For those of you having knowledge and/or experience about engine design, a question:

Xterras have a 3.3L V-6 engine. My wife's Acura has a 3.2L V-6 engine. X = 180 HP, Acura = 225 HP in the base version and 260 ( ) in her Type-S. Obviously there's more at work here than engine size, so my question is what variables aside from engine displacement affect an engine's power output?

Air flow, head design, compression ratio, bore vs. stroke sizes, the weight/balace of the rotating assembly.....

The list is endless. Our engine is pretty gutless IMO. But comparing it to your wifes Acura, which probably has more engine parts made from aluminum and is meant to be revved to 7-8k and probably utilizes some sort of VTEC timing controller, is worthless. Her car's engine is so much more advanced than ours. We still ahve distributers, and a belt driven fan. I'm suprised there's no carburator under the hood lol.

Horsepower isn't the whole story. You have to examine the whole power range between engines.

The X 3.3 is definately gutless when compared to the acura, however the X weighs more and the Torque curve starts at a much lower RPM and is exactly what you have to have for off road and or towing, etc.

Everyone has an opinion on what to do to gain 5-10 HP, but there are few proven examples I.e. Dyno specs, so save your money and do things as you need to. You're lucky in my opinion that you can modify things without concern for warranty.

On my Gen2 I intend on replacing the belt driven fan with a variable speed electric, adding Headers and dual exhaust, but not until it is out of warranty in 2010. That is if I can still buy Gas!

I read a great article a few years ago in Car and Driver about science behind horse power in small engines. Torque and Horsepower are proportionate for a given displacement. A truck engine and car of engine of the same displacement may have vastly different horsepower ratings because as horsepower goes up torque goes down. A high revving Honda engine has very short strokes with high HP but less torque, hence having to rev the hell out of it to take off while an Xterra you could let the clutch out and never touch the gas. Semi trucks are another good example. 12 to 14 liter engines with long strokes and slow RPMS with thousands of pounds of torque to pull 80,000 to 100,000 pounds but has less horsepower than your average Mustang GT. But all that goes out the window when you throw in superchargers and turbos.

A big factor is the fact that first gen V6 X's have Single Overhead Cams (SOHC) as opposed to dual overhead cams (DOHC). I can almost guarantee that your wife's Acura has dual overhead cams, therefore most likely 4-5 valves per cyliner. An engine's efficiency at taking in fresh air/fuel and disposing of exhaust gases is greatly influenced by valve design, and the V6 Xterra has only two valves per cyliner.

Thanks for the insights, that's what I was curious about.

Throw a 5000# trailer on the back of them and do a comparison...

Cam design has a lot to do with this. Back in the day when engines were shared between product lines a motor may have powered a tractor and a car. The only real difference between them would have been the intake, exhaust, and cam.