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  • · Registered
    67 Camaro SS/RS L78 M20 Convertible
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    503 Posts
    Sorry i cant send messages, so i have to answer here:

    Thank you so much for the answer. I talked to Chris a bit, i want a cam that peaks at 7000rpm. So it will be in the 250s timing wise and 600+ Lift area.

    So even more than yours. I will also go for an air-gap since it will feed the "small" 402 enough to 7000. plus an 850 AED annular carb. With stock 781s 500+ hp should be possible..

    Thank you for explaining the dyno differences, i knew there must be something i forgot.. otherwise those numbers would never add up.

    · Registered
    67 Camaro SS/RS L78 M20 Convertible
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    503 Posts
    So how can this 145hp gap be explained?

    - CR is 9.5:1 instead of 11:1, so maybe minus 15hp.

    still 130 hp difference. Is it ALL coming from the duration of the camshaft? 242° vs 224° ? Lift is even the same..

    What is your opinion?

    In the future i will ask chris straub for a full custom grind for my engine and do a full roller conversion. I wann it to peak at 7000rpm, redline at 7400. I think i will end in the 500+ hp range, just like you..

    PS: Sorry, somehow i am cant send you privat messages. You can delete these public posts and send me PN if preferred.

    · Registered
    67 Camaro SS/RS L78 M20 Convertible
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    503 Posts
    -2) I found an articel about an engine very similar to mine:

    What i have (L78 original):
    402, 9.8CR with stock 781s and a Hyd. Fl. Tappet Magnum 270h Cam (In/Ex: 224@0.050 & 0.510 Lift). On top a non-rpm Performer 2-O Intake with 750 Edel Carb breathing into 2"into3.5" Hooker Headers.

    The car in the article is a 402, 9.5 CR with 820 Heads and same 270h Cam. Unkown Intake and Stock headers.

    Here is the article:
    -http://www.superchevy.com/how-to/engines-drivetrain/sucp-1110-402-big-block-cylinder-head-swap-head-games

    They say the TFS heads increased hp by 30, so 280 must have been the hp with 820 heads.

    Thats 145hp below what hotrod measured in this article with a full stock L78:

    -https://www.hotrod.com/articles/chevrolet-lied-stone-stock-1969-l78-396-big-block-makes-50-hp-more-than-factory-rating/

    So how can this 145hp gap be explained?

    · Registered
    67 Camaro SS/RS L78 M20 Convertible
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    503 Posts
    Hi there,
    i saw a lot of posts from you and am very interested in your build, since it already resembles mine to a certain amount, but will become even more similar in the future.

    There are 2 reasons i contact you.

    1.) One is about details of your 408 Build.

    2.) Second is to ask you about your opinion, why the hp in a certain build is so low? I will explain what i mean.

    -1.1) What was the Peak rpm of your engine? 6500 or 6800?
    -1.2) And you used headers, right?
    -1.3) May i ask about your timing curve? intial/total @ what rpm?

    · Premium Member
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    672 Posts
    Have you heard of my issue before do to a lack of vacuum ? Yes, I think your solution is the best as you won't have the contamination in the cylinders.
    I would assume they are on an angle(30 degrees)and NOT 90 degrees to the collector so exhaust flow would draw from the PCV line creating a vacuum ?

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    8 Posts
    Thanks for your input on my 396 head gaskets. If I can, I'd like to ask you some specific questions about the head gaskets:
    1. Would my best option be a gasket with the two irregular holes open on the ends of the gasket that are open?
    2. If my block has the three 1/2" holes at the bottom, should I punch/cut the head gaskets to expose these holes?
    3. Is the optimum gasket one that has the end holes and the three 1/2" holes all open and matched to the block?
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