3" to 3.5" or 4" or 5" dp how much gain?
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By that measure, we can assume the same with our little 231 ci motors. That DP isnt flowing "only" 140.5 cubes. Its flowing 30-40psi through a motor where the heads flow 340cfm at 28" of vacuum. I have a set of these heads (I used to have a 99 cobra) that I ported for street use that flow 300cfm@ 28", and flow 283cfm at only .400 lift, and 242@.300 lift. These modular ford heads have extremely high low lift and "average" flow numbers. Plus its using pretty efficient turbos that are flowing ALOT of air at those boost levels. Imagine what those heads are flowing at say, 35psi through race heads at 10,000 rpm. Boost is just a measure of resistance. It doesnt really mean much. Flow is what matters. Each one of those small DP's are probably flowing as much air as an 8 or 9 second turbo regal does through 1 downpipe. We are talking close to 2000 hp here.Louie L. said:Remember those Dps are huge when they are only flowing 140.5 ci.
As far as the flowmaster muffler thing, thats really not much of an issue. Flowmasters suck on all cars. They dont flow for ****. Ironic name for a muffler that doesnt flow worth a damn. :biggrin: If anything, the distance from the compressor to the expansion area (muffler) may make a difference, but probably not much. Anytime a pulse hits an area of greater or less volume, a reversion wave bounces back to the origin. Same goes for intake manifolds, headers or anything that flows a fluid or gas. If the length of the port resonates at a given rpm, and you have a pinch point or an expansion area that pings a reversion wave back at a different rpm, things will be all screwed up. The cross sectional area should be a size that causes the charge to reach supersonic speed at the same rpm the tuned runner is designed to resonate at. If its way mismatched, you'll have a runner, or a tube that inherently resonates at a given rpm, but because of the diameter and resulting low pressure, it cant. Its traveling too slow to resonate at any rpm below 10 million gajillion rpm. By the time you reach 10 million gajillion rpm and the flow has reached supersonic speed, the runner is way too long to resonate at that rpm.
Im getting off track here. The pulses are dampened quite a bit by that compressor wheel, but still there. Its more of an issue of the exhaust hitting a huge area and stalling out. When the hot gas stalls out, the new gases trying to get out hit a wall.
I could also imagine the inside of a huge DP rusting from condensation. Mist can form if the gas is de-compressed so fast that the gas cools to a temperature that is less than the equilibrium vapor pressure of water at that reduced temperature. (called the Joule-Thompson effect). Its what causes those condensation cloud bursts on fighter jets. Not that anyone cares about that...just my mind wandering.
But most likely Im just talking out of my ass cause Im bored and the huge DP would probably make alot of power. :tongue:
Anytime a pulse hits an area of greater or less volume, a reversion wave bounces back to the origin. Its more of an issue of the exhaust hitting a huge area and stalling out. When the hot gas stalls out, the new gases trying to get out hit a wall.
well...now were starting to get somewhere...when the 5" dp thread was first posted..jace claimed a theory,..so I ran this theory by a buddy of mine(who builds exhaust systems for D.E.I)..I gave my opinion based on RELIABLE input from a person that has many,many yrs. experience in the physics of exhaust behavior on the internal combustion engine!
but I got slamed and gang raped by the "oh my god it's huge crowd"....and I see that jace has not commented on this yet!...flame suit on!
well...now were starting to get somewhere...when the 5" dp thread was first posted..jace claimed a theory,..so I ran this theory by a buddy of mine(who builds exhaust systems for D.E.I)..I gave my opinion based on RELIABLE input from a person that has many,many yrs. experience in the physics of exhaust behavior on the internal combustion engine!
but I got slamed and gang raped by the "oh my god it's huge crowd"....and I see that jace has not commented on this yet!...flame suit on!
Bingo! I think the problem with the Buick design though it the 90º bend right off the exducer and the need to fit the wastegate puck in there too. I'm sure there is a point where pipe size expansion reversion and choke point of the bend. I"m going external gate so puck clearance isn't an issue for me but most of ya'll are running internals so still an issue there. I'd guess that somewhere between 3" and 3.5" on an internal gate pipe you hit the crossover between the bend and the reversion pulse. I don't know much about he performance changes with internal gates but I'm probably going to be running a 3" since I already have the tube in stainless and if I can fit it a megaphone off the exducer to the 3" bend. Got to love a hybrid in a 60's full sized car.Joe Tiano said:Anytime a pulse hits an area of greater or less volume, a reversion wave bounces back to the origin. Its more of an issue of the exhaust hitting a huge area and stalling out. When the hot gas stalls out, the new gases trying to get out hit a wall.
well...now were starting to get somewhere...when the 5" dp thread was first posted..jace claimed a theory,..so I ran this theory by a buddy of mine(who builds exhaust systems for D.E.I)..I gave my opinion based on RELIABLE input from a person that has many,many yrs. experience in the physics of exhaust behavior on the internal combustion engine!
but I got slamed and gang raped by the "oh my god it's huge crowd"....and I see that jace has not commented on this yet!...flame suit on!
Did you see how tight the DP bend is on the twin turbo pro-5.0 car I posted up? Its pretty tight, but I do agree that if anything were a bottleneck, it would be the bend, not the diameter. But even that bend shouldnt really hurt much of anything. I think the lack of a gradual leadout from the exhaust wheel is a problem. The flow comes out and falls off a sharp cliff and then into the elbow/DP. There is some guy on here who made a little web page showing the work he did on stock elbows and turbos. One of the things he did was make a nice radiused leadout from the exhaust wheel. I thought here was a guy who gets it. That sharp edge creates a buttload of turbulence. Most people might think that sharp edge would only hurt flow, if the flow were going towards the wheel, but thats not the case. Once again, you're dealing with a very sudden, rapid expansion and cooling of the gases. Sharp edges are usually bad no matter what direction the flow is going.
I think a good downpipe design would be like this: You have 1 piece of pipe that is the same diameter on the inside, as the diameter of the exhaust wheel (or actual bore that it sits in....at least a bore size that would accomodate most of the turbos we use, but not any bigger. The section that aims toward the wastegate puck would be cut out, and a much smaller pipe would be cut and siamesed with the bigger pipe and welded together so you have 2 sections...one is the DP and one is for the wastegate puck. It would be just like the ATR DP, except the big pipe would be alot smaller..the size of the turbine bore. This siamesed pipe assembly would be welded to a plate (flange) that mounts it to the turbo...a billet steel or iron flange with counterbored holes so you could use clean looking socket head cap screws to mount it. Then this "big" pipe would do the 90 degree bend and taper into a larger and larger diameter as it swung around. It would be hard to manufacture, but it could be done if small sections of different sized elbows were welded together, so you get a multi-stepped out elbow. The elbow would end with a flange that the remaining section of downpipe would attach to. It would be a 2 piece design in the end. Ceramic coating would be nice too. :biggrin:
I think a good downpipe design would be like this: You have 1 piece of pipe that is the same diameter on the inside, as the diameter of the exhaust wheel (or actual bore that it sits in....at least a bore size that would accomodate most of the turbos we use, but not any bigger. The section that aims toward the wastegate puck would be cut out, and a much smaller pipe would be cut and siamesed with the bigger pipe and welded together so you have 2 sections...one is the DP and one is for the wastegate puck. It would be just like the ATR DP, except the big pipe would be alot smaller..the size of the turbine bore. This siamesed pipe assembly would be welded to a plate (flange) that mounts it to the turbo...a billet steel or iron flange with counterbored holes so you could use clean looking socket head cap screws to mount it. Then this "big" pipe would do the 90 degree bend and taper into a larger and larger diameter as it swung around. It would be hard to manufacture, but it could be done if small sections of different sized elbows were welded together, so you get a multi-stepped out elbow. The elbow would end with a flange that the remaining section of downpipe would attach to. It would be a 2 piece design in the end. Ceramic coating would be nice too. :biggrin:
Makes me want to turn the turbo sideways and run the pipe straight back then have it dodge the headers and such under the firewall. Probably way too much work though for a stock type system. That would also create a probem on getting the exhauste into the turbine since it would need a 90º bend just before the turbine inlet.
Reality, unless you are running a sprint car or something, there will always be compromizes in the design of the system. I might try that idea of yours Vader if I can find a flange for the exducer. Probably I'll just make a tapered section from the flange to the bend enterance and maybe a 2 step bend with a 2.75' and 3" pipes No puck tube needed for me. Mine will be stainless though. We'll see how many wacky ideas we come up with that make it onto my monster hybrid.
Reality, unless you are running a sprint car or something, there will always be compromizes in the design of the system. I might try that idea of yours Vader if I can find a flange for the exducer. Probably I'll just make a tapered section from the flange to the bend enterance and maybe a 2 step bend with a 2.75' and 3" pipes No puck tube needed for me. Mine will be stainless though. We'll see how many wacky ideas we come up with that make it onto my monster hybrid.
I dont know if I conveyed my idea well enough. The section of pipe that mates to the turbine bore would have to sit in there pretty deep so the flow doesnt drop out and then get compressed again to get back into the pipe. The 2 pipes may have to be isolated from one another until the wastegate puck tube runs into the big pipe. It may look goofy to have 2 separate tubes going into one big one, but I always cared more about go than show. The mounting flange would take some design work and have to get cut in a CNC. I could draw it up in CAD and make a CNC routine (I have mechanical desktop, solidworks, edgecam and surfcam..also mastercam but that program sucks balls. Dont know why in the world its so popular. Its like DOS for making CAM programs), but I would end up having to pull my turbo off the car and measure everything up. Wish I could do it but my GN is my only car and daily driver. I have a powerstroke turbo here at work on a shelf but thats not much help to anyone. Its a leftover from back when we made some turbo assembly stations for Allied Signal (Garrett) back in 1998 and 2000. Guy handed me a free turbo and some asswipe here at work tore it apart and lost some parts.
I can barely use TurboCAD, but I'm a scientist not an engineer. I know what you are talking about in the exducer to downpipe attachment area, the idea of the seperate wastegate chanell makes good sense because the bypass flow also creates turbulence right at the mouth of the exducer. I'm planning on a GT40R or 42R turbo and all hybrids need custom downpipes and I plan on making as few compromises as I can afford on this engine. The stepped radius on the bend might not be neccessary for me but I could see it being useful for a stock application. I'll run this by the thermodynamicist at work and see what he thinks is the optimal compromise. How far off the turbo, ie lenght of straight pipe, is the bend?
Thanks,
Thanks,
Dont think it would really matter as long as you can fit in the largest radius you can get. You could just keep the pipe the same size as the turbine bore and stay there all the way out, but I wouldnt do that. Some gradual stepping out would be the way to go.CTX-SLPR said:
I just thought of an easier way to make the elbow with a nice taper from small to large...for cheap. If you want a 3" DP where it maxes out....buy a 3" elbow. Slice it right down the middle so you end up with 2 halves of 180 degree sweeps. With a mallet and whatever other tools you need, form one end of the elbow half to neck down to the smaller radius you need, where it mates to the turbo. Do the same to the other pipe half. After you form it, you will end up with more than a 180 degree sweep. Cut the extra material off so you end back up with 180 degrees on both pipe halves. Weld them together and wallah! If done right, it should be a perfect taper!
Done right being the opporative word here. Thats not exactly and easy thing to do. Take a band saw to it and slice it in half, do the math for the circumfernce and the rate of taper you want and mark the pipe halfs up based off of the midline of the halfs and then connect the dots with a straightedge. Then you'd have to hammer the edges together and try to get it perfectly round again.VadersV6 said:I just thought of an easier way to make the elbow with a nice taper from small to large...for cheap. If you want a 3" DP where it maxes out....buy a 3" elbow. Slice it right down the middle so you end up with 2 halves of 180 degree sweeps. With a mallet and whatever other tools you need, form one end of the elbow half to neck down to the smaller radius you need, where it mates to the turbo. Do the same to the other pipe half. After you form it, you will end up with more than a 180 degree sweep. Cut the extra material off so you end back up with 180 degrees on both pipe halves. Weld them together and wallah! If done right, it should be a perfect taper!
As far as the straight section, I'd try to make as much of the expansion in the straight as possible, less bizzare fabrication in the bend. We'll see what the guy says at work.
norbs...look here..www.globaltecheng.com.. global technology and engineering..I have found these to be the best prices... good luck...and go 3.5" 
joe
joeNot remotely as difficult as this. Band sawing it straight is not hard. Form it around a solid round chunk of steel thats of the diameter you want. Cut off the excess and weld the 2 halves in place. No need to calculate anything. Do it WWII old school style...CTX-SLPR said:
how many different steel mandrels will you be forming around for a taper? I can see doing the ends that way but the middle is considerably more difficult especially with your changing diameters. I'd have to see the finished product before I believe that process is easy.VadersV6 said:
You dont need to taper around the bend, necessarily. You could stick that bar of steel in a lathe and cut it to get the shape you want. Dont know if you have access though. Sometimes I take for granted, all the stuff I have at my disposal.
Maybe this could be cut and fit, then a 90 degree elbow connected to it...
Exhaust parts
Maybe this could be cut and fit, then a 90 degree elbow connected to it...
Exhaust parts
Ah... I see, you're talking constant diameter bend with a stepped enterance and exit... Now we are the same page. Thats exactly what I"m talking about except make the straight seciont pre bend as long as possible so you as gradual area increase as possible.
Got ya now,
Got ya now,
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