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Views: 4,198  ·  Replies: 19 
> displacement VS efficiency, SOHC VS DOHC
s12drifter
  Posted: Mar 14 2013, 07:27 AM


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I'm kinda curious to hear what everyone's views on this are.

At what point does a efficient engine overpower a displacement engine?

Lets take this as an example a RB20DET vs a L31ET clearly the L31ET has more displacement but the RB20 has a more efficient combustion chamber, better head flow, and with that a limit in where it can make power and torque (because of it's size) vs a L31ET while having more displacement and toque it's limits are in the head simply because it cannot flow any more air then what the turbo and head/port design allow it to.

so with that at what point does efficiency over power or overcome displacement?

of course displacement+flow=win but say you don't have a option for that?

no replacement for displacement, correct? Well, what if you have displacement but not a so well flowing head?

MetalMan777
Posted: Mar 14 2013, 08:23 AM


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The only thing that matters to horsepower output is total combustion less total friction with a time relation. Assuming we stick with pistons, anyway. Other heat engines may not correlate. How much air your engine can breathe (and how effectively carbureted) is probably the biggest factor in the above equation.

What are you trying to accomplish? Formula 1 engines suck enough air to generate 700-800 horsepower, with very little displacement. Semi trucks make half that power with 4, 5 or more times the displacement.

The old adage: No replacement for displacement has never been true. Even back in the early days of the hot rod, the benefits of forced induction and increased aspiration were common knowledge.

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Tygur
Posted: Mar 14 2013, 09:33 AM


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^ Pretty much ^

The more air you get, the more fuel you can utilize, the more power you can create.

The fuel has to burn at a certain ratio to air (14:1 ish) Say for the sake of argument you have, of the same type of construction architecture, some 6.0L V8 NA @6000RPM, you are moving a lot of air. Then you have a 3.0L V6 Turbo @6000 RPM, which forces the equivalent amount of air in. You can make relatively the same amount of power. But the V6 has less surface area for friction, less inertia to overcome, so it can use more of that power by getting it to the wheels and not 'bleeding it off' through heat/friction. Theres a lot more to it than that, just oversimplifying a bit as an example. Of course, the NA would be taking in that ratio of air at all RPMs, and the turbo would have to spool, the V6 may be able to reach higher RPM, etc. The atomization and burn wave would be a bit different because one is sucking in and the other is pushing it in, but you get the idea. What do you think of that analysis? Wrong? Plausible? I'm not all that great at the physics/chemistry behind it all but thats how it has always come across in my head.
backalleyracer
Posted: Mar 14 2013, 09:34 AM


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putting a new head on a "L31" is still an L31

Nomake Wan
Posted: Mar 14 2013, 09:38 AM


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If there was no replacement for displacement, my 4.1L inline-six engine would be a mega beast compared to those puny little 2.8L Japanese whatchamacallits, or hell even the 3.6L V6 in our work truck!

Except... it's not. derp.gif
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Tygur
Posted: Mar 14 2013, 09:59 AM


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Also take into account that Horsepower = (RPM * Torque) / 5252. You basically get horsepower calculated out of how much torque the engine produces at certain RPM. The more rpm, the more it multiplies the HP. Generally smaller engines take advantage of tech that lets it rev higher, so that it makes less torque from displacement but creates enough horsepower through RPM. (see: several Hondas and F1 etc)

This post has been edited by Tygur on Mar 14 2013, 10:00 AM
Spaz
Posted: Mar 14 2013, 10:20 AM


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1987 is the point when the efficient engine took over. Sorry, had to get that dig in first.

There is NO replacement for displacement, period. You'll always get those who claim turbo-4s are better than V8s, etc, etc... But in the end if you put an equal CFM per liter forced induction unit on a high displacement motor, what happens? Bigger gains.

Higher displacement will always display more desireable power production traits no matter what kind of setup you're running.
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Tygur
Posted: Mar 14 2013, 10:38 AM


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Right, but I think what people were getting at is NA displacement vs small forced-induction. In which case it simply becomes "can the forced induction push as much air as the larger engine is doing normally" which most times, it can. If you put equal forced induction on both, displacement wins hands down, all other tech being equal because it can simply get more air. /rant

Sorry, I'll go sleep now lol
Rudy
Posted: Mar 14 2013, 12:33 PM


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MetalMan777
Posted: Mar 14 2013, 01:11 PM


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QUOTE (Dorifuta @ 38 minutes, 30 seconds ago)
So head flow does matter hugely.

Nothing matters more than the cylinder head.
s12drifter
  Posted: Mar 14 2013, 01:44 PM


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QUOTE (Cactus @ 32 minutes, 17 seconds ago)
Nothing matters more than the cylinder head.

this is what im getting at right here...

example BMW 1.5 liter 5 valve per cylinder F1 engine in qualifying trim pumps out OVER 1,500hp, i understand it's a race engine but it's the 1.5 liter.

this is more then some V8's wish they could make.

of course if you have a high flowing cylinder head with a big displacement you will see a increase with less effort.

SOHC vs DOHC

i was using the L31 VS RB20det as a example;

they are both boosted
they are both inline 6 (they also share the same firing order and main number)

however one is sohc with a old 60's design and one is a more modern design BUT they both have limits, the L28 can only make sure much power because of cylinder head restriction and the RB20 can make over 1,000hp BUT is limited because of it's small displacement. (although the RB25 head is better then a rb20 head)
Nomake Wan
Posted: Mar 14 2013, 03:22 PM


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QUOTE (Spaz @ 5 hours, 1 minutes ago)
Higher displacement will always display more desireable power production traits no matter what kind of setup you're running.

Oh this is priceless. Once I swap a 302 into the Maverick, I will give you the original 4.1L engine for free. Please, just turn it into something that puts out crazy power. Note that the 2.8L turbo Datsun engine I have in storage is good for between 300 and 400 HP and I so far have put... 1.5k into it including the engine itself? It'll cost a bit more than that to finish it (not to mention buying another Z shell) but point is, not a whole lot of cash, something you should know quite well considering how many digits have gone into that Evo. wink2.gif

So yeah, man! 4.1L Ford Inline-Six! It's 4.1L! Huge displacement! Should be easy to make desireable power production traits right!? awesome.gif
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chillined
Posted: Mar 14 2013, 06:21 PM


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QUOTE (Nomake Wan @ 2 hours, 59 minutes ago)
Oh this is priceless. Once I swap a 302 into the Maverick, I will give you the original 4.1L engine for free. Please, just turn it into something that puts out crazy power. Note that the 2.8L turbo Datsun engine I have in storage is good for between 300 and 400 HP and I so far have put... 1.5k into it including the engine itself? It'll cost a bit more than that to finish it (not to mention buying another Z shell) but point is, not a whole lot of cash, something you should know quite well considering how many digits have gone into that Evo. wink2.gif

So yeah, man! 4.1L Ford Inline-Six! It's 4.1L! Huge displacement! Should be easy to make desireable power production traits right!? awesome.gif

facepalm.gif
Note that he didn't name off any examples, because every head flows differently. He means that if the head parameters are the same, a bigger engine will always display more desireable power production traits no matter what kind of setup you're running.

And we get it, your 4.1 blows. cool.gif
Spaz
Posted: Mar 14 2013, 06:35 PM


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QUOTE (Nomake Wan @ 3 hours, 10 minutes ago)
Oh this is priceless. Once I swap a 302 into the Maverick, I will give you the original 4.1L engine for free. Please, just turn it into something that puts out crazy power. Note that the 2.8L turbo Datsun engine I have in storage is good for between 300 and 400 HP and I so far have put... 1.5k into it including the engine itself? It'll cost a bit more than that to finish it (not to mention buying another Z shell) but point is, not a whole lot of cash, something you should know quite well considering how many digits have gone into that Evo. wink2.gif

So yeah, man! 4.1L Ford Inline-Six! It's 4.1L! Huge displacement! Should be easy to make desireable power production traits right!? awesome.gif

* <------ The point.







* <------ You.

I guess I should have worded my last sentence better, but considering I was on about power adders vs displacement, was it really that great a stretch of logic to assume that I was talking turbo/supercharger/nitrous/meth as opposed to herp derp I can make power with a pushrod motor and an economy cam?

This post has been edited by Spaz on Mar 15 2013, 08:56 PM
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Soran
Posted: Mar 15 2013, 05:32 AM


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My Jetta does 160hp stock and 190hp with a light tune.

For a puny 1.4 liter engine i'm not complaining since i pay less road tax
chillined
Posted: Mar 15 2013, 12:17 PM


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That's actually pretty awesome. I wonder how much power you can get out of the new Dodge Dart turbo.
Tygur
Posted: Mar 15 2013, 01:34 PM


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Agreed, thats a lot for a 1.4, also lately some of the Ford EcoBoost engines are up there as far as HP/Litre. They did a good job of that, and direct injection really shines on boosted applications.

Actually it works even better for larger displacement engines that don't rev as high. Direct injection doesn't get as much time to mix with air, so it has a hard time atomizing at high RPM without lots of tech or special design. But it keeps things a lot cooler in the combustion chamber which allows higher boost levels.
s12drifter
  Posted: Mar 15 2013, 02:36 PM


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QUOTE (Soran @ 9 hours, 4 minutes ago)
My Jetta does 160hp stock and 190hp with a light tune.

For a puny 1.4 liter engine i'm not complaining since i pay less road tax

that is more the a stock VG30E and VG30ET

proving displacement doesnt mean shit.

Soran
Posted: Mar 15 2013, 03:59 PM


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I bought the Jetta twincharged model because of the power you get from such a small engine (In Singapore, road tax is calculated by engine displacement).

Also, Singapore being such an urban city i prefer having decent low-end torque, which at 250nm of it kicking in at 1500-2000rpm i'm not complaining

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Tygur
Posted: Mar 15 2013, 05:00 PM


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QUOTE (s12drifter @ 2 hours, 23 minutes ago)
that is more the a stock VG30E and VG30ET

proving displacement doesnt mean shit.

I guarantee that if you had a larger engine using the same tech you would make much more power. And larger displacement generally has more torque and doesn't need to rev to the moon. Of course if you pour tech into a 1.0L you can do some wild stuff, but those gains are exponential when adding displacement. If displacement meant nothing, nobody would bore/stroke their engines.