Old Engines are inefficicent at creating power/torque,WHY? 3

[mechanicat16]

Why do old engines produce such little power for their displacement, for example, the 1968 426(7.2L) hemi produced 425HP.The modern 6.1 L hemi produces about 425 HP, the same as the 7.2! Why is this?

 

[GregLocock]

That was about 6 months of the average wage in 57, say $20000 today

http://www.socialsecurity.gov/OACT/COLA/AWIgrowth.html

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[izzmus]

I always found it ODD that throughout the 60's, the engines were getting larger, the cylinder heads better, the camshafts hotter, the compression higher, but peak HP stayed right at 425hp.

One exception was the Chevy ZL-1, which allegedly did make an honest 435hp. Yet, remove the log exhaust manifolds and install headers, and it would jump to 550-575hp.

Or, how about all of the Quadrajets that had little tabs on them that prevented the secondaries from opening fully?

And then there all of those Japanese market cars that happen to make exactly 276hp, and the same engine in the US makes 300, 320hp.

 

[JayMaechtlen]

Improvements in specific power are surely due to the many factors mentioned above, such as materials and technology improvements. In addition, here in the US especially, gas was cheap. It is still cheap compared to much of the world.
So, why should I spend $$$$ on a little motor that makes lots of power, when I can spend only $ or $$ on a bigger motor that does the job? That bigger motor will probably be cheaper to fix, and may even live longer. The initial cost of that nifty 'efficient' motor may totally eat the savings in fuel down the road.
Economic/market competition has given us lots of great choices out there...
cheers
Jay

Jay Maechtlen

http://home.covad.net/~jmaechtlen/

 

[dicer]

Just curious. What better materials are used in the basic auto engine of today?
It seems pretty much the same stuff of the good old days.
The biggest improvement is induction and exhaust systems from and to the cylinder, accurate ignition, tight control of A/F etc.

 

[izzmus]

I can't think of any 60's engines that used molded plastic intake manifolds, with or without variable runner lengths.

 

[BrianPetersen]

Finite-element design techniques were either nonexistent or in their infancy back then, also. The materials in structural applications (crank, rods, pistons etc) might be the same or very close, but modern designs make better use of the capabilities of those materials.

 

[patprimmer]

Piston to bore clearances are a lot tighter now. I presume because of better shape and design re skirt flex, but also due to alloys and heat treatments that reduce expansion.

Surface coatings also aid in this tight clearance technology I think.

The relatively reduced cost of higher precision machining is a major area of improvement

Regards
Pat
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[JWaterstreet]

This discussion almost touched on one of the most important, often overlooked, considerations for "street power". You see enthusiasts, such as the "rice burner" crowd spending thousands of dollars to up the net horsepower of their tiny engines. Some of these engines make considerable HP at a particular high RPM, without most realizing that the narrow band of torque improvement results in no really practical way to harness, given the transmissions in use. (i.e. narrow band torque in a wide band transmission...)

 

[SomptingGuy]

That's more of a matching problem. Traditional auto boxes work best with lumbering agricultural low-revving engines. Stick them on a modern, efficient, high revving engine and you end up with an undriveable dog. Stick them on a slick, 6-speed manual and you have a driving machine.

- Steve

 

[LionelHutz]

WHY aren't we further along the curve? Because they limited themselves to a long stroke OHV pushrod port injected configuration. For a more modern layout, look at the 4.5 l V8 in the new 458 Italia. 570 hp naturally aspirated, 127 hp/l vs 70 for the hemi.

We aren't further along the curve because, in my opinion, manufacturers are more interested in meeting fuel economy numbers than having large peak power numbers.

Sure, Ferrari makes some impressive engines. But then I'd expect nothing less with the price their cars cost. However, looking at the numbers doesn't impress me a huge amount. That engine is just built to rev quite high to get the large HP numbers - HP is proportional to T x rpm. I have a few user modified Corvette's with "crappy old school" pushrod engines which would have fun playing with that Ferrari and those Corvettes didn't give up much drivability or fuel economy to get the big power numbers they have.

 

[Junior37c]

I'd like to point out that the displaced volume is a rather arbitrary means of comparing engines. Personally I thought outright mass or geometric size is a much more relevant comparison. Doesn't sell as well on the paper perhaps, but I for one am extremely impressed with the LS7's mass specific output, at roughly 480lbs, fully dressed with alternator, power steering pump, AC pump, etc, I think outputting 505hp is extremely impressive, and a much more relevant way to compare powerplants.

When picking a prime mover for a project, the power to mass ratio (watts/gram) is a much more relevant concern than the power/cylinder swept volume.

 

[GregLocock]

Agreed, on some other planet, that's the way we'd do it.



Cheers

Greg Locock


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[RossABQ]

I think an excellent example of this metric (power/mass) is one that totally shocked me; they are selling kits to put LSx engines in Porsche 911's! In the rear no less! The kicker? The LSx engines weigh LESS than the Porsche turbo engines!

YouTube has plenty of videos of these.

 

[Junior37c]

I've seen some of those engines ya. And yes society seems so caught up in the cylinder swept volume that they neglect the more basic metrics. There seems to be an assumption that an engine with a larger swept volume will be massier. Altho you take that little 4 cylinder box 4 turbo, and start laying turbochargers, intercoolers, block braces into it. The mass starts to rise very quickly, not to mention the fact that it's running 4 cams where the GM V8 is running 1. From a power to mass standpoint it's usually "cheaper" to just sweep more volume than it is to add more gizmos. Not to mention you generally get a very favourable power curve as a bonus.

Faye Taylor would be spinning in his grave if he could see the directions we've developed down in the last 10 years.

 

[NormPeterson]

Junior - engine displacement is at least a rough indicator of potential output. Whether a given engine design specifically targets up toward the "ultimate" potential or somewhere lower on the scale is an entirely separate question.

Mass specific output is fine for comparing engines "in a vacuum" (figuratively, of course). But output per unit engine mass indicates little about how any given engine will be perceived when in service.

Ignoring forced induction applications, specific torque (peak) doesn't vary a whole lot either way from a little over 70 ft-lb/liter. Meaning that a first-cut estimate of acceleration based on torque, gearing, and vehicle mass isn't going to yield comparative results all that different from what you'd get using engine displacement, gearing, and mass instead. Gearing can be dropped out if the vehicles being compared are reasonably similar in that respect.


Norm

 

[Tmoose]

2014 - FIA and NASCAR invite Mars to compete in the earthling Formula 1 and NASCAR series for the 2015 season. The three leading Martian constructors say sure, as long as they can use the 16 liter piston type engines they've developed for their equivalent auto racing series whose rules that stipulate a limit on engine power/engine mass.

 

[Junior37c]

Norm: I concur. BMEP and Piston speed is the fast and dirty way of calculating a rough estimate of power output. But even that method shows very clearly that a higher bore:stroke ratio is going to net you a higher amount of power with the same BMEP. Sadly there's a lot more to engine design than just peak power. I mean there's certainly a place in the enthusiast crowd for dyno queens, but general consumers also care about how it feels to drive, whether it gets good fuel mileage (which is generally in good proportion to the mass.)

10-14 bar BMEP is the rule of thumb I use. The 70ft*lbs gets tricky, I've dealt with 2-stroke motocross engines that when set-up properly make nearly 4 times that.

 

[ornerynorsk]

The 426 hemi was ADVERTISED at 425 hp for insurance/liability reasons. Ever had one on a dyno? My brother, who is the Mopar authority in the upper midwest, has seen a bone-stock hemi dyno at over 800 hp. This motor is insane!

 

[GregLocock]

absorption dyno or inertia?





Cheers

Greg Locock


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[RossABQ]

I've seen plenty of dyno runs on the MoPars with 426 hemi's back in the day, freshly broken in, none of them approached 2 HP/c.i. This kind of test was a monthly feature in Hot Rod, Car Craft, et al every month back then. ('69 - '72) They were "conservatively rated" but I've never heard of it being anywhere near 1/2 actual. 454 Chevies of the period were routinely reported in the mid-400's at the crank (stock, absorption dyno, corrected, etc.), hemi's were not that much better.

I'd be curious to see what a decent modern DIS system by itself would do to those dyno figures!