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how about Mac headers

This is a discussion on how about Mac headers within the External Engine forums, part of the LSx Technical Help Section category; Originally Posted by 94 Formula I picked up 22rwhp taking my Flowmaster 3" catback off and replacing it with a ...

  1. #21
    LTX N20LT4's Avatar
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    Quote Originally Posted by 94 Formula View Post
    I picked up 22rwhp taking my Flowmaster 3" catback off and replacing it with a SLP loudmouth.

    I also have the Mac Mid-length headers and I also cut the ball off the ends and put 2.5" flange. I did a custom 2.5" y-pipe and make over 440rwhp.

    Just my o2
    My Flowmaster 3/3 works just fine for me!

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    INMY01TA, did you felt the diference between mids and LT's

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    Senior Member INMY01TA's Avatar
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    Quote Originally Posted by Mr.Gomez View Post
    INMY01TA, did you felt the diference between mids and LT's
    Didn't necesarrily feel a difference (but meter wont detect <10hp) but I did pick up a tenth with them and a ported TB. Long tubes noticably sound better also.

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    Quote Originally Posted by INMY01TA View Post
    Didn't necesarrily feel a difference (but meter wont detect <10hp) but I did pick up a tenth with them and a ported TB. Long tubes noticably sound better also.
    thanks for the info

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    Formulatastic yellowv's Avatar
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    Mac middies are very good headers. They will gain damn near as much as LT's and have great clearance. I have seen a lot of cars run damn good with Mac's.

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    Member 94 Formula's Avatar
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    Quote Originally Posted by Mr.Gomez View Post
    nice, how does is sound? have you take it to the 1/4 mile?
    It sounds great!

    I have run it in the 1/8th on street tires and it did low 8's at high 85-88mph.

    Thanks

  7. #27
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    EDIT: Disregard the first part...it looks like they do have flanges.....

    I don't know if the Mac headers are the same on LSx's as they are w/ Mustangs, but I would never have recommended them on stangs b/c Mac didn't use a flange to connect the primaries. Heat cycles make the primaries want to warp, so if they have to come off for any reason, they can be difficult to get back on. Agian, this was w/ 302/351-based Ford motors, so I'm not positive about Mac's products for LS motors.

    As far as the cat-back goes, if you already have an aftermarket system, why not just swap mufflers and save some cash over replacing the whole system. Unless the pipes are a small diameter or don't have mandrel bends, there is no reason to replace them agian.

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    do you guys think I could brake the 400rwhp marker with Mac-mids, ORY,diferent muffler( for better flow), FAST 90/90. Volant cold air, hypertec programer (came with the car), 160' thermostat, under drive pully, and 224 cam?
    Last edited by Mr.Gomez; 08-22-2007 at 09:00 AM. Reason: spesific

  9. #29
    Member 94 Formula's Avatar
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    Quote Originally Posted by Mr.Gomez View Post
    do you guys think I could brake the 400rwhp marker with Mac-mids, ORY,diferent muffler( for better flow), FAST 90/90. Volant cold air, hypertec programer (came with the car), 160' thermostat, under drive pully, and 224 cam?
    Yes!

    The hypercrap has to go..Then get a custom tune and you could hit 400.

    I did 380rwhp with the 224 cam.

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    should I reprogram my computer back to stok now, or should I do that before the dyno tune the car?

  11. #31
    Member 94 Formula's Avatar
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    Quote Originally Posted by Mr.Gomez View Post
    should I reprogram my computer back to stok now, or should I do that before the dyno tune the car?

    Wait until you are ready to dyno tune the car...

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    thanks for the help

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    94 Formula, how many hp were you making before getting the Stage II 6.0L Heads?

  14. #34
    Member 94 Formula's Avatar
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    Quote Originally Posted by Mr.Gomez View Post
    94 Formula, how many hp were you making before getting the Stage II 6.0L Heads?
    On my 99 Camaro I was making 380rwhp with full bolt-ons and the 224 cam with a custom tune.

    Then I changed my cam to a larger one and put the heads on.

    Cam specs now are 233-233 / 578-113lsa

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    Quote Originally Posted by N20LT4 View Post
    My Flowmaster 3/3 works just fine for me!
    Mine worked fine also and sounded great. I just picked up a nice amout of power selling it to another member.

    I am not the only one who has picked up power changing out flowmaster.

  16. #36
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    Quote Originally Posted by Mr.Gomez View Post
    do you guys think I could brake the 400rwhp marker with Mac-mids, ORY,diferent muffler( for better flow), FAST 90/90. Volant cold air, hypertec programer (came with the car), 160' thermostat, under drive pully, and 224 cam?
    With a tune no problem . Especially in an M6 car.

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    Senior Member INMY01TA's Avatar
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    Quote Originally Posted by Mr.Gomez View Post
    do you guys think I could brake the 400rwhp marker with Mac-mids, ORY,diferent muffler( for better flow), FAST 90/90. Volant cold air, hypertec programer (came with the car), 160' thermostat, under drive pully, and 224 cam?
    I dont think so. Maybe 370-380 on a Dynojet.

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    Quote Originally Posted by INMY01TA View Post
    I dont think so. Maybe 370-380 on a Dynojet.
    icould get 370-380, but it is posible to reach 400, it all depends how my car reacts to the mods.

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    Quote Originally Posted by 94 Formula View Post
    Mine worked fine also and sounded great. I just picked up a nice amout of power selling it to another member.

    I am not the only one who has picked up power changing out flowmaster.
    What car did you swap the Flow on - LS or LT?

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    Quote Originally Posted by INMY01TA View Post
    Mac headers were popular years ago when the only long tubes availible costed a small fortune. Nowadays with Pacesetters and Hookers and such, there's not much point to em.I switched from Macs myself a couple years ago.

    So are you saying that we would be better off buying Pacesetter lts + ofy > Mac lts + ofy? Im in a toss up too!

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