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Old 04-21-2020, 01:22 PM   #1
Vanspeed
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Default Exhaust diameter

I ordered some u bends for my Flathead to make my own exhaust during this at home quarantine. My Ď36 engine is stock but I have a set of redís headers. I ordered 1.75 u bends but I was shipped 1 5/8 instead. Would this make a huge difference? I was planning on no mufflers, just wondering what the smaller diameter pipe is going to do as far as sound?
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Old 04-21-2020, 01:36 PM   #2
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Default Re: Exhaust diameter

About 25 years ago, I spent a lot of time and effort putting a 2" system all the way back on a '36 I had. (The car had a set of Fenton headers). Later, I found out that not only did it not help anything, and produced a "hollow" sound that was inferior too that which smaller pipes produced. I have heard that 1 1/2" pipes are just about right for dual "straight pipes" on a flathead.

And let's face it; modified exhaust on a flathead is more about "The Sound" than performance.
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Old 04-21-2020, 03:08 PM   #3
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Default Re: Exhaust diameter

Yeah I am not going on performance. It will still feel powerful to me since it is in my ‘29 coupe that used to have only 40 hp. I just want the sound to be right.
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Old 04-21-2020, 03:24 PM   #4
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Default Re: Exhaust diameter

Quote:
Originally Posted by Vanspeed View Post
I ordered some u bends for my Flathead to make my own exhaust during this at home quarantine. My Ď36 engine is stock but I have a set of redís headers. I ordered 1.75 u bends but I was shipped 1 5/8 instead. Would this make a huge difference? I was planning on no mufflers, just wondering what the smaller diameter pipe is going to do as far as sound?
No direct experience with 1 5/8 inch tubing as I have always used 1 3/4, but wouldn't think it would make a big difference. At least better than 2 inch.
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Old 04-21-2020, 03:52 PM   #5
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Default Re: Exhaust diameter

1 5/8 will work just fine. I think the stock 40 exhaust pipe is 1 5/8".
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Old 04-21-2020, 04:00 PM   #6
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Default Re: Exhaust diameter

There is a question whether duals help performance on a flathead at all with any size pipes as opposed to a single exhaust system.
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Old 04-21-2020, 04:42 PM   #7
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Default Re: Exhaust diameter

https://www.google.co.nz/url?sa=t&rc...PnDFsEn3muWED4
While not relevant to total exhaust length and diameter , it may give you a good laugh as to how smashed headers affect flow.
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Old 04-21-2020, 07:11 PM   #8
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Default Re: Exhaust diameter

I am going to run with it and fab up my pipes. If it isn’t what I like I am only out $60 so I could always change it.
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Old 04-21-2020, 07:12 PM   #9
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Default Re: Exhaust diameter

Also has anybody ran an equalizer tube? I hear that it is not needed on flatheads which I understand but I wonder how one would effect the sound?
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Old 04-21-2020, 07:15 PM   #10
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Default Re: Exhaust diameter

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Also has anybody ran an equalizer tube? I hear that it is not needed on flatheads which I understand but I wonder how one would effect the sound?
I heard a flathead with an equalizer tube a few years ago and it seemed to kill the beloved flathead sound.
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Old 04-21-2020, 07:16 PM   #11
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Default Re: Exhaust diameter

I would think that duals on a flatty add little to performance unless you are running a full out racing engine. That "smashed header: video tells the same story - no difference.
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Old 04-21-2020, 07:40 PM   #12
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Default Re: Exhaust diameter

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Originally Posted by Vanspeed View Post
Also has anybody ran an equalizer tube? I hear that it is not needed on flatheads which I understand but I wonder how one would effect the sound?
An equalizer tube would change the sound of a flathead and accomplish nothing performance wise.
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Old 04-22-2020, 12:24 PM   #13
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Default Re: Exhaust diameter

I have little different experience. I have full length 1 3/4 exhaust with long Smittys.
There was annoying rapp when accelerating , I thought that it was because of plugged heat risers and unplugged them , same rapp. I made small (app 1") equalizer tube and app was gone and nice flathead sound is there all the time. Maybe I was just lucky...
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Old 04-22-2020, 12:31 PM   #14
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Default Re: Exhaust diameter

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Originally Posted by vilanar View Post
I have little different experience. I have full length 1 3/4 exhaust with long Smittys.
There was annoying rapp when accelerating , I thought that it was because of plugged heat risers and unplugged them , same rapp. I made small (app 1") equalizer tube and app was gone and nice flathead sound is there all the time. Maybe I was just lucky...
You are correct, that is part of what the equalizer tube does, it cancels out some frequencies. A traditional Hot Rod engine would not have had one, so the sound is going to be different. But if you like that way it sounds with it installed then there you go.
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Old 04-22-2020, 01:21 PM   #15
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Default Re: Exhaust diameter

A '47 car came with 1 3/4" diameter exhaust, correct?
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Old 04-22-2020, 03:27 PM   #16
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Default Re: Exhaust diameter

Not trying to hijack the thread.....I just bought a set of Brockmans and could only get 2” inlet-outlet.....I had also planned on using 13/4 “ pipes......I have manifolds for duals .....is there an issue with bushing down on the inlet-outlet?......thanks.....Mark
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Old 04-22-2020, 05:19 PM   #17
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Default Re: Exhaust diameter

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Not trying to hijack the thread.....I just bought a set of Brockmans and could only get 2Ē inlet-outlet.....I had also planned on using 13/4 ď pipes......I have manifolds for duals .....is there an issue with bushing down on the inlet-outlet?......thanks.....Mark
No, that's a common way to do it.
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Old 04-22-2020, 05:39 PM   #18
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Default Re: Exhaust diameter

Ok....Thanks!.....Mark
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Old 04-22-2020, 08:59 PM   #19
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Default Re: Exhaust diameter

Quote:
Originally Posted by vilanar View Post
I have little different experience. I have full length 1 3/4 exhaust with long Smittys.
There was annoying rapp when accelerating , I thought that it was because of plugged heat risers and unplugged them , same rapp. I made small (app 1") equalizer tube and app was gone and nice flathead sound is there all the time. Maybe I was just lucky...
Interesting. I do no want my exhaust to have that annoying rapp. Thanks for your input.
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Old 04-23-2020, 01:00 AM   #20
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Default Re: Exhaust diameter

That’s the only “rap” I can stand listening to��.... Mark
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