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Old 09-23-2008, 11:38 PM   #121
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whoops read the whole thread for background info!
I did and didn't find what I was looking for, but what you just posted answered all my questions. Thanks.
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Old 09-24-2008, 12:23 AM   #122
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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.
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Old 09-24-2008, 12:33 AM   #123
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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.
No y8s, you don't understand. It's like blowing through a straw...
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Old 09-24-2008, 12:48 AM   #124
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No y8s, you don't understand. It's like blowing through a straw...
oh I do understand.

blowing through a straw would actually be easier if the end was flared like a velocity stack. there's a mismatch in pressures at the opening.
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Old 09-24-2008, 02:39 AM   #125
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y8s, patsmx5 is being sarcastic...
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Old 09-24-2008, 02:40 AM   #126
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jc_rotor, trust us, you'll want the transition to be gentler, which is what you get if you ovalize the primaries.
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Old 09-24-2008, 11:01 AM   #127
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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.
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Old 09-24-2008, 11:10 AM   #128
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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.
DAMMIT. Does this mean I should sell my Absurdflow manifold?
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Old 09-24-2008, 11:15 AM   #129
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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.
We aren't talking about collectors. We are talking about the transition at the flange.

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?
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Old 09-24-2008, 11:18 AM   #130
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DAMMIT. Does this mean I should sell my Absurdflow manifold?
Yeap. Mild steel is inferior to SS. All your welds are gonna crack. Plus the crushed pipes at the flange are less reliable. And your flange is wrong. Who would want such a manifold???? Don't even try to sell it, just scrap it for short steel.
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Old 09-24-2008, 11:45 AM   #131
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And why does a N/A motor need back pressure?

Isn't it obvious: The more back pressure that exhaust has to push against, the more power that is wasted.
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Old 09-24-2008, 12:51 PM   #132
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Yeap. Mild steel is inferior to SS. All your welds are gonna crack. Plus the crushed pipes at the flange are less reliable. And your flange is wrong. Who would want such a manifold???? Don't even try to sell it, just scrap it for short steel.
Damn that sucks for me then. At least I have Artie's money already.
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Old 09-24-2008, 01:05 PM   #133
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a naturally aspirated car that needs a small amount of backpressure.
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?
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Old 09-24-2008, 01:35 PM   #134
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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.
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Old 09-24-2008, 02:38 PM   #135
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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.
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Old 09-24-2008, 03:02 PM   #136
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Yeap. Mild steel is inferior to SS. All your welds are gonna crack. Plus the crushed pipes at the flange are less reliable. And your flange is wrong. Who would want such a manifold???? Don't even try to sell it, just scrap it for short steel.
I never said that a mild steel manifold with ovalized primaries was wrong, or even an option, I just dont understand why youre over here preaching for me to do it one way when a mild steel and a SS manifold are different. Theres nothing WRONG with doing it that way, its not going to make THAT much difference. Mild steel IS inferior to SS, so go with mild steel if you want, but Id much rather have stainless. Ive already shown you the numbers to prove that.

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.
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Old 09-24-2008, 03:20 PM   #137
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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.
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Old 09-24-2008, 03:25 PM   #138
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anyone willing to supply the manifold and DP for the test? Will be returned when testing is done. Would pay shipping both ways. I have to finish the kit first though.
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Old 09-24-2008, 03:30 PM   #139
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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.
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Old 09-24-2008, 03:48 PM   #140
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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.
your mom doesn't count. names? references?
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