Varrying horsepowers on same sized engines?

Question

Why is it that two cars, both with 3.5 liter engines get incredibly different horsepower. The Chevy Impala LS and the Lexus IS 350 for example both have the 3.5 V6 engine (the Lexus is slightly less efficient with 3 less MPG highway).

Obviously the vechicles way different weights, but HP is based on engine output.

I figure it all comes down to engineering, (I assume the IS doesn't come with a stock turbo). Naturally Lexus spent more money engineering, so why wouldn't chevy just put up the cost to do the engineering, and save more in the long run by having equally powerful cars for less?
I can't imagine it costing that much more money to make changes in the engine, for GM to decide against it. Even the base Grand Prix has a 3.8 liter, 200 HP engine, which is embarrasing compared to lexus.

I'm and advid fan of American brand vechicles, I hope there's a decent reason

Answer 1

Chevy uses a pushrod motor or OHV (overhead valve).

Lexus uses a DOHC (double overhead cam) motor

DOCH is way more efficent than a pushrod motor, even if the same displacement.

Answer 2

Displacement is but one factor in how much power an engine produces. Cam profile has a major impact on power... and of course, keep in mind that HP is a measure of power over time, so the rev limit also can also have a major impact on peak power.
Also there are issues of how the engine is tuned both in terms of fuel injection as well as exhaust back pressure and other elements. Differences in engine components can allow for less power loss as well. And there is also the basic layout of the engine, from pushrod to ohc, and even from V to inline to boxers. This is just for naturally asperated engines. When you introduce forced induction into the equation, there are even more variables.

As for the why question... keep in mind that very few engines are simply designed from scratch. And in the cases where this is done, you are usually looking at a car with a $100k+ price tag. Most often existing engines are used, or at least the basic block with some new components. In these cases the engine may be the most appropriate for a planned design, but it's original design many years ago may have been aimed at a completely different use, which could mean it's power curve is very different. Differing power curves also could mean you have two extremely similar engines, with similar performance, but dissimilar power peaks.

Answer 3

It is because of the different stroke. A very short stroke= more horsepower but little torque. Longer stroke=more torque but less horsepower. For instance, a large diesel 7.3 liter v8 truck may only have 180 horsepower but it could literly pull a house because it has so much torque. But i'm sure your grand prix with only 20 more horsepower couldn't do the same. It's all about how the car is engineered and the different orientation of the cylinders.

Answer 4

From year to year the Japanese automakers will adopt and implement changes to their model lines very rapidly, even from such areas as the race car circuit.
The Big three in the states are slower off the mark when it comes to adopting new technology.
I too prefere to shop at home (American steel) but sometimes better technology makes for a good arguement to buy foriegn.

Answer 5

not uncommon. All in ignition timing, gas transport, valve tuning (Camshaft), intake and exhaust. diverse tuning brings diverse working dynamics and potential transport.