they do quite well for a bit of time.problem is,if you don't notice the skip/misfire/loss of power or rpm and that creamy oil,,the exhaust valve will pit so bad around the stem that it just breaks off.we know the drill after that.

I have had a drink or 10 so, forgive me! I saw air-j mention the zz502 cam is that what you planing to run with the l-29 vortech heads? That was the rout I was planning to take. Tore down my engine saw scared piston wall, long story short now in building a 540 for my 22zx. L29 heads in stock form can only support 510 lift. To run the zz cam the valve guids will need to be machined down for clearance with the access lift.along with new spings, and valve rotator eliminator's. There's hit and miss info available on forums about this setup just be careful what you believe. I would deal fine using stock gen 6 crank as well with this set up. Should be 400hp whit hour head work. Yet I stand to be corrected if need be. I read for months on this subject.

It was kind of a inside joke from another thread i dont think he has any intention of running the rumpita rumpita with the 7400 heads .

[Yea , but me, and ill bet you , dont have to worry about that happening .ive seen enough of other peoples motors grenade over fumbled riser gasket installs melted inner hose linings ect .beezwax or chapstick your riser gaskets and you can take a quick peek down the exhaust while your girlfriend grabs a fresh beer .thats how i caught a inner crack in a imco once before it did any damage to #8 .new spark plug and spare mani swap was out that afternoon

So much for the "reply with quote " still learnin the ropes of the new phone .

i will probly do a little guide work to get around 550 lift, but i ain't going under 112 lobe sep. that zz is 110lsa and 550 lift approx. i have a flat tappet 560 lift 230 duration cam i am gonna leave in my MK4 block. i hafta get a degree wheel and play a little to edjimicate myself a lil more on cams in general and this one in particular.

Do you already have exhaust ? I have a set of imco risers for standard merc cast manifolds. I planed to use them on a similar project. But plans changed. They're dry to the tip.

I did a lot of research on whether the black motors came equipped with inconel, and I was told by an engineer at Mercury Racing that the black motors came with whatever GM equipped them with, so he wasn't sure what kind of valves were in there. Only the blue motors were disassembled and blueprinted, and those had the upgraded Manley exhaust valves.

well my L29 is blue so i guess it has the good stuff...good cast crank, good 3/8ths rod bolts, good cast pistons, good low rise q-jet intake...but apparently the OE truck exhaust valve is the next best thing. and this motor is being built to be second best at best...probably put it in the
crownie after running it in the pantera for the season.

Considering what can happen, it's money well spent buying Inconel valves imo. Any money you can spend to increase Valvetrain reliability in a BBC is a win win.