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Thread: what exhaust size do you think

  1. #1
    Member CRAFTSMAN
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    what exhaust size do you think

    what exhaust size do you think for my 700hp street motor,with a 4" collector would you go with a 3" or a 3-1/2 exhaust thanks Ron612.

  2. #2
    Senior Member MASTER BUILDER
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    You planning on mufflers? How many?
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!

  3. #3
    Member CRAFTSMAN
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    yes two mufflers, im thinking on Flowmaster 435408 In/Out: 3-1/2'' Body: 9'' Chamber: do you think 3- 1/2 exhaust is to much ?

  4. #4
    Senior Member DYNO OPERATOR
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    bigger is almost never better

    Your collector is and had better be a tuned length and diameter for your engines needs. A three and one half inch conventional collector is real big on 700HP FYI. If you run a exhaust pipe the same size as your collector the engine see's a 8' long collector and tunes the power band for 2000 RPM or a lot less RPM if you will, the longer the collector the lower the tuned length. For reference, your engine can have a collector length between a short 10" in drag only trim and long 24" in street trim maximum. You can use a reducer cone at the end or your collector that reduces the size of the pipe a 1/2" or so so the velocity of the gas changes to tell the engine where the collector ends, then you can go back to the collector size if you want to. However, you will not see and advantage with the huge diameter collector pipe extension. The pipe weighs a lot and bends get very expensive or restrictive and you loose heat that in turn hurts gas velocity.
    Bruce

  5. #5
    Member CRAFTSMAN
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    dang bruce english please lol :lol: i,m looking at lemon headers to make me a set 2-1/8 or 2-1/2 primary's to a 4" collectors then a set of jeg's #520-11139. 4" to 3-1/2. then tubing to the muffler still 3-1/2 to The turn downs. or would you go with a 3" what would you change. Ron612

  6. #6
    Senior Member DYNO OPERATOR
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    If you have already contacted a header builder then go with there recommendations. If ultimate performance is your goal then the primary size and length are very important, so saying you are using 2.125" to 2.5" for your primary diameter tells me that you have no idea what you need. Get on a site called headerdesign.com and input you HONEST engine and chassis variables and you will be shocked what you end up with in actual primary diameters and length. as for the collector, it is just as important and the primary's, sizing and length. Everything after the collector is just a performance inhibitor in one way or another so you should just focus on the header and collector configuration for now. You should not have any problem with power on the street with a potato in the muffler if you have 700HP in your street motor don't you think?
    Bruce

  7. #7
    Member CRAFTSMAN
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    With all your knowledge with headers, it's too bad you aren't here to do it for me. :lol:

    I have a midplate on my car, and looking at standard headers, they look like they would hit the midplate. So I'm looking at custom-built headers to fit to get the most performance, but I haven't talked to anyone yet, just thinking out loud.

    Thanks for your input - Ron612

  8. #8
    Senior Member DYNO OPERATOR
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    It is a shame you are so far away. I would be in the mood to build a set for you by monday if you lived closer to michigan. However, you may find that an old 70's chevelle or skylark header picked up at a swap meet may fit ok with your set up, you never know. Go on that site I mentioned previously to find out what you need for your engine / chassis set up, as for diameter and length primarys, then you will increase you odds of getting a set cheap at a swap meet or equal. Custom pipes are worth what you pay for and seldom are under $2000 with collectors if they are any good. A weld up kit comes primitive, but likely will fit out of the box with the pipe uncut in a tube car. Yours would require more effort. Re-fabing one pipe per side on a new out of the box set is much less expensive than doing all 8 primaries custom................ Some say that a monkey can weld with a MIG. Tig requires more skill to do it well.
    Bruce

  9. #9

    header

    i tryed the formula and if you put in more then 600 HP then it tells you the HP is unreasonable and so this formula wont work for any car making more then 600 flywheel HP unless im doing something wrong and i no it wont be the first if i did LOL

  10. #10
    Senior Member DYNO OPERATOR
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    Re: header

    Quote Originally Posted by promod45
    i tryed the formula and if you put in more then 600 HP then it tells you the HP is unreasonable and so this formula wont work for any car making more then 600 flywheel HP unless im doing something wrong and i no it wont be the first if i did LOL
    I went there to check on what you were seeing. When it sees that the horsepower is unrealistic, one of your variables are in left field like peak HP rpm too low or too little compression. Try it again and you will see that a 496 with 900 hp at 7500rpm comes in just fine with 15 to one comp. The program is fun to see what changes in pipe requirements for higher and lower peak HP and so on.
    Bruce

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