You stated that you are running Vortec heads. These are fast burn heads and cannot support the amount of timing you are running. Generally about 28 degrees is the most advance you can run without detonation. They also can run higher compression than a traditional cylinder head.

Hardend exhaust seats. What is the chamber size? I was thinking they're just over 100cc's however his chambers could be opened up also to help the flow. He probably has flat top pistons to achieve his 10.5 to 1 comp. Not the greatest flowing heads however I'm just happy to know they offshore boat in the land down under.

You know, now that I think about it, you never do hear of to many boat engines with those heads???

I think he must be mistaken on the vortech heads part..i dont believe edlbrock makes a airgap intake for that head yet..He probably has the standard 088 head..

I know of a couple of guys running them. Their main advantage is the combustion chamber. I think it is a 98cc. They're happy with them, but I think its only because they had the 330hp motors and the heads provided an instant upgrade in compression ratio and really livened up the motors.

I definately have the Vortec heads (10141279...96-up...oval..CLOSED.."Vortec 7400", 100cc chambers) Technically speaking, now 105cc.

I had them openened slightly to allow better flow and I had the oval ports matched to the Felpro gaskets. I then bought the RPM Air-Gap manifold (PN 7561 - Oval Ports) and had it CNC Flowed and port matched as well. .I had the heads resurfaced / shaved 0.020" to 55Ra which will also help with the comp ratio. The combination of head chamber size and my pistons allow for about 10.5:1 Comp. They run the standard valve size (2.065" I & 1.72" E) with the large oval ports and a better exhaust port profile (which Merlin and Dart use on their heads now too.) Reason you don't see many marine engines with them (IMO) us that too many people think that all oval ports are too small and they 'must' run Rect ports to make any power in a boat! Truth is, the Vortec heads flow better than all the other ovals and the exhaust port profile makes them a far more efficient head! Only downfall is I'd like a set of 2.19" intake and 1.88" exhaust Iconel valves in there to open them up!

I'm interested to learn more about the 'fast burn heads' thoughts though from Bobl. I hadn't heard that before and it is well worth considering. So if I set the timing to 8 deg initial withthe 20 deg curve (for 28 total) and give that a go it should be safer? Or will it possibly make more power?

Cheers all. Good discussion!

Hey bud, "fast burn" I think that's claimed due to the cleaner castings and unique or different chamber design. Supposodly the fuel atomizes better than that of comparable or previous casting heads. More efficient. If he could explain perhaps it would make sense however I wouldn't change your timing yet. Be careful with to low of total advance also as valves tend heat up more than normal. Hopefully someone will chime in that knows for sure. I've always been a big fan of oval port heads myself especially for marine application. On my most recent 496 builds I was even very close to staing with oval ports as well. 496's, depending on other components etc. You can have good results with rec. or oval. With the desired power I wanted to achieve the cams I used pretty much dictated the size of my intake runners. I ended up with 310cc's. The ovals would have worked well also but would have worn out quite few carbides in the process. Very understandable for a quick fix on Comp. ratio to wake up a stock 454/330. I don't know for certain however those heads may limit your top end RPM to around the 5,300 or so however I don't think you want to run much more than that anyway. I found some stock flow numbers and it looks like they fall off much over .525-.550 lift. I would like to talk to you about some other things also so I'll send you a PM. I'm just curious as to the cam your using vs your heads. I'll talk to Valako and get his input tomorrow.

John
What's your weather like there this time of year?

From what I understand the 049 castings and the 781 casting actually both flow better than the vortec heads, despite the new casting on the exhaust profile. I know street racers that are going mid-10's on the 781 heads, and they wouldn't think of trying to get that out of vortec heads. Allegedly, according to them, it would take too much port work to get the vortec heads to flow as good as the 781 heads, if its even possible.

GhostRider,
How tall are the intake ports at the gasket? As long as everything holds together and you can boat trouble free that's not all bad either. Down the road maybe you can change your heads out. With your other components a good set of aftermarket heads would really wake that thing up. Do you have any speed shops around where you live. As much as I have always wanted to visit I have yet to do so. You pay my ticket and I will carry on a couple of heads with me for luggage and we'll get your boat really moving.

These heads have the heart shaped combustion chambers. I've built and dynod several engines very similar to this. HP is around 450 at 5500 rpm(but I don't run quite as large a cam) They will detonate with very much timing. Because of the chamber design, combustion occurs much faster, thus requiring less lead time for ignition. This information has been documented many times. Pull the timing back and give it a try. BTW I own Full Throttle Marine and build marine engines for a living(so you know my background).