how do you make factory manifold 2.5" outlets?

Discussion in 'Street/strip 400/430/455' started by DR BOOST, Jan 24, 2020.

  1. DR BOOST

    DR BOOST Member

    trying to keep the manifold on my 67 skylark with a 430. i would like to modify them to mate up with a 2.5" exhaust. Has anyone done this and know what to do?
     
  2. No Lift

    No Lift Platinum Level Contributor

    You chuck them up in a big drill press and use a 2 3/8" hole saw. That is the I.D. of 2 1/2" exhaust pipe. A 2 1/2" opening would leave the flange paper thin. Even doing the 2 3/8" you have to be very careful because it can get thin in there. Other possibility is to get in there with a grind stone and figure on working it for a couple of days.
     
  3. 12lives

    12lives Control the controllable, let the rest go

    IF you aren't concerned about flow, you can use short pieces of pipe at the stock diameter to step it up to 2 1/2. Start with a short piece of the stock downpipe with the "bell" so you can use the stock flange. That's the way my muffler guy did mine on a 350.
    Greg Gessler used to port the stock manifolds so they flowed a lot more, but he no longer is porting. I do not know how big the exit was or what the pipe size was that he recommended. Now if you could find a set of those...
    You might also want to check with Mike at TA. He may know someone who can help.
     
  4. No Lift

    No Lift Platinum Level Contributor

  5. DR BOOST

    DR BOOST Member

    Thank you for the replies. i am going to dig into this and i will post what i find.
     
  6. Bigpig455

    Bigpig455 Fastest of the slow....

    I have a set of manifolds that appear to have different ends welded on, I've heard they used Ford F-250 Diesel manifolds for the ball flange and outlet. Theyre an honest 2.5 inches, and the drivers side couldnt have been carved out of an a stock 67 manifold which had no ball flange at all....I dont know who did these, but they are very,very nice.

    upload_2020-1-26_7-54-20.jpeg upload_2020-1-26_7-55-7.jpeg
     
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  7. Starc Traxler

    Starc Traxler Well-Known Member

    Jim Rogers does excellent work
     
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  8. 12lives

    12lives Control the controllable, let the rest go

    Mike - I would think the T/A pipes would leak due to the smaller bell size on the flange. Maybe not. Have you done this?
     
  9. pbr400

    pbr400 68GS400

    I have the TA downpipes and stock manifolds. They fit nice and don’t leak.
    Patrick
     
  10. Brett Slater

    Brett Slater Super Moderator Staff Member

    Patrick,

    Which downpipes and have you done any port work to the outlets?
     
  11. pbr400

    pbr400 68GS400

    The ones in the above link (I put TA’s 2.5” system on my ‘68) and no, these manifolds are essentially stock. I plan to add Jim Rodgers’ ported units so what’s on there now are unmodified.
    Patrick
     
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  12. Jim Rodgers

    Jim Rodgers Well-Known Member

    Looks like an early set of manifolds I did. Those would have been done 12-15 years ago.
     
  13. 12lives

    12lives Control the controllable, let the rest go

    Patrick - Sorry, I am unfamiliar with your car. Are those stock 400 manifolds? Or did you upgrade to a 455?
     
  14. pbr400

    pbr400 68GS400

    I’ll check the casting numbers tomorrow and see what they’re from. I can’t remember.
    Patrick
     
  15. Bigpig455

    Bigpig455 Fastest of the slow....

    They're all of that old, the guy I sold them from sold the car over 20 years ago..
     
  16. Stevem

    Stevem Well-Known Member

    First off more important then the size of the outlet is how ruff they are on the inside and getting that smoothed out.

    Here's the flowtest results from a simple 4 minute long clean up on a Exh port with just a 80 grit polishing roll used to just remove the carbon and rust scale build up along with before and after shots.

    Total flow gain from 4 minutes work up to .550" lift is 32.7 cfm.

    Lift. Flow stock.--- Flow cleaned off

    .050" 22.4.------22.5

    .100. 43.8. ------44.2

    .200". 89.9. -------91.5

    .300" . 120.2.-------128.4

    .400". 149.5.--------153.5

    .450" 156.4.----------161.3

    .500". 161.--------------167.2

    .550". 166.6.-------------174

    .600". 167.2.-------------177

    .650"--------------------180
     

    Attached Files:

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  17. Philip66

    Philip66 Well-Known Member

    That's really impressive for such a small amount of work! It's easy to get caught up looking for HUGE gains when a couple of small improvements can actually give you better bang for the buck.

    Is there more to be had with more work in those ports, or is there diminishing returns? Would another 20 minutes improve flow or is it really just about changing the surface texture?
     
  18. Stevem

    Stevem Well-Known Member

    Within areas where the Exh flow/ gas speed is the fastest and the hottest then wall texture and how gradual the changes are in shape and size that take place are paramount in utilizing the amount of flow area in the best way.
     
  19. SpecialWagon65

    SpecialWagon65 Ted Nagel

    I thought we were talking about exhaust manifolds?
    I heard about Gessler's way back when I was in the Carolinas. Tom Baker had them on his convertible- I had not ever heard of
    Greg but was struggling with header fitment in my Wagon. I purchased manifolds from Greg and the 455 fit perfect without the headers.
    Since then...I had him do some 350 manifolds, 65 GS Nailhead, another set of 400/455s. Great jobs, glad to see Jim has been doing them.
     
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  20. Starc Traxler

    Starc Traxler Well-Known Member

    These are a set of 67 manifolds that Jim Rogers did for my stock appearing build fully ported and 3" outlet.
     

    Attached Files:

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