No difference in the cam, head, or block. There was a guy not long ago that was looking for 198 bits, and there will be again, I'm sure.
If you decide to work the chambers and ports, read up. There is water very close to the ports. Doc posted some photos showing how close. Going to oversize valves doesn't require sizing up on the seats. You can easily hit water cutting for a larger seat, and it won't matter for the valve sizes that won't shroud on the bore. There are options like Chevy small block valves, and Ford 300 valves, though you may find you have to turn the Ford valves down a bit for clearance. I turned mine down, and back cut them. Oversize valves generally won't give big gains until you are .060 over with the bore. If you choose to use larger valves, make sure to check chamber alignment of the bores. You risk tagging the deck with a valve, especially when cutting the deck and/or head for compression. Generally speaking, there aren't a lot of gains in over-bores, as it doesn't add many cubes. 0.100" over is a 238. The only way to make a big difference in cubes is stroking, but the 225 is already well under-square, so Piston to wall speeds, and reciprocating forces are not ideal for high rpm operation with a stroke. If the operating envelope is kept in check, that can be OK. The head won't flow well enough to take advantage of higher revs anyway. A stock 225 can survive at 5500 as long as it's put together right. Some folks run higher, but tend to find weaknesses rather quickly. A 225 at 6000rpm is a time bomb. 7000 rpm is asking for trouble right away with all but the top drawer builds. With a stroker like mine, you can hear the engine getting unhappy anytime it's over 5000 rpm. At 5500 it makes unpleasant noises. It's also a bit pricey to stroke the slant substantially if your not going for a smaller rod journal. I had my crank welded up to get back to the standard rod journal with a 4.475" stroke. I don't know what Doc did with his 4.500" stroke crank. With four mains, even the forged crank is going to flex at higher revs, so surface hardening or coatings aren't going to live long. I didn't bother. The bearing area is huge, so as long as your oil and filter habits are good, it won't make much difference in life expectancy. Once up above 4000 rpm operating ranges, oil pump drive gears become "a thing." There's plenty to read on this forum about ways to mitigate oil pump gear failures. At lower rpm, aeration and cam walk are lesser. With a boat, higher rpm may not be desired. Of course if your going with Stainless or surface piercing drives, cavitation might be less an issue.
Compression, careful head work, cam selection and ignition system would be what I would concentrate on. All selected for the desired operating envelope, and fuel grade. Bigger is often not better.
Enjoy the journey!
CJ
|
If you use the 198 rods, you will need different pistons than stock (with lower compression height - around 1.6" instead of the stock 225 at 1.74". Unless you are doing a high compression, high HP engine, the 198 rods are really not worth the trouble and expense.