SBC Vortec heads - 062 or 906??
 

Question - which casting number would be best for a mild SBC buildup? Why?

I've heard the 062 flows just a tiny bit better than the 906, but the 906 has inconnel seats in them which I'm thinking might be better for a marine engine use...

- the rest of the combo is a basic 355 with flat-tops (4 valve reliefs, -7cc), I'm re-using the XM262H cam/lifters, and was thinking of replacing the 'centerbolt' or "tbi" heads with some vortec castings and matching RPM Air-Gap intake.

Also - how much HP do you guys think they're worth over the older (whatever is stock on a '95 5.7L non-magnum engine) with this setup? (Is it really worth the hassle of getting a set rebuilt and swapping intakes?)

I have posted a similar reply before, but I purchased the standard Vortec castings from Summit Racing not the ones with Iconel. I removed the stock heads from a 1990 / 91 Mercruiser 260. Kept the same pistions, installed the Vortecs, an Edelbrock Performer manifold, 1.5 roller Rockers, XM256 cam, Outer Z28 valve springs, new Mercruiser manifolds and risers. This is a heavy 3300+lb Wellcraft Eclipse 21 1/2 ft. Cuddy. Before mods, ran about 52.7 on GPS with a Mirage 21P. After mods turned a Mirage 23P at 5000 - 5100 rpm and 60.3 on GPS (a lot of propeller slip on this antique hull). So all these mods together picked up around 7 mph. I can only estimate that might be 300 propshaft HP from the previous 230 propshaft HP, but only a guess. There is a bit more in it with the right prop.

either one will work fine...I would use the std performer and not the RPM on that app. Rob

nice gains!.......A Merc Revolution 4 would be a great prop for that boat

I actually tried a labbed Revolution 4 in 23"P. Slippage decreased but not enough to compensate for rpm loss. I think it only turned about 4700 instead of 51 - 5200 and it was at least 1 mph slower but better midrange than the Mirage 23P. Ran a 25"P labbed Laser and it turned about 5000 rpm with similar speed to the Rev 4 but slipped bad coming onto the plane. Tried a stock 23P Mirage Plus and it was at least 1 mph slower than the 23P Mirage (because it turned around 200 rpm less). Put more cup in my old 23P Mirage, lost rpm and speed.
I think I need to have my 23P Mirage labbed and I could probably pick up another 2 - 3 mph. Hardly worth it for an old boat like this (but in excellent condition).