Swapping long stroke for short stroke and bigger bore

[Grp5L]

Below is what Dynomation made of it. The two engines are plotted on there, as you can see they are so close it's difficult to tell them apart.

[In-Tech]

Some years ago, with an A class offshore race boat to which the rules were 1 1050 carb, roller cam, Iron fully ported heads, 510" max inches.
Engine A was short stroke combo 3.750 x 4.625 with a rpm area of 76-7800. The boat was not a lightweight and was a consistent back of the pack finisher. It would haul ass down the straights , but die a miserable death in the corners.

Engine B was built with the same 510" rules, but long stroke, 4.5 and small bore, 4.250, roller cam, ported iron heads that started life as oval and were turned into small rectangular port heads, 1050 carb, and rpm range was 68-7000

Boat would now handle the corners, they did not have to trim the drive to keep rpm up, it would just walk around the corners and accelerate down the straight. It required an entirely different drive,)ie skeg depth for example) prop set up (bigger), and was flat lining at the top of the straight, but it became a mid/upper pack finisher.
They both made about the same power, but the rpm range was different and the torque of the long stroke engine gave it some ass to get around the corners.

You are talking about two different boats now, so original boat couldn't get around the corner not due to power but because it couldn't keep the corner speed=bad boat IMO.
I've been around plenty of boat stuff from drag hydros to offshore to ski race. The ski race guys always wanted more power so I got involved. Original combo was ~1250hp on death row(EGT 1650+). When I was finished we were at 1540hp and EGT's were stable in the mid 1400's. We built 5 of those. The boats picked up an average of 20mph but when we went racing, the skiers fell off at the same speed. They race for an hour so if you "fix" the bottom of the hull so your skier could go 1 mph faster, that's a friggin mile. Fix your boats, I'm done,
Not trying to be a jerk here, just saying that is not an apples to apples comparison.

[kimosabi]

Trend today modern engines is undersquare. Why?

Because it suits the way the majority of us drive in everyday life.

So how come the Barra straight six performance engines are undersquare.

[Grp5L]

Trend today modern engines is undersquare. Why?

Because it suits the way the majority of us drive in everyday life.

So how come the Barra straight six performance engines are undersquare.

The clue is in the title of it: "Performance engine". Most people worldwide don't drive performance engines in their daily lives. My parents, the guy next door, my work mate, they just want to get to the shops and they want to do it over and over again at no more than 4krpm. They don't care how lively an engine feels.
BMW build performance engines, they are square.
It's not really answering the original question though....

[gruntguru]

Trend today modern engines is undersquare. Why?

Compact combustion chamber allows higher compression, better fuel efficiency, lower emissions.

[digger]

You also don't need much valve area if you can simply turn up the boost

[gruntguru]

Modern engines are mostly 4-valve, so engine design can be more undersquare and still breathe OK. The valve area required is dictated by displacement and rpm. Adding boost just increases the air density passing through the valves - the power curve will look the same, just higher.

[kimosabi]

I'm asking the questions because I want to try to make a point. The big bore/short stroke = more power theory is IMO only related to inefficient head design. Everything else can be remedied be it balance, bob weight, ring pack/drag, windage etc etc. All the naughty trade offs that comes with a long arm.

Enter the Mercury SB4. Yes still oversquare but talking the normal small block v8 config it would be a "stroker" right? 4.125 bore/4" stroke. Still, it's a 750hp @ 8000rpm pump gas engine.

[Belgian1979]

Why would you be able to ever make a fair comparison. Each engine requires specific components, camshafts etc to make the most of a combo will change dramatically.

[digger]

I'm asking the questions because I want to try to make a point. The big bore/short stroke = more power theory is IMO only related to inefficient head design. Everything else can be remedied be it balance, bob weight, ring pack/drag, windage etc etc. All the naughty trade offs that comes with a long arm.

Enter the Mercury SB4. Yes still oversquare but talking the normal small block v8 config it would be a "stroker" right? 4.125 bore/4" stroke. Still, it's a 750hp @ 8000rpm pump gas engine.

You aren't going to get the long stroke to better the short stroke friction if you put the same effort into both

[kimosabi]

Why would you be able to ever make a fair comparison. Each engine requires specific components, camshafts etc to make the most of a combo will change dramatically.

Definitely agree.

[pdq67]

I like to look back at the little Studebaker V-8 engines B & S combinations. And if not mistaken, they are long rod engines. Their 224, 232, 259, 289, and 304 engines... All little buggers that run like the wind...

And personally, I liked my old junk301 way better than I liked my Strong Arm 406!! It's an rpm deal to me is all. I'd rather bounce the tach needle off the peg than go for grunt Way more fun to rpm it.

pdq67