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Lamb View Drop Down
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    Posted: 03-April-2014 at 3:08PM
I just got my custom built headers and one of the tubes where it connects to the flange has a restriction. The tubes are 1.75 inches except at this location, it is 1.5 inches at the weld. Do I need to worry about this causing a performance issue?
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Dan the ranchero man View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dan the ranchero man Quote  Post ReplyReply Direct Link To This Post Posted: 04-April-2014 at 10:24AM
Unless you are doing some serious racing were that 10th of a sec makes a difference I would say "NO".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote OleDutchD Quote  Post ReplyReply Direct Link To This Post Posted: 04-April-2014 at 12:46PM
What size motor, chassis and who built them?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 04-April-2014 at 3:01PM
shouldn't be a big deal, most standard off the shelf headers have 1.5" tubes. yeah whatcha workin" on???
JOHN
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Lamb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lamb Quote  Post ReplyReply Direct Link To This Post Posted: 10-April-2014 at 6:57AM

They are going on a 408c stroker with 2v heads. They were built by company in the northwest; I would rather not give the name as I don't want to put myself in harms way. I am spending a lot of money on my engine and I don't want the headers to cause an issue. I know this is for street use; however, I want it to be right. I am a long time off road VW engine builder and I could see the difference if one of the exhaust tubes had a restriction. I realize that they only had 4 cylinders, which may be why it was so critical compared to an 8 cylinder engine.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lamb Quote  Post ReplyReply Direct Link To This Post Posted: 10-April-2014 at 7:09AM
Thanks, I realize that there are 1.5 inch headers and if all of the tubes were this size I would not have an issue. My concern is all but one are 1.75 inches and the larger tubes will flow different than this one 1.5 restrited tube.
 
I am rebuilding a 73 gran torino 2 door formal roof. The engine was a 351c with 2v heads and an FMX automatic tranny; I am stroking the engine to a 408 and keeping the 2v heads with modifications. I want to keep the low end torque with the HP in the low range as well as this will be a daily driver. I had the FMX rebuilt with a level 3 shift kit and a ridged band instead of the standard flex band.
 
The body is getting a total overhaul as well as an all new interior. So it is important to me that I make sure that this one restricted tube is not going to be an issue for me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote OleDutchD Quote  Post ReplyReply Direct Link To This Post Posted: 12-April-2014 at 2:14AM
In this particular case, a picture really IS worth a thousand words... would be most helpful. Now... I'll say this so YOU don't have to... it SOUNDS as if you're talking about FPA's. I run them (1-5/8" x 1-3/4" stepped), myself, on a 351W/C6 combo w/ Trick Flow heads, in my '72 and am very pleased with them. Good stuff. That aside, and trying to read between the lines, here, forgive me if I don't get this completely right:

1) Are you, by chance, talking about either the #4 or #8 tubes near the firewall?

2) Are you saying all eight tubes are 1-3/4" OD, and this one is stepped down to 1-5/8" before the flange, or that the 1-3/4" tubing had to be manipulated in such a way, due to routing/space limitations, that it has been somehow reduced in order to make a tight bend?

In my own application, the #8 tube (driver's side) is a tight fit. The last bend was cut slightly off-tangent in order to make the final turn into the flange. And, as the exhaust bolt pattern is OEM Ford, there is some minor distortion of the tubes to clear the header bolts.
These are NOT equal-length, tuned, headers and #8 tube is the shortest of all eight. If that is the affected tube, I wouldn't be too concerned as that reduction you speak of would only serve to make that particular tube think it was longer.

I run the latest version of PipeMax on my PC. Just inputting some basic values for a 408 Cleveland w/ 2V heads, w/ 10:1 CR and a conservative torque cam @ 218*/230* duration...



Disregarding the file name on top (manipulated an existing file), you can see and compare what PipeMax predicts/describes for header dimensions. When you look at sizes, etc, keep in mind that this program gives tube dimensions in OD.

Edited by OleDutchD - 12-April-2014 at 3:11AM
Just an analog guy stuck in a digital world!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote OleDutchD Quote  Post ReplyReply Direct Link To This Post Posted: 12-April-2014 at 3:04AM
FWIW... when you're looking at the tables, if the dimensional values seem odd, keep in mind that PipeMax used computational fluid dynamics. It doesn't care what someone's opinion of tubing size (diameter OR length) should be. The vast majority of headers are built, primarily, based upon what will fit a given engine/chassis. After THAT, the tube diameter is generally a compromise in order to satisfy multiple possible configurations. If you were to have a set of purpose-built headers fabricated (based on an exact application), you likely wouldn't recognize them, physically, compared to off-the-shelf.... and there would probably be a smoking hole where your wallet used to be.


Just an analog guy stuck in a digital world!
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