A few updates and questions. Again, this is the 5.7 GSPLKD engine non Vortec. I’m wanting to go with the XM270HR cam as recommended. I do have the 4 barrel, but it either needs rebuilt or replaced. Also, I am looking at an intake upgrade. What should be done, if anything, to the Vortec heads I am wanting to use ? They were removed from a 98 Silverado.
with the motor being a non-vortec, its a left over 1995 or earlier. you may have flat tappets. if so, your limited on the cam. an XM268H is the largest flat tappet you can go. however before you buy anything, you need to verify what you have
how many intake manifold mounting bolts do you have? 8 or 12? if 12, non-vortec heads and you will need to pull the intake to determine which cam you have. only some of the pre '96 boat blocks got rollers.
if the heads are stock vortec heads from a 98 silverado... to expand on post #3
at a minimum, get a valve job, get the press-in studs removed and replaced with ARP screw in studs. get the guides cut for teflon seals, get the spring pockets cut for a higher profile cam.
I would highly recommend SS valves, however if your on a budget, dont worry too much. then again, if you look at your local racing classifieds, you can probably pick up a set of vortec heads with a fresh valve job and all the upgrades done for less than you can modifiy the heads. usually about $400 a pair
If you have a roller cam now, the XM264HR is a reasonable improvement over stock. this cam can be run with 1.6:1 rockers. the 270 is largest cam you can go with wet exhaust as you are then knocking on the point of reversion. recommend sticking with the stock 1.5 or the aftermarket 1.52:1 rocker arms with this cam.
a 2" plenum spacer will help mid-range torque
First, find out what cam and lifters you have now, and compare the specs. Frankly, there's better (and simpler) ways to get power than changing the cam. Dial in the carb, have the distributor curve checked, get a free flowing K&N filter/flame arrestor. Start with the basics.
stock cam is extremely mild. there is a bit of power to be had there. rocker arm ratio change will help.
the specs that GM used for the 260hp 5.7's
202 duration intake
214 duration exhaust
395" lift intake
404" lift exhaust
112 lobe separation.
k&n filter wont help, same spark arrestor is used on BBC's as the SBC's. inlet airflow is not limited
distributor curve is electronic