I am looking to get a few more HP'S under the hood of my 5.7 Hemi. I have already got a cold air intake, 8.5 Taylor racing wires and plugs, 40 super series flowmaster, and a superchip. Will headers make much more of a difference?

 

only on the middle to upper end of the RPM's. your low end torque will suffer a bit.

I put on a complete 2-1/2" aftermerket system on my little toyota, the low end did suffer, but above 2500rpm I can tell a big difference.

 

Yes headers will make a diference. And you should look into getting the 6.1L cam or if you want serious power get the KRC 218cam.

 

this interview of Dodge engineers who designed the 5.7 Hemi is worth a read:

http://www.motorage.com/motorage/art...on%20Injection

note the bit that says:

"The cast iron exhaust manifolds have also been carefully designed and flow-tested. The engineers report that at full-load on the dyno, these manifolds flow within 2.2 percent of a 4-into-2-into-1 exhaust header."

2.2% more than 345
is 352 hp

there is probably a bit more hp gain than this when the header is installed because it will lean the air to fuel ratio from the factory 11.8 more toward the best power level near 13.1 but remember that there is danger in this leaning...particularly to catalytic converters, exhaust valves and piston ring lands.

 

Adding headers will give you an extra gain in HP there is no doubt about that. You'll get a hell of a lot more than a 2.2% increase though by adding some high performance headers onto the configuration you have going for you right now. However this also depends on what type of exhaust you have on it right now. If I was you I would replace the entire exhaust system as well all at once. Keep your super 40s, but see if you cant get a decent cat-back system to attach it to and swap out your cat for a high flow cat and add/replace the "Y" pipe and you should notice a dramatic difference over what you have now. And it should sound alot meaner too if Im not mistaken..........

 

Go fot the 4:56 gears.
You get no HP increase but your MPG will get better and your truck will really get up and go !!!!!!
I've read a lot on this and am busily saving up right now. Best bang for your buck aparantly.
Al.