[Blazin72]

I pulled a valve cover off the 305 in my boat today to see which heads it had. They're 416 castings, some on here have said those heads do have some potential. I'm not looking for anything major, maybe a 20-30hp increase. I'm thinking about a set of Vortec heads and a small cam to get me where I want to be. Are the Vortec heads a worthwhile upgrade over the 416s?

[F-BIRD'88]

If you want a head that you can bolt on and go faster than the vortecs will certainly do that for ya. They will need some performance valve train mods and machining to get them ready for performance use.

Your 416 castings have good performance potential (easy 30+ hp) but will need full porting and larger 1.94" valves and some mods also. The porting required takes time but is worth the result.
Based on airflow alone you can fully port a 416 head w/1.94" valves to equal and/or exceed vortec head flow. The vortec heads have a superior combustion chamber thou.
They are ultimately a better head.

So you have two good ways to get the power you are after.
a moderate marine friendly cam swap and compression ratio increase will help also.

The fully ported/preped 416 head route is a little cheaper buy only if you do all the porting yourself then get a machinist to finish them. ( valve job etc.) You can do some other stuff to like drill and pin the rocker studs.

[Blazin72]

Thanks for the info. How about marine intakes? I know there are aluminum intakes that have copper plating in the water crossover to reduce corrosion. I'm looking to find one of these as well. I wouldn't worry too much about it except that I do plan on running it in salt water this summer.

[Lil Big Mec]

The 416 heads have smaller combustion chambers than standard Vortec heads, so a head swap would reduce your compression ratio somewhat. I believe the Vortecs are 64cc and the 416 are 58cc.

[Blazin72]

Yes, they would be milled to bring the chambers as close to 58cc as possible. How thick is the deck surface on the Vortecs? Does anybody know how much would have to be removed?

[F-BIRD'88]

For the 416 heads there is a Mercruiser cast iron hi rise hi performance manifold. it works with both a Qjet and a Holley carb pattern. It is the same as the Holley 300-36 street dominator / GM Z28 hirise except is cast iron. You can even buy it from GM.
If you go vortec there is a cast iron Mercruiser Vortec manifold also. Fits a Qjet. it is not a hi rise design thou.
Fine for a 305. You must use a Vortec style manifold with vortec heads. Mercury Marine Mercruiser Small block motors use GM Vortec heads so marine manifolds are available.

A Car aluminum manifold will work but will corrode eventually in salt water. Many people trailer their boats and run fresh water thru the drive to flush out the salt water after use. I recommend you do that.
Once you've increased the power of your 305 by improving the heads and swapping cams you may have to rejet your Mercruiser Qjet carb. Edelbrock Metering rods and jets work fine in this carb.

[Koolaid]

Be careful on the highrise cast iron intake F-Bird is talking about - they are great manifolds for high rpm's and using in circle track where cast iron is dictated, BUT - everything I've read says you are losing torque with those under 4500rpms and that they shine in 4500+ applications. That might be a little high for a boat?

[curtis73]

Originally Posted by Blazin72

Yes, they would be milled to bring the chambers as close to 58cc as possible. How thick is the deck surface on the Vortecs? Does anybody know how much would have to be removed?

Don't

Vortecs have thin decks. They are designed well and don't typically crack or warp, but the amount you'd have to mill to get 58cc would certainly not be satisfactory.

There are 305 Vortec heads as well... Probably worth 20 hp alone.

As far as the cooling goes, you could go to closed cooling, or use a vortec iron marine intake. Its tough to find bronze-lined aluminum intakes, but they're out there. On Ebay look for a seller by the name of michiganmotors, they have them.

[F-BIRD'88]

Originally Posted by Koolaid

Be careful on the highrise cast iron intake F-Bird is talking about - they are great manifolds for high rpm's and using in circle track where cast iron is dictated, BUT - everything I've read says you are losing torque with those under 4500rpms and that they shine in 4500+ applications. That might be a little high for a boat?

That iron hi rise dual plane manifold is a direct copy of the old 69 70 Z28 LT1 manifold and Holley 300-36 dual plane with full divided plenum. It was cast in iron specificly for Mercury Marine. If it had a bad torque curve, short on low end torque Mercury would not be using them. I/O boat motors are all about torque. It has a strong broad torque curve. The best you'll get in the required rpm range. it makes more upper end (above 4500rpm) power than a typical stock low rise manifold but gives up nothing on the low end. Be ware of mis-information.
This is a Marine manifold first. The fact that Circle track guys picked up on it and use it is secondary.
There is nothing wrong with the low end output of this manifold.

[Hippie]

Originally Posted by F-BIRD'88

That iron hi rise dual plane manifold is a direct copy of the old 69 70 Z28 LT1 manifold and Holley 300-36 dual plane with full divided plenum.

...................


There is nothing wrong with the low end output of this manifold.

I'll second that, the old Z/28 intake is one of the best all around street manifolds ever made. It has excellent torque characteristics from an idle up. Where you lose bottom end is when people get grinder happy and think they're making it better by removing the plenum divider.

[Koolaid]

I mis-spoke stating torque when I was thinking throttle response. Here is the link to my information:

http://www.castheads.com/marine_high_rise.php

[F-BIRD'88]

Originally Posted by Koolaid

I mis-spoke stating torque when I was thinking throttle response. Here is the link to my information:

http://www.castheads.com/marine_high_rise.php

This manifold has no lack of throttle response.
Don't know where the author got that idea.

[runn141]

Originally Posted by F-BIRD'88

If you want a head that you can bolt on and go faster than the vortecs will certainly do that for ya. They will need some performance valve train mods and machining to get them ready for performance use.

Your 416 castings have good performance potential (easy 30+ hp) but will need full porting and larger 1.94" valves and some mods also. The porting required takes time but is worth the result.
Based on airflow alone you can fully port a 416 head w/1.94" valves to equal and/or exceed vortec head flow. The vortec heads have a superior combustion chamber thou.
They are ultimately a better head.

So you have two good ways to get the power you are after.
a moderate marine friendly cam swap and compression ratio increase will help also.

The fully ported/preped 416 head route is a little cheaper buy only if you do all the porting yourself then get a machinist to finish them. ( valve job etc.) You can do some other stuff to like drill and pin the rocker studs.

i done the same thing to a set of 416s cut to 1.94s and they gave me no more power than the set of 882s ported and polished. i cant see them being as good or better than a vortec, vortec looks to have a better chamber design.

[Koolaid]

Originally Posted by F-BIRD'88

This manifold has no lack of throttle response.
Don't know where the author got that idea.

Take it however you want - I don't have any reason to doubt Brezinski.

[Hippie]

Low end torque IS throttle response and they were comparing it to a stock cast iron small block intake. Almost every carburetor intake manifold on the planet gives up some throttle response and torque to the standard iron SBC intakes at low RPM. The few that don't are all done by 4500 too. I know plenty of people that ran the Z/28 high rise on everything from a stock 283 to a built 406 and it worked very well. If ever there was a true "one size fits all" intake for the SBC this was it. Other intakes do better in other areas but this one works well from idle to 6500. The only ones that come close are either shameless copies or very, very similar and I think we all know which ones I'm talking about..........