Blown 346 Posted October 31, 2013 Report Share Posted October 31, 2013 Racing engines will do better without back pressure, But everyday vehicles need it as back pressure will help with the air fuel charge. There is so much info on back pressure and exhaust we would all be here for days. Were not talking about race cars here. if we were i would agree no back pressure make more HP. Quote Link to comment Share on other sites More sharing options...
Brentd Posted October 31, 2013 Report Share Posted October 31, 2013 I agree there is a ton of info out there. My understanding is we don't need nor should we want back-pressure. We want scavenging, which will increase our exhaust gas velocity, back-pressure would result in a loss of performance. I think there is a slightly misunderstood interpretation as to what people think they are referring to when they call it back-pressure. I think a loss in velocity has been called a lack of back pressure. Ideal situations, including regular passenger cars would follow the mantra that every vehicle would have its exhaust system sized proportionate to the amount of flow the motor could produce. Ever wondered why civics have such tiny exhaust, thats why, they have to decrease the size of pipe to allow for a faster flow which would promote better scavenging which in turn would help evacuate the spent gases in the cylinders. And as far as the air fuel charge, i believe (and even more so in larger cams) they actually benefit each other, the overlap in valve events actually help exhaust gases to leave the cylinder because of the negative pressure directly behind the exhaust valve caused by scavenging and the positive pressure of intake charge, you can load the cylinder with a denser intake charge and if the cam is specd for your specific exhaust and intake it works even better. This is what i have been told, as well as what i have researched. Summit racing has some seriously detailed information on this topic. I could be way off because i am not an exhaust expert, this is just a subject that i have been researching at great lengths here lately before i bite the bullet and start from the back of the truck and work my way forward. I want to make sure i get it just right. I really wanted to stay true dual 3" but i am finding it probably will hurt me because the diameter pipe may be too large and slow the velocity of my exhaust doen. Quote Link to comment Share on other sites More sharing options...
2003_SuperSport Posted November 1, 2013 Report Share Posted November 1, 2013 X2 on the x-pipe! That is my goal for my exhaust. 2003_Supersport, I liked the idea of sticking with the 3", if i am shooting for 500 n/a can i stay with 3" dual, my vmax is 3" dual to a di so super 40 right now, but the plan was to do 1 3/4 lt's to 3 in dual no cats x pipe to muffler of choice at time of install to dumps after axle 500rwhp would be the point I would consider running 3" exhaust all the way back on a bigger cube N/A build... At that point I'd be looking at getting some 1-7/8 primaries too.... ( I am in the market just have no funds lol) But still 2.5" would be plenty if it were a true dual with each bank having its own muffler at 2.5" with a x-pipe to help equalize if your pipes are different lengths and create that extra vortex for scavenging.... I don't understand why you would stick with a 3" di muffler as that would be like necking down your3" pipes to 1.5" and back to 3"... To me that sounds like it would be a little louder due to the six inches of exhaust being stuffed in a 3" hole rather than letting it breath with each bank having its own 3"muffler.... The total volume of 2.5" true duals is like having a single 5" pipe so why would I want to stuff a 3" single muffler on my theoretical 5" pipe... make it sound louder LOL like the people who have old ford pick-ups and 1" tips for sound and crackle.... Like was discussed we don't want alot of backpressure so why add a smaller hole in the middle of our 6" combined bank flow... let them breath with individual mufflers and add the x-pipe to eliminate any unequal pressure from different length pipes and help scavenge baby LOL Quote Link to comment Share on other sites More sharing options...
Brentd Posted November 1, 2013 Report Share Posted November 1, 2013 Lol...thats what i meant, it will be dual all the way back, no shared mufflers. I summarized it a bit too much. Yea i want it pass gas with the best of them. No tips, no way no how! I like the exhaust to take a big ol dump right after the axle. My uncles always ran dual 3 or 4 inch chrome tips straight out the back and i have always hated that. Unless i can afford a high dollar exhaust setup that comes with its own branded tips, it will be dump city. Quote Link to comment Share on other sites More sharing options...
2003_SuperSport Posted November 1, 2013 Report Share Posted November 1, 2013 (edited) Lol...thats what i meant, it will be dual all the way back, no shared mufflers. I summarized it a bit too much. Yea i want it pass gas with the best of them. No tips, no way no how! I like the exhaust to take a big ol dump right after the axle. My uncles always ran dual 3 or 4 inch chrome tips straight out the back and i have always hated that. Unless i can afford a high dollar exhaust setup that comes with its own branded tips, it will be dump city. I want to do dumps too but I like my 45 degrees out the sides... I would have never heard my exhaust bounce back and forth from right bank to left on acceleration with out them though... Now that it is equalized I can dump them next to eachother... screw it just weld turndowns right on the back of the mufflers lol Edited November 1, 2013 by 2003_SuperSport (see edit history) Quote Link to comment Share on other sites More sharing options...
Brentd Posted November 1, 2013 Report Share Posted November 1, 2013 Turndowns on the muffler....u r a braver man than i lol. I got so lucky that we were able to cut the pipe at just the right angle and it sounds great with no drone. i had a truck years back that i had it pointed straight down and it drove me crazy. A friend of mine cut off his tailpipe in an attempt to hide it, he had a magnaflow, it screamed off the inside of the rocker panel and after a few days he used an exhaust clamp to put the piece back on Quote Link to comment Share on other sites More sharing options...
Jake99 Posted November 1, 2013 Report Share Posted November 1, 2013 Im also surprised at how much the exhaust can change the power curve of the engine, say dual 2.5 vs single 3.5 they both flow about the same but the single 3.5 gives you more mid range torque vs dual 2.5 is more of a high rpm hp. Iv always liked the ypipe and single 3in with a cutout, you get high exhaust speed of the single 3in yet you dont run into back pressure problems at the high rpm. Also yes we have noticed driveabilty, idle quality, tuning is all better with a little more back pressure. As far as drone go's, im about to hurt myself with this magnaflow it sucks so bad in mine, im going to try the resonater tube on mine from the link I posted and see if it works, I will report back with the results when I get it done. Quote Link to comment Share on other sites More sharing options...
Blown 346 Posted November 1, 2013 Report Share Posted November 1, 2013 What magnaflow mufflers are you guys using? I have no drone with mine. Im using the 5X8X18 Quote Link to comment Share on other sites More sharing options...
Black04SSS Posted November 1, 2013 Author Report Share Posted November 1, 2013 I hear ya Jake99 (no pun intended)! It is literally painful at around 70mph. If I was more brave, I would try the resonator tube along the muffler body and see how that works as well. Definitely keep us posted on your results! I have one 12599 (3" DI/DO with integrated X, 22" long, oval body) and two 14419 (3" SI/SO 14" long, 4" overall width, round body) mounted in the pipes right before the muffler. The droning is only very slightly lower with the added mufflers in front of the 12599. I initially installed the 12599 by itself to replace the stock one. The thing about tubular piping and flow is one has to consider the effect of laminar flow and how it effectively reduces the volume of air that the pipe can move. This is why dual 2.5 pipes will never flow as much as a single 5" pipe. The lesser surface area of the large single tube means it will outflow the two smaller tubes. And there is almost nothing we can learn from a race application exhaust system when it comes to daily driven street vehicles. Race applications mean WOT nearly 100% of the time and zero care for loudness or drone. Scavenging is the only positive thing an exhaust system can offer to help make more power (or shape power) compared to no exhaust at all. Backpressure is never a good thing. I think when some of you say backpressure, you mean a scavenging effect. That may be due to pipe sizing and bending being tuned to create velocity in the system or by merging multiple banks (or primaries in the case of headers) together at specific distances and angles. Quote Link to comment Share on other sites More sharing options...
Jake99 Posted November 1, 2013 Report Share Posted November 1, 2013 Yeah, I guess when I said race I mean more just modifing, most of the stuff I work on is all street cars/truck used as daily drivers just want more performance. I personally hate anything loud even a full blown drag car I would put mufflers on. I guess what I was saying is ls engines love there exhaust flow, from all the engine's iv ever worked on these seem to like large headers/exhaust the most. Anyways im off topic but yeah trying to get a nice sound without the drone seems to be hard to do for some reason, iv never tryed a corsa muffler before but that's what im going to try if I cant get rid of it on mine. Quote Link to comment Share on other sites More sharing options...
kevinh Posted November 2, 2013 Report Share Posted November 2, 2013 I have one 12599 (3" DI/DO with integrated X, 22" long, oval body) and two 14419 (3" SI/SO 14" long, 4" overall width, round body) mounted in the pipes right before the muffler. The droning is only very slightly lower with the added mufflers in front of the 12599. I initially installed the 12599 by itself to replace the stock one. I have a simmular exaust parts in my truck (2 1/2" DI/DO with integrated X, 18" long, oval body) and two (2 1/2" SI/SO 12" long, 3 1/2" overall width, round body) I asked the installer why he used 2.5" instead of the 3" muffler and he stated that it was easer to use a pipe spreader to spread the 2.5 openings to fit the stock exaust tubing rather than to shrink or fill in the differance between the stock exaust tubing(less chance of leaks). With just the muffler it had a bad drone at about 2500 to 3500 RPM. Then he installed 2, 2 .5" ressonators mounted in the pipes right after the drivers side and passenger side exaust comes side by side passed the 90 deg. bend just pass the cab. I asked if it mattered where he added the ressonators, he said closer to the cab the better, because that is where you are hearing the vibration at. It worked no more drone. Quote Link to comment Share on other sites More sharing options...
canadianVRss Posted November 3, 2013 Report Share Posted November 3, 2013 There are some massively incorrect mathematics and misinformation in this thread.... 2 2.5" pipes don't flow anywhere close to what a single 5" does. As a pipe gets larger its flow rate grows exponentially. A 2.5" pipe has 4.91si of internal area. Take 4.91 and times it by 2 for (one for each bank) and you get 9.82si (for a true dual system). One 5" pipe flows 19.63si. It would take 4, 2.5" pipes to have the same square inch area inside and there for same flow. The thing about tubular piping and flow is one has to consider the effect of laminar flow and how it effectively reduces the volume of air that the pipe can move. This is why dual 2.5 pipes will never flow as much as a single 5" pipe. The lesser surface area of the large single tube means it will outflow the two smaller tubes. This guy knows ^^^ Quote Link to comment Share on other sites More sharing options...
Cramer Posted November 3, 2013 Report Share Posted November 3, 2013 One thing that is to be taken into account is the pressure that is flowing through the tube also. It takes more pressure to flow through a 5" tube effectively than it does with a smaller tube. Exhaust is flowed by pressure waves unlike a liquid. A exhaust tube which is to large will have no or little velocity to essentially expel gasses and will create pressure walls. Just like blowing through a straw vs blowing the same amount through a paper towel roll. Sent from my Motorola RAZR MAXX using Tapatalk 2 Quote Link to comment Share on other sites More sharing options...
Brentd Posted November 3, 2013 Report Share Posted November 3, 2013 sinr said what I was trying to say. just because you have a larger diameter pipe doesnt mean that it will flow as well, because the pulses can lose velocity in a large pipe or several large pipes. I have been informed that running true dual 3" exhaust would not be as beneficial as true dual 2.5 or 2 3/4 because of the loss of velocity the exhaust gases would have in a 3". tthis is why I said the pipe size and the way it is ran should be proportional to the amount of flow the motor is producing. the paper towel roll is a perfect example, if I ran an exhaust too big for my motor then I would lose the scavenging effect halfway downstream and defeat the purpose, which is supposed to be exhaust pulses that can maintain their velocity as much as possible through the entire length of the exhaust so they dont bottleneck or slow down the pulses coming in behind them Quote Link to comment Share on other sites More sharing options...
JC03SS Posted November 3, 2013 Report Share Posted November 3, 2013 I have a magnaflow with 2.5" dual in and out. Pacesetters no cats and cutouts, dumped after the muffler. I'm in love with the sound. You can hear the cam perfect now. It's a little loud when taking off but at 70 has a nice rumble. It doesn't have much drone at all but the overall sound I don't see how it could sound any better. I think a lot of guys look for that perfect sound but want it quiet but loud and that's gonna be hard to do. When people hear my truck they say wow it sounds amazing and you can tell it's all about business. Quote Link to comment Share on other sites More sharing options...
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