New Turbo Kit in the works.
09-23-2008, 11:23 PM
#122
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,338
Total Cats: 573
so like.. pipe flow and change in pipe cross section affects flow rate. there's losses associated with changing flow area. you'll have to whip out some pipe flow equations or friction equations but there is a measurable loss.
it's the same why planes dont have square asses.
it's the same why planes dont have square asses.
Reply
0
0
09-24-2008, 10:01 AM
#127
Junior Member
Thread Starter
Join Date: Sep 2008
Posts: 79
Total Cats: 0
It would be one thing if the gas had been traveling at a set velocity for x amount of feet before the transition, but it is being forced out of the port, which is a very short distance, at a high pressure. Its going to take the shape of whatever is there and by ovalizing the primary, you are doing nothing but changing the shape of the tubing. since the ID of the pipe is bigger than the opening of the port, and theres no way to change that, and the shape of the port isnt drastically elliptical (its ~26.5 mm, by 45 mm), there is nothing restrictive about the transition. Its not going to cause reversion and about .3 inches from the elliptical port is where the circular tubing begins.
The collector is a MUCH more important transition but most people make it very abrupt. The gases have been traveling through a set diameter at a constant velocity before changing from a smaller diameter to a larger one and from 1 1/2" to 3" is a much more abrupt change no matter how you look at it than from the port to the primary. So is that bad for flow?
The only time you need to be concerned with going from a smaller diameter to a bigger diameter in exhaust is when you are concerned with a naturally aspirated car that needs a small amount of backpressure. On a turbo car it isnt as much of an issue.
The only thing ovalizing the ports is going to do is make it less reliable. Not to mention its going to take longer, and require more fabrication. It is not simpler or prettier or better. Its just different.
The collector is a MUCH more important transition but most people make it very abrupt. The gases have been traveling through a set diameter at a constant velocity before changing from a smaller diameter to a larger one and from 1 1/2" to 3" is a much more abrupt change no matter how you look at it than from the port to the primary. So is that bad for flow?
The only time you need to be concerned with going from a smaller diameter to a bigger diameter in exhaust is when you are concerned with a naturally aspirated car that needs a small amount of backpressure. On a turbo car it isnt as much of an issue.
The only thing ovalizing the ports is going to do is make it less reliable. Not to mention its going to take longer, and require more fabrication. It is not simpler or prettier or better. Its just different.
Reply
0
0
09-24-2008, 10:15 AM
#129
It would be one thing if the gas had been traveling at a set velocity for x amount of feet before the transition, but it is being forced out of the port, which is a very short distance, at a high pressure. Its going to take the shape of whatever is there and by ovalizing the primary, you are doing nothing but changing the shape of the tubing. since the ID of the pipe is bigger than the opening of the port, and theres no way to change that, and the shape of the port isnt drastically elliptical (its ~26.5 mm, by 45 mm), there is nothing restrictive about the transition. Its not going to cause reversion and about .3 inches from the elliptical port is where the circular tubing begins.
The collector is a MUCH more important transition but most people make it very abrupt. The gases have been traveling through a set diameter at a constant velocity before changing from a smaller diameter to a larger one and from 1 1/2" to 3" is a much more abrupt change no matter how you look at it than from the port to the primary. So is that bad for flow?
The only time you need to be concerned with going from a smaller diameter to a bigger diameter in exhaust is when you are concerned with a naturally aspirated car that needs a small amount of backpressure. On a turbo car it isnt as much of an issue.
The only thing ovalizing the ports is going to do is make it less reliable. Not to mention its going to take longer, and require more fabrication. It is not simpler or prettier or better. Its just different.
The collector is a MUCH more important transition but most people make it very abrupt. The gases have been traveling through a set diameter at a constant velocity before changing from a smaller diameter to a larger one and from 1 1/2" to 3" is a much more abrupt change no matter how you look at it than from the port to the primary. So is that bad for flow?
The only time you need to be concerned with going from a smaller diameter to a bigger diameter in exhaust is when you are concerned with a naturally aspirated car that needs a small amount of backpressure. On a turbo car it isnt as much of an issue.
The only thing ovalizing the ports is going to do is make it less reliable. Not to mention its going to take longer, and require more fabrication. It is not simpler or prettier or better. Its just different.
Explain how ovalizing the ports is going to make the manifold less reliable. I think you are WAAAAAYYYYY over exaggerating this. I have NEVER seen or heard of this causing a failure. Not even once. It's pretty much common practice.
If you used regular flanges, you could buy them pre made for less money than you will have in your fancy flanges.. No fabrication time is less than some.
It would be simpler and it would be easier. I can crush 4 pipes using a vise in probably under a minute. And all at no cost. How much are those fancy flanges gonna cost? Crushing pipes is cheaper and pretty simple. Jig it for repeatability.
And everyone agrees it is better for flow. I'm surprised you think the collector transitioning is super important, but then say a step in size at the flange won't matter.
And why does a N/A motor need back pressure?
Reply
0
0
09-24-2008, 12:05 PM
#133
Boost Pope
iTrader: (8)
Join Date: Sep 2005
Location: Chicago. (The less-murder part.)
Posts: 33,026
Total Cats: 6,592
Mind explaining to me how that works? I'd always assumed that with a N/A engine, the purpose of using not-too-large pipes was to increase the velocity of the exhaust gas through the system, thus enhancing the scavenging effect on the cylinder towards the end of the exhaust cycle and during the overlap period.
Perhaps you are in possession of some piece of vital data that I missed?
Perhaps you are in possession of some piece of vital data that I missed?
Reply
0
0
09-24-2008, 12:35 PM
#134
jc, a Miata has tiny exhaust ports. So transitioning to a 1.5" sch10 primary (which is actually closer to 1.7" ID) is a big x-sectional area change. Too big to do within a 3/8" or even 1/2" thick head flange. You want to do it gradually. You want to do it in the primary for these cars.
This will be cheaper, perform better, and be stronger (if you do the inside+out weld I suggested earlier). You wanted an inexpensive manifold. When did machining flanges on a CNC become less expensive than laser or waterjet cutting?
BTW the reason your flange transition works for Integras is because Integras have monster exhaust ports that are much much much closer to the x-section of the pipe you're using.
This will be cheaper, perform better, and be stronger (if you do the inside+out weld I suggested earlier). You wanted an inexpensive manifold. When did machining flanges on a CNC become less expensive than laser or waterjet cutting?
BTW the reason your flange transition works for Integras is because Integras have monster exhaust ports that are much much much closer to the x-section of the pipe you're using.
Reply
0
0
09-24-2008, 01:38 PM
#135
Junior Member
Thread Starter
Join Date: Sep 2008
Posts: 79
Total Cats: 0
Too bad the ports on the B18 are only 3.5 mm taller, and are 3.7 mm shorter. Not a "monster difference" , just a slightly different shape.
The ID of the primaries is 1.61" exactly.
They are pretty much the same area, the miata port measures 45.7 mm by 26.5 mm, and the B18 mesures 42.2mm by 30mm. I have two heads sitting right next to each other and theyre basically the same. I can take a picture if you like?
By ovalizing the primary , you still have the same area? you just change the shape? Thats what ive been trying to say, you still have basically the same x-section that the gas has to change the shape of after exiting the port so its not going to make a difference. Its much easier to do this way.
I dont know where you read that I want a cheap manifold? Id like to keep production costs down but this is a Tubular equal length SS manifold. I dont expect it to be cheap. Flanges cut out on the water jet are $60 a piece. Flanges that I send my drawings to by CNC machined are $75, and they fit better. Im already getting it CNCd so its not any more expensive for 4 more cuts.
Joe we are basically saying the same thing. You want the exhaust pipes to be sized to the exhuast pulse, so they create positive pressure (backpressure) and push and pull each other out respectively.
Maybe backpressure wasnt the right term, but in either case big pipes on a turbo car is a good thing.
The ID of the primaries is 1.61" exactly.
They are pretty much the same area, the miata port measures 45.7 mm by 26.5 mm, and the B18 mesures 42.2mm by 30mm. I have two heads sitting right next to each other and theyre basically the same. I can take a picture if you like?
By ovalizing the primary , you still have the same area? you just change the shape? Thats what ive been trying to say, you still have basically the same x-section that the gas has to change the shape of after exiting the port so its not going to make a difference. Its much easier to do this way.
I dont know where you read that I want a cheap manifold? Id like to keep production costs down but this is a Tubular equal length SS manifold. I dont expect it to be cheap. Flanges cut out on the water jet are $60 a piece. Flanges that I send my drawings to by CNC machined are $75, and they fit better. Im already getting it CNCd so its not any more expensive for 4 more cuts.
Joe we are basically saying the same thing. You want the exhaust pipes to be sized to the exhuast pulse, so they create positive pressure (backpressure) and push and pull each other out respectively.
Maybe backpressure wasnt the right term, but in either case big pipes on a turbo car is a good thing.
Reply
0
0
09-24-2008, 02:02 PM
#136
Junior Member
Thread Starter
Join Date: Sep 2008
Posts: 79
Total Cats: 0
I dont mind people like JKav commenting because I know he has some basis for his opinion, but it seems like some of you just repeat what you hear/read in a book. Ive talked to multiple people who design manifolds for high HP 4 cyl motors and they have all said Im heading in the right direction.
I guarantee you that the focus manifold we did last month isnt going to gain any power by ovalizing the ports. Its making 265HP on 12 psi in a stock zetec motor. Which is more power than anyone else with the same turbo and engine setup.
Im not saying this is the only way to do it, or that your way is wrong and my way is right. This just seems to be the best solution for the particular manifold that im designing. If you have some secret data that will contribute to my decision like a flow comparision or a dyno chart, by all means, I welcome it. But unless you have some basis for saying its going to make a difference, dont say it will.
This will be my 4th manifold for 4 different cars and so far all of them have performed extremely well.
Reply
0
0
09-24-2008, 02:20 PM
#137
how about you build a manifold/downpipe your way put it on a miata and dyno it. Take the same car and switch the manifold/downpipe to another tubular (maybe several) manifold already available from other vendors, dyno those and see what happens. That's the only definitive way to end the debate.
Reply
0
0
09-24-2008, 02:30 PM
#139
Okay, my mistake. The ports are similar in area. Nevertheless, the point remains--you're making a major geometry change in a very short distance (the thickness of the flange). The 'wider and shorter' Miata port exaggerates this change compared to the Integra, even if their port areas are similar. I don’t know why this is a difficult concept to grasp?
And yes the area of the primary changes when you squish it. If you squished it down til you could barely slip a feeler gauge in there, then the area is approaching zero…
Look, you can build it however you want. You can CNC the entire manifold from a block of dry ice and drizzle it in nutella if it makes you happy. I'm just offering ways to make your production manifold cost less, warp less, be stronger and perform better.
And yes the area of the primary changes when you squish it. If you squished it down til you could barely slip a feeler gauge in there, then the area is approaching zero…
Look, you can build it however you want. You can CNC the entire manifold from a block of dry ice and drizzle it in nutella if it makes you happy. I'm just offering ways to make your production manifold cost less, warp less, be stronger and perform better.
Reply
0
0
