I thought 540 was the magic number.

You cant hear it thru the screen but that was supposed to be sarcastic.

yep,guess i should have got that.LOL

i know the old merc 900sc,s were 542 cu in.bore&stroke was 4.440 by 4.375

The fact is, times are changing. 20 years ago, if you wanted big HP numbers, you had to go BIG. Back in the days when a 454 engine in a early 90's truck made a whopping 230HP. Now, you have engine with 100 cubic inches less, making upwards of 400HP off the showroom floor in the auto world.

Today we have fabulous cylinder head choices, and superchargers that are a far cry from what was offered 20 years ago. You need to think about something. These engines are making in some cases, almost 2.5-3HP per cubic inch with forced induction.

557 X 2.5 =1392HP.

572 X 2.5= 1430HP.

In the grand scheme of things, 38HP means absolutely nothing at the 1400HP level. 2-3% of total engine power. And, to make up 40HP at that level, well, theres a lot of ways to do it. I think what these guys are shooting for, is power, AND reliability. They probably like the thicker cylinder walls, shorter stroke for RPM and strength, and overall lighter rotating assembly. These engines are running the pistons way down in the hole, and I'm sure to get a respectable pin height and rod length, the shorter stroke allows for room in a 10.2 block. You also have to remember, you're working with a 10.2 platform. You only have so much room for Stroke/rod/piston. If you want to run a conventional style open chamber head, a reasonable piston dish, and keep a large squish area, you have to look at the options. A 4.750 stroke in a 10.2 block, just isn't gonna be an easy 7.5:1 high boost engine. Generally speaking, going from a 4.25 stroke to a 4.750 stroke, with same piston, same chamber, will bump compression about a full point. So say from 8:1 now becomes 9:1. Anyone know what size dish you'd need in a 632 to get to 7.5:1?

Im not sure if im making sense with what im trying to say. There is so many things that go into these engines from an engineering standpoint, I can guarantee the engineers at Mercury Racing, guys at Sterling, etc, know all about the 632CI, and sonny's big cubic inch stuff. However, they choose not to go that route, and I am positive its not based on cost.

I imagine we will be having a similar discussion 20 years from now as well. As technology gets better things will get cheaper to produce at this level and we will see more improvements across the board. Remember, 454s used to be big.......

I'm glad I stumbled across this thread.
It's great reading for me as I was having damn near the same conversation last weekend with one of my neighbors who I knock beers back with when he's not out working for their race team customers.
But his input was different, perhaps because of the nature of his sport.
He said for my refresh or rebuild or if I start from scratch is to go with the longer stroke and smaller bore for more torque as that's what my boat wants since it's always under a load while operating, and dump my dominators for a pair of carbs that are built to the needs of my current displacement at the chosen rpm range. He's told me from the get go that he had no idea why Merc put these huge carbs on such a small displacement engine.
I've always taken his insight as the Gospel itself as he's enjoyed a lifetime of racing, tuning, and working within their industry but not really with any boat racers. He said he'd build me a set of carbs to my needs or tell me what to purchase and tune them to my powerplants and for my boat don't aim for super high rpms but for more torque at lower revs for longevity since she ain't no speed demon anyhow.
I'm curious as to where I'd find an online chart noting which bore and stroke combinations net what displacements
and what combinations y'all or some of your friends have utilized with good success for longevity.
My powerplants are stock 525SC's with 500 hours. I have seawater cooled chillers beneath my blowers and smaller pulleys for more boost. I never go over 5100 rpm and I seldomly go there due to the time on my engines and would prefer not to start from scratch with bigger blocks but work with what I have even if I need to purchase a new crank and rods to go with new pistons which I already figured I'd have to purchase.
As always thank for y'alls insight, I've always got great info from this forum from you guys.

Thanks,
Kelly

this is the formula,bore times bore times stroke times.7854 times number of cylinders.

Kelly. Hands down, the best bang for the buck in a 525sc, is a cam, head, and most importantly a blower swap. I am making 800HP and 740FTlbs with 468ci with 6.5 lbs of boost on pump gas. It's a docile engine. The dominator carb wasn't the limiting factor on the 525sc, the blower, flat tappet cam, and GM iron heads were.

505 cid is the magic number...out fontana engine made 3000 + hp and lived 1/4 mile!