the procharger should help out a bit on the top end and yes it will probably rob a few low end tq. It's more of a give a little to take a little. I don't personally think you will have to get a3" to hit 300 with the procharger being how far your going with your setup. But it wouldn't hurt. I kept the 2.5" flex and trubendz made my kit with it able to bolt straight onto the flex with a 2.5" flange. I think this is probably a better way to go insted of getting the 3" flex all the way back just so that there is a litle more back pressure in the exhaust for the tq.

Just the way i went and what i believe could be wrong.

[MillerTime]

You want to keep your exhaust small enough to keep it hot until it exits the tail pipe. If the exhaust is to cold at the end then it will cool down and become denser thus harder to move. It is very possible that you will see no change from a 2.5" to a 3".

Just my opinion...

[ArmyFocus]

so would you all agree then that a 2.5in would be the best compromise since I'm not going turbo?

Jason

[tallguy2.3]

get a 2.75 lol
i think Walter is developing one or something

[SVTFocus101]

No body really knows for sure, it comes down to opinions, the bolt on exhaust, intake, headers this and that, are tuning tools, none will generally make much horse power if any on their own. Getting a 3’ could benefit you, I would suggest if you went with a 3’ exhaust get it tuned to maximize the better flow. For me, sense I am getting the Xios kit, I will be going with a 3’ exhaust.

[SVTFocus101]

Originally Posted by MillerTime

You want to keep your exhaust small enough to keep it hot until it exits the tail pipe. If the exhaust is to cold at the end then it will cool down and become denser thus harder to move. It is very possible that you will see no change from a 2.5" to a 3".

Just my opinion...

That’s completely untrue, exhaust will not cool down enough at all to make it harder to move because it became denser . Bigger or smaller exhaust is not to determine how cooled it is when it exits to intern find the most efficient way to keep it hot enough to exit more efficiently. I don't know were you heard this, but your batting -20 with that. Anyway to my point PIPE DIAMETER
A 3" bore is adequate for an engine that produces about 250-350bhp. 4" bores would be good for a 400+bhp setup. You would be getting it mandrel bent right Army? Because as you already know I am sure; mandrel bent piping allows gases to flow better in the curves of the exhaust pipe as opposed to press bent piping. The disadvantage is that it's more expensive. For some who don’t know, mandrel bending is a process that allows the diameter of the pipe to be maintained even through the bend. With pressed bent piping, the diameter of the pipe is smaller in the bend. This can cause turbulence of the air flow. As a result, some efficiency will be


So, I say do the 3' exhaust Armym if your pusing 240-250+ IT will be good to have.

[belacyrf]

Originally Posted by SVTFocus101

That’s completely untrue, exhaust will not cool down enough at all to make it harder to move because it became denser . Bigger or smaller exhaust is not to determine how cooled it is when it exits to intern find the most efficient way to keep it hot enough to exit more efficiently I don't know were you heard this, but your batting -20 with that.

You are completely wrong. Pipe Diameter has a DIRECT EFFECT on exhaust temps, which have a direct effect on exhaust velocity, which has a direct effect on the exhaust pulse. THe exhaust pulse if at it's optimum will create a scaveging effect pulling the rest of the exhaust out of the combustion champer allowing cleaner air to be used for the next cycle creating more power.

If you go to a larger diameter exhaust, the large diameter will allow the air to cool becoming more dense. Dense air is slower air.

Here's a few quotes for you to read up on:

The Exhaust Pulse
To gain a more complete understanding of how mufflers and headers do their job, we must be familiar with the dynamics of the exhaust pulse itself. Exhaust gas does not come out of the engine in one continuous stream. Since exhaust valves open and close, exhaust gas will flow, then stop, and then flow again as the exhaust valve opens. The more cylinders you have, the closer together these pulses run.

Keep in mind that for a "pulse" to move, the leading edge must be of a higher pressure than the surrounding atmosphere. The "body" of a pulse is very close to ambient pressure, and the tail end of the pulse is lower than ambient. It is so low, in fact, that it is almost a complete vacuum! The pressure differential is what keeps a pulse moving. A good Mr. Wizard experiment to illustrate this is a coffee can with the metal ends cut out and replaced with the plastic lids. Cut a hole in one of the lids, point it toward a lit candle and thump on the other plastic lid. What happens? The candle flame jumps, then blows out! The "jump" is caused by the high-pressure bow of the pulse we just created, and the candle goes out because the trailing portion of the pulse doesn't have enough oxygen-containing air to support combustion. Neat, huh?

Ok, now that we know that exhaust gas is actually a series of pulses, we can use this knowledge to propagate the forward-motion to the tailpipe. How? Ah, more of the engineering tricks we are so fond of come in to play here.

Just as Paula Abdul will tell you that opposites attract, the low pressure tail end of an exhaust pulse will most definitely attract the high-pressure bow of the following pulse, effectively "sucking" it along. This is what's so cool about a header. The runners on a header are specifically tuned to allow our exhaust pulses to "line up" and "suck" each other along! Whoa, bet you didn't know that! This brings up a few more issues, since engines rev at various speeds, the exhaust pulses don't always exactly line up. Thus, the reason for the Try-Y header, a 4-into-1 header, etc. Most Honda headers are tuned to make the most horsepower in high RPM ranges; usually 4,500 to 6,500 RPM. A good 4-into-1 header, such as the ones sold by Gude, are optimal for that high winding horsepower you've always dreamed of. What are exhaust manifolds and stock exhaust systems good for? Besides a really cheap boat anchor? If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! Something to keep in mind, though, is that even though an OEM exhaust may make gobs of low-end torque, they are not the most efficient setup overall, since your engine has to work so hard to expel those exhaust gasses. Also, a header does a pretty good job of additionally "sucking" more exhaust from your combustion chamber, so on the next intake stroke there's lots more fresh air to burn. Think of it this way: At 8,000 RPM, your Integra GS-R is making 280 pulses per second. There's a lot more to be gained by minimizing pumping losses as this busy time than optimizing torque production during the slow season.

Pipe Sizing
We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.

Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. For engines making 250 to 350 horsepower, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches. If you have an engine making over 400 to 500 horsepower, you'd better be happy capping off the fun with a 4 inch exhaust. Ah, the drawbacks of horsepower. The best alternative here would probably be to just run open
exhaust!

These are taken from here. http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

Please feel free to dispute these with facts.

[Winkty]

http://forums.focaljet.com/forced-in...ead-first.html

Read thru the sections about exhuast size in that thread. It'll answer your questions.

[SVTFocus101]

Sorry, Army, one more thought about 3' pipe, as it could be adouble edged sword as well, too much gas speed indicates that that the system may be too restrictive hurting top end power, while too little gas speed tends to make the power curve excessively 'peaky' hurting low end torque. Larger diameter tubes allow the gases to expand; this cools the gases, slowing down both the gases and the waves.
Exhaust system design is a balancing act between all of these complex events and their timing. Even with the best compromise of exhaust pipe diameter and length, the collector outlet sizing can make or break the best design. The bottom line on any exhaust system design is to create the best, most useful power curve. All theory aside, the final judgement is how the engine likes the exhaust tuning on the dyno and on the track.
And this one os from http://www.burnsstainless.com/TechAr...ry/theory.html

[DJ Sures]

i wrote this last year for a simular discussion on another site..... (i use math for everything when building my motors. math is fact.)


BIGGER IS NOT ALWAYS BETTER. BUT SOMETIMES ITS REQUIRED

Restrictive Exhaust
A restrictive exhaust creates backpressure in the exhaust system that hurts your vehicle’s performance in two ways:

- The engine has to work harder to force exhaust gases out of the cylinders.
- Engines cannot scavenge burned exhaust gases out of the cylinder efficiently. This leaves exhaust gases in the cylinder to dilute incoming air/fuel mixtures and rob your engine of horsepower.


Pipe Diameter
A common misconception is that the larger the diameter, the better the system. But bigger isn’t always better. Systems that are too large in diameter can actually hurt performance.

As a general rule, switching to a performance system that is 1/4” to 1/2” inch larger than stock will provide you with the best horsepower increases. To determine which pipe diameters will be best for your system, decide what RPM range your engine will operate at, most of the time. Smaller diameter pipes will produce low- to mid-RPM torque. Larger diameters produce mid- to high-RPM torque.


CFM
CFM = Cubic Feet per Minute
CID = Cubic Inches Displacement

with my puny 2.0 Litre motor (if it were natural asperated) the converted CID is 122.047488 cubic inches.

To calculate the CFM of my nautral asperated motor i used this equation. which my natural asperated CFM is: 955 CFM.

CFM= (Engine Displ (cu in) x Full Load RPM x Eff. x (Exh. Temp Deg F+ 460)) / (C x 941760)

CFM= exhaust flow rate in cubic feet per minute.
Efficiency= .85 for naturally aspirated engines
Efficiency= 1.4 for turbo charged engines
Efficiency= 1.2 for engines with scavenging blower
C= 1 for two-cycle engine C= 2 for four-cycle engines

If Exhaust temperature is not available, use:
T= 1200 Deg F for gasoline engines
T= 900 Deg F for diesel engines

Now that you understand CFM.. Let's move on and reference this chart...
This chart is natural asperated. It will help you understand what size exhaust you need for your goal horsepower. As you can tell also, a 2.5 Litre motor can make 200 horsepower easily with only a 2.5 Exhaust. But what happens if you have a Forced Induction 2 litre making 300 HP?


Magnaflow also has some information on their website

What does this mean to Forced Induction?
Now this is the crazy part. We've been discussing Natural Asperated as you'll notice i've been repeating. Because soon as you "ADD" boost, the CFM is all wacky because you're adding to CID. This is the reason why...

Atmosphere at sea level is 1 bar (15 psi), here in Calgary it's approx 12 PSI.

Note: When you drive down to sea level, ur motor will feel like a 3 PSI upgrade

But when you add an additional 5 PSI, the absolute manifold pressure will reach 17 PSI in Calgary. That's a 25% increase of air volume. So the CFM calculations are off and need an extra number to honour additional forced induction.

How do we factor in boost?
Well since we discussed what a "bar" is (15 psi) and all our equations are assuming absolute manifold pressure to be atmospheric pressure. Then we simply need to add a multiplier into the equation of how much bar boost (7 PSI Boost would be 0.47 bar). So the equation including boost would look like this...

CFM= (Engine Displ cu in * Bar Boost * Full Load RPM * Eff. * (Exh. Temp Deg F+ 460)) / (C * 941760)

CFM= exhaust flow rate in cubic feet per minute.
Efficiency= .85 for naturally aspirated engines
Efficiency= 1.4 for turbo charged engines
Efficiency= 1.2 for engines with scavenging blower
C= 1 for two-cycle engine C= 2 for four-cycle engines

If Exhaust temperature is not available, use:
T= 1200 Deg F for gasoline engines
T= 900 Deg F for diesel engines

What do we do with CFM?
Well a quick rule of thumb is an exhaust should flow 2.2 CFM for every horsepower you'd expect to make. This will supply zero loss from backpressure. So using the above equation to calculate CFM, you can verify your horse power requirements by using the 2.2 factor on your true engine horsepower.

That's it!
So anyway, when someone asks "why does your 2 litre need a 3 inch exhaust?".. You can send him here so he'll learn.

[SVTFocus101]

Originally Posted by belacyrf

You are completely wrong. Pipe Diameter has a DIRECT EFFECT on exhaust temps, which have a direct effect on exhaust velocity, which has a direct effect on the exhaust pulse. THe exhaust pulse if at it's optimum will create a scaveging effect pulling the rest of the exhaust out of the combustion champer allowing cleaner air to be used for the next cycle creating more power.

If you go to a larger diameter exhaust, the large diameter will allow the air to cool becoming more dense. Dense air is slower air.

Here's a few quotes for you to read up on:

Okay you're right. I was wrong. I didn't think from what I understood how hot it was at the tail pipe, I can understand through out the system, I guess I thought he was referring just to the tailpipe… Ultimately the dyno will tell all. Some cars will loose w/ bigger some will gain.






These are taken from here. http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

Please feel free to dispute these with facts.

k

[MillerTime]

http://www.moddedmustangs.com/forums...ded-vt726.html

http://www.newcovenant.com/speedcraf...r/exhaust.html

http://forums.corvetteforum.com/showthread.php?t=303958
(Look at Bottom of Forum)

so a mild 350 will be good for dual 2.5 which will flow the same as a single 3". So if your motor is putting out the same power as that then yea you might need a 3"

So if your putting out the same power as a 300 - 350 small block yea you need a 3"....

I will let the charts talk for its self.

And Yes the extra surface area of the Pipe takes more energy from the Exhaust (causing it to cool down) the farther it is from the motor. Thats why Cats are generally put as close to the motor as possible. so as your driving air is going under your car is cooling off your exhaust. So unless you are putting out the extra power (heat) from your motor to keep it hot. It will Cause the Exhaust to cool down and become "heaver".

I don't think you can dispute same heat out put with larger exhaust/heat sink will cause for lower exhaust temps.

I could be just blowing smoke... but what ever...

[ArmyFocus]

holy intense exhaust info batman. lol. Thanks bela and DJ Sures and everyone else for the info. I'll take my time with this and read through the articles and such. If I do go with a larger exhaust I'll probably go with one from Trubendz and more than likely a 2.5in system, but I wanted to get info beforehand to see if I would even need 3in. Thanks guys!

Jason

[BUR_ZX3]

DJ that was an EXCELLENT post! You too Bela! Great info there!!!!


The short answer to your question: Depends on how much HP you're pushing. The long answer: Lots of math.

But generally once you cross the 200whp line, start looking to go to 2.75" exhaust.

[tallguy2.3]

wow, awesome info. lol I tried to do some calculations as if my car was at 13psi turbo'd and tried to work backwards to get the hp, and lets just say I made a mistake. Theres no way a turbo'd dura at 13psi is going to make 5500whp.

[belacyrf]

One thing I kinda disagree with DJ on is his generalization of FI exhaust. Since turbos and superchargers are very different animals. A turbo is a huge obstruction directly in the path of the exhaust pulses. The turbo requires the heat to spin, the heat is it's energy. After the turbo, the exhaust pulses are shot to heck and so is gas velocity. So going big after a turbo really has no detriment. Going to small does.

[ClintB1321]

originally posted by BUR_ZX3
But generally once you cross the 200whp line, start looking to go to 2.75" exhaust.

Opps, i'm running a 2.5 inch exhaust and i dynoed at 221whp this morning

[DJ Sures]

Originally Posted by belacyrf

One thing I kinda disagree with DJ on is his generalization of FI exhaust. Since turbos and superchargers are very different animals. A turbo is a huge obstruction directly in the path of the exhaust pulses. The turbo requires the heat to spin, the heat is it's energy. After the turbo, the exhaust pulses are shot to heck and so is gas velocity. So going big after a turbo