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416 and 243's

This is a discussion on 416 and 243's within the Internal Engine forums, part of the LSx Technical Help Section category; Goal of 550 on motor. able to be driven on long trips with ac, and road racing. Give pros and ...

  1. #1
    Member RealLiveMD's Avatar
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    416 and 243's

    Goal of 550 on motor. able to be driven on long trips with ac, and road racing.
    Give pros and cons of this setup before I buy.
    Forged 416 or 427 about same price from Thompson with 1 year warranty.$4800
    EPS custom cam $400
    patriot ported 243's with 2.08, 1600 valves $500
    new thompson lifters $160
    new ls6 oil pump$160
    ls2 timing chain, from old motor
    Ls6 intake old motor
    78 mm throttle body old motor
    New upgraded fuel injectors $300
    conversion kit ls1 to ls3 $400
    tune $700
    1 3/4 headers free
    700 hp monster clutch new and already own
    built t56 own
    strange s60 4.11 1000 miles own.


    I also still have my 78 mm nitrous plate and stand alone system which could get me to 700 hp if I needed it. I figured I'd save some money on the fast intake and Trick flow heads because I could get the extra hp from nitrous if needed. Let me know if i've listed all I need and your thoughts

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    What block are you using?

  3. #3
    Member RealLiveMD's Avatar
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    ls3 block

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    I would suggest getting a 427 LS7, LS7 style heads, and a LS7 FAST Intake.

    I have a 427 LS3 and I'm slightly disappointed in what the motor made with cathedral port heads. I left almost 100hp on the table because I decided to cheap out on the block and not get the LS7.

  5. #5
    James Bond Spikito's Avatar
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    The LS7 and LS3 block are pretty much the same though, the LS7 was a better casting process, and I think better cooling vanes. I don't see how the block alone could have gained 100 hp. Unless the LS7 block accepts different heads than the LS3, but then your problem REALLY lies in your heads.

    I dunno, please correct me

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    Quote Originally Posted by Spikito View Post
    The LS7 and LS3 block are pretty much the same though, the LS7 was a better casting process, and I think better cooling vanes. I don't see how the block alone could have gained 100 hp. Unless the LS7 block accepts different heads than the LS3, but then your problem REALLY lies in your heads.

    I dunno, please correct me
    You can't run LS7 heads on a LS3 block because of the minimum 4.125" bore required for them. Nicely ported LS7 heads can flow almost 25% more air than any LS3 or LS1/2/6 heads.

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    James Bond Spikito's Avatar
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    oh ok, i misread your initial sentence, I thought you were saying you had a 427 LS3 with LS7 style heads.

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    Quote Originally Posted by Spikito View Post
    oh ok, i misread your initial sentence, I thought you were saying you had a 427 LS3 with LS7 style heads.
    I wish I did, lol. I actually have cathedral port heads. They're not terrible, but my next engine build will not be budget anything

  9. #9
    Member RealLiveMD's Avatar
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    So I know that the cathedral port heads and ls6 intake should leave roughly 35 hp on the table; however, Im just not convinced that makes a difference if the motor is forged and I could simply opt for a 175 shot if needed above the 125 I usually would feel comfortable spraying. BTW, I have a stand alone nitrous kit that I run c16 in.

  10. #10
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    Any reason why you are picking 243s over LS3 heads?

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    Quote Originally Posted by 95cam86roc View Post
    Any reason why you are picking 243s over LS3 heads?
    He can reuse his stock rockers.

  12. #12
    Moderator Firebirdjones's Avatar
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    Nothing wrong with cathedral port heads on 400+ cubes if you go with a good set of castings. Frankly Patriot 243's will leave alot of untapped HP on the table. I'd much rather prefer an aftermarket casting from AFR, TFS, etc....

    I'm not a huge fan of the square port LS3 heads. They are popular for budget oriented builds, but they generally produce a weak torque curve below 4000-4500 rpms even on most of the 408 builds I've seen and generally have a very narrow rpm band between peak torque and peak HP. Works fine if you run enough gear, say 4.30 or more. If you want chest pounding peak HP numbers then these heads work, but I much rather prefer more power under the curve with a mild rear gear for a street oriented car that sees minimal track time. I'd rather have 427 plus cubes for the big heads.

    You can easily make 500+ rwhp with a cathedral port 408 build. I'd also rather see a FAST intake setup on a max effort build like this. But in the end it's your wallet that will tell you what you need to do.

    Honestly I've been looking into a 408 build for my wifes daily driver, with Texas Speed ported 243's and the stock LS6 intake to keep everything looking stock. A very mild camshaft profile, all in an attempt to create a good mid range torque monster with good street manors that drives like a stocker. Don't care much about peak HP.

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    Quote Originally Posted by 95cam86roc View Post
    Any reason why you are picking 243s over LS3 heads?
    Because I already own them.

  14. #14
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by RealLiveMD View Post
    Because I already own them.
    Are they stock castings or did you buy them from Patriot with their work already done?

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    Quote Originally Posted by Firebirdjones View Post
    Are they stock castings or did you buy them from Patriot with their work already done?
    I bought them from patriot

  16. #16
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by RealLiveMD View Post
    I bought them from patriot
    Ah okay, wasn't 100% sure from the description.

    Sounds like you got what you got already. I like the custom cam idea, you at least should have a cam profile that will maximize the combo you want to use. Put it all together and see what it makes. It might be enough to satisfy.

  17. #17
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    You forgot the price of:

    - tires
    - upgraded drive shaft
    - lower control arms
    - relocation brackets
    - torque arm
    - sub-frame connectors
    - upgraded pan hard bar (optional)
    - upgraded brakes so you can stop that power (optional)
    It's on jackstands.

  18. #18
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    Quote Originally Posted by 35th-ANV-SS View Post
    You forgot the price of:

    - tires
    - upgraded drive shaft
    - lower control arms
    - relocation brackets
    - torque arm
    - sub-frame connectors
    - upgraded pan hard bar (optional)
    - upgraded brakes so you can stop that power (optional)
    I have all that plus Strabo combo standalone nitrous and cleanest garage kept f body u will see. Otherwise I would have just bought a zo6

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