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#31
03-17-2018, 01:52 PM
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Mustang: 435 horsepower @ 6500 rpm and 400 ft.-lb. of torque @ 4250 rpm Chevrolet Camaro SS (data from gmauthority.com): 426 hp (318 kW) @ 5900 rpm and 420 lb.-ft. ( @ 4600 rpm http://gmauthority.com/blog/gm/gm-engines/ls3/ 
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#32
03-19-2018, 10:35 AM
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I agree that high(er) specific output is neat as an exercise in engine design/engineering, and is a benefit when rules/regulations restrict displacement to a given maximum, but how is it better when the only limit to displacment is practicality? All the parts are operating under more stress than the larger displacement engine producing the same power. The smaller displacement Ford engine doesn't even return better fuel economy. Worse, in fact. GM's LS3 V8 is way more compact, 40 lbs lighter, far fewer moving parts, returns better fuel economy, operates under less stress, doesn't have to be revved so high, etc, etc. Where are the "drawbacks" with the GM design? Last edited by HodgdonExtreme; 03-19-2018 at 10:57 AM.
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#33
03-19-2018, 04:28 PM
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One thing that I don't understand is your reference to a stress comparison . How are you measuring this factor ?
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#34
03-19-2018, 05:18 PM
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#35
03-19-2018, 10:06 PM
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But also, any given power (actually torque, really) output at any given time corresponds to an amount of airflow. The smaller engine producing equal power has equal airflow. Equal air in a smaller place means higher pressure. In engine engineering land we call this "brake mean effective pressure". It's higher for the Ford, meaning it is being stressed more. Edit to add: In fairness, there are parts of the OHV arrangement in the GM V8 that are more highly stressed than the DOHC Ford... Namely the valves and the cam. The 2V OHV design mandates big heavy valves, requiring big strong valvesprings...and it's always better to have lighter valvetrain components. However, the GM LS V8 has a dynamite track record on valvetrain stuff, when you don't modify it and/or overspeed it. Last edited by HodgdonExtreme; 03-19-2018 at 10:14 PM.
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#36
03-19-2018, 10:09 PM
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...he'd have a point
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#37
03-20-2018, 07:26 AM
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The flathead will run on fuel that no modern engine will tolerate . Since you went the octane route , I will point out the octane rating is simply a measure to rate a fuel's resistance to improper burn. Efficiency negates the need for higher octane rating . According to an SAE paper written by a Shell chemist , the fuel that Shell supplied Honda for their F1 engines in the turbo era of the late 80'a had an octane ratine that would have come in at the high 50's or low 60's . Because the combustion chambers were so efficient , this highly tuned engine ran on a fuel mixture that would have likely destroyed any modern road engine . They were able to seek higher flame propagation speeds at the expense of knock suppression because of efficiency . How does this relate ? None of these engines are operating at peak output all of the time and the associated parts are designed to live within the stresses that they exist in . It is common knowledge that the weak link in a pushrod engine is the valve train . By eliminating the pushrods and rocker arms , long term reliability has been enhanced . If you want stress , look to the diesel , and they are known for their longevity . I just had to do a rebuild of my one Ford 400 top end . A burnt valve in number 6 and a broken exhaust valve spring in number 7 sealed the deal . I doubt that this engine has ever been to it's redline , yet something eventually broke and that took place in the valve train . The block , pistons , etc are just fine . The 4 valve per cylinder OHC layout is anything but new and is quite reliable . I have no doubt that a detuned version of the Ford engine would work just fine and be reliable . As far as practical application , torque is a far more usable number than HP . Since the Ford engine here uses a longer than typical stroke for a 302 engine , it's torque numbers should be better than it's counterparts that use a 3" stroke . Regardless of your loyalties , I find it good that some companies are willing to try different paths while some are staying with a 70 year old standard .
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#38
03-20-2018, 10:36 AM
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I have no brand loyalties with automobiles, but I do love to critically analyze engine/automotive design considering that has been the foundation of my education and experience.
There are always lots of ways to skin the cat, and it is REALLY fun to compare/contrast them with one another. Sometimes you can't objectively conclude which approach solves a given problem better than the other. Other times you can. For example, the Saturn V moon mission launch vehicle was clearly the better approach as compared to the Soviet N1 vehicle. When I consider the design problem Ford and GM are trying to solve with their two different approaches; a cost effective, durable, high performance engine for an enthusiast vehicle - The LS V8 appears to me, objectively, to be the simpler, more elegant and superior design approach. I might add the LSx debuted in 1997, and has a dynamite track record it can point to. Meanwhile the Ford OHC V8 debuted in 1991 and it wasn't until 2015 that Ford finally figured out how to extract some real power from it. But hey, at least the Ford 5.0L Coyote DOHC engine actually gets the job done... The N1 rocket didn't!
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#39
03-20-2018, 08:02 PM
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I believe that most of the automotive world would have differences with you about your superior claim . Elegant is not what I would call an objective word/term . Detune both engines to a basic passenger car level and there is reason to believe that the Ford engine will be more economical simply because of it's smaller displacement .
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