Hey guys, I'm in a process of getting parts to put together a 408. As of right now all I have is a 6 liter iron block. As this my first engine build I'm looking for advice on what to get. I'm looking towards 500whp NA with a flat torque curve. I'm most likely gonna be ordering a complete rotating assembly from Texas speed. But what about heads and cam? Which ones should I get. And what else would I need besides the rotating assembly. Thank you for the help

Bang for the buck I would get some CNC 243 heads.

This is a quote from Thompson.

I'd go 1.0mm over bore (.040") DNJ hyper pistons on production rods and crank for 372 cubes; approximately 11.25:1 compression ratio
Texas Speed PRC 225cc as cast heads and their 228/232 range cam
with 1&7/8" headers and a FAST 92 intake you would have a strong user
friendly combo that would have power everywhere
And if it only makes 450 or 470 rear wheel horsepower; that's still quite a
powerful "first engine"

i forgot to mention that the block is already bored 30 over. And I already have 1 7/8th headers so that what I was planning on using so that's good. But I really have my eyes set on a 408. It's not gonna be a daily just a weekend/track car

those are the ones that came on ls2 correct? Cause that's what I was thinking about buyback is it true they don't offer much room to grow after?

If that's the case, I would do a 370"...spend the extra $1,000 you were gonna put on the stroker crank on the heads. It will be BADASS!

I agree! I don't even have my 408 running yet and already wish I would have done some things differently. A great set of heads is where the power's at.

but the price difference between a 408 and a 370 is 500$ which definitely won't get me a good set of heads

That five hundred bucks would be the difference between some Re done 243/799 heads and perhaps a set of Mamo 223 Sportsman's or some Tooley touched up Trick Flow 220 as cast heads.
Killer heads on a 370 is better than just good heads on a 408
Cubic inches, specially from stroke becomes a law of diminishing returns. Piston Speed, ring friction and rod angularity all become power robbing factors. It will make more torque but usually makes a lower horse per cube ratio. Your money; just giving you free knowledge

if the two motors had the same heads and a comparable cam which one would u recommend

The GM engineers did a great job picking the 3.622" stroke with the 6.098" long rod and a 1.34" compression height piston. I'm a big fan of increasing the bore size to promote breathing. You could pickup some LS3 pistons and have your block bored to 4.065" for a 376" combo. KCS had a nice combo like this before
IMO this build would suit your power goals reliably

It would be foolish to bore the block out to fit bigger pistons if you do not have to.
If you are good at 30 over, there is no reason to go any bigger.
60 over on an iron block is pushing it, 65 is even worse.
Plus in the long term if you stay 30, you could rebuild to 40 or 60 down the road.
No need to max bore at this time.

PS: forget stock rods. Go forged pistons and rods and do it right. As far as size, if you want tq, the 4 inch stroke of a 408 will win hands down.
I had a forged 6.0 and it was a solid motor, but never put down the tq of comparable 408s. But it was a monster on the bottle.

if you want to build something, spend the money on solid parts. If you are going to use stock parts, go to a yard and pull a motor. It will be cheaper.

thats what I was planning on doing, a complete forged rotating assembly that way I wouldn't have to worry about the internals down the road. And I was planning on staying at 30 over and going with the 4 inch crank

I was also thinking about going for 11:1 compression what do you guys think about that?

That's where I was going with my post...Pick up a stock 6.0 crank for $100, buy forged pistons/rods, and spend the extra $900 (to your head budget) getting some BA heads!

LS3 heads on a 408ci engine should make that and then some. You could probably even do it with a stock ported LS3 intake, but there are some good aftermarket intakes too.

I'm finishing up my LS3 headed 6.0L iron block build, but I went with a little more stroke than 4". Feel free to read my build thread here.

i was looking into ls3 heads but they seem to loose quite a bit of power downlow compared to 243 heads. Im not really shooting for peak numbers, I'd rather have a good curve all the way through. Ls3 heads would make a ton more power up top tho if I'm not mistaken?

The LS3 ports are big. They're lazy on a stock stroke 6.0L or 6.2L, which is why you see that low end loss compared to a cathedral port head. It's even worse if the cam isn't spec'd very well.

However, on a 400ci engine, they're more appropriately sized. They'll have good airspeed, good low end power, and will still be able to feed a larger engine like a 408. You're going to have to spend a lot more money on a cathedral head to get the same performance.