1990 gmc with the 454 in it. Pre-vortec, so I don’t know if that makes a difference. Anyways, it has low compression due to the #7 or #8 cam lobe being worn off but not sure which one.
There's two cam lobes per cylinder. Are you SURE the cam lobe wear is the reason for the low compression?
Have you done a cylinder leakdown test to rule out failed rings, or defective valve seal?
All the metal worn-off the cam lobe and lifter bottom has been circulating in the oil system. Some of that debris will be caught in the oil filter, some has gone through the engine bearings, hydraulic lifters, etc. Be sure to clean and inspect EVERYTHING. This includes removing the pain-in-the-*** threaded plugs along the lower left edge of the block so the oil drillings can be cleaned with a brush.
Those plugs generally have a recessed square wrenching surface. A #3 Robertson bit works nicely. They're generally REALLY TIGHT.
what should I look for in a performance camshaft and lifters for when I go to replace it. I want to milk more power out of it.
If power is a concern--and you've already had cam lobe failure already--the first thing you need to look into is a roller cam and a set of conversion roller lifters.
The cam should be a step-nose (Gen 6) style, which uses an OEM thrust plate to control cam movement fore-and-aft; instead of a stupid aluminum or nylon "button" banging against the timing cover. Most Mark IV blocks have the bolt holes for the thrust plate already drilled 'n' tapped. Some don't have the holes, but they have the casting bosses so the holes can be easily added.
The roller lifters are taller than the stock flat-tappets; you'll need shorter pushrods.
The original cam is very mild. The TBI computer will likely need to be re-tuned to suit the new cam. California frowns on this, and other states are sure to follow.
And since I’m going to be cracking into the engine anyways, if I go full fledged rebuild what other mods should I throw in that will gain power but not decimate my wallet. TIA!!
Zero-deck the block, or use thin embossed steel-shim head gaskets. You want not more than 0.045 piston-to-head clearance. I'd shoot for less, depending on piston-to-cylinder wall clearance and the expected maximum RPM.
ALWAYS degree the cam. Most I've done are withing a degree of where they're supposed to be; but you never know unless you check it.
SOME (not all) Mark IV blocks are set up for parallel-flow cooling between the block and the head. The difference is three additional small holes on each side of the block, at the head gasket surface, and the matching head gaskets that also have those three holes. Most Mark IV blocks have series-flow coolant circulation--which works but is slightly less preferable than parallel-flow. The big deal is that if you put a parallel-flow head gasket on a series-flow block, you'll have overheating that NOTHING will solve until you drill the three holes in the block, or change the gaskets.
(All Gen 5/6 blocks are set up for series-flow coolant.)
The TBI cylinder heads--in stock form--are pretty pathetic. They can be reworked by an expert to make decent power and torque. Or replaced by other OEM castings, but the real gains are from aftermarket aluminum heads (which also remove significant weight from high 'n' forward on the vehicle. You'd want very conservative port sizes to maintain lower-rpm torque.
The Mark IV 454 in my boat had Gen 6 Vortec heads for awhile. I was not impressed. Now I've got some older Mark IV OEM iron castings--oval port, "open chamber" but with big valves installed. Still a little shy of my power goals.
