James B.

iTrader: (1)

The stock heads flow well but the springs are so weak the valves float over 5000 RPM and power falls off. The E-Tec heads are proven. For a naturally aspired 350 I would suggest the 170's. The 200's are for bigger cubes and/or huge cam and/or boost.
I believe the valvesprings in the 170's will handle 6000RPM. (200's springs handle 6500). You don't want to spin the stock bottom end over 5800 anyway, which is convenient since the PCM will only go to 5800 maximum.
The stock intake and injectors will support 350HP. Beyond that you'll have to replace the manifold with something true multiport - the stock PCM will support standard injectors.
The E-Tec heads have the same chamber volume as the stock iron Vortec heads. It would have been nice if they were a little smaller to bump the compression up a little bit, the aluminum will take higher compression without detonation. (GM Fastburn heads are 62cc chamber but they've got D-shaped exhaust ports like an LT4 and require custom headers.) The aluminum will at least afford you the ability to increase timing a little bit, dropping from the 195 thermostat to a 180 would let you get a little more over that.
A set of E-Tec 170's on a mild cam with roller rockers and long tubes could easily make 350HP on a Vortec 350 block.

Tig

iTrader: (2)

Would that be 350RWHP? Or crank HP?
What cam and rollers would you go with with that combo? And would the same power be made with Thorley Tri Ys?
What intake manifold would you replace the stock one with?
Thanks James, I appreciate the info.
Six 3" mufflers? Do you have any pics of that?

Fast355

I am going to go with 350 RWHP.. My 9:1 compression 350 with ported 906 vortecs, Reed custom grind cam (TINY), edelbrock victor jr 2bbl vortec carb manifold with a 454 TBI unit on top and doug thorley Tri-Y headers in my 1983 G20 Van made 370 RWHP @ 5,900 and 360 RWTQ @ 3,700. I am a firm believer in the Thorley Tri-Y headers, they really pump up the power where you need it for passing and freeway flying.

Tig

iTrader: (2)

Thanks Fast
Is the manifold a bolt on or does it involve any mods? I notice it doesnt come with the egr. Do they make them with it or is it in my best interest to delete it for more ponies? If how do you delete it? Where is the best place to get a 454 TBI unit? Is this bolt on to? One thing I need is for it to pass emissions. With these mods will it pass?
sorry for all the questions, I appreciate the info.

Fast355

My setup was a TBI engine to begin with, but it was an example of what can be done just as easily with a Vortec top-end. Many companies have Multi-Port Fuel Injection, MPFI intakes that will work with vortec style heads. Also, just because you have a "vortec" engine does not mean you need to run vortec heads, if you ditch the CSFI setup. I setup a 305 in a Camaro with a Holley manifold for MPFI and a 454 TBI for the air meter. You don't have to run the 454 TBI since your not TBI, but it makes a nice high flowing throttle body assembly for cheap on Ebay or the like.

I do not have to worry about emissions, so I do not run EGR. Passing emissions really depends on what you have to do. If you have visual inspections you are going to have to run a marine intake with an external EGR or the factory intake.

Tig

iTrader: (2)

Unfortunately emissions around here is pretty strict and only getting worse.
The only aftermarket manifold w/EGR is the Marine manifold? Does anyone make a Marine manifold complete for my motor? My biggest problem is time, I need something that I can bolt on and go. If that even exsists.

Is 350HP even possible with the stock manifold?

Fast355

350 HP is VERY possible with the factory intake manifold and spider assembly, although I would recomeend a MFI spider update. The factory intake manifold definately responds to porting as well. The biggest issue with it is there is just too much junk inside of it to block the air flow.

mds2004

350 is about max you will put out to the flywheel. HIghest Ive seen with the stock intake manifold is 330rwhp and thats with a 383.

Tig

iTrader: (2)

I'm sorry, I'm pretty new to Chevys and dont know all the terms or abbreviation. What is a MFI spider update? What is MFI and is there a schematic of it somewhere? I will look for a stock manifold and start porting, sounds like a good project.


330 would make me happy.
I wish I knew this, I just swapped my tranny. I wouldve upgraded the flywheel at the same time. Any suggestions on an aftermarket one?

Thanks guys, I appreciate the help and info.