exhaust
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eric240sxracer
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Scott McLellan
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I got a question. I was thinking about going with the Hotshot header and building a custom 2.25 catback with all mandrel bends. First, does anyone know where you can get the 2 bolt flanges for 2.25 and 3. The way I understand, the hotshot's collector size is 3" and I would like to buy a universal high flow cat and weld on 3" flanges to both ends of the cat and then bolt on a 3" to 2.25" reducer. Then I was wondering if I needed to put in all those little tiny 5 degree bends between the cat and the resonator and axle if anyone has done this before? I was thinking I would use a Flowmaster 60 series. This muffler is specifically designed to work with import engines to reduce resonation- if that is a word. I was also planning on using a resonated pace setter tip. Has anyone had any experience with this flowmaster muffler? I don't think, correct me please if I'm wrong, but i don't think I'll need a resonator inbetween the cat and the muffler. In the flowmaster catalog it recommends using a resonator when there is a 6' length of uninterrupted pipe which I guess makes sense but when I tape-measured the length, it was about 5.5'. That's close. If you think I need a resonator do you know where I could get a performance type 2.25 resonator. So I guess I'm just wondering what all this will end up sounding like. Hotshot - 3" high flow cat - 2.25 mandrel bent - (resonator?) - 2.25 center in and out - pace setter resonated tip. I know it is hard to guess what all this will sound like but how loud do you think this would end up being? I definately don't want it to sound ricy, though, so if this plan is a bad one please make some suggestions. Thanks and sorry for writing a book here.
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eric240sxracer
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Scott McLellan
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Scott McLellan
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Sorry eric240sxracer, i didn't really answer your question, but i think you want the cat to be as close to the header as possible, preferably directly after the header. Your rear O2 sensor will have to be mounted behind the cat somehow as well. I personally think that 2.5 piping is too big for a mostly stock NA KA but there is no right or wrong answer for this because people have made both work. My flowmaster catalog reccomends using 2.25 mandrel bent piping for 4 cylinders with a single exhaust with up to 200hp. I think when people say that their 2.5 exhaust pulls harder in higher rpm's it's because there isn't any power in lower rpms and they just feel the rpm band where the 2.5 is actually helping them while a 2.25 won't sacrifice lower rpms so there won't be as much as a difference between the lower rpms, where it is harder to feel a diference in power, and higher rpms. I would find it very interesting for somone to test this though, a 2.25 versus 2.5 piping test on the same engine and not basing the results on purely peak hp (even though I bet they would be very close to the same) but on overall hp AND torque cause torque is what moves your car.
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eric240sxracer
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aaronsnocker1
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WongFeiHung
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aaronsnocker1 wrote:i would suggest not using the pacesetter tip. I have a pacesetter exhaust and it sounds really riced out. kind of like a 2 stroke dirt bike or a jet ski.
Does your exhaust have a resonator in it?
Personally, I have a 2.5" Exhaust on my little assed 1.6L engine.(bring the flames its a Honda boy LoL)
I had a 2.25" and now have a 2.5" exhaust. I gained roughly 1 whp througout the powerband on my little car.
The important thing with exhausts is not back pressue....its exhaust velocity. If you can keep a consistant flow of exhaust, the velocity will help scavenge the spent gasses from the cylinders.
If you have a 3" collector. Stay 3" mandrel the whole way through. Make sure you have a straight through resonator and muffler on there as well. :thumbup:
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Scott McLellan
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So Spade, if you had a header with a 4" collector would you run mandrel bent 4" piping all the way back?
"The important thing with exhausts is not back pressue....its exhaust velocity. If you can keep a consistant flow of exhaust, the velocity will help scavenge the spent gasses from the cylinders."
You see the bigger pipe you have the more volume it has which means the same amount of air doesn't have to move as fast to go through it. This is called "less" velocity. To get the burnt gasses out of the combustion chamber more efficiently, which in turn allows the engine to pull in a fresh air/fuel charge which results in a power increase, you reduce the restrictions in your exhaust system, not eliminate them. By increasing the size of your piping you allow the engine to expell the burnt gasses easier, obviously. BUT, a smaller pipe will force the burnt gasses to have a greater velocity. The reason why you want this velocity is because when the exhaust valves open, you want the air that is in the exhaust system to be moving away and out so that it helps "pull" the spent exhaust out of the cylinder, not sitting still in the exhaust because the piping is so big the gasses have very little velocity. Too small of a pipe will obviously create restrictive back pressure, though. The only real solution, if you want optimum power, is to create an exhaust system that balances the exhaust velocity with the ability to expell the spent gasses then. The ideal set up is going to be different depending on where you want your power to occur in the rpm's range. It is obvious that as engine speed increases the amount of air going thru it will also. So if you want top end power, then you will want a relatively larger pipe because the exhaust gasses will still be able to move at a sufficient velocity at higher speeds, but at lower rpms you will most likely suffer a little. I personally think that unless your KA is heavily modded giving it the ability to move more air, such as with intake, porting job, higher compression, different cams, or whatever, even a 2.5 inch could be a little to big. If some of these mods are in your future plans though, sure go with the 2.5 b/c it will be liveble until then, just not optimal until you do those mods. But if your KA is stock or just has an intake, I think you will gain more power with a 2.25" exhaust. As for the straight thru resonator and muffler it is all personal preference based on the sound you want. Obviously an all straight thru set-up will reduce back pressure which is good but there are companies that use engineering to create a good flowing muffler and reduce sound or create a different tone without creating back pressure. The muffler I was thinking of using, a Flowmaster Delta Flow 60 series, uses no packing material that can blow out that most straight thru mufflers use, by using chambers designed to create minimal restrictions. It also has an internal design, "delta" shape, which cancels out some sound resulting in a different tone that I think will sound good in my opinion.
If anyone sees anything wrong here PLEASE correct me!
-Scotty
Also does anyone know where you can get 2 bolt exhaust flanges in the 3" and 2.25" size? Thanks!
"The important thing with exhausts is not back pressue....its exhaust velocity. If you can keep a consistant flow of exhaust, the velocity will help scavenge the spent gasses from the cylinders."
You see the bigger pipe you have the more volume it has which means the same amount of air doesn't have to move as fast to go through it. This is called "less" velocity. To get the burnt gasses out of the combustion chamber more efficiently, which in turn allows the engine to pull in a fresh air/fuel charge which results in a power increase, you reduce the restrictions in your exhaust system, not eliminate them. By increasing the size of your piping you allow the engine to expell the burnt gasses easier, obviously. BUT, a smaller pipe will force the burnt gasses to have a greater velocity. The reason why you want this velocity is because when the exhaust valves open, you want the air that is in the exhaust system to be moving away and out so that it helps "pull" the spent exhaust out of the cylinder, not sitting still in the exhaust because the piping is so big the gasses have very little velocity. Too small of a pipe will obviously create restrictive back pressure, though. The only real solution, if you want optimum power, is to create an exhaust system that balances the exhaust velocity with the ability to expell the spent gasses then. The ideal set up is going to be different depending on where you want your power to occur in the rpm's range. It is obvious that as engine speed increases the amount of air going thru it will also. So if you want top end power, then you will want a relatively larger pipe because the exhaust gasses will still be able to move at a sufficient velocity at higher speeds, but at lower rpms you will most likely suffer a little. I personally think that unless your KA is heavily modded giving it the ability to move more air, such as with intake, porting job, higher compression, different cams, or whatever, even a 2.5 inch could be a little to big. If some of these mods are in your future plans though, sure go with the 2.5 b/c it will be liveble until then, just not optimal until you do those mods. But if your KA is stock or just has an intake, I think you will gain more power with a 2.25" exhaust. As for the straight thru resonator and muffler it is all personal preference based on the sound you want. Obviously an all straight thru set-up will reduce back pressure which is good but there are companies that use engineering to create a good flowing muffler and reduce sound or create a different tone without creating back pressure. The muffler I was thinking of using, a Flowmaster Delta Flow 60 series, uses no packing material that can blow out that most straight thru mufflers use, by using chambers designed to create minimal restrictions. It also has an internal design, "delta" shape, which cancels out some sound resulting in a different tone that I think will sound good in my opinion.
If anyone sees anything wrong here PLEASE correct me!
-Scotty
Also does anyone know where you can get 2 bolt exhaust flanges in the 3" and 2.25" size? Thanks!
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WongFeiHung
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LongIsland240
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TrunkMonkey
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whatever diameter your header's collector ends in is the minimum diameter your exhaust needs to be. anything smaller hinders the header from scavenging the exhaust gases effectively.Scott McLellan wrote:You see the bigger pipe you have the more volume it has which means the same amount of air doesn't have to move as fast to go through it. This is called "less" velocity. To get the burnt gasses out of the combustion chamber more efficiently, which in turn allows the engine to pull in a fresh air/fuel charge which results in a power increase, you reduce the restrictions in your exhaust system, not eliminate them. By increasing the size of your piping you allow the engine to expell the burnt gasses easier, obviously. BUT, a smaller pipe will force the burnt gasses to have a greater velocity. The reason why you want this velocity is because when the exhaust valves open, you want the air that is in the exhaust system to be moving away and out so that it helps "pull" the spent exhaust out of the cylinder, not sitting still in the exhaust because the piping is so big the gasses have very little velocity. Too small of a pipe will obviously create restrictive back pressure, though. The only real solution, if you want optimum power, is to create an exhaust system that balances the exhaust velocity with the ability to expell the spent gasses then.
-demetrius
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Scott McLellan
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"whatever diameter your header's collector ends in is the minimum diameter your exhaust needs to be. anything smaller hinders the header from scavenging the exhaust gases effectively."
I'm not trying to be a pain, just thought I'd add some.
One thing that needs to be said is that the reason why header collectors are bigger is because they are "collecting" the exhaust gasses from each primary, hence the name. Obviously where two different streams of air, traveling at diff. speads (because not all cylinders are firing at the same time), collide you are going to need a little extra room where the gasses can "simmer down" a little. Once the gasses have been combined into that one pipe the name of the game is keeping that gas moving. To scavenge the gasses you absolutely need velocity. Let's say you have a golf ball representing the actual amount of exhaust gas produced from one cylinder in an engine(I know solid and gas but humor me here). Let's say that that golf ball comes out of a header collector into a 1 in. exhaust pipe. Obviously the ball will not fit but in the case of a gas it will, it will just be a major restriction. This setup is going to have very good velocity but bad flow capability. Because the "ball" of gas is going to have to be pushed thru the too small pipe(in other words back pressure), you can throw out the scavenging effect idea. Now, let's say that that same ball comes out of the collector into a 4 in. pipe. Well that fixed the flow capability but now you are going to lose the scavenging effect because that ball is not filling or even coming close to the pipe's inside walls to create a sort of suction created as the momentum of the ball pulls the air behind it. The last setup is the pipe that "fits just right." The ball comes out of the collector and because the pipe diameter is big enough for the ball to travel through it, velocity is okay. But also, as the ball travels through the pipe, it fits snuggly enough that it pulls, or scavenges, the air behind it creating a sort of momentum that goes clear back to pulling air out of the cylinders which is where the power from an exhaust is actually coming from. That said, I did leave out a factor -engine speed. As engine speed increases, the size of the "ball" is going to increase proportionally, obviously. So the goal is to create a pipe size that is effective at the most used rpm's. I think most would agree that choices for a stock to mild KA would be 2.25 in. and 2.5 in. Because a KA could probly work with both sizes it is just personal preference. In my opinion, since I probly spend 95% of the time in the lower 3/4 of the rpm's I would go with a 2.25 although I think I could live with a 2.5. You also have to factor in that 2.5 is going to be louder, too. If you are worried about top end I really don't think you will lose any with a 2.25 if you have a good flowing muffler, high flow cat, and mandrel bends. The idea that isn't true though is that you need to use whatever piping your header collector is because you need to base the size of your piping on the amount of exhaust gasses your particular engine will produce. Consider that stock piping is 2 in. with a restrictive muffler, resonator, cat, and cast exhaust manifold. 2.25 piping has approxiamately 21% more cross section area than 2 inch. I will run 2.25 in., when I get the money:) and time. One more example I thought of is the hour-glass shaped header collectors on those high output Winston Cup engines. At the smallest part you would think it would barely be big enough for a honda but, it builds power by using the velocity-scavanging-and other factors like wave pulses and stuff. Granted, those things are precisely tuned for each specific engine but still. Okay, I have definately put in my 2 bucks here.:oface
If I am wrong anywhere please explain where :thinker
-Scotty
I'm not trying to be a pain, just thought I'd add some. One thing that needs to be said is that the reason why header collectors are bigger is because they are "collecting" the exhaust gasses from each primary, hence the name. Obviously where two different streams of air, traveling at diff. speads (because not all cylinders are firing at the same time), collide you are going to need a little extra room where the gasses can "simmer down" a little. Once the gasses have been combined into that one pipe the name of the game is keeping that gas moving. To scavenge the gasses you absolutely need velocity. Let's say you have a golf ball representing the actual amount of exhaust gas produced from one cylinder in an engine(I know solid and gas but humor me here). Let's say that that golf ball comes out of a header collector into a 1 in. exhaust pipe. Obviously the ball will not fit but in the case of a gas it will, it will just be a major restriction. This setup is going to have very good velocity but bad flow capability. Because the "ball" of gas is going to have to be pushed thru the too small pipe(in other words back pressure), you can throw out the scavenging effect idea. Now, let's say that that same ball comes out of the collector into a 4 in. pipe. Well that fixed the flow capability but now you are going to lose the scavenging effect because that ball is not filling or even coming close to the pipe's inside walls to create a sort of suction created as the momentum of the ball pulls the air behind it. The last setup is the pipe that "fits just right." The ball comes out of the collector and because the pipe diameter is big enough for the ball to travel through it, velocity is okay. But also, as the ball travels through the pipe, it fits snuggly enough that it pulls, or scavenges, the air behind it creating a sort of momentum that goes clear back to pulling air out of the cylinders which is where the power from an exhaust is actually coming from. That said, I did leave out a factor -engine speed. As engine speed increases, the size of the "ball" is going to increase proportionally, obviously. So the goal is to create a pipe size that is effective at the most used rpm's. I think most would agree that choices for a stock to mild KA would be 2.25 in. and 2.5 in. Because a KA could probly work with both sizes it is just personal preference. In my opinion, since I probly spend 95% of the time in the lower 3/4 of the rpm's I would go with a 2.25 although I think I could live with a 2.5. You also have to factor in that 2.5 is going to be louder, too. If you are worried about top end I really don't think you will lose any with a 2.25 if you have a good flowing muffler, high flow cat, and mandrel bends. The idea that isn't true though is that you need to use whatever piping your header collector is because you need to base the size of your piping on the amount of exhaust gasses your particular engine will produce. Consider that stock piping is 2 in. with a restrictive muffler, resonator, cat, and cast exhaust manifold. 2.25 piping has approxiamately 21% more cross section area than 2 inch. I will run 2.25 in., when I get the money:) and time. One more example I thought of is the hour-glass shaped header collectors on those high output Winston Cup engines. At the smallest part you would think it would barely be big enough for a honda but, it builds power by using the velocity-scavanging-and other factors like wave pulses and stuff. Granted, those things are precisely tuned for each specific engine but still. Okay, I have definately put in my 2 bucks here.:oface
If I am wrong anywhere please explain where :thinker
-Scotty
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TrunkMonkey
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. i suggest you do some research on how a header works, but in the mean time...-
TrunkMonkey
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Scott McLellan
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Hey demetrius, I read that link about the exhausts you mentioned and I must say I am suprised. Numbers don't lie. I will mention that I have several magazines that have a lot of info on headers and how different primary size effects where your torque peak occurs, ect. so I do understand how this stuff works. Believe it or not they didn't use the whole "golf ball" thing....
-Scotty
-Scotty-
C-Kwik
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I would not neck down the exhaust after the collector. It's going to disrupt flow. If velocity is a problem at the diameter of the collector, then the header was designed with too large a collector in the first place. You can't make up for poor scavenging of a collector that is too large by reducing the size of the exhaust down the line. The column of gas will slow down too much at the collector as it is and ruin the whole process. Ideally, in terms of preformance, you want the primaries to join at a properly sized collector and the rest of the exhaust should then maintain the same diameter up until the exit.
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Scott McLellan
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Not sure about s13 piping but s14 is 2 in. stock.
I have a question for you guys then. Not trying to be mouthy, but why do they even make collector reducers then?
Piping size is a tuning factor for an engine, that is why there are different sizes. A header company can make a sufficiently large collector and allow the owner to "tune" their particular setup. That is why Hotshot probly makes a collector in the 2.5 in. size, to allow tuning to a heavily modded engine down to an otherwise stock engine. That is where reducers come in. If a 2.5 collector is too big for an engine because it should actually be a 2.25 collector, then obviously it is not going to be a restriction to neck down to a 2.25, right? This isn't rocket science. Before I say anymore, here are some facts: stock piping is 2 inch. Going to a 2.25 dia. pipe has 26.6% greater cross section area, 2.5 has 56.3%, and 3.0 has 125%. As you can see, 1/4 in. means a 25% diff. in flow. This is a fairly large diff. Stock engine displacement for a KA24 is around 150 cubic inches. Flowmasters catalog has a chart that reccomends 2.25 inch for a 150-200 cu. in. engine that is putting out 150. The 2.5 in. piping is recommended for 150-200 cu in. engine that is putting out 200 hp. Being at the small end of the 150-200 engine size and definately not putting out 200hp, (unless you add up the "30 hp" from that intake and the other "15 hp" from the header in those adds) it is reasoned that 2.25 in. dia. piping would be the best. The only difference there will be is a very slight gain on the top end with a loss in the lower end torque for the 2.5 that in reality will not allow your car to have as much real world power (acceleration) as the 2.25 that will give as it will also help with lower end torque as well as allow the engine to breath freely on the top end.
I did find it convenient that the link where the guy dynoed the 3 in. exhaust didn't even try the 2.25. Somebody find two back-to-back dyno charts with 2.25 and 3 in piping on a KA that proves 2.5 produces more across the entire power band, or better yet, some 1/4 mile ET's that prove 3 is better than 2.25 and I'll shut up forever. Of course the same type of muffler, cat, ect. would need to be used. I'm just trying to back up my opinion with some "research" so that incorrect info. is not posted.
I have a question for you guys then. Not trying to be mouthy, but why do they even make collector reducers then?
Piping size is a tuning factor for an engine, that is why there are different sizes. A header company can make a sufficiently large collector and allow the owner to "tune" their particular setup. That is why Hotshot probly makes a collector in the 2.5 in. size, to allow tuning to a heavily modded engine down to an otherwise stock engine. That is where reducers come in. If a 2.5 collector is too big for an engine because it should actually be a 2.25 collector, then obviously it is not going to be a restriction to neck down to a 2.25, right? This isn't rocket science. Before I say anymore, here are some facts: stock piping is 2 inch. Going to a 2.25 dia. pipe has 26.6% greater cross section area, 2.5 has 56.3%, and 3.0 has 125%. As you can see, 1/4 in. means a 25% diff. in flow. This is a fairly large diff. Stock engine displacement for a KA24 is around 150 cubic inches. Flowmasters catalog has a chart that reccomends 2.25 inch for a 150-200 cu. in. engine that is putting out 150. The 2.5 in. piping is recommended for 150-200 cu in. engine that is putting out 200 hp. Being at the small end of the 150-200 engine size and definately not putting out 200hp, (unless you add up the "30 hp" from that intake and the other "15 hp" from the header in those adds) it is reasoned that 2.25 in. dia. piping would be the best. The only difference there will be is a very slight gain on the top end with a loss in the lower end torque for the 2.5 that in reality will not allow your car to have as much real world power (acceleration) as the 2.25 that will give as it will also help with lower end torque as well as allow the engine to breath freely on the top end.
I did find it convenient that the link where the guy dynoed the 3 in. exhaust didn't even try the 2.25. Somebody find two back-to-back dyno charts with 2.25 and 3 in piping on a KA that proves 2.5 produces more across the entire power band, or better yet, some 1/4 mile ET's that prove 3 is better than 2.25 and I'll shut up forever. Of course the same type of muffler, cat, ect. would need to be used. I'm just trying to back up my opinion with some "research" so that incorrect info. is not posted.
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WongFeiHung
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Scott McLellan
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TrunkMonkey
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Scott McLellan wrote:I have a question for you guys then. Not trying to be mouthy, but why do they even make collector reducers then?
limited space. there may be all the room in the world for the correct size collector, but the rest of the underbody may not be so generous.
I did find it convenient that the link where the guy dynoed the 3 in. exhaust didn't even try the 2.25.
he didn't bother to try the smaller exhaust because the results of the larger system were much better than expected. note, that this is on a bone stock engine. no headwork, cams, high compression...nothing. any breathing mods from here on out will only be complimented with the larger exhaust.
you can argue this until you're blue in the face. less back pressure is a good thing. there is a limit to how big you can go before you start to do more harm then good, but on the KA that limit is more than 3 inches.
-demetrius