Yes per revolution but what's stopping the smaller cid from just turning more revolutions to make up the difference, to be able to displace the same amount of air, Cubic Feet per Minute?
Static and Dynamic Displacement and HP
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Yes per revolution but what's stopping the smaller cid from just turning more revolutions to make up the difference, to be able to displace the same amount of air, Cubic Feet per Minute?
In a sense yes cause turbos blowers nitrous etc. Is added displacement they force your engine to displace more and so does rpm. Question is what's does static cid add that rpm can't ?
Yes It don't change the physical dimension of your engine but how much air over time or cubic inches per minute or commonly measured cfm yor engine can displace. Which is what were ultimately talking about how much air/fuel you can displace and efficiently you can turn it into rotational power.
True are we talking small or large differences
Usually, but if the gain is mainly from increase VE% and or efficiency then can make more hp at similar rpm's
Goes back to money and know how. It's all relative though. What does one consider high rpm? What's the purpose? I told the boys at work that we turned my 360 to 7200 on the dyno and the jaws hit the floor. I wasn't sure what was happening at first then realized I was talking to a bunch of RV cammed 350 Chevy guys lol.
A 408 is 12% more cid than a 365 so a 365 would need to turn about 12% more rpm. Also which would be similar piston speeds for both, so even if you took both engines to max piston speed both engine would be able to displace the same amount of air (cfm).
Exactly. I'm not sure what the exact question is. If you want to make a 2 litre engine generate 800 hp its been done. Is it fun to drive to the grocery store? Will it last 100k? Is it cheap? WIll the rods go through the pan one day? These are all questions engine designers have dealt with. You need some requirements to determine which one of the infinitely variable combos will be best for you.
True, thanks for playing along
but the question is really for those that say displacement always makes more hp, if the true answer is it's combo dependent and with the parts we generally use favor larger displacement I could accept that, it's what I suspect what's going on if there's truth in larger engine built with similar parts generally win out. But if it's always 100% of the time and a smaller engine like 360 vs 408 gonna need eg. 20-30 more cam degrees and 50 cfm of head flow etc.. Still the question would be why.
If everything ELSE is equal and on a level playing field, yes, the bigger displacement will make more power. But that doesn't seem to be the rule book you want to use, so we need more specifics.True, thanks for playing along
Fair enough if that's true, but question would still be why there's not even a theory?
If you asked me why more displacement makes more torque I could answer in one sentence. Torque is force applied to the crank a bigger cylinder allows more fuel and air to be burned in the combustion process applying more pressure to the piston which in turns applies more force to be multiplied by the crank through the rod.
None for added displacement and hp? Just got to go on cause we say so.
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Rat Bastid
Dunamis Metron
Noooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo!!
I did NOT just read that and have a visual in my mind….
Noooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo!!!
Rat Bastid
Dunamis Metron
IF the RPM are the same. You can’t have both.
It’s almost 2023. The parts are cheap to make 8k nothing for RPM.
You can have all the displacement you want, and all the torque. If you don’t have RPM you have a TV.
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Yeah but I DON'T WANT 8K rpm I don't care if it's FREE! lol
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Finally, I get to say it;
Not everybody is a drag-racer.
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If you're a streeter, you gotta think about operating the throttle at less than WOT.
And just as importantly, you gotta marry that engine to a transmission and a reasonable cruise rpm.
Say with 3.23s and a 727auto, Top of Second gear is around 126mph@8% slip @8000, which IMO is kindof useless, for a streeter to have.
What I mean is, as soon as you install that lil screamer into an actual workload, the whole game changes.
if you marry the smaller engine to an A518, and cruise at the same rpm as 3.23s would get you ,say 65=2600 in loc-up, then you could run 3.23/.69=4.68s rounds to 4.56s. Now 8000 in Second gear, comes to around 89mph@8% slip, still, IMO, kindof useless, for a street machine.
What a streeter should really want, IMO, is an engine that can make adequate power at reasonable rpm, Yet also cruise at a reasonable rpm.
With 3.23s 65=2615 in loc-up; that is a reasonable cruiser gear.
But the starter gear is just 7.91, so whatever displacement engine you stick in there, it has to work with that 7.91 handicap. And that means it is gonna have to make some honest torque down there. Ok so sure, you can stall a smaller engine up and get to the torque, I get that. But
what if you have chosen a manual trans? Are you willing to forever after slip it to 20mph to get moving briskly enough?
I'm a dump-it-and-go kindof guy......
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and then there's trying to tune a small-cid/8000 rpm engine,
to go out on beer runs at 1:00 in the morning........ lol
Not everybody is a drag-racer.
--------------------------------
If you're a streeter, you gotta think about operating the throttle at less than WOT.
And just as importantly, you gotta marry that engine to a transmission and a reasonable cruise rpm.
Say with 3.23s and a 727auto, Top of Second gear is around 126mph@8% slip @8000, which IMO is kindof useless, for a streeter to have.
What I mean is, as soon as you install that lil screamer into an actual workload, the whole game changes.
if you marry the smaller engine to an A518, and cruise at the same rpm as 3.23s would get you ,say 65=2600 in loc-up, then you could run 3.23/.69=4.68s rounds to 4.56s. Now 8000 in Second gear, comes to around 89mph@8% slip, still, IMO, kindof useless, for a street machine.
What a streeter should really want, IMO, is an engine that can make adequate power at reasonable rpm, Yet also cruise at a reasonable rpm.
With 3.23s 65=2615 in loc-up; that is a reasonable cruiser gear.
But the starter gear is just 7.91, so whatever displacement engine you stick in there, it has to work with that 7.91 handicap. And that means it is gonna have to make some honest torque down there. Ok so sure, you can stall a smaller engine up and get to the torque, I get that. But
what if you have chosen a manual trans? Are you willing to forever after slip it to 20mph to get moving briskly enough?
I'm a dump-it-and-go kindof guy......
-----------------------------
and then there's trying to tune a small-cid/8000 rpm engine,
to go out on beer runs at 1:00 in the morning........ lol
Rat Bastid
Dunamis Metron
Finally I get to say it:
Not everyone wants their muscle car to drive like a junk assed Hyundai.
Some of us don’t care about 3800 RPM down the road. In fact, some of us get a giant hard on from it.
Some of us will work on the tune until 260 at .050 on a 104 LSA will idle at 750 RPM. Even though we don’t let the idle that low because we use cam lobes that scare old ladies and make little kids cry. And some of us get a hard on from that.
Some of us will put up with headers that hang lower because the tubes are actually big enough to actually make some power. We also don’t drive our muscle cars like four wheel drives so out header and our deep pans aren’t bashed up.
Those are just a few things that some of us are into.
I still think 500 cubes with an Indy top end will make more power than a screaming 340.lol
273,
Your premise in post #1 is wrong, but not all your fault.
The volume [ cfm or any other measure of volume ] of air ingested by the engine is the same at all rpm, based on the CID. What varies is the air's density.
The term VE refers to volumetric efficiency, but it is incorrect, but has been in such common use, it just got accepted over the years. What is being compared is the weight of air being drawn into the engine, not the volume.
Your premise in post #1 is wrong, but not all your fault.
The volume [ cfm or any other measure of volume ] of air ingested by the engine is the same at all rpm, based on the CID. What varies is the air's density.
The term VE refers to volumetric efficiency, but it is incorrect, but has been in such common use, it just got accepted over the years. What is being compared is the weight of air being drawn into the engine, not the volume.
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