paintman

which are better and why

Larry D

based only on my own dyno experience with various engine combinations it depends on what rpm range you are looking for. The oval ports will be more responsive and make good power (tend to make power early with nice flat curve ) but will fall off about 5800 ( and I mean fall on face they are done) also as a note I am talking about ported oval ports that have been done by a good head shop flowed gasket matched etc with larger valves etc. Lingenfelter did mine.
the rec port head I have run over 7600 and made over 750 natually asperated HP but big heads and cams tend to be soft on bottom start to make power after 4000 or so

so I guess it all depends on how you want to use the boat snappy, easier idle low rpm (5500 or so max) go with oval ports I should note you are probably limited to about 600 hp with this set up ( mine made 588 hp at 5750 and was 502 ci 8.5 compresion , with flat tappet hydralic cam [I forget the cam specs but could look it up if you are interested] these were nice reliable engines you could probably do alittle better with todays hdy rollers


if you are more intersested in the higher rpm stuff or are building over 502 ci [540 or something ] go with something on the lines of dart pro 1s [they are a smaller rec port]

paintman

larry d- thanks for the input, and i want to get up to 550hp or more.......whats the standard head setup on a 454? are mags, mpi's all similar etc......... i have yet open up my motor( will this next offseason) so the internals im unsure of, but it used to be a fuelie -currently has a cutler intake and an 850 holley dbl and a stainless marine exhaust .... cheers

jeff1000man

I have used the ovals with just the valve upgrade and no port work and made over 650HP with them.

No matter how you set them up. unless you are going over about .650 on the lift and planning on turning over 6K rpm's, go with the oval heads on your 454.

bump the compresion a little to around 9.5

nice cam from marine kinetics and you will have a nice engine.

Get some good exhaust to go with it.

jeffswav

Just to clear a few things up, there are peanut port ovals and Large Ovals. I believe the other guys must have been talking about the Large Ovals. Peanut port heads run out of HP before 5k. I have a 489 stroker engine and I have 820 large ovals. As was said the Rec port heads are needed on 540's or bigger.

paintman

so are the large oval port heads after market items or standard merc/gm heads

Larry D

yes large oval ports can use darts, the Gm casting 409 I believe needs to be ported he is right the peanut heads were used on low rpm truck engines you don't want them

ezstriper

you want to use 781 or 820 castings...amd in a lot of cases will work better on boats in the rpm we run..

jeffswav

I used the GM 820's because of the 110cc chambers. I used flat top pistons and needed to get the compression up. GM 781's use 118cc chambers and are a good choice. Aftermarket large ovals would be good also typically with 280 ish intake runners.