100 horsepower per liter naturally aspirated
06-02-2007, 11:06 PM
#22
Originally Posted by Gannet
Well, Europe has always been oil-poor. So, to prevent their balance of payments from getting out of whack, the Europeans started very early on to encourage excellent fuel economy. The "encouragement" took the form of high gasoline taxes, and also highly progressive yearly registration taxes on vehicles based on...you guessed it, engine displacement. Actually, they started out trying to tax horsepower directly, but the manufacturers played shenangians with their "advertised" ratings (surprise!) and the governments soon turned to something that could be easily measured.
The USA, being oil-rich, never went down that path. The size and power of our cars are not "artificially" constrained by onerous taxes, so our engineering solutions have been "more correct", in that they are solutions to meet the needs of the purchasers, not the Gov't. Well, until the late '60s, anyways.
From an engineering point of view, it would be much more interesting to talk about the power/$$ (both production and maintenance), or the power/weight, or the power/size, or the power/fuel used. Those are all relevant criteria when selecting an engine for an application. But power/displacement? An arbitrary measurement brought to you entirely by the tax man and racing commissioners, both of whom are looking for something that's easy to measure, not necessarily something that's real-world relevant, or that has anything to do with engineering.
The USA, being oil-rich, never went down that path. The size and power of our cars are not "artificially" constrained by onerous taxes, so our engineering solutions have been "more correct", in that they are solutions to meet the needs of the purchasers, not the Gov't. Well, until the late '60s, anyways.
From an engineering point of view, it would be much more interesting to talk about the power/$$ (both production and maintenance), or the power/weight, or the power/size, or the power/fuel used. Those are all relevant criteria when selecting an engine for an application. But power/displacement? An arbitrary measurement brought to you entirely by the tax man and racing commissioners, both of whom are looking for something that's easy to measure, not necessarily something that's real-world relevant, or that has anything to do with engineering.
It's interesting that we (they) are measuring efficiency as output per liter of displacement. Why? Where does that come from?
And we Americans are supposed to be the ones who aren't worldly.
06-02-2007, 11:13 PM
#23
Originally Posted by Quick Double Nickel
I really just wanted some people to chime in on how it appears to be easier for some motors to obtain the 100 hp/l mark.
In other words, by spinning an engine higher, you will "make" more horsepower without actually increasing its power output. It is a way to "cheat" with the numbers.
So HP/L is a figure that selects for high-revving engines with low displacement.
Since there is no rational reason why you would WANT to select for low displacement outside of class racing and the land of taxes-on-displacement, this is a nonsense measurement for most situations.
You could probably get your LS1 to make more HP/L by de-stroking it so that it makes less power but has less liters and maybe revs higher. But what would that accomplish besides getting you your ricer certification? NOTHING.
So stop asking about HP/L. Put away the ricer math!
06-03-2007, 12:12 AM
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Originally Posted by quarter double nickel
This is one I've been thinking about for a while, so I though I'd post it on here to see what everyone has to say.
While 100 horsepower per liter output from a large V8 motor, such as the LSx, is no new thing, retaining stock, or near-stock drivability, while doing so is. With the multitude of new combos coming on board with at or over 500 rwhp from a 5.7L it seems that we've hit that magical mark of 100 hp/L, but has the drivability suffered? These new combos seem to have cams in the 23x range at .050, which isn't much like stock in my opinion. I know a lot is to be gained in the tune of the engine with regards to drivability and ultimate power production, but there are a lot of trade-offs to get to that mark.
There have been a number of import car makers that have accomplished this in production cars with a multitude of different naturally-aspirated combinations (the 1999? 1.6L Si Civic, and 4.2L Audi V8 come to mind), but nothing from the domestic car makers and their proprietary V8s. So, the question is: How do you obtain this lofty goal and maintain production-spec drivability, emissions, and fuel consumption? Are DOHCs, VVT (and lift), or smaller motors the only way to accomplish this?
While 100 horsepower per liter output from a large V8 motor, such as the LSx, is no new thing, retaining stock, or near-stock drivability, while doing so is. With the multitude of new combos coming on board with at or over 500 rwhp from a 5.7L it seems that we've hit that magical mark of 100 hp/L, but has the drivability suffered? These new combos seem to have cams in the 23x range at .050, which isn't much like stock in my opinion. I know a lot is to be gained in the tune of the engine with regards to drivability and ultimate power production, but there are a lot of trade-offs to get to that mark.
There have been a number of import car makers that have accomplished this in production cars with a multitude of different naturally-aspirated combinations (the 1999? 1.6L Si Civic, and 4.2L Audi V8 come to mind), but nothing from the domestic car makers and their proprietary V8s. So, the question is: How do you obtain this lofty goal and maintain production-spec drivability, emissions, and fuel consumption? Are DOHCs, VVT (and lift), or smaller motors the only way to accomplish this?
Second, HP/L is meaningless, as so many others have said. It's bullsh*t used by ricers to claim that their engine is better than ours when we beat them. Look, if you want a real measure of efficiency, our 7.0 liter LS7 makes 505 HP (under-rated by 30, Fadi's dyno'd 454 to the wheels), but returns 30 miles to the gallon, as reported by many. However, your 2.0L(?) S2000, gutless POS that it is with NO torque whatsoever, is reported to get >25MPG by owners.
Q: Which makes more HP/L?
A: The Honda.
Q:Which makes more HP?
A: The Chevy.
Q: Which returns better mileage?
A: Chevy.
Q: Which is more efficient?
A: Chevy.
Q: What have we learned from this?
A: HP/L is ricer math, and is pretty much useless. (Thanks, J-Rod)
06-03-2007, 01:35 AM
#25
Originally Posted by black_knight
You have your answer already: Because HP numbers can be inflated if an engine spins to a high RPM range, regardless of the fact that it may be a gutless wonder.
In other words, by spinning an engine higher, you will "make" more horsepower without actually increasing its power output. It is a way to "cheat" with the numbers.
So HP/L is a figure that selects for high-revving engines with low displacement.
Since there is no rational reason why you would WANT to select for low displacement outside of class racing and the land of taxes-on-displacement, this is a nonsense measurement for most situations.
You could probably get your LS1 to make more HP/L by de-stroking it so that it makes less power but has less liters and maybe revs higher. But what would that accomplish besides getting you your ricer certification? NOTHING.
So stop asking about HP/L. Put away the ricer math!
In other words, by spinning an engine higher, you will "make" more horsepower without actually increasing its power output. It is a way to "cheat" with the numbers.
So HP/L is a figure that selects for high-revving engines with low displacement.
Since there is no rational reason why you would WANT to select for low displacement outside of class racing and the land of taxes-on-displacement, this is a nonsense measurement for most situations.
You could probably get your LS1 to make more HP/L by de-stroking it so that it makes less power but has less liters and maybe revs higher. But what would that accomplish besides getting you your ricer certification? NOTHING.
So stop asking about HP/L. Put away the ricer math!
Like I said earlier, I really think the LSx engines are the best engines on the market, because they integrate best into the vehicle. We don't have to like the high specific output import engines, but we should respect the technology that makes them what they are. Honda are just applying technology that is developed from race engines where swept displacement is fixed, and power needs to come from somewhere else.
06-03-2007, 02:29 AM
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What we are talking about has already been done, the CTS-VR has a Katech built LS2 with 515 restricted hp. Its not stock (12.1CR/roller cam/cnc heads) but definitely within the realms of what you can accomplish in the aftermarket. And without the restrictors it would put out an estimated 600 hp. And thats with a 7,000 rpm power beak and 5600 rpm torque peak so nothing that you couldn't drive on the street.
06-03-2007, 03:39 AM
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Originally Posted by Formulated
Come on guys, the Honda S2000 engine has a 90.7mm stroke, and the LS1 has a 92mm stroke. Very close, so stop talking about a short stroke being the solution.
The method Honda takes to achieving high specific output is high flow 4 valve cylinder heads, and VTEC. The high rpm lobes on a VTEC camshaft are really agressive. I had a set of aftermarket cams in my Prelude that had over 250 degrees duration a t .050", but the car idled like stock on the smaller set of lobes. The formula Honda uses for power is heavily weighted by engine speed. I just wish they made bigger engines. 120 hp/liter is great, but if you only have 2 liters, it's not much power.
This is why I think the BMW V8's are such a good benchmark for high specific output engines. BMW builds 100hp/liter V8s that meet all of the requirements put on passenger cars. The problem is that they are very complicated and expensive.
Any engine is a complex machine, and you can't just make passive statements that bore/stroke/etc... are the solution. There are lots of ways to get power. The important thing to realize is that we race cars, not dynos. And, we all have fixed budgets. That's where the LS1 is such a good platform. It's relatively simple, very robust, and not expensive. It's larger than the competition's engines, and appears to be not a very elegant solution. But, it is really very elegant when you take cost into consideration. By making the engine larger, GM can create lots of low speed power, and lower engine speed is better fuel economy.
I have lots of respect for the production high specific output engines by Honda and BMW because I love seeing technology. However, I like GM's solution better because it results in a better vehicle overall.
The method Honda takes to achieving high specific output is high flow 4 valve cylinder heads, and VTEC. The high rpm lobes on a VTEC camshaft are really agressive. I had a set of aftermarket cams in my Prelude that had over 250 degrees duration a t .050", but the car idled like stock on the smaller set of lobes. The formula Honda uses for power is heavily weighted by engine speed. I just wish they made bigger engines. 120 hp/liter is great, but if you only have 2 liters, it's not much power.
This is why I think the BMW V8's are such a good benchmark for high specific output engines. BMW builds 100hp/liter V8s that meet all of the requirements put on passenger cars. The problem is that they are very complicated and expensive.
Any engine is a complex machine, and you can't just make passive statements that bore/stroke/etc... are the solution. There are lots of ways to get power. The important thing to realize is that we race cars, not dynos. And, we all have fixed budgets. That's where the LS1 is such a good platform. It's relatively simple, very robust, and not expensive. It's larger than the competition's engines, and appears to be not a very elegant solution. But, it is really very elegant when you take cost into consideration. By making the engine larger, GM can create lots of low speed power, and lower engine speed is better fuel economy.
I have lots of respect for the production high specific output engines by Honda and BMW because I love seeing technology. However, I like GM's solution better because it results in a better vehicle overall.
A comment to go with what I highlighted above: The size of the LS1 is part of what makes it so great. Pushrod engines are small relative to OHC engines. The LS1 is pretty small and lightweight given that it contains 5.7L of displacement.
06-03-2007, 08:58 AM
#29
218 hp/litre N A on pump 91
These are numbers my 800 cc 2 cylinder single exhaust snowmobile put up while tuning to make it daily driver safe. Peak hp was 175.6 at 8400 (burning 92.8 lb/hr af at 13.04:1), peak tq was 111.1 at 8200.
These are numbers my 800 cc 2 cylinder single exhaust snowmobile put up while tuning to make it daily driver safe. Peak hp was 175.6 at 8400 (burning 92.8 lb/hr af at 13.04:1), peak tq was 111.1 at 8200.
06-03-2007, 11:03 AM
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I think there is one valuable, large market where HP/L does matter, and that is in motorcycles, specifically sportbikes. This is what the buyers want. They want a 160-180hp powerplant, packaged in a bike small enough that ones legs can comfortably fit across the width, and they want it to weigh as little as possible. So by everyone's logic here, a pushrod motor would be superb. It weighs less, costs less, is physically smaller, and once you double the displacement, you can make the same power outputs.
Now let's look at this fact, the only sportbikes that sell are DOHC, high specific output, very high revving, torqueless wonders. What are the Japanese thinking? Well let's find an automobile, low specific output engine that fits the bill. How about the GM 2.4l DOHC I4 used in late model Cavy Z24s? It makes like 160hp, and with just a 6200rpm redline, has healthy low end torque models. First of all, it's a terrible choice because it's an iron block, but it could be alloy so let's ignore that. The engine won't fit in a Honda Goldwing, let alone a CBR. And if you did get it to fit, you couldn't fit your legs around it, the weight would be significantly more, and you'd still get raped by the engine with 1/4 the displacement. The fact is, with an inline configuration, DOHC engines are just as compact as pushrod engines. But because of the flow levels attainable by the DOHC engines, they make MUCH more power, and have much higher specific outputs. Perfect for sportbikes.
The only downside to a high specific output engine is that they are high RPM engines. RPM kills engines. But since sportbikes rarely get ridden, and certainly don't rack up miles like cars, there's no problems with the bike's engines only lasting to 40,000 miles. So the next problem with high rpm, the lack of low end, off idle torque. The S2000 sucks to drive for that reason. How many of you ride sportbikes? Is there ever a complaint of not enough low end? I had the chance to ride a CBR1000RR a year or two ago. I pulled it out of my driveway, and let the clutch out. 30mph. I didn't even have to touch the throttle, besides what I needed to do so it wouldn't stall. There wasn't much power, but the accelerative force was tremendous, at ANY engine speed. Fact is, the bike is so light because of the high technology employed, that it doesn't take much to get it moving WELL ahead of traffic.
Lastly, let's compare it to the low specific output, pushrod sportbikes. Errr, sportbike. The Buell. Is Buell still a company? They sell fewer bikes than GM does doughnuts. The largest displacement sportbike Buell makes is 1200cc. And with a power output just shy of 100hp, it is not exactly exciting. In fact, there isn't a 600cc sportbike that couldn't walk away from it. So linearly speaking, in order to get the Buell to compete even with other 1000cc bikes, it needs over 160hp, meaning it needs 1950cc, aka 2.0l. Find me a 2.0l powerplant that will fit inside a sportbike, and we're good to go right? Well, not really. It weighs 20lbs MORE than the leading 1000cc sportbike. In fact, of the big 4, everyone weighs significantly less than the Buell. So now it needs even MORE power, aka even more displacement, just to keep up. And that's not event taking into account the significant weight that'd be added by having a 2.1l powerplant.
I like looking at HP/L, because it shows true performance tuning. It shows levels of volumetric efficiency reached that was never thought possible. It shows the technological, and engineering, advances that we have made. However, I can realize that in a car, it is for the most part dismissable.
Now let's look at this fact, the only sportbikes that sell are DOHC, high specific output, very high revving, torqueless wonders. What are the Japanese thinking? Well let's find an automobile, low specific output engine that fits the bill. How about the GM 2.4l DOHC I4 used in late model Cavy Z24s? It makes like 160hp, and with just a 6200rpm redline, has healthy low end torque models. First of all, it's a terrible choice because it's an iron block, but it could be alloy so let's ignore that. The engine won't fit in a Honda Goldwing, let alone a CBR. And if you did get it to fit, you couldn't fit your legs around it, the weight would be significantly more, and you'd still get raped by the engine with 1/4 the displacement. The fact is, with an inline configuration, DOHC engines are just as compact as pushrod engines. But because of the flow levels attainable by the DOHC engines, they make MUCH more power, and have much higher specific outputs. Perfect for sportbikes.
The only downside to a high specific output engine is that they are high RPM engines. RPM kills engines. But since sportbikes rarely get ridden, and certainly don't rack up miles like cars, there's no problems with the bike's engines only lasting to 40,000 miles. So the next problem with high rpm, the lack of low end, off idle torque. The S2000 sucks to drive for that reason. How many of you ride sportbikes? Is there ever a complaint of not enough low end? I had the chance to ride a CBR1000RR a year or two ago. I pulled it out of my driveway, and let the clutch out. 30mph. I didn't even have to touch the throttle, besides what I needed to do so it wouldn't stall. There wasn't much power, but the accelerative force was tremendous, at ANY engine speed. Fact is, the bike is so light because of the high technology employed, that it doesn't take much to get it moving WELL ahead of traffic.
Lastly, let's compare it to the low specific output, pushrod sportbikes. Errr, sportbike. The Buell. Is Buell still a company? They sell fewer bikes than GM does doughnuts. The largest displacement sportbike Buell makes is 1200cc. And with a power output just shy of 100hp, it is not exactly exciting. In fact, there isn't a 600cc sportbike that couldn't walk away from it. So linearly speaking, in order to get the Buell to compete even with other 1000cc bikes, it needs over 160hp, meaning it needs 1950cc, aka 2.0l. Find me a 2.0l powerplant that will fit inside a sportbike, and we're good to go right? Well, not really. It weighs 20lbs MORE than the leading 1000cc sportbike. In fact, of the big 4, everyone weighs significantly less than the Buell. So now it needs even MORE power, aka even more displacement, just to keep up. And that's not event taking into account the significant weight that'd be added by having a 2.1l powerplant.
I like looking at HP/L, because it shows true performance tuning. It shows levels of volumetric efficiency reached that was never thought possible. It shows the technological, and engineering, advances that we have made. However, I can realize that in a car, it is for the most part dismissable.
06-03-2007, 11:05 AM
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My engine reach this magical number for a DD NA Pump Gas this size...
A kind of dream I had since the end of the Sixties where the F1 engines where just over the zone.
Details in the thread below:
https://ls1tech.com/forums/dynamometer-results-comparisons/648228-video-idle-plus-streetability-wot-my-511rwhp-fti.html
Christian
A kind of dream I had since the end of the Sixties where the F1 engines where just over the zone.
Details in the thread below:
https://ls1tech.com/forums/dynamometer-results-comparisons/648228-video-idle-plus-streetability-wot-my-511rwhp-fti.html
Christian
06-03-2007, 12:57 PM
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Why is it that every time somebody brings up something on this forum about a concept that is somewhat foreign to his or her normal logic it's instantly called "ricer math"? The intent of this thread was never to say one type of engine is better than the other. If that's want you want to debate, go over to the ricer forums and debate it with them. The only reason I mentioned the Honda motor and the Audi motor is because there are no domestic engines to reference that I know of in a production car. Hence the import reference. I realize that all the inherit problems that come along with a peaky, smaller displacement motor. I just wanted to get some input on how it could be done in a production, large-displacement domestic V8.
06-03-2007, 01:35 PM
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Something I thought about the other day - tell me if I am wrong.
OHC is generally the better platform in short stroke engines, pushrod is generally the better platform in long stroke engines. With such a short stroke and high RPM's, the heads need don't have a lot of time to move air in a single stroke. Having 4 valves per cylinder can allow better breathing at these higher RPM's and allow the torque to continue longer than a 2V engine. In a long stroke engine, pushrod makes sense due to this http://www.cheersandgears.com/forum...topic=15551&hl= which is contained in the OHC vs pushrod thread, helf-way down the first page in the advanced section.
Does my thinking make sense? Not to mention that it seems GM follows this belief with most of their recent cars. The small displacement engines tend to be OHC lately, and the big displacement engines seem to all be OHV.
OHC is generally the better platform in short stroke engines, pushrod is generally the better platform in long stroke engines. With such a short stroke and high RPM's, the heads need don't have a lot of time to move air in a single stroke. Having 4 valves per cylinder can allow better breathing at these higher RPM's and allow the torque to continue longer than a 2V engine. In a long stroke engine, pushrod makes sense due to this http://www.cheersandgears.com/forum...topic=15551&hl= which is contained in the OHC vs pushrod thread, helf-way down the first page in the advanced section.
Does my thinking make sense? Not to mention that it seems GM follows this belief with most of their recent cars. The small displacement engines tend to be OHC lately, and the big displacement engines seem to all be OHV.
06-03-2007, 10:33 PM
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Originally Posted by FieroZ34
I think there is one valuable, large market where HP/L does matter, and that is in motorcycles, specifically sportbikes. This is what the buyers want. They want a 160-180hp powerplant, packaged in a bike small enough that ones legs can comfortably fit across the width, and they want it to weigh as little as possible. So by everyone's logic here, a pushrod motor would be superb. It weighs less, costs less, is physically smaller, and once you double the displacement, you can make the same power outputs.
Now let's look at this fact, the only sportbikes that sell are DOHC, high specific output, very high revving, torqueless wonders. What are the Japanese thinking? Well let's find an automobile, low specific output engine that fits the bill. How about the GM 2.4l DOHC I4 used in late model Cavy Z24s? It makes like 160hp, and with just a 6200rpm redline, has healthy low end torque models. First of all, it's a terrible choice because it's an iron block, but it could be alloy so let's ignore that. The engine won't fit in a Honda Goldwing, let alone a CBR. And if you did get it to fit, you couldn't fit your legs around it, the weight would be significantly more, and you'd still get raped by the engine with 1/4 the displacement. The fact is, with an inline configuration, DOHC engines are just as compact as pushrod engines. But because of the flow levels attainable by the DOHC engines, they make MUCH more power, and have much higher specific outputs. Perfect for sportbikes.
The only downside to a high specific output engine is that they are high RPM engines. RPM kills engines. But since sportbikes rarely get ridden, and certainly don't rack up miles like cars, there's no problems with the bike's engines only lasting to 40,000 miles. So the next problem with high rpm, the lack of low end, off idle torque. The S2000 sucks to drive for that reason. How many of you ride sportbikes? Is there ever a complaint of not enough low end? I had the chance to ride a CBR1000RR a year or two ago. I pulled it out of my driveway, and let the clutch out. 30mph. I didn't even have to touch the throttle, besides what I needed to do so it wouldn't stall. There wasn't much power, but the accelerative force was tremendous, at ANY engine speed. Fact is, the bike is so light because of the high technology employed, that it doesn't take much to get it moving WELL ahead of traffic.
Lastly, let's compare it to the low specific output, pushrod sportbikes. Errr, sportbike. The Buell. Is Buell still a company? They sell fewer bikes than GM does doughnuts. The largest displacement sportbike Buell makes is 1200cc. And with a power output just shy of 100hp, it is not exactly exciting. In fact, there isn't a 600cc sportbike that couldn't walk away from it. So linearly speaking, in order to get the Buell to compete even with other 1000cc bikes, it needs over 160hp, meaning it needs 1950cc, aka 2.0l. Find me a 2.0l powerplant that will fit inside a sportbike, and we're good to go right? Well, not really. It weighs 20lbs MORE than the leading 1000cc sportbike. In fact, of the big 4, everyone weighs significantly less than the Buell. So now it needs even MORE power, aka even more displacement, just to keep up. And that's not event taking into account the significant weight that'd be added by having a 2.1l powerplant.
I like looking at HP/L, because it shows true performance tuning. It shows levels of volumetric efficiency reached that was never thought possible. It shows the technological, and engineering, advances that we have made. However, I can realize that in a car, it is for the most part dismissable.
Now let's look at this fact, the only sportbikes that sell are DOHC, high specific output, very high revving, torqueless wonders. What are the Japanese thinking? Well let's find an automobile, low specific output engine that fits the bill. How about the GM 2.4l DOHC I4 used in late model Cavy Z24s? It makes like 160hp, and with just a 6200rpm redline, has healthy low end torque models. First of all, it's a terrible choice because it's an iron block, but it could be alloy so let's ignore that. The engine won't fit in a Honda Goldwing, let alone a CBR. And if you did get it to fit, you couldn't fit your legs around it, the weight would be significantly more, and you'd still get raped by the engine with 1/4 the displacement. The fact is, with an inline configuration, DOHC engines are just as compact as pushrod engines. But because of the flow levels attainable by the DOHC engines, they make MUCH more power, and have much higher specific outputs. Perfect for sportbikes.
The only downside to a high specific output engine is that they are high RPM engines. RPM kills engines. But since sportbikes rarely get ridden, and certainly don't rack up miles like cars, there's no problems with the bike's engines only lasting to 40,000 miles. So the next problem with high rpm, the lack of low end, off idle torque. The S2000 sucks to drive for that reason. How many of you ride sportbikes? Is there ever a complaint of not enough low end? I had the chance to ride a CBR1000RR a year or two ago. I pulled it out of my driveway, and let the clutch out. 30mph. I didn't even have to touch the throttle, besides what I needed to do so it wouldn't stall. There wasn't much power, but the accelerative force was tremendous, at ANY engine speed. Fact is, the bike is so light because of the high technology employed, that it doesn't take much to get it moving WELL ahead of traffic.
Lastly, let's compare it to the low specific output, pushrod sportbikes. Errr, sportbike. The Buell. Is Buell still a company? They sell fewer bikes than GM does doughnuts. The largest displacement sportbike Buell makes is 1200cc. And with a power output just shy of 100hp, it is not exactly exciting. In fact, there isn't a 600cc sportbike that couldn't walk away from it. So linearly speaking, in order to get the Buell to compete even with other 1000cc bikes, it needs over 160hp, meaning it needs 1950cc, aka 2.0l. Find me a 2.0l powerplant that will fit inside a sportbike, and we're good to go right? Well, not really. It weighs 20lbs MORE than the leading 1000cc sportbike. In fact, of the big 4, everyone weighs significantly less than the Buell. So now it needs even MORE power, aka even more displacement, just to keep up. And that's not event taking into account the significant weight that'd be added by having a 2.1l powerplant.
I like looking at HP/L, because it shows true performance tuning. It shows levels of volumetric efficiency reached that was never thought possible. It shows the technological, and engineering, advances that we have made. However, I can realize that in a car, it is for the most part dismissable.
06-03-2007, 11:57 PM
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Originally Posted by LSGunZ28
It still isnt an important factor. or at least not one of the most important ones. Its a BS argument. if used in comparison with other equations, then yes it should be acceptable. But Id rather have a 75 Hp per liter 6 liter than a 100 hp per liter 3.5 liter engine. thats why I was suggestiing variable valve timing, a small cam for low end and bigger cam for high end, you get the best of both worlds.
My point wasn't that HP/L is important, it's that it is in sportbikes, where power required from a given weight/size is of the utmost in importance. And since, in inlines, size is related to displacement, HP/L becomes a VERY important figure.
06-04-2007, 01:09 AM
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the reason bikes are peaky is because if you made any real amount of trq they would be basicly unridable. imagine 150ftlb in a 300 lb bike.
hp/l is pretty useless. but the only way to make more hp in an n-a engine without more displacement is more rpm-while being able to flow
my dd has 110 hp/l revs to 9000, weighs 2600 and gets 35mpg when i drive sanely. doesnt mean it is fast. i would get demolished by most of you. but it is fun to drive and gets good mileage.
hp/l is pretty useless. but the only way to make more hp in an n-a engine without more displacement is more rpm-while being able to flow
my dd has 110 hp/l revs to 9000, weighs 2600 and gets 35mpg when i drive sanely. doesnt mean it is fast. i would get demolished by most of you. but it is fun to drive and gets good mileage.
06-04-2007, 01:43 AM
#39
Some corrections, here:
Excuse me but what does size and weight have to do with LITERS? Nothing. Don't compare power per liters, compare power per size/weight.
Obviously, the pushrod designs don't provide physically smaller packaging in bike style engines. I would suppose this is because there aren't enough cylinders for it to "pay off." Maybe an engineer can correct me if I'm wrong.
But the bottom line is still that "liters" as such is not relevant.
No, that's simply not true. There's a reason they don't make inline, DOHC 8 cylinder engines: they're huge. Also inline engines are quite heavy when compare to vee configured ones of the pushrod or OHC variety, at least once you go beyond 4 cylinders. Check out the weight of BMW's inline 6 on the old M3: it weighed more than an LS1, I think.
Clearly, sport bike engines are too different from automobile engines for meaningful comparison in this regard.
But, bear in mind: this only works if you are comparing two engines of similar configuration, application, and output. Like say an LS1 vs an LS2 or LS7. But even then, what is the sense in it? All three of those weigh the same and are the exact same size, so why compare power per liter? Why should liter-specific output be meaningful rather than total output or output per weight or output per fuel consumption? I have yet to hear a reason for that apart from displacement-restricted racing or taxes.
Originally Posted by FieroZ34
I think there is one valuable, large market where HP/L does matter, and that is in motorcycles, specifically sportbikes. This is what the buyers want. They want a 160-180hp powerplant, packaged in a bike small enough that ones legs can comfortably fit across the width, and they want it to weigh as little as possible.
So by everyone's logic here, a pushrod motor would be superb. It weighs less, costs less, is physically smaller, and once you double the displacement, you can make the same power outputs.
But the bottom line is still that "liters" as such is not relevant.
The fact is, with an inline configuration, DOHC engines are just as compact as pushrod engines.
Lastly, let's compare it to the low specific output, pushrod sportbikes. Errr, sportbike.
I like looking at HP/L, because it shows true performance tuning.
Last edited by black_knight; 06-04-2007 at 01:53 AM.
06-04-2007, 01:46 AM
#40
Originally Posted by Quick Double Nickel
Why is it that every time somebody brings up something on this forum about a concept that is somewhat foreign to his or her normal logic it's instantly called "ricer math"?
If you don't think that it's ricer math, then answer one simple question: WHY? Why do you want horsepower PER LITER? Why not horsepower per engine size/weight/fuel consumption/$?