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402 or 427

This is a discussion on 402 or 427 within the Internal Engine forums, part of the LSx Technical Help Section category; I am starting to plan my next project and I am unsure if I should go with the less expensive ...

  1. #1
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    402 or 427

    I am starting to plan my next project and I am unsure if I should go with the less expensive 402 or go all out and get the 427. Also my heads are ARE with 2.02/1.57 valves and need to know if the larger cubes should get 2.08/1.60 valves. This is not a daily driver so just looking to have fun on the weekends with it. Thanks for the help.

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    Member 99SS'Vert's Avatar
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    I'd say get the 402. The difference in cost isn't really worth a few extra horsepower.
    Although, a 427 with some LS7 heads and a big cam ........

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    Thanks for the info. I agree with you, I think the 427 is more for bragging than anything. I am going to go for the 402. I have a set of ARE ported LS1 heads that are pretty trick but I was told to go with a new set of heads that aren't LS1 ported like AFR. Would you agree or just freshen the heads I have know?

  4. #4
    Slow'er'Ass Mr. Luos's Avatar
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    My 402 made 526 RWHP.

    427 is going to be a lot more expensive.

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    what other mods do you have as far as engine bolt ons? Also do you think the extra coin is worth the extra horsepower? Thank you.

  6. #6
    Slow'er'Ass Mr. Luos's Avatar
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    I don't.
    You can make a 402 see 550 RWHP with an M6 car. Of course you need a large cam and the best heads. The heads are the expensive part.
    Of course, so is the shortblock.

    I am a fully modded car.
    http://www.domesticdisturbance.us/mrluosta.htm
    All mods at that link.
    2008 Trailblazer SS
    Yank PTB3600, Kooks 1 7/8" LT's, 4" intake, E-fans, Magnaflow, Sonnax kit, tranny cooler, tune.
    Lowered, HID's, tinted.

    1999 Pontiac Trans Am WS.6 #1747 SOLD
    531.1 RWHP 481.3 FT/Pounds all motor.

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    Very nice car. Looks just like mine. I noticed you used the larger valves 2.08/1.60 and the larger Header size. I have been recommended against this but it seems to have worked for you any opinions on this.

  8. #8
    Slow'er'Ass Mr. Luos's Avatar
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    Any reasons why these people were against it???

    Those larger valves won't work so well on a stock bore motor. But the 4" bore

    The larger headers are also not so good for the more stock motors. But when you have as much air moving in and out as my motor does...I wanted it to be effective. Probably lost a little low end grunt (like I have much to worry about with a stroker) put picked up power up top.

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    They said that even with the 402 the heads can only be machined so much and can only move so much air that they never really needed the larger valves.

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    Slow'er'Ass Mr. Luos's Avatar
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    I had flow numbers before and after the larger valves were installed.
    Flowed 13cfm more.
    Of course...flow isn't everything, but it gives you an idea.

    The trick is getting the air in and then getting it out.
    Some are right, bigger isn't always better.

    Not having any problems with mine though. Making VERY good power for budget heads.

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    Well the other good thing about your set up is that your heads are ready for anything you can throw at it, maybe just a freshen every so often. With the smaller valves you can only go so far with your set ups, so I actually like your set up. Who did you get your parts from? I used Thunder Racing in the past but they do not do larger engines and I have used Agostino before but they are to expensive.

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    Slow'er'Ass Mr. Luos's Avatar
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    Byunspeed (heads, suspension, all kinds of other stuff)
    Texas Speed (motor, cam, other little things)
    Thunder (not all that much though, but a good shop)

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    Thanks for all the info. It has helped alot.

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    Value = 402
    = LS7

    If I had 13K burning a hole in my pocket then LS7, otherwise stick with the 402.

  15. #15
    where is a good place to purchase a 402 crate engine...........who has a good rep........

  16. #16
    Senior Member MadSeason's Avatar
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    Quote Originally Posted by sw21chedda
    where is a good place to purchase a 402 crate engine...........who has a good rep........
    www.exoticperformanceplus.com

  17. #17
    Slow'er'Ass Mr. Luos's Avatar
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    As well as Futral, TSP.
    Just not SLP.

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    402 all the way

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    Senior Member MadSeason's Avatar
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    here ya go.... build this up, MTI 455
    http://www.motorsporttech.com/print/...rochure01.html

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    Quote Originally Posted by 99SS'Vert
    I'd say get the 402. The difference in cost isn't really worth a few extra horsepower.
    Although, a 427 with some LS7 heads and a big cam ........
    You right in that a 427 w/ LS7 heads would make KILLER power and

    be pimp as hell.....but I'll bet you could get better results for the same or less $$$ going with an iron block 408 and a procharger. That is what I'm starting to dream about....

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