Made the discovery today that one of my remanned 330hp engines has been bored .060. I calculated that as being close to 468ci. This is a twin engine application, so I have concerns on balance of hp production. Will be mounting the other engine on the stand in a couple minutes and will see if it too has been bored. I would be suprised if it has been, but it would be nice.

That being said.. 2 questions:

1.) How much hp difference will there be between these two engines with equal components. As a straight percentage, this is 3.1% more displacement. If the engines were 400hp as 454s, this 3.1% would make the 468ci engine 412hp. Sound right?

2.) Will this difference be noticable in the boat?

BT

What kind of boat is this in?? I really don't think you will ever notice even 12 hp in a twin engine application, even if you were getting that extra hp. Simply changing the displacement doesn't necessarily add hp as you have figured it (using your 3.1% increase in displacement). If you can't use that extra displacement by changing other components (pistons, headwork, etc...) you will not see much of a hp increase. If it did, we'd all be boring out our blocks and adding pistons.

I disagree with that. Cubic inches has a direct correlation on horse power. Take this simple example, a 454 engine making 454 horsepower equals 1 hp per cubic inch of displacement. If all things were kept the same, a 468 cu.in. motor has to make 468 hp. If not, then what is the sense of stroking motors? Why don't we all run small blocks? The key here is "ALL THINGS BEING EQUAL"
Back to BTs' question---- I don't see how that slight amount of cubic inch difference will make a big difference. We have all seen identical motors make slightly different power on a dyno.

Thanks fellas. The boat is a 30' scarab. The other engine turns out to be .040 over, so the difference is now definately neglible.

I think Checkmate is on the money with the cubes question. Unless displacement is the bottleneck, it should be a direct correlation to hp. I also believe Waterfoul is on the money in that, that change alone without considering the system at large won't matter.

The real question is, is cid directly related to hp if all else remains relatively constant, and cid is not the bottleneck? I'm trying to figure out the linear quality of cid to hp.

BT

The other side of that coin:
If the cam and heads worked just right with 454 cubic inches, they may not work as well at 468. The 468 could even make less power. Lets put it this way, theres nothing you can do about it now so dont sweat it and enjoy the boat!

bluethunder,

With all components remaining the same, going from a 454 to a 468 you might see 1hp per added cubic inch---12-14hp. However, going from a 454 or 468 to a 502 things are going to start opening up! One of the major reasons is because a going from the 454/468's smaller bore size to the bore size of a 502 has a big effect on unshrouding the valves with the Big Block Chevy. That's why BORE NOTCHING is so beneficial to a 454 and can be to a 468 as well. The 502 bore size of 4.470" will not benefit as much from a bore notching job as a 454 which has a bore size of 4.250". Getting into the 502's larger bore size will already take care of the valve shrouding problem. My engines have a 4.500" bore and we only had to remove an extremely small amount of material for the bore notching that was done to my blocks because it's not near as critical as it is with a 454. Valve size has a lot to do with it too.

With the extremely small difference in power I wouldn't go to the expense of boring out one block just to match the other---I doubt you'll see it unless of course you just HAVE to do it that way. Tell you what, use the larger cubed engine that the power steering pump and pulley will be mounted to. With the little difference between the 454 and 468, mounting the power steering on the 468 will help balance the power and even the scales a little.

But if you can do yourself a cheap favor and do a bore notch job on each block---it's worth about 30hp!

Mark/KAAMA

If my math is correct, I have a 463cid and a 468 cid. Great idea with the power steering pump Kaama!

BT

I agree with an earlier comment. If a 454 makes 454 hp, then a 700 cu in motor with the same cam, heads, intake, exhaust, and carb will not make 700hp. The heads will have been maxed out way before the 700hp, as well as other components.

Let's say the 700 cu in motor only shows 600hp. NOW you have a second datum to plot a hp/cu.in. curve.

The curve won't be a straight line, but you can start with one and then throw a little curve to it that favors the low side.

Bottom line is, a 454 vs a 468, all other things being equal, won't show any appreciable difference on the tachometers. Relax.

Truth be known, last year the .040 engine was showing 100-200 more rpm over the .060 engine. May have been having a little carb problem though.

BT

Kaama,

Tell me more about notch boring...are there websites about this?

Thanks,

Kirk