What's the difference?

[Scalded Dog]

I'm just trying to understand some basics... how do our modern V6s and V8s create 50+ hp per cylinder, when just a few short years ago, we were getting sub- 20 hp out of each cylinder? Why do we have more "ooomhp" (see what I did there?!?) per cylinder? Is it simply larger bores, longer strokes, bigger injectors... or what?

[HeavyIOM]

Modern technology.

[Bhobbs]

More efficient intakes and exhausts, cylinder heads, cams and fuel injection.

[LOWDOWN]

In a word or two, "Volumetric Efficiency", predicated by electronics. Not only have engines become MUCH more powerful, but they've become cleaner AND return much better fuel economy.

40 years ago, a 500 hp engine in a 3,400 lb. car would be lucky to have given you double-digit mileage...

[DGthe3]

Originally Posted by Scalded Dog

I'm just trying to understand some basics... how do our modern V6s and V8s create 50+ hp per cylinder, when just a few short years ago, we were getting sub- 20 hp out of each cylinder? Why do we have more "ooomhp" (see what I did there?!?) per cylinder? Is it simply larger bores, longer strokes, bigger injectors... or what?

Making an engine larger (bigger bore/longer stroke) won't change the hp/l because it increases the displacement while increasing the power.

There are several things that have been happening that have led to increased specific output of naturally aspirated engines. One of the biggest things that has happened is they spin the engines faster

Horsepower = torque x rpm/5252

Lets say you've got an engine from the 90's making 300 hp at 5000 rpm, it'll be making 315 ft-lbs of torque at that speed. But a more modern engine (of the same displacement) that peaks later, 6500 rpm, but still makes the same torque will be make 390 hp. There is a lot that went into allowing that sort of thing to happen, its not just a matter of moving the redline up but that is the net result.

Anyways, engine speeds aren't the only thing at play. And simply spinning an engine faster isn't enough, other technologies need to come be used in order to make it viable. Technology such as variable valve timing. The problem with a conventional cam is that its most efficient in a single rpm band, above or below which it becomes less than ideal from a number of perspectives (fuel economy, emissions, idle quality, power & torque). VVT allows for intake and/or exhaust profiles to change depending on the engine speed. Engineers don't have to sacrifice high rpm power for low rpm emissions (and other problems) anymore.

Lastly, direct injection has been a big improvement. Instead of mixing the fuel with the air charge in the intake, the fuel is injected directly into the engine (hence the name). Among other benefits, this helps to cool the air charge better which in turn allows for higher compression. A higher compression engine converts fuel to power more efficiently. This can help economy (use less fuel for the same power) or it can help performance(use just as much fuel and get more power).

There are other things that have helped but thats where the bulk of the improvements have come from.

[Scalded Dog]

Thanks, all... that gives me some better understanding.