03-23-2011, 09:20 AM
So im looking for my budget build to go for about 2500 dollars on motor before transmission is matted. Thusfar I have got that I am looking for a short block 350 with 9:1 compression and for the top end here is what I have discovered
-Vortec heads L31-pocket ported ($400) upgraded valvesprings and new seals, 1.6:1 roller-tipped rockers
-Edelbrock Performer RPM intake (vortec style)
-Holley 750-cfm carburetor
-Hooker 1-3/4-inch street headers
-COMP Cams Xtreme Energy Camshafts (Summit racing part # CCA-12-675-4)
Does everything sound like a good fit for a budget build 350 with respectable power?
03-23-2011, 11:12 AM
That's a common-enough recipe, but I'd change the cam, valves, and rockers. I'd get aftermarket valves, and I'd choose heads that don't have a mystery port job. Most DIY porting of Vortecs actually ruins the excellence of the intake ports.
The recipe you propose, with 1.5:1, did 372 HP at 5400 rpm on Westech's dyno, with un-ported heads, and about 10:1.
HotRod did a 9:1 Vortec 350, but with the GMPP HOT cam kit. It did 401 HP at 5600. But don't give the credit to the rockers. The Vortec intake ports stall above 0.475" lift. That's reason enough to forget the 1.6:1 rockers.
When I had Vortecs on the SuperFlow 1020, I saw 238 cfm at 0.475". but 228 cfm at 0.485", and as I closed the valve, the flow never climbed back above 228.
You can hear it when the port stalls. Well, if you're running the bench, you can hear it. It's turbulence.
It's best to not get into it, rather than try to get out.
So, Vortecs will perform best if the intake valve never opens enough to get that turbulence. Stock GM cams that GM used with Vortec heads never had anywhere near 0.475" lift.
Anyway, I'd go with aftermarket undercut, swirl-polished, back-cut, stainless 1-piece valves. At 0.200"-0.400", they added 11 cfm to the un-touched intake ports, and even more on the exhaust side.
Exhaust port porting is helpful if done right. Enlarging the port exit doesn't help, and tapering the guide boss is of little help by itself, though it should still be done. Lightly.
Phone just rang, gotta go.
03-23-2011, 12:56 PM
the heads im ordering from crate engine depot which are the stock vortec heads.. im going to do the mild port job myself and upgrade the springs and seals in order to handle the cam that i chose. So with upgrading the heads with those components it wont handle up to the performance of the cam?