I have just started to rebuild my first engine and in need of some guidance. I have a 66 Impala with a 327, powerglide combo. The engine began smoking heavily and after some investigating... a rebuild was the only option. I would like to increase performance all around as much as possible during this build. The major dilemma is what cam to use and why? Every where I go and call people will never recommend the same cam specs actually, most of the time it's not even close. The car is a weekend driver and it's will keep the powerglide trans. Fast off a roll would be the most fun.
Here is what I have so far,
HEI distributor
Vortec Heads 062 casting, stock rockers (refurbished by local machine shop)
Holley 750 CFM
ProComp PC22026 Air Gap Intake
Speed Pro +.030 Pistons Flat top
Hasting Rings
Stock Rods
Stock Crank, polished and tapped for center bolt
Cleavite Bearings
Melling Oil Pump
Felpro Gasket Kit
I would prefer to buy a Compcam or a Lunati kit to include cam and lifters. I would like to get to 400hp/400tq whether it's realistic or not is why I'm here posting for answers. Thanks!
Getting 400 horses from a 327 is a little more difficult than from a 350. It'll take a bit more cam and some 1.6 rockers.
The flat top pistons might get you into more compression that pump gas is comfortable with but to compute that I'd need clearance from the piston crown to deck, head gasket thickness, and exactly which pistons to get at how many ccs are the valve reliefs. You need to work both the static and dynamic compression ratios especially with a bigger cam which tends to bleed compression under the torque peak RPM. To recover this requires extra compression, so all of these dimensions need to be worked out before buying pieces.
With parts roughly the same as what you sight a 350 with a Comp XE268 and 1.6 rockers would tease the 400 mark. Since power and displacement walk hand-in-hand for an equivalent configuration one could assume a 327 would make about 380. It's not quite that simple but close enough for two engines with only a 33 cubic inch difference.
The big problem is to get that 20-30 hp out of the 327 will take revving the engine to a higher RPM. To do this the Vortec heads need some work as the valve springs on these things are a small diameter and enlarging the pocket sometimes weakens the port roof if not actually breaking through. So the safer bet is the same size spring but one of better quality and strength. Beehives work best as they use a smaller thus lighter retainer so they have better valve control with less spring. Otherwise single wound 1.28 with damper will fit and provide upwards of 340 pounds of open pressure without having to carve out the pocket.
The next problem is the top of the valve guide, the stock 062 type casting will not tolerate lifts beyond .45 inch and you will need more so the guide needs to be machined down.
The stock Vortec rocker is self guiding and the rocker stud is pressed in. The spring pressure needed for a better cam is going to push the limits of the press in studs, these really need to be replaced with screw in studs which require machine shop milling down of the existing pads and tapping the hole for the screw in stud.
The 1.6 rocker should be a quality piece with at least a roller tip. If you use the self guided rocker then push rod guides are not needed. However the Vortec head is not configured for push rod guides so if the rocker selection is not the self guiding type then guides need to be used and accommodated under the screw-in rocker studs and hardened push rods used.
Making no bones about it, turning a rebuilt Vortec head into a performance piece is fairly detail involved and rather expensive. This is why aftermarket and GMPP's performance versions of the Vortec are so popular, as they can be had ready to support a high output engine for about the same cost as rebuilding production Vortecs into performance pieces.
Bogie
