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Thread: **HEADER HELP**

  1. #1
    Senior Member SENIOR BUILDER
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    Oct 2005
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    Wellington , New Zealand
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    **HEADER HELP**

    I need your guys help. I have a 2800lbs braket car.632 BBC Brodix BB3 xtra mild port head. 16-1 compression, Enderle bird catcher injection on a Victor 2r Tunnel ram. 850/850 lift 4-7 swap cam. 1.80 powerglide and 4.86-1 rear ratio.Im wondering what size collector inlet and outlet and what size primeries( or stepped primeries) and approx what length primeries for my application. Any help would be much appreciated.

    James hone
    "The only thing better than Cubic inches is more of them"


    GO THE ALL BLACKS!!!!!!!!

  2. #2
    Senior Member DYNO OPERATOR
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    Apr 2008
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    504
    The horsepower of your engine needs to be known or assumed to configure a appropriate headder design for your car. If you would like some basic dimensions I will indulge you. The bb3 extra will like 2.25" primarys off the head. You might step the headder to enhance the top end horsepower with a step if no good info is known on your engine, 1/2 way between the head and the collector is a good starting point. The primarys may like to be 26" to 28" long from back of exh valve to collector. a little longer than that will only help the bottom end torque. As for the collector I like to use Merge collectors. Using the step pipe to 2.375" at the collector should have a 4.5" outlet 12" long if you are making big Horsepower with a choke maybe of 4". I like to use SPD for the collector. Chris Hill is the owner and is invaluable to me when I need help designing headders that work. I would not go buy parts based on this write up alone. The engine power #s are the ultimate deciding factors in the collector sizing. The headder flange and how it fits the exhaust port is the money shot and deserves some attention to get the fit right the first time. I take plane paper and rub a pencile no its side to transfer the exact port relationship to the fasteners to make the flange fit correctly. Believe it or not if you choose but every cylinder head reguardless of whom makes it often is as unique as a snow flake in the aftermarket head business. There are so many different port designs and porting jobs that change often you don't know what will fit untill you know. I realise that I did not answer your question the way you may have hoped, but no one can without more info on the engine actual power and RPM you plan to buzz. I hope this gives you something to work with for starters.

  3. #3
    Senior Member DYNO OPERATOR
    Join Date
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    Quote Originally Posted by TopspeedLowet
    The horsepower of your engine needs to be known or assumed to configure a appropriate headder design for your car. If you would like some basic dimensions I will indulge you. The bb3 extra will like 2.25" primarys off the head. You might step the headder to enhance the top end horsepower with a step if no good info is known on your engine, 1/2 way between the head and the collector is a good starting point. The primarys may like to be 26" to 28" long from back of exh valve to collector. a little longer than that will only help the bottom end torque. As for the collector I like to use Merge collectors. using the step pipe to 2.375" at the collector should have a 4.5" outlet if you are making big Horsepower with a choke maybe of 4". I like to use SPD for the collector. Chris Hill is the owner and is invaluable to me when I need help designing headders that work. I would not go buy parts based on this write up alone. The engine power #s are the ultimate deciding factors in the collector sizing. The headder flange and how it fits the exhaust port is the money shot and deserves some attention to get the fit right the first time. I take plane paper and rub a pencile no its side to transfer the exact port relationship to the fasteners to make the flange fit correctly. Believe it or not if you choose but every cylinder head reguardless of whom makes it often is as unique as a snow flake in the aftermarket head business. There are so many different port designs and porting jobs that change often you don't know what will fit untill you know. I realise that I did not answer your question the way you may have hoped, but no one can without more info on the engine actual power and RPM you plan to buzz. I hope this gives you something to work with for starters.
    These figures were based on 1150 hp and 7600 RPM 4.60" bore 4.75" stroke using a 12" long collector. to give a context. Sorry I left that out.

  4. #4
    Senior Member SENIOR BUILDER
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    1132 HP @ 7400RPM
    920lbs at 4800
    "The only thing better than Cubic inches is more of them"


    GO THE ALL BLACKS!!!!!!!!

  5. #5
    Senior Member DYNO OPERATOR
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    Quote Originally Posted by jrthone
    1132 HP @ 7400RPM
    920lbs at 4800
    I would say that I gave you some pretty good free advice knowing the power numbers now. Stall near bottom of torque curve and shift 5 % over peak horsepower and you should fly. You must have more than one carb for that high of RPM peak horsepower. What did you dyno with. They must have been fairly good don't you think? Ill bet they were longer than 28" torque is very low rpm.

  6. #6
    Senior Member SENIOR BUILDER
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    36inch long primeries 5 inch collectors 2.375 stepped to 2.5.

    What do you think??
    "The only thing better than Cubic inches is more of them"


    GO THE ALL BLACKS!!!!!!!!

  7. #7
    Senior Member DYNO OPERATOR
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    The primaries are old school long. They were able to run that over size pipe because of the excessive length. That explanes the super low torque RPM. I would rather move the torque way higher to be more useful by shortening the primaries. This will move the peak HP higher. Unless you plan to blow NO2 at this engine the collector is way too big in dia. You are proving how a headder works by making the primarys longer you can make them larger and get a similar result as a proper sized shorter pipe will act. I prefer to size them for the shortest length so you can fit them in the car. If pipes you dynoed with fit your car well I would get a Merge collector from SPD in california to top them off for now and go have fun. My 582 Profiler headed 1205 HP 924# monster uses 2.375 to 2.5 total 25" long with 4.5 to 4.0" merge collector 12" long. Your conventional valve head will not move that much air as the profiler no matter what you do to them. Your Torque is crazy high unless some engine builder dynoed the motor for you then the # would be in question HIGHLY I might add. Sounds you have a decent set of pipes that seem to work well for you. Think what a nice set might do?
    If I had to weld in New Zealand would I have to hold the tig rod in my other hand? (':lol:') Have fun in 09 and kick some but at the track!


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