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Unread 10-25-2011, 03:36 AM   #1
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Why such low power output from large American engines?

Not 100% sure if this is the right place for this, but here we go:

Why do so many American-built engines have such low power output for their size?

Before I go on, I should clarify that I'm not trying to be inflammatory or to bash American engines. I'm coming at this from the viewpoint of a Brit who considers anything above a 3.0L to be a large engine; I have two Jeeps, a 3.7L KJ and a 4.0L ZJ, and I'm genuinely puzzled as to why both of them have such low power output.

In an edition of the UK TV show Top Gear which had a feature on older American cars, the presenter Jeremy Clarkson said "How do Americans manage to get so little power out of such large engines?", and I do think he's got a point!

Taking the 4.0L first, I was actually shocked when I looked up the stats and saw that it only produced 190 hp when it first rolled off the line. I used to own a BMW with a 2.5L I6 that produced 175 hp and was also silky-smooth and delivered better fuel economy.

Now sure, you expect Jeep engines to be less smooth than a sedan and if you're worried about fuel economy then you just don't buy a Jeep period, but still - a 4.0L I6 that only produces 190 hp? From a British perspective, I'd expect an engine of that size to be outputting 250 hp upwards. Ditto the 3.7L in the KJ.

Are there historical engineering reasons behind the large displacement/low power output trend in American engine-building?

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Unread 10-25-2011, 03:41 AM   #2
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You forget that the 4.0l I6s goal is not to produce power, but rather lot's of low end torque, something those similar BMW engines do not. Even TVR's Straight 6 (also a 4.0) doesn't produce as much torque at as low of an RPM as the AMC/Chrysler 6. Granted at higher revs the TVR 6 produces numbers at the 400bh range, but that doesn't help you when offroad. Just some food for thought.
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Unread 10-25-2011, 04:14 AM   #3
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OK, I can how that makes sense for offroading, but when you compare American engines in offroad vehicles with European/Japanese ones, the American engines still seem to produce less power for any given displacement, and I wouldn't say that American offroad vehicles are notably more capable than those from European or Japanese manufacturers.

That's why I wonder if there's some kind of historical reasoning still at play behind the engineering of American motors.
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Unread 10-25-2011, 04:21 AM   #4
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I'm betting that emissions/the EPA play a big part. CAFE is another factor also.
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Unread 10-25-2011, 07:23 AM   #5
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In older American engine designs, the big displacement and low power was done because it led to a very flat power curve. Look at the shape of the BMW I6 power curve compared to the Jeep I6 power curve, and there's a huge difference.
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Unread 10-25-2011, 07:26 AM   #6
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ive been looking at wrx sti's recently, ive found some that have more whp than my moms camaro has at the flywheel by a lot too
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Unread 10-25-2011, 07:32 AM   #7
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A lot of the emissions nonsense required on vehicles does greatly limit their performance numbers and especially in the 70s during the gas crisis the performance went down almost yearly sometimes. Compare the numbers for the AMC V8s from the early 70s to the late 70s and you'll see what I mean. For instance the 304 in my CJ7 came factory rated for 125 HP @ 3200 and 220 FT-LB @ 2400. Talk about some low numbers! However once I'm done and have the emissions garbage off, a better intake, a better carb, and a far less restrictive exhaust I expect that HP number to be much more reasonable.
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Unread 10-25-2011, 07:40 AM   #8
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Originally Posted by relgnarw View Post
I'm betting that emissions/the EPA play a big part.
Surely if that was the case, the trend in the USA would have been towards much smaller, more fuel-efficient engines for the last 30 years or so?

I suspect that comptiger5000's point about the flat power curve probably has a lot to do with the historical basis, coupled with a perceived lack of need to make engines more efficient and get more power out of smaller displacements. The impression we get over here is that the US motor industry has somewhat had its head in the sand for decades, thinking that gas was always going to be plentiful and cheap and so fuel economy wasn't a major issue for consumers, and it's only now waking up to the painful reality that fuel efficiency really does matter.

@MightyLampshade - I can't really agree about the "emissions nonsense" for two reasons. One, I think curbing vehicle emissions as much as possible is important (which does sit rather uneasily with the fact that I own two gas-guzzlers), and two, European and Japanese manufacturers have to contend with very heavy emissions regulation too, but they still achieve generally higher power output than comparably-sized American engines.

To be brutally honest, I imagine that the much greater historical importance placed on efficiency and fuel economy by European and Japanese manufacturers probably has a lot to with the comparative differences.
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Unread 10-25-2011, 11:25 AM   #9
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also alot of the european and japanese motors are turboed from the factory. there aint many american gas motors that are turboed or supercharged from the factory. any forced induction is gonna play a big part in power. like one person mention a wrx sti with more wheel hp than a camaro. pull the turbo off and make it just a regular wrx and the camaro has gods more power. the euro and jap cars on just all motor dont really start making more power than american until they get to big motors like a lambo or ferrari. but they have the price tag to go with them also.
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Unread 10-25-2011, 01:07 PM   #10
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also alot of the european and japanese motors are turboed from the factory
Some are, most aren't. The vast majority of European and Japanese cars are normally-aspirated. Turbochargers and superchargers are typically only used on engines intended for luxury or prestige high-performance sedans, and only rarely for offroaders/SUVs.
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Unread 10-25-2011, 01:11 PM   #11
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Originally Posted by AVR2 View Post
Some are, most aren't. The vast majority of European and Japanese cars are normally-aspirated. Turbochargers and superchargers are typically only used on engines intended for luxury or prestige high-performance sedans, and only rarely for offroaders/SUVs.
Obviously most offroaders don't use force induction. I was talking in general of all apps. And I aint saying all all motor foreign cars don't make power. But they do usually lack in torque. My zx10 made 172 on the dyno but only 81ft lbs. And it made peak power at like 10,500 rpms. Kinda useless for offroad.
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Unread 10-25-2011, 01:53 PM   #12
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A lot of it has to do with the archaic design of the 4.0. The basic design has been around for a long time and has been relatively unimproved, and this was/is true for a lot of engine designs including the Mopar v8 magnums, older Chevy (pre-LS) motors, and old Ford push-rod v8's. Compare current US vehicle engine outputs to those made overseas and you will see they are much more comparable.
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Unread 10-25-2011, 02:13 PM   #13
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Quote:
Originally Posted by AVR2 View Post
Not 100% sure if this is the right place for this, but here we go:

Why do so many American-built engines have such low power output for their size?

Before I go on, I should clarify that I'm not trying to be inflammatory or to bash American engines. I'm coming at this from the viewpoint of a Brit who considers anything above a 3.0L to be a large engine; I have two Jeeps, a 3.7L KJ and a 4.0L ZJ, and I'm genuinely puzzled as to why both of them have such low power output.

In an edition of the UK TV show Top Gear which had a feature on older American cars, the presenter Jeremy Clarkson said "How do Americans manage to get so little power out of such large engines?", and I do think he's got a point!

Taking the 4.0L first, I was actually shocked when I looked up the stats and saw that it only produced 190 hp when it first rolled off the line. I used to own a BMW with a 2.5L I6 that produced 175 hp and was also silky-smooth and delivered better fuel economy.Now sure, you expect Jeep engines to be less smooth than a sedan and if you're worried about fuel economy then you just don't buy a Jeep period, but still - a 4.0L I6 that only produces 190 hp? From a British perspective, I'd expect an engine of that size to be outputting 250 hp upwards. Ditto the 3.7L in the KJ.

Are there historical engineering reasons behind the large displacement/low power output trend in American engine-building?

This isn't the case with many of today "American" made cars. I have Cobalt with a 2.2 4cyl. that has about 150 hp and up to 35 mpg, this is a relatively inexpensive care. There is a turbo version with a 2.0 4 cyl. with 260 hp. Ford focus has decent power for a small motor also has gets good mileage and still a lower priced car. The new Chevy Malibu has a small 4 cyl. motor that claims to have 169 hp and I am sure it gets decent mileage. Ford probably has something similar and I would bet Chrysler does too.
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Unread 10-25-2011, 02:24 PM   #14
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does it matter? yes america has been living off it's own for some time . then when americans started to buy imports , because they were better , the industry started to wake up . so will we see more power for less? you bet!!! it all takes time . why would a manufacturer retool to do better if the sheep were still buying his crap ?
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Unread 10-25-2011, 02:35 PM   #15
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Originally Posted by AVR2 View Post
...To be brutally honest, I imagine that the much greater historical importance placed on efficiency and fuel economy by European and Japanese manufacturers probably has a lot to with the comparative differences.
I don't think anyone's gotten the real reason yet: Punitive registration tax rates based on displacement in many european countries.
Europeans love big displacement motors - european governments make sure that they can't afford them.
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