i would like to know the hp increase over stock heads and high rise manifold verses vortec heads and manifold.can i use the same ditributer and carb?and does anyone know who might have to pairs as i have twins.1991 350 s

For a idea, one article I had read was that the vortecs produced 25-40 hp over earlier cast iron heads. If you change to vortec heads, you just have to buy new vortec intakes, like edelbrock has a air gap dual plane which is a very nice intake, I ran vortecs and this intake on a 383 a few years ago. Only thing is the heads need machining to handle cams bigger then .460 lift, I spent a good chunk of money, getting them machined for, screw in studs, guideplates, bigger springs and guides had to be cut down..

Yes you can use the same disributer, and for the carb depends on if its a holley or stock quadrajet, I don't know if they make vortec intakes for quadrajets or not, if not you will have to use a adapter or use a holley carb.

You can get these vortecs for $480-$500 a set.

Travis

The flow potential and resulting hp increases will be severely limited in this application without a cam change. The stock Merc cam is the roadblock to making more power due to its limited lift and duration, it does not exceed the flow potential of the stock heads and intake, let alone optimize your aftermarket pieces. It has been my experience that just the head/intake swap, without the cam change, will yield very minimal increases.
Protopline offers a "906" Vortec replacement head that is cut for high lift w/ screw in studs that flows very well for nearly the same money as the Vortecs.
Bob

thanks guys what cam can i use? i don't want to cause reversion.im running emi exhaust with ss risers and silent choice.

also running in salt water.yes i do flush but i would like to stick with an intake with bronze water jackets or cast manifold.

http://www.sallee-chevrolet.com/Inta...on_Vortec.html

Here is your intake, Stock cast appearing, fits Vortec, and taked a Quadrajet.

http://www.sallee-chevrolet.com/Cyli...ds/Vortec.html

and your heads.

I am interested in doing this same conversion, lets hear about the Cams.

I didn't do it, but looked into it. Remember to optimize your quench. A stock 350 should have a deck height of about +0.025" above your stock flat top pistons. If you use the stock composite marine head gasket (0.039") that'll give you a quench of about 0.064", which is really no quench at all (especially for vortec heads). If you use a high quality shim gasket (0.015 to 0.018), you'll get good quench. But watch your compression ratio. You may want the 72cc Vortecs rather than the 64cc to keep the CR within reason.

As for cams (I assume you are flat, not roller), the Comp XE262 would do good, although the exhaust lift might be a problem (I think its around .480). Also the XM 262, XM 256 or XE256. I like the XE's LSA of 110 (versus 112) better.

Not an expert, but I got an opinion.

OK, this may be a "Stupid" question, but, Has anyone tried to replace the cam with the engine in the boat??? I have the manifolds off, so it would be no problem to pull the intake, and heads, anybody think I can get in & around it enough to lower the oil pan, pull the timing cover, and regasket the pan & get it back together???