Most Power Per Cube???

Discussion in 'OT Driven' started by Ronin, Mar 29, 2005.

  1. Ronin

    Ronin Guest

    The other week me and my brother were debating over engines and my lack of knowledge didnt get me very far, as far as most power per cubic inch, is the HEMI design the most power efficient? I really have no idea on this subject.
     
  2. Cue-Ball

    Cue-Ball I hate you, Milkman Dan

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    No. Turbocharging is probably the most efficient way to make power. If you're talking n/a only, then hemispherical heads don't make as much difference as a good intake and exhaust system, well designed runners, valve size, etc, etc, etc. Keep in mind that because of the way hemispherical heads are designed, you're generally stuck with 2 valves per cylinder and OHV only. I'm fairly certain that an OHC, 4-valve engine is going to give you the most power per cubic inch, but that power will come at high revs. 2-valve engines don't make as much power, but have more torque and more power available down low, in general.
     
  3. Ronin

    Ronin Guest

    yeah I told my bro that HEMIs were valve disadvantaged that they can only have 2 valves, but then he started BS'ing and I just gave up.


    Advantages of 4 valves:

    The valves can have more total area so can flow more gas when fully open.

    Several small valves have a larger seat area than one big one! This means greater flow at times when the valve is only slightly opened.

    Each valve is lighter, so can be opened faster and closed faster, resulting in more flow.

    Extra seat "length" means better heat transfer so narrower seats can be used giving better low lift flow.

    credit: http://www.tuning.wanadoo.co.uk/valves-inlet-exhaust-head.htm


    Cant really find any good fair cross comparisons between HEMI and high tech 4-valve engines etc.
     
  4. Buick Muscle

    Buick Muscle Guest

    WRONG.

    4 Valve, Double overhead cam, while probably giving you more power per cubic inch, isn't neccesarily the most efficient way to make power.

    Increasing Displacement is the most easiest, efficient way to increase power and torque across a powerband. Thats why the newest ZO6 motor is a Overhead Valve design.

    A Viper engine is 2 Valve, and is dreadfully responsive.
     
  5. Ronin

    Ronin Guest

    we arent talking about the best ways to make power, we are talking about what design makes the best power:displacement ratio.
     
  6. matrix243

    matrix243 Earn this. Earn it.

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    mmm, another ohc vs ohv debate. here come the ls owners.
     
  7. Demon Of Dreams

    Demon Of Dreams Feed me with lies and hate, and from that, I will

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    smallblock chevy + 32valve heads = win
     
  8. MAD PUNK inDC

    MAD PUNK inDC Sic Semper Tyrannis

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    What people forget to calculate in when debating OHC vs OHV, is the wiegh of the engine. OHC engines are much heavier than OHV, and thus loose some of thier advantage just by default of having to overcome that. There are other things that OHC engine suffer from as well as OHV, but if you look at the most powerful, and fastest cars, from the SCTA, to the NHRA, and even the fastest street car record holders all of them are OHV.
     
  9. ices

    ices New Member

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    by power do you mean torque or horsepower?

    if you're talking about the latter, then i think the s2000 (dohc) is one of, if not, the most efficient stock engines.
     
  10. matrix243

    matrix243 Earn this. Earn it.

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    the cost of developing high output OHC engines is what governs wide use, not their ability to produce big power.
     
  11. matrix243

    matrix243 Earn this. Earn it.

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    both. displacement and dimensions effect power/torque output.
    *in most cases*
     
  12. Cue-Ball

    Cue-Ball I hate you, Milkman Dan

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    The OP asked about how to make the most power per cubic inch. We don't need another debate about the merits of OHC vs. OHV. We don't need to debate weight, complexity, manufacturing costs, ease of repair, etc. The question is simple: What type of engine gives the most power per cubic inch.

    If you discount forced induction, and you look at horsepower per cube, i think you'd find that OHC is better than OHV. That's doesn't mean that it's a better engine design in every aspect, but just that it can produce more maximum horsepower for a given displacement.

    1.3L rotary Mazda RX-8; 238 hp; 183hp/liter
    2.0L OHC Honda S2000; 240hp; 120hp/liter
    7.0L OHV Chevrolet Corvette Z06; 500hp; 71hp/liter

    These are just examples of stock cars. Obviously, you can get more through tuning and aftermarket parts, but those are pretty damn wide margins. I think this gives a good idea of how the different engine types would be ranked. Nobody in their right mind would take the RX-8 over the Z06 for outright power, but the RX-8 still makes more power per liter/cube, and that's what the question was about.

    Saying "NHRA cars are OHV and they're the fastest!" is just retarded. Every sanctioning body has rules and regulations about what can and cannot be done. Of course a nitromethane fueled, 500+ cubic inch, supercharged car is going to be faster than a 1.6L n/a pump gas Corolla. That's not exactly a level playing field and doesn't say anything about engine design. You have to compare apples to apples and consider what those racers would be doing if they had no rule book to follow.
     
  13. ices

    ices New Member

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    yeah, but in the case of the s2000 (as well as most small displacement engines), they have rediculously high horsepower output numbers but lowwwwww low low torque numbers.

    in any case, i'd say that DOHC+forced induction would yield the most power. they have an inherently higher number of valves, which have a higher combined circumference, which allows for a better flow when the valves are only slightly opened. also, dedicated cams for the intake and exhaust valves allow for more efficient and effective tuning
     
  14. Cue-Ball

    Cue-Ball I hate you, Milkman Dan

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    Only if you discount the rotary and other non-automotive engine types. The Shelby GT-500 only makes 450hp from 5.4L supercharged DOHC. That's just over 80hp/liter. Cars like the Mitsu Evo and SRT-4 make about 300hp out of 2.0L turbo DOHC (~150hp/liter). Better than the Mustang, but still not even close to the n/a rotary. So, it all depends on who's making the car and how stock you wanna leave it. I'd still take the GT-500 or the Z06 over the RX-8 though. ;)

    What's the highest hp/liter, pump gas car that anyone here can come up with? Forced induction or naturally aspirated?

    There was a guy on AutoWeek making over 1000hp on a 2.0L three rotor Mazda. Don't know if that was pump gas or not, but that's 500hp/liter!
     
  15. matrix243

    matrix243 Earn this. Earn it.

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    And in alot of cases your sacrificing torque for horsepower by increasing bore and shortening the stroke, hence F1 engines. The heavier the vehicle, the more torque is demanded.
     
  16. ices

    ices New Member

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    haha, true, but rotaries are notorious for their lack of low end torque (because of their small displacement) which is also true for the s2000, but i guess that's why i don't really consider it a "powerful" motor.

    however, "power" has a lot to do with the powerband and torque curve, and when you get the power, which is why s2000's and rx8's (although they put out good HP numbers), aren't made for the drag strip

    but, *for the most part*, i still think that DOHC+turbo is the best. the flow of DOHC plus the torque and efficiency of turbocharging is your best bet.

    i'd also like to entertain the idea of turbo diesels. while their horsepower numbers are relatively low, their torque numbers are impressive

    STI, 300tq/2.5ltr=120tq/ltr
    Volkswagen Passat TDi, 247tq/2ltr=123.5tq/ltr

    the 5.9 liter I6 turbo diesel in the ram 2500 makes 610 tq, which although is not as efficient as the passat, is still damn impressive. most gasoline engines would be hardpressed to make numbers like that

    also, i heard that it's easy to get big gains from diesel engines, using only basic mods like bolts-ons, and a chip
     
    Last edited: Mar 31, 2005

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