Hi Kinglui. I recently purchased a 92 Z-28 with the 5.7 and looking on upgrading the engine too. I am not a gearhead (yet) but here is what I have found out by reading a lot of posts on this site. What year is your car, that might help other people to give some good insight. There has been a lot of comparisons with different intakes on this site and others.
TPI was designed to produce lots of tourge in the 1,500-5,500 rpm range on a 5.0 litre engine. Chevy put TPI on a 5.7 without a redesign for the bigger engine. The stock TPI manifold does not flow alot and I believe is the biggest restrition in the engine intake "chain". From what i've read, the heads, cam and intake all need to be carefully selected together to make power or tourqe in the rpm range that you want. Also check out some of the stickies in the TPI or alternative intake pages. I believe all of the below are emission legal with EGR provisions. There are some more but these seem to been the prevalent ones discussed.
1) big mouth intake & large flow runners from TPIS - similar to existing intake but has better flowing intake and larger runners for more power. It also keeps same rpm band and gives you more torque. Some people even port these items to remove metal for more improved airflow.
http://www.tpis.com
2) F.I.R.S.T. injections intake - is a new base, runner and intake that acts similar to TPI. Members here have described it as TPI on steriods (unit is alot larger than stock). I believe it flows more air than the TPIS system. It will move the rpm band up a little to 5,800rpm. Search member Badss posts as he has the intake and did some great testing.
http://firstfuelinjection.com/products.htm
3) HSR (holley stealth ram) - different intake from the first two. It will allow for higher engine HP (around 400) but accomplishes this by raising rpm band to around 6,500rpms. It will take away some lower end torque vs the TPI system. Most people say they don't notice the loss. A lot of people seem to like this intake as it gives them a niced balanced increase of HP and tourqe throughout the rpm band.
http://www.holley.com/91403201.asp
4) TPIS Miniram - similar to the holley stealth ram in that it creates max HP but at a higher engine RPM.
http://www.tpis.com
At this point I am leaning to the FIRST intake. I am not looking to make my car a wild drag car or high rpm screamer. The FIRST intake is similar to stock TPI in looks and function. I believe it is an intake that Chevy should have designed for the 5.7 to achieve its full potential and mantain their intent with the camaros/firebird of huge low & midrange torque. With the higher rpm systems you have to start upgrading more things for the car to work properly (gears, tranny, injectors, etc.) My goal is to keep my car stock as possible but have it be a street monster. Any way you go I think you will be satisfied with the increased performance. Good luck!
