408 build need help
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Teching In
Joined: Jul 2012
Posts: 42
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408 build need help Help any one? I am going with a 6.0 iron block 408. I want to be around 14:1 comp. I will be running e-85 fuel. I have to keep the looks stock. So that means intake and exhaust stock. I am goin to buy a trailblazer ss intake and get it ported. I would like to be around 700 + H.P. Heads are my main ? would a set of 317 ported or set of cnc patriot heads be better. The cam I am looking at is .617 .624 116lsa 231-239 @ 50
The 317 heads are low compression large chambers. You might be better off getting CNC ported 5.3 heads if you want them to look stock. You'll probably need domed pistons. Good luck finding a combination that has enough piston to valve clearance for that high CR. I calculate you need 5cc domes on the pistons with 59cc compression chambers to make 14:1 CR. Might want to clay the piston tops to check clearance before you do a final assembly.
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Joined: Jun 2003
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What are you trying to do. Are you running a stock class or something. With a stock intake manifold and stock exhaust manifolds 700hp sounds a little far off regardless of what heads you use.
The LS3 heads would deff. be your best bet at getting there but you will need to make sure you get L92 pistons as well. The LS3 intake doesn't do to bad if you have to run a stock intake.
You're going to want a good custom cam for a 14:1 deal.
The LS3 heads would deff. be your best bet at getting there but you will need to make sure you get L92 pistons as well. The LS3 intake doesn't do to bad if you have to run a stock intake.
You're going to want a good custom cam for a 14:1 deal.
TECH Senior Member
Joined: Feb 2009
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I forgot to mention $325 each,thats a good price.he could mill the heads after he gets the pistons.ls3 heads flow pretty good for the price ,but you need ls3 offset rockers.you should talk to some of the peeps in the gen4 section for cam ideals.you will need big injectors and fuel pumps.
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Launching!
Joined: May 2012
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From: NC
You can get 700 from a 408 but i believe you underestimate what it will take to get there and do it reliably. Valvetrain stability will become a large factor and your absolute main concern. You will most likely have to fly-cut a set of custom pistons to allow for enough valve lift while also allowing for the intended static CR. Since you will need to spin it high in order to achieve this goal you will need to gap the PTV clearance on the safer side to allow for expansion and rod stretch. I would recommend using heads with ports on the smaller side to help with torque availability and/or compensate accordingly with very tall rear gears to make up for the torque - otherwise it will run like a dog at low RPM's but kick in at 3500 to the top.
You will need a custom ground camshaft to compensate for the lack of exhaust flow - you will be losing 30HP or more without upgrading the exhaust.
I would look at a NOS cam in order to get there IMHO.
You will need a custom ground camshaft to compensate for the lack of exhaust flow - you will be losing 30HP or more without upgrading the exhaust.
I would look at a NOS cam in order to get there IMHO.
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