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New LS3/L99 Heads

This is a discussion on New LS3/L99 Heads within the Internal Engine forums, part of the LSx Technical Help Section category; Does anyone have Dyno# with these heads. they are new and just came out.. they make them for a 3.900 ...

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    Member WARP211's Avatar
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    New LS3/L99 Heads

    Does anyone have Dyno# with these heads. they are new and just came out.. they make them for a 3.900 bore and also 4.00 bore too.. They are suppose to be CNC ported and have a max flow of 315cfm I think it could be more correct me if I'm wrong. Anybody with some positive input would be nice.. More interested with an LS1/LS6 but any input would do..

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    Firebird Encyclopedia 9T8W66's Avatar
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    L92/LS3 heads have been around for awhile now.
    I've heard rumors about a small bore versions coming out through GMPP but haven't seen any solid info yet.
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    Member WARP211's Avatar
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    Yeah I read some info in the new GMHTP.. They did a C6 and swap the stock heads for some CNC ported ones It gain like 40HP.. Just the heads on a LS3.. it also had a cam, tune, LTH, and Intake.. Check it out..

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    Moderator Firebirdjones's Avatar
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    Ya I've seen that article. I personally don't like the idea of those huge intake runners on a small cubic inch motor. Probably work fine when you get up near 400 cubes. But on a smaller motor the large intake runner would make for a pretty soft engine down low.
    As a matter of fact the stock cathedral port heads with 200cc intake runners are on the large side for only 346 cubic inches.
    They stuck these square port heads on an LS2 a while back and ran a dyno comparison,,,and even that motor at 362 cubes went very soft down low and didn't start making more power until near 4,000 rpms. That would need some rear gear to take full advantage of.

    I don't know why they would bother making this head for the small 3.9 inch bore motors unless you want to spin it to the moon and run 4.56-4.88 gears.
    Keep in mind the square port idea is nothing new and has been around on big block chevy's since 65,,,even then they only used that on the high HP applications and was nothing smaller than a 396.
    Last edited by Firebirdjones; 02-22-2009 at 08:17 AM.

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    cutting and welding mark21742's Avatar
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    couldn't you just knock the stock valve seats out of these heads and have new ones put in and machined for a slightly smaller valve to clear the smaller bore of 3.9 ? don't know about gains, but that should be all that's needed to run them on a 346

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    Moderator Firebirdjones's Avatar
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    I'm betting they will have to install smaller valves to clear the small bore of the 346.

    But as most of us know,,,,cylinder heads flow less on smaller bore engines due to valve shrouding,,,,so they aren't going to perform as well as they do on the bigger bore engines. I still think it's going to make for a very sluggish engine that is very peaky up top and turning alot of rpm to get there.
    These heads have an intake runner size somewhere around 260cc,,,,A little bit much for such a small engine. Thats on par with big block chevy oval port heads.

    I remember Smokey doing something like this back in 69 with a bigblock (porcupine) type cylinder head that was specifically cast to fit a small block and installed on the little DZ 302 engines. I saw one of these in person installed in a camaro, and if I remember right it wasn't that great of a runner.

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