For everything header related
11-12-2013, 05:28 PM
#28
The term you are looking for is scavenging. In V8's longtubes have a higher rpm scavenging affect that when you reach a certain rpm the velocity of the exhaust from each cylinder begin to work with each other and pull the exhaust from the cylinder instead of it being pushed by the piston. I know a merge collector adds to this effect but the theory is the same with all motors. Shorty headers give you better scavenging on the bottom end but have no real effect in the higher end. longtubes sacrifice some low end power with little scavenging until a certain rpm and that gives you better midrange to high end power when the scavenging goes into effect.
If that doesn't make sense please let me know lol
If that doesn't make sense please let me know lol
11-12-2013, 07:20 PM
#34
The term you are looking for is scavenging. In V8's longtubes have a higher rpm scavenging affect that when you reach a certain rpm the velocity of the exhaust from each cylinder begin to work with each other and pull the exhaust from the cylinder instead of it being pushed by the piston. I know a merge collector adds to this effect but the theory is the same with all motors. Shorty headers give you better scavenging on the bottom end but have no real effect in the higher end. longtubes sacrifice some low end power with little scavenging until a certain rpm and that gives you better midrange to high end power when the scavenging goes into effect.
If that doesn't make sense please let me know lol
If that doesn't make sense please let me know lol
Without going into a long exhaust theory discussion, here's what i'm saying.
Exhaust pulses leave the cyl travelling the same "speed" every time. It's a function of cyl pressure and timing events, but for arguments sake, at WOT you will get the pulse of exhaust pressure moving through the primary at the same speed, regardless of RPMS.
As RPMS rise however, the TIME bewteen cyl firing events is less, so you need a shorter length tube (primary) for each pulse. Your scavenging effect relies on the negative pressure wave going back to the exhaust port and creating a vacuum at the right time to suck out the next exhaust charge. The longer the tube, the lower the RPM has to be for this to work properly. Now you can play with that by changing tube size and therefore overall volume, but same diameter tubing, you will get the same scavenging effect from a longer tube at a higher RPM.
On header design, they are trying mainly to smooth actions at the collectors, and there is a lot of other though going into it, longtubes usually are more expensive and have more actual design thought into them because they aren't space constrained to stock dimensions like a shorty header. The most effective design is a 180 degree header that joins evenly split cylinders, but physically it's not practical on anything but a full-race application.
Sorry for OT rant, did a lot of exhaust system theory reading back when I worked at a marine exhaust company.
11-12-2013, 09:30 PM
#37
gonna be selling my vibrant lt headers soon here fyi, probably within a week or so. But exhaust really depends on what you have. On a nearly stock car, you will notice almost nothing, realistically 5hp give or take is very minimal.
The power gains you will see by throwing an exhaust on a car is actually because it will lean out your a/f mixture. There is a much more complicated way of explaining this, but I would prefer not to go into that.
Without a tune all you are doing is leaning out the mixture, this will produce more hp.
The gains you will get are limited to the smallest point in the exhaust, if you pump water through a 2 inch pipe, and increase the pipe to 3in halfway through, it will still only flow at the 2in rate. So when you get a gmpp exhaust which is 2.25in (correct me if I'm wrong), having a 3 inch downpipe doesn't really do much.
Now, for the gains you will see with a larger exhaust compared to a smaller exhaust. There is a complicated way of putting this, I will try and simplify it. Certain diameters have an amount of air that can travel through them. There is a general hp number we give to justify certain sizes of exhausts. Say 250hp to 300hp you should have a 2.5in exhaust, and 300hp and up you should have a 3in exhaust. This is based on the amount of exhaust that is expelled from your car, and making sure your exhaust is actually able to push all of this air (exhaust) out. To kill a myth, if you go to big you do not actually lose backpressure, you actually lose """""VELOCITY.""""""
Looking at how the velocity of an exhaust works. Your exhaust comes out in spurts of exhaust from each cylinder, not actually a constant flow. If your exhaust is too big, this will not fill the exhaust and will amount to a low velocity. This think of a pipe with a water pump, you have a water pump pushing water through a pipe full of water, if you have 3 gallons going through a 2 inch pipe, it will move a lot faster than if you were pumping the same amount of water through a 3 inch pipe. Now, this will actually create a suction effect, to put it simply, and assist in pulling exhaust fumes out of the cylinder when it fires (simplest way I can think to put this). This is not backpressure, this is velocity helping the engine work (hopefully I explained this correctly).
Now if you have a higher hp car, and your exhaust is restrictive, it will slow the speed at which your car car push the burned air/fuel out, this is what you are trying to accomplish with upgrading your exhaust, but picking an exhaust that is too large, you can have nearly the same effect. Hopefully this was somewhat informative, and hopefully I didn't butcher any details lol, I'm bored at school between classes.
The power gains you will see by throwing an exhaust on a car is actually because it will lean out your a/f mixture. There is a much more complicated way of explaining this, but I would prefer not to go into that.
Without a tune all you are doing is leaning out the mixture, this will produce more hp.
The gains you will get are limited to the smallest point in the exhaust, if you pump water through a 2 inch pipe, and increase the pipe to 3in halfway through, it will still only flow at the 2in rate. So when you get a gmpp exhaust which is 2.25in (correct me if I'm wrong), having a 3 inch downpipe doesn't really do much.
Now, for the gains you will see with a larger exhaust compared to a smaller exhaust. There is a complicated way of putting this, I will try and simplify it. Certain diameters have an amount of air that can travel through them. There is a general hp number we give to justify certain sizes of exhausts. Say 250hp to 300hp you should have a 2.5in exhaust, and 300hp and up you should have a 3in exhaust. This is based on the amount of exhaust that is expelled from your car, and making sure your exhaust is actually able to push all of this air (exhaust) out. To kill a myth, if you go to big you do not actually lose backpressure, you actually lose """""VELOCITY.""""""
Looking at how the velocity of an exhaust works. Your exhaust comes out in spurts of exhaust from each cylinder, not actually a constant flow. If your exhaust is too big, this will not fill the exhaust and will amount to a low velocity. This think of a pipe with a water pump, you have a water pump pushing water through a pipe full of water, if you have 3 gallons going through a 2 inch pipe, it will move a lot faster than if you were pumping the same amount of water through a 3 inch pipe. Now, this will actually create a suction effect, to put it simply, and assist in pulling exhaust fumes out of the cylinder when it fires (simplest way I can think to put this). This is not backpressure, this is velocity helping the engine work (hopefully I explained this correctly).
Now if you have a higher hp car, and your exhaust is restrictive, it will slow the speed at which your car car push the burned air/fuel out, this is what you are trying to accomplish with upgrading your exhaust, but picking an exhaust that is too large, you can have nearly the same effect. Hopefully this was somewhat informative, and hopefully I didn't butcher any details lol, I'm bored at school between classes.
11-13-2013, 11:23 AM
#38
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^huh, never thought about the temperature changing and effecting density! Im kinda just theorizing there, I have a moderate understanding of exhaust systems from reading (not nearly as much as you, exhaust theory, interesting), figured since all the other post on this before me had been worthless crap, I would give it the ol 1 2. The water annalogy was the best I could come up with at the moment lol, its more perceivable than a gas.
11-13-2013, 02:59 PM
#39
^huh, never thought about the temperature changing and effecting density! Im kinda just theorizing there, I have a moderate understanding of exhaust systems from reading (not nearly as much as you, exhaust theory, interesting), figured since all the other post on this before me had been worthless crap, I would give it the ol 1 2. The water annalogy was the best I could come up with at the moment lol, its more perceivable than a gas.
You touched on the important point that most people forget, which is velocity. Bigger is only better if you are post-turbo or something where it really only matters to get the exhaust out of there as quickly as possible.
Motordyne, builds some awesome exhaust for the Z car platforms, is run by an actual rocket scientist, and his engineering approach to the designs has come up with some very cool ideas as it relates to an N/A application (diffuser tips, tuned test pipes, etc). Boost changes things, but a supercharged engine basically acts like a much larger displacement N/A engine on the exhaust side when in boost.
11-13-2013, 07:03 PM
#40
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a rocket scientist??????????? Holy **** batman! I guess either way I didn't really account for pressure, like I said I was in between classes, just pretty much brainstormed the whole thing lol.
11-15-2013, 10:29 AM
#41
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04-23-2014, 08:56 PM
#42
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So on a stock application, would I be better with shorties or a long tube setup? Craziest I might go with this car would be a GM Stage 2, that's it.
My main thing is I want something nice but still bearable on long drives. I am going to be installing either a ZZP, GMPP, or Corsa 2.5 in. muffler and am considering a catted 2.5 ZZP downpipe. Just looking for minimal to no drone.
My main thing is I want something nice but still bearable on long drives. I am going to be installing either a ZZP, GMPP, or Corsa 2.5 in. muffler and am considering a catted 2.5 ZZP downpipe. Just looking for minimal to no drone.
04-23-2014, 09:01 PM
#43
I'd advise a ported stock manifold for the best combo of stockish sound and reliabilty while still giving you the power of a good shorty header. Long tubes get very expensive and if you aren't planning on pushing a lot of power they really aren't necessary. If you want a small power bump from stage 2 I would just drop pulley size a bit rather than spend a bunch on overkill exhaust parts.
04-24-2014, 09:39 PM
#44
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I'd advise a ported stock manifold for the best combo of stockish sound and reliabilty while still giving you the power of a good shorty header. Long tubes get very expensive and if you aren't planning on pushing a lot of power they really aren't necessary. If you want a small power bump from stage 2 I would just drop pulley size a bit rather than spend a bunch on overkill exhaust parts.
Last edited by Pinky Demon; 04-24-2014 at 09:45 PM.
04-24-2014, 09:54 PM
#45
Yeah I'm actually shipping one out tomorrow and in the middle of porting another. I haven't been keeping cores to do them though, been kinda a case by case basis. I have a FS thread up now but the one listed is sold, I should have another next week or so.
05-28-2014, 11:59 AM
#47
06-19-2014, 06:22 PM
#49
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Header dp combo?
What should I go with ? I want to do a zzp stage 3 I got the cai already but need exhaust before I buy stage 3 kit on header should I run short or mid length or long tube? And y? I will run with cat so it's not to loud and to keep check engine lights off bit do I need extra bung for wideband? I'm not sure of wat it is sorry I'm new to this plz help also let me kno if anyone has any combos for sale header and down pipe
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