4in to 3.5in exhaust?

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05-05-2020 | 05:46 PM

Onesickflhxs

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4in to 3.5in exhaust?

Would it hurt if I was to go down in exhaust tail pipe size so i could build my own tailpipes? Or would it be better just to open the transom hole from 4 to 4.5inch? Collector size on header is 4in. BBC 502

05-05-2020 | 06:56 PM

AllDodge

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Don't have any idea what your working on, but in some cases there is no issue

05-05-2020 | 07:02 PM

Onesickflhxs

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90 donzi blackwidow with a 502. Tryin to make my own jacketed pipes from header to thru transom. Lightning is no help and dnt wanna spend a dime with then but same time new exhaust is out my range. I dnt want to but I can make the transom hole bigger and run it full length and bigger. I was goin to just weld a bung to the header and dump water thru transom but if heard yes and no on doing that. Would it really be bad for just 10inch of tail pipe being dry bad?

05-05-2020 | 07:10 PM

AllDodge

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If your 502 is stock, no mods, then I don't see an issue necking it down. The standard exhaust will be more restrictive then the tail pipes.

Will your tail pipes be double wall and water empties at the transom or single wall connected to headers ?

05-05-2020 | 07:15 PM

Onesickflhxs

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Quote:

Originally Posted by AllDodge

Mild bore 502 with a 112 sep cam alum heads.it has lightning headers that were hacked bad at the extensions so I was gonna make a 4.5 or 5in pipe with a smaller one inside to keep water jacketed and jus go thru the transom. People keep telling me weld up the water exit and dump over board.. but nearly would be a issue I hear

05-05-2020 | 07:23 PM

AllDodge

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I think your going to need someone else's input. From my thoughts is the headers don't look good, don't think I would use them.

05-05-2020 | 07:31 PM

Onesickflhxs

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Ya they look bad as there extension was never fully connected. I ran Them didnt see any water thru the ports but not 100%.but at same time I not even wanting to reuse them. Lol

05-05-2020 | 07:37 PM

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From: On A Dirt Floor

OP - are talking ID of inner pipe when asking if 3.5 is okay? Wet or dry exhaust stream ?

05-05-2020 | 07:43 PM

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Maybe this will help.
Quoting myself, dry exhaust :

Quote:

Originally Posted by SB

The following is from inputs I entered on a 502 with 625 or so HP.

Quoting myself from a earlier post

BTW: The program givea much, much more info than I have posted below. But it will give you a good idea on things.

Remember, the 'collector' is not just the headers collector. If risers and tails are same ID, which most re, then they too are part of the collector.

Do not let yourself end up at a worst length collector. It can/will kill performance.

Pipemax
Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

502.176 CID from 3800 to 6300 RPM
--- Single Primary Pipe Specs --- Diameter= 1.899 to 2.024 Length= 33.7 to 36.7 inches long ---

2-Step Primary Pipe Specs ---
1st Dia. inches= 1.899 Length= 16.9 to 18.4
2nd Dia. inches= 2.024 Length= 16.9 to 18.4
--- 3-Step Primary Pipe Specs ---
1st Dia. inches= 1.899 Length= 16.9 to 18.4
2nd Dia. inches= 2.024 Length= 8.4 to 9.2
3rd Dia. inches= 2.149 Length= 8.4 to 9.2

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 3.466 to 3.716 Tuned Lengths= 19.4 best and also 9.7 or 38.8

--- Header Collector Specs (Megaphone or Diffuser Cone Shape) ---
Diameter= 2.966 taper to 3.966 Megaphone/Diffuser Length= 19.4 inches

Best HP/TQ Tuned Collector Lengths= 19.4 , 38.8 , 77.6 , 155.2 inches long
Worst HP/TQ Loss Collector Lengths= 29.1 , 58.2 , 116.4 , 232.8 inches long

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness
---- Primary Pipe's Harmonics ----
1st Harmonic = 149.4 inches long ... typically never used
2nd Harmonic = 56.5 inches long ... longest recommended
3rd Harmonic = 33.7 inches long ... highly recommended , best Torque Curve
4th Harmonic = 23.4 inches long ... shortest recommended
5th Harmonic = 17.5 inches long ... typically never used
6th Harmonic = 13.8 inches long ... typically never used
7th Harmonic = 11.1 inches long ... typically never used
8th Harmonic = 9.2 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 155.2 inches long ... longest with Mufflers and TailPipes
Note: Worst = 116.4 inches long for HP/TQ Loss
2nd Harmonic = 77.6 inches long ... longest recommended with Mufflers
Note: Worst = 58.2 inches long for HP/TQ Loss
3rd Harmonic = 38.8 inches long ... more bottom-end Torque
Note: Worst = 29.1 inches long for HP/TQ Loss
4th Harmonic = 19.4 inches long ... highly recommended , best Torque Curve
5th Harmonic = 9.7 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.9 inches long ... reduced Torque , not recommended

05-05-2020 | 08:47 PM

#10

Onesickflhxs

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Sb can you message me plz. I think my headers are junk anyway (lightning) I just wanted to try make my own jacketed pipes or go thru hull honestly I'm stuck big time