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Old 01-21-2019, 06:40 PM   #1
deputydog
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Default Turbo header primary size

Was getting ready to v band my truck manifolds for my hot side when I came across a set of SW 1 3/4 turbo headers with 2 1/2 collector so i picked them up for great price. Was measuring things and the primaries measure 1 3/4 OD with an ID around 1 5/8. The research I did shows a 1 3/4 primary is good for my 5.3 with a billet wheel S480/LJMS cam. further research shows some header manufacture use OD and others use ID....bottom line is the 1 5/8 ID going to be ok for my 5.3 S480?
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Old 01-21-2019, 08:56 PM   #2
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Default Re: Turbo header primary size

FYI (if you didn't know already) All tubular headers are measured by O.D. whereas headers constructed from pipe - e.g. Sch 10 or Sch 40 - are measured by I.D.



As for the 1 3/4" headers you have, install them and let 'er rip!! LS truck manifolds are in the 1 1/2" I.D. range and tons of guys are making 150 m.p.h. (in the 1/4 mile) or better power with them. So I would think you would be fine. That's what I hear anyways.
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Old 01-21-2019, 09:58 PM   #3
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Thanks for reply...also learned the ID of vibrant 2 1/2 v band flange is only 2.325
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Old 01-21-2019, 10:48 PM   #4
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Default Re: Turbo header primary size

Quote:
Originally Posted by deputydog View Post
Thanks for reply...also learned the ID of vibrant 2 1/2 v band flange is only 2.325
Because they are a butt weld style v band. They also make an ID style that will slide over the tubing. Keep doing your research. There is lots of good info out there. You just need to learn how it applies to your application. Your primaries only need to be as large as your exhaust ports.
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Old 01-21-2019, 11:45 PM   #5
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Default Re: Turbo header primary size

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Originally Posted by mufflerguy View Post
Because they are a butt weld style v band. They also make an ID style that will slide over the tubing. Keep doing your research. There is lots of good info out there. You just need to learn how it applies to your application. Your primaries only need to be as large as your exhaust ports.
Actually no smaller area than minimum square area of port. Slightly greater ok. Too much area kills velocity affecting spool.
That said you can go smaller to increase response, but you do so at the expense of top end power.
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Old 01-22-2019, 06:46 AM   #6
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Default Re: Turbo header primary size

Quote:
Originally Posted by deputydog View Post
Was getting ready to v band my truck manifolds for my hot side when I came across a set of SW 1 3/4 turbo headers with 2 1/2 collector so i picked them up for great price. Was measuring things and the primaries measure 1 3/4 OD with an ID around 1 5/8. The research I did shows a 1 3/4 primary is good for my 5.3 with a billet wheel S480/LJMS cam. further research shows some header manufacture use OD and others use ID....bottom line is the 1 5/8 ID going to be ok for my 5.3 S480?
I run 1/5/8 on my 306 sbf , 88mm runs 140 in the 8th.
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Old 01-22-2019, 05:00 PM   #7
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Default Re: Turbo header primary size

Plug/Wite clearance on those headers? Most are a nightmare.
I can change my plugs in 20 minutes.
I really like the stock manifolds.

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Old 01-22-2019, 06:28 PM   #8
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Ohio boys made 2k in power on stock manifolds back about 10yrs ago..the stockers will go a long way..no real reason for aftermarket unless u need a custom fit
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Old 01-22-2019, 07:10 PM   #9
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Default Re: Turbo header primary size

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Originally Posted by BruceWilkie View Post
Actually no smaller area than minimum square area of port. Slightly greater ok. Too much area kills velocity affecting spool.
That said you can go smaller to increase response, but you do so at the expense of top end power.
Huh? Pretty sure that's what I just said........

"Your primaries only need to be as large as your exhaust ports"
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Old 01-22-2019, 07:59 PM   #10
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Thanks all...I agree I could have used my truck manifolds and v banded them but brand new SW headers for $450 was no brainer.

My exhaust ports are 1.570 by 1.175 so my 1.625 ID will be fine. For some reason I always assumed all talk of 1 3/4 of 1 7/8 for headers or 2 1/4 or 2 1/2 on hotside was ID but I see it's all OD...heck the 2 1/2 stainless for my hotside is 2.370 ID so im not concerned about it being to big anymore.
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Old 01-22-2019, 10:21 PM   #11
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Default Re: Turbo header primary size

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Originally Posted by mufflerguy View Post
Huh? Pretty sure that's what I just said........

"Your primaries only need to be as large as your exhaust ports"
You're not wrong!
Just clarifying the part of the port size that matters most. Often the exit end of port is of greater area than area near the short turn.
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Old 01-23-2019, 08:42 AM   #12
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Default Re: Turbo header primary size

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Originally Posted by BruceWilkie View Post
You're not wrong!
Just clarifying the part of the port size that matters most. Often the exit end of port is of greater area than area near the short turn.
I believe this is what they refer to as the "choke point" of a port. Again, thanks all for the replies was more concerned with the ID of my header primaries for the HP goals than anything else. My heads are unported LS 243 heads so the exhaust port opening is 1.570x1.175, so I'm good with the 1.625 ID.
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Last edited by deputydog; 01-23-2019 at 08:43 AM.
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Old 01-23-2019, 03:30 PM   #13
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Default Re: Turbo header primary size

Guys just keep in mind the smallest CSA of a port acts more like a flow orifice while a tube has friction loss as well as equivalent lengths of straight pipe for all the bends. They are apples and oranges to put it very simply and not directly comparable.
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Old 01-23-2019, 08:45 PM   #14
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Default Re: Turbo header primary size

Put 1inch primaries on there. It should spool like dremel tool.
If small is good then exceptionally small should be even better.
You might not even need a converter. Direct drive is the way of the future.
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Old 01-23-2019, 10:19 PM   #15
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Put 1inch primaries on there. It should spool like dremel tool.
If small is good then exceptionally small should be even better.
You might not even need a converter. Direct drive is the way of the future.
Or you can always treat it like a blower car and slap some 2" primaries on there.
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