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Cam / head power gains with stock exhaust manifolds?

This is a discussion on Cam / head power gains with stock exhaust manifolds? within the Internal Engine forums, part of the LSx Technical Help Section category; Live in the republik of kalifornia where emission laws suck. Wanted to add some power to my 01 m6 SS. ...

  1. #1
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    2001 Camaro SS M6

    Cam / head power gains with stock exhaust manifolds?

    Live in the republik of kalifornia where emission laws suck. Wanted to add some power to my 01 m6 SS. I currently have a lid and came with slp dualdual cat back system. Would like to add long tube headers but haven't found anything that would pass the smog visual inpsection ( needs exemption number from CARB to do so). Was thinking of adding ls6 heads and a cam that won't be too noticable and leaving stock exhaust manifolds (01s went back to cast iron design instead of tubular steel).

    Will this work or am i wasting my time? Has anyone found a long tube set that is california certified? How much gain is likely with this setup? Any cam suggestions?

    Thanks fellow ls1 fans!

  2. #2
    Moderator Firebirdjones's Avatar
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    All long tubes are illegal in Cali because it moves the location of the cats. So you won't find any that are CARB certified.

    The 01-02 manifolds are the best flowing Fbody manifolds as far as those go. They aren't horrible pieces by manifold standards.

    LS6 heads and camshaft would certainly give you a boost in HP, with a bump in compression, a 6500 rpm redline, all while idling smooth and still passing emissions.

    I've always been a fan of modifying an engine on the inside while keeping the outside complete stock appearing/sounding. There are substantial gains to be found while still using stock exhaust manifolds. If you were real serious about it, I prefer to send the exhaust manifolds out to have them extrude honed.
    There are even camshafts that are custom ground particularly to use with the stock manifolds. Called sleeper cams. Can't remember who was doing that as it's been a while since I've seen them. I doubt they have a CARB certification though. Might be worth checking.

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    Thanks for the info! Was thinking along your lines-keeps it stock looking outside and pump up the internals. Most smogChecks don't know how to tell if been modified this way. And if numbers pass would likely be OK.

    Used this same approach on My ktm 530exc street licensed dirt bike- it has all the emissions stuff still on it so the forest rangers or police officers can't hassle me but everything is decommissioned (vent lines plugged, rejetted, etc). Most folks just pull everything off and hope they don't come across a ranger who knows something about Ktms.

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    Old Member, New Username BrownsMillsAntz's Avatar
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    1995 Z28 w/ LS1 Swap

    LT's are illegal in NJ and most of the guys I know run them...as long as your not throwing any codes the inspector wont know one way or another

    Heads/Cam/Intake/Stall.
    404 Rwhp uncorrected @ 6400

  5. #5
    Are you able to swap motors in cali? I wondered this before because then you cant use the "stock exhaust" lol

  6. #6
    Senior Member Naaman's Avatar
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    98 Z28 Vert M6

    This is interesting... so what's cheaper: machining the 241s or upgrading to LS6 heads? I suppose with the head swap, there would be no vehicle down time, either, so that's a plus. As for the exhaust manifolds being "extrude honed," what is this? It sounds interesting. Is it like porting the manifold, or just smoothing it out or what? In interested in this too, since I want to keep my car legal.

  7. #7
    Moderator Firebirdjones's Avatar
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    Extrude honing has been around a long time. It really got popular in FAST racing the last few years because stock exhaust manifolds are required in that class.

    To put it simply, they basically blow abrasive materials through the manifolds at very high pressures. This erodes and opens the ports and smooths the transitions etc... Much like hand porting or CNC porting but able to get into areas you can't reach with a dremel or CNC machine.

    Doesn't make as much power as a good long tube header but when you are limited to manifolds for class racing or emissions, it's a viable option. They also do intake manifolds and an assortment of other things. Not necessarily cheap though.


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