100 horsepower per liter naturally aspirated
07-08-2007, 04:53 PM
#661
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^One correction. OHV layouts are more complex than OHC. OHC layouts dont need a cam tunnel. The valve train does not involve both the heads and the block. Just a belt or chain to the crank sprocket. No pushrods in an OHC.
OHV was actually invented after OHC by a long shot, as a more compact alternative. WWII tank engines were DOHC in some cases.
I'm not going to touch the original topic. 30 plus pages. Yeah.
OHV was actually invented after OHC by a long shot, as a more compact alternative. WWII tank engines were DOHC in some cases.
I'm not going to touch the original topic. 30 plus pages. Yeah.
07-08-2007, 04:54 PM
#662
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well i dont know much but it seems to me that you are saying since you have to run a large cam to make big power and thus leading to low rpm power loss so why dont the make a lifter like rhodes lifters and this should help cure the probeblem? let me know if im right
07-08-2007, 05:03 PM
#663
Originally Posted by black_knight
The benchmarking is all wrong. Even Engineermike, in a sideways fashion, is admitting this.
Originally Posted by black_knight
...I don't care if you use it to guesstimate the effects of changes on engines that have very similar configurations.
Originally Posted by black_knight
I'm not too hopeful of that, though. If he was prepared to actually listen and consider the possibility that he might have done something wrong, I would think he would have done it by now.
Mike
07-08-2007, 05:38 PM
#664
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Originally Posted by engineermike
Hey do you think you could find a picture of the porsche engine stripped down to the bare long block also? That thing has the fan, ac compressor, air intake piping, even the muffler! You can't even see the Porsche long-block! Of course the LS1 long-block is smaller.
Mike
Mike
width... not height.
the point was.... for the size it makes more power. You can stuff more displacement in a pushrod then any OHC motor created. this is one of the reasons it is a better choice.
If you think it is an intellectual argument to disagree that displacement is more effective at creating power then additional valves per cylinder you are mistaken. Fact is those wonderful 4.6 or 5.4 DOHC 4 Valve motors have heads that are freaken huge... the motors are huge. Look at a Lambo or Ferrari motor... HUGE! Yet all three have something in common compared to a LSX or SBC........ very little low end torque, and typically high RPM capabilities. Wooo hoooo... we can all build an LSX to see more RPM...... hence why the LSX > *
07-08-2007, 10:04 PM
#666
Originally Posted by black_knight
It means it's time for the 
I said it before, but if the thread should be locked, it's because the original subject has been discussed little or none in 33 pages, thanks to you.
Mike
07-08-2007, 10:58 PM
#667
Originally Posted by engineermike
I said it before, but if the thread should be locked, it's because the original subject has been discussed little or none in 33 pages, thanks to you.
07-09-2007, 06:03 AM
#668
Originally Posted by black_knight
The thread should be locked because the original subject is based on a flawed premise...
No one is forcing you to stay and discuss this, you know.
Last edited by engineermike; 07-09-2007 at 06:09 AM.
07-09-2007, 06:32 AM
#669
Originally Posted by engineermike
... in your opinion.
No one is forcing you to stay and discuss this, you know.
No one is forcing you to stay and discuss this, you know.
See how stupid that is? Geez, either it's a fact that it's flawed or its not. Either way, it's not a matter of opinion. You disagree with me, so just say that. None of this "opinion" BS.
07-09-2007, 08:37 AM
#670
Originally Posted by black_knight
...See how stupid that is? Geez, either it's a fact that it's flawed or its not. Either way, it's not a matter of opinion. You disagree with me, so just say that. None of this "opinion" BS.
What's "stupid" is you wanting the thread locked because you disagree with the question that was asked! I disagree with lots of questions that are asked, but I don't spend 34 pages explaining why I don't like their question. I simply close the window.
I guess I just never realized that you, black_knight, were a member of the elite INTERNET THREAD POLICE SQUAD that goes around determining if each thread that's started is actually a valid discussion or not.
Mike
07-09-2007, 02:28 PM
#671
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Originally Posted by Forteen3GT
width... not height.
the point was.... for the size it makes more power. You can stuff more displacement in a pushrod then any OHC motor created. this is one of the reasons it is a better choice.
If you think it is an intellectual argument to disagree that displacement is more effective at creating power then additional valves per cylinder you are mistaken. Fact is those wonderful 4.6 or 5.4 DOHC 4 Valve motors have heads that are freaken huge... the motors are huge. Look at a Lambo or Ferrari motor... HUGE! Yet all three have something in common compared to a LSX or SBC........ very little low end torque, and typically high RPM capabilities. Wooo hoooo... we can all build an LSX to see more RPM...... hence why the LSX > *
There it is.
Power and torque / size, weight, and cost.
or
Peak BHP / L.
You are the consumer and get to choose what you want.
-Louie (being a smartass)
07-09-2007, 03:38 PM
#672
I post this purely out of humor, since the Porsche vs. LSx picture is grossly skewed by accessories, intake plumbing, and the full exhaust system. . . And, yes, the horizontally opposed 6 cylinder is as wide as a V-8, for obvious reasons.
Power and torque / size, weight, and cost:
Peak BHP / L:
It really is amazing what can be done when you actually use high hp/liter technology to reduce the size and weight of an engine. The latest version of the little 2.8 liter v-8 is making 455 hp at only 200 lb of engine weight. Clearly, not all high-displacement high-hp engines are light weight, nor are all high hp/liter engines, but when you use the available technology (DOHC 4V with direct-acting bucket lifters) in an effort specifically to reduce size and weight, the results are impressive. I'd like to see a 200 lb pushrod engine with maximized displacement make 455 hp NA with existing production technology and still have a smooth idle and 100,000 mile durability...
Mike
Power and torque / size, weight, and cost:
Peak BHP / L:
It really is amazing what can be done when you actually use high hp/liter technology to reduce the size and weight of an engine. The latest version of the little 2.8 liter v-8 is making 455 hp at only 200 lb of engine weight. Clearly, not all high-displacement high-hp engines are light weight, nor are all high hp/liter engines, but when you use the available technology (DOHC 4V with direct-acting bucket lifters) in an effort specifically to reduce size and weight, the results are impressive. I'd like to see a 200 lb pushrod engine with maximized displacement make 455 hp NA with existing production technology and still have a smooth idle and 100,000 mile durability...
Mike
07-09-2007, 04:44 PM
#673
Originally Posted by engineermike
It is your opinion that hp/liter is useless.
It's a fact or it isn't. None of this "your opinion my opinion" BS.
I already told you what hp/L was useless for yet you continue to switch the focus. Since you're not a total idiot, I have concluded you are deliberately lying about my position.
07-09-2007, 08:54 PM
#674
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In my opinion... and because every a**hole has one...
I think hp/L is useful... If i didn't have any my engine would definitely suck
, I'll take all I can get!
In before the !
I think hp/L is useful... If i didn't have any my engine would definitely suck
, I'll take all I can get! In before the
!
07-09-2007, 09:14 PM
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In all seriousness, this thread should be locked, there was nothing wrong with the original question... It could be restated as:
Is it possible for large displacement V8 to reach a specific output of 100 hp/L and retain near factory driveability?
- Please reply as to whether you believe it's possible or not and state the reasons why.
- If you don't agree with the question being asked, getting asked, please don't respond.
I personally believe it's very possible as long there variable cam timing and/or lift involved. If some people think lower hp/L engines are the greatest thing invented (such as the LS1 for example). Then why not take the "greatest engine in the world" (LS1) add infinitely variable cam timing and lift, produce more potential power, more potential torque, better idle, higher redline, and higher efficiency? Oops we increased hp/L by doing that, now the "greatest engine in the world" just became a POS... Or something designed by Ford or the Japanese, or something like that...
Is it possible for large displacement V8 to reach a specific output of 100 hp/L and retain near factory driveability?
- Please reply as to whether you believe it's possible or not and state the reasons why.
- If you don't agree with the question being asked, getting asked, please don't respond.
I personally believe it's very possible as long there variable cam timing and/or lift involved. If some people think lower hp/L engines are the greatest thing invented (such as the LS1 for example). Then why not take the "greatest engine in the world" (LS1) add infinitely variable cam timing and lift, produce more potential power, more potential torque, better idle, higher redline, and higher efficiency? Oops we increased hp/L by doing that, now the "greatest engine in the world" just became a POS... Or something designed by Ford or the Japanese, or something like that...
07-09-2007, 10:11 PM
#676
ATTENTION QUICKDOUBLENICKEL AND ANYONE ELSE INTERESTED IN THE ORIGINAL TOPIC!
This is my analysis of whether or not 100 hp/liter (570 hp from 5.7 liters) is possible with the LS1 architechture with good driving characteristics. I define good driving characteristics as a glass smooth idle, low emissions, and decent fuel mileage.
Benchmarking:
I picked out three engines to benchmark. Two of them achieved 100 hp/liter, while the other has a very high piston speed.
1. 1992 Yamaha Seca II. This is a 600 cc streetbike engine that makes 100 hp/liter (61 hp) at 8500 rpm using 10/1 compression and 2 valves per cylinder. We can't rev a stock stroke LS1 to 8500 rpm (see "Bottom End" below) so we have to play with the numbers a bit.
2. Patrick G's LS1. Stock bottom end 346 LS1 with AFR 205's and a lumpy cam. It makes 500 rwhp (about 100 hp/liter) at 6500 rpm.
3. LS7. This is chosen simply because the accepted max piston speed for production engines stayed below 4000 ft/min for years, and GM demonstrated that you can get to ~4700 in a production engine.
Bottom End:
In order to make 100 hp/liter, you have to have a high bmep, or alot of rpm. 2 valve heads can achieve a very high bmep, but you have to use alot of overlap, which is out of the question for smooth idle and low emissions. See #2 above, which achieves a bmep of 200 psi at 6500 rpm. Not bad. #1 above only gets a bmep of 155 psi, but it's way up at 8500 rpm.
8500 rpm is alot for a 350, so we have to look at piston speed. #3 above reaches a piston speed at fuel-cut of over 4700 ft/min, which is astounding for a production engine. Assuming we can bump that up a tad to 4800 ft/min, then the rpm limit of the stock 3.62 stroke becomes 8000 rpm at fuel-cut. Take about 500 rpm off this and peak hp needs to be at 7500 rpm. We gotta' cut it close here.
We need to see if the Seca II engine could still achieve 100 hp/liter but at 1000 rpm lower. You could raise the compression from 10 up to 11.5/1, which has been demonstrated to work on the street. That would bump it up to about 66 hp at 8500. Play with the cam timing to lower peak hp back down to 61 hp (100 hp/liter) and the rpm at peak drops to about 7900. Any lower than this is getting into 4v bmep territory.
So now, we're basically screwed. The fuel-cut needs to be at 8000 rpm to limit piston speed and peak power is at 7900 based on demonstrated low-overlap 2v technology. Not good. Based on this, I doubt you could get 100 hp/liter (that's 570 hp out of 5.7 liters) and a smooth idle out of a 2v LS1 using the stock 3.62" stroke. The fuel cut needs to be at about 8500 rpm to take advantage of peak power at 7900. At 4800 ft/min piston speed, the stoke would have to be shrunk to 3.4". To stick with 350 cid, the bore would have to be enlarged to 4.050, which isn't unreasonable at all.
So now we've determined that the peak power will be at 7900 rpm, rev limiter at 8500 rpm, bore x stroke to be 4.050" x 3.400", and bmep at peak power to be 165 psi.
Cylinder Heads:
This is where things need to get exotic. You can't put a big cam in this thing to get 100 hp/liter, so the heads have to flow exceptionally well, especially at low and mid lift. Unfortunately, I couldn't find the intake valve size in the Seca II motor, but I do know that the ports are at a very high angle. The LS7 and L92 went that direction by raising the port off the deck surface considerably. Valve skirt area needs to be maximized, so very large valves are needed. I don't think you can fit the LS7 valves in a 4.050" bore, but correct me if I'm wrong. At minimum, this project would take a set of heavily worked L92 heads. Raising the roof's and epoxying the floors would help to prevent flow-separation along the floor at 8000 rpm.
Intake Manifold:
Of course, no existing production intake manifold would work at the required rpm. SP might do the trick.
The basic runner length equation says that you need an 11" runner to peak at 7600 rpm. This is from the valve, so it's significantly shorter than the stock intake, which is no surprise.
For runner cross-sectional area, using traditional formulas, I calculate something in the area of 3.2 in^2. That's a diameter of 2". Other calculations say 2.5", which is quite a bit bigger.
Camshaft:
The camshaft is somewhat tricky and will look like no other existing camshaft. The following is somewhat qualitative and generic, but you'll get the idea.
Overlap: We know we have to keep the overlap at less than -12 deg @ .050" in order to keep the stock idle. This has been demonstrated with some aftermarket cams. We can put the overlap period a couple degrees late to help get the rpm range up.
IVC: In order to get the peak way up at 7900 rpm, the IVC will need to be in the neighborhood of 58 deg ABDC. For comparison, most aftermarket LS1 cams are in the 40 - 46 range.
EVO: I would normally choose an EVO around 70 deg BBDC to match the rpm range of the intake, but an EVO that early will kill the gas mileage. EVO doesn't generally have a dramatic effect on power, so we can put it at a more conventional 55 deg BBDC.
The final spec's come out at about 230/230-121, installed 2 deg retarded. That doesn't sound as ridiculous as I expected, consider the LS7 cam is 210/230-120, +4.
Anyone have any technical comments?
Mike
This is my analysis of whether or not 100 hp/liter (570 hp from 5.7 liters) is possible with the LS1 architechture with good driving characteristics. I define good driving characteristics as a glass smooth idle, low emissions, and decent fuel mileage.
Benchmarking:
I picked out three engines to benchmark. Two of them achieved 100 hp/liter, while the other has a very high piston speed.
1. 1992 Yamaha Seca II. This is a 600 cc streetbike engine that makes 100 hp/liter (61 hp) at 8500 rpm using 10/1 compression and 2 valves per cylinder. We can't rev a stock stroke LS1 to 8500 rpm (see "Bottom End" below) so we have to play with the numbers a bit.
2. Patrick G's LS1. Stock bottom end 346 LS1 with AFR 205's and a lumpy cam. It makes 500 rwhp (about 100 hp/liter) at 6500 rpm.
3. LS7. This is chosen simply because the accepted max piston speed for production engines stayed below 4000 ft/min for years, and GM demonstrated that you can get to ~4700 in a production engine.
Bottom End:
In order to make 100 hp/liter, you have to have a high bmep, or alot of rpm. 2 valve heads can achieve a very high bmep, but you have to use alot of overlap, which is out of the question for smooth idle and low emissions. See #2 above, which achieves a bmep of 200 psi at 6500 rpm. Not bad. #1 above only gets a bmep of 155 psi, but it's way up at 8500 rpm.
8500 rpm is alot for a 350, so we have to look at piston speed. #3 above reaches a piston speed at fuel-cut of over 4700 ft/min, which is astounding for a production engine. Assuming we can bump that up a tad to 4800 ft/min, then the rpm limit of the stock 3.62 stroke becomes 8000 rpm at fuel-cut. Take about 500 rpm off this and peak hp needs to be at 7500 rpm. We gotta' cut it close here.
We need to see if the Seca II engine could still achieve 100 hp/liter but at 1000 rpm lower. You could raise the compression from 10 up to 11.5/1, which has been demonstrated to work on the street. That would bump it up to about 66 hp at 8500. Play with the cam timing to lower peak hp back down to 61 hp (100 hp/liter) and the rpm at peak drops to about 7900. Any lower than this is getting into 4v bmep territory.
So now, we're basically screwed. The fuel-cut needs to be at 8000 rpm to limit piston speed and peak power is at 7900 based on demonstrated low-overlap 2v technology. Not good. Based on this, I doubt you could get 100 hp/liter (that's 570 hp out of 5.7 liters) and a smooth idle out of a 2v LS1 using the stock 3.62" stroke. The fuel cut needs to be at about 8500 rpm to take advantage of peak power at 7900. At 4800 ft/min piston speed, the stoke would have to be shrunk to 3.4". To stick with 350 cid, the bore would have to be enlarged to 4.050, which isn't unreasonable at all.
So now we've determined that the peak power will be at 7900 rpm, rev limiter at 8500 rpm, bore x stroke to be 4.050" x 3.400", and bmep at peak power to be 165 psi.
Cylinder Heads:
This is where things need to get exotic. You can't put a big cam in this thing to get 100 hp/liter, so the heads have to flow exceptionally well, especially at low and mid lift. Unfortunately, I couldn't find the intake valve size in the Seca II motor, but I do know that the ports are at a very high angle. The LS7 and L92 went that direction by raising the port off the deck surface considerably. Valve skirt area needs to be maximized, so very large valves are needed. I don't think you can fit the LS7 valves in a 4.050" bore, but correct me if I'm wrong. At minimum, this project would take a set of heavily worked L92 heads. Raising the roof's and epoxying the floors would help to prevent flow-separation along the floor at 8000 rpm.
Intake Manifold:
Of course, no existing production intake manifold would work at the required rpm. SP might do the trick.
The basic runner length equation says that you need an 11" runner to peak at 7600 rpm. This is from the valve, so it's significantly shorter than the stock intake, which is no surprise.
For runner cross-sectional area, using traditional formulas, I calculate something in the area of 3.2 in^2. That's a diameter of 2". Other calculations say 2.5", which is quite a bit bigger.
Camshaft:
The camshaft is somewhat tricky and will look like no other existing camshaft. The following is somewhat qualitative and generic, but you'll get the idea.
Overlap: We know we have to keep the overlap at less than -12 deg @ .050" in order to keep the stock idle. This has been demonstrated with some aftermarket cams. We can put the overlap period a couple degrees late to help get the rpm range up.
IVC: In order to get the peak way up at 7900 rpm, the IVC will need to be in the neighborhood of 58 deg ABDC. For comparison, most aftermarket LS1 cams are in the 40 - 46 range.
EVO: I would normally choose an EVO around 70 deg BBDC to match the rpm range of the intake, but an EVO that early will kill the gas mileage. EVO doesn't generally have a dramatic effect on power, so we can put it at a more conventional 55 deg BBDC.
The final spec's come out at about 230/230-121, installed 2 deg retarded. That doesn't sound as ridiculous as I expected, consider the LS7 cam is 210/230-120, +4.
Anyone have any technical comments?
Mike
07-09-2007, 10:28 PM
#677
Originally Posted by EdmontonSS
In all seriousness, this thread should be locked, there was nothing wrong with the original question... It could be restated as:
Also, designing an engine for 570 hp at 5.7 liters is not a very good idea. Design for a power, weight, fuel economy, etc target instead: for all you know, it would be easier to reach your goal with more cubes. Unless you're designing for a racing class, it doesn't make sense to restrict that.
Also, if an LS7 intake can take a 427 to 7000 RPM, then I imagine it would take a 350 up higher.
07-09-2007, 11:17 PM
#678
Since we're after glass smooth idle, low emissions and fuel economy,what is wrong with using VVT to the max of its capability? We should be able to create a cam profile even more mild than what is currently used for better idle quality and increased low end throttle response. As long as combustion temps remain in a realm where NOx isn't a concern. We should then be able to use MAP, TPS and knock sensors to introduce more duration as required to keep knock at bay with progressively later IVC values. Once we're well above normal operation for street engines, say 4500 and up, we know that larger cam profiles really shine.
Imagine taking the best part of a towing engine's torque curve and being able to smoothly transition through the mid-range to the best part of a TRex's power curve. Don't get me wrong, I'm well aware there is no such thing as free lunch, so there's plenty of chances it wouldn't work as well as my little example states. Wouldb't it be nice to debate that for a change of pace?
Imagine taking the best part of a towing engine's torque curve and being able to smoothly transition through the mid-range to the best part of a TRex's power curve. Don't get me wrong, I'm well aware there is no such thing as free lunch, so there's plenty of chances it wouldn't work as well as my little example states. Wouldb't it be nice to debate that for a change of pace?
07-09-2007, 11:29 PM
#679
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Originally Posted by engineermike
ATTENTION QUICKDOUBLENICKEL AND ANYONE ELSE INTERESTED IN THE ORIGINAL TOPIC!
This is my analysis of whether or not 100 hp/liter (570 hp from 5.7 liters) is possible with the LS1 architechture with good driving characteristics. I define good driving characteristics as a glass smooth idle, low emissions, and decent fuel mileage.
Benchmarking:
I picked out three engines to benchmark. Two of them achieved 100 hp/liter, while the other has a very high piston speed.
1. 1992 Yamaha Seca II. This is a 600 cc streetbike engine that makes 100 hp/liter (61 hp) at 8500 rpm using 10/1 compression and 2 valves per cylinder. We can't rev a stock stroke LS1 to 8500 rpm (see "Bottom End" below) so we have to play with the numbers a bit.
2. Patrick G's LS1. Stock bottom end 346 LS1 with AFR 205's and a lumpy cam. It makes 500 rwhp (about 100 hp/liter) at 6500 rpm.
3. LS7. This is chosen simply because the accepted max piston speed for production engines stayed below 4000 ft/min for years, and GM demonstrated that you can get to ~4700 in a production engine.
Bottom End:
In order to make 100 hp/liter, you have to have a high bmep, or alot of rpm. 2 valve heads can achieve a very high bmep, but you have to use alot of overlap, which is out of the question for smooth idle and low emissions. See #2 above, which achieves a bmep of 200 psi at 6500 rpm. Not bad. #1 above only gets a bmep of 155 psi, but it's way up at 8500 rpm.
8500 rpm is alot for a 350, so we have to look at piston speed. #3 above reaches a piston speed at fuel-cut of over 4700 ft/min, which is astounding for a production engine. Assuming we can bump that up a tad to 4800 ft/min, then the rpm limit of the stock 3.62 stroke becomes 8000 rpm at fuel-cut. Take about 500 rpm off this and peak hp needs to be at 7500 rpm. We gotta' cut it close here.
We need to see if the Seca II engine could still achieve 100 hp/liter but at 1000 rpm lower. You could raise the compression from 10 up to 11.5/1, which has been demonstrated to work on the street. That would bump it up to about 66 hp at 8500. Play with the cam timing to lower peak hp back down to 61 hp (100 hp/liter) and the rpm at peak drops to about 7900. Any lower than this is getting into 4v bmep territory.
So now, we're basically screwed. The fuel-cut needs to be at 8000 rpm to limit piston speed and peak power is at 7900 based on demonstrated low-overlap 2v technology. Not good. Based on this, I doubt you could get 100 hp/liter (that's 570 hp out of 5.7 liters) and a smooth idle out of a 2v LS1 using the stock 3.62" stroke. The fuel cut needs to be at about 8500 rpm to take advantage of peak power at 7900. At 4800 ft/min piston speed, the stoke would have to be shrunk to 3.4". To stick with 350 cid, the bore would have to be enlarged to 4.050, which isn't unreasonable at all.
So now we've determined that the peak power will be at 7900 rpm, rev limiter at 8500 rpm, bore x stroke to be 4.050" x 3.400", and bmep at peak power to be 165 psi.
Cylinder Heads:
This is where things need to get exotic. You can't put a big cam in this thing to get 100 hp/liter, so the heads have to flow exceptionally well, especially at low and mid lift. Unfortunately, I couldn't find the intake valve size in the Seca II motor, but I do know that the ports are at a very high angle. The LS7 and L92 went that direction by raising the port off the deck surface considerably. Valve skirt area needs to be maximized, so very large valves are needed. I don't think you can fit the LS7 valves in a 4.050" bore, but correct me if I'm wrong. At minimum, this project would take a set of heavily worked L92 heads. Raising the roof's and epoxying the floors would help to prevent flow-separation along the floor at 8000 rpm.
Intake Manifold:
Of course, no existing production intake manifold would work at the required rpm. SP might do the trick.
The basic runner length equation says that you need an 11" runner to peak at 7600 rpm. This is from the valve, so it's significantly shorter than the stock intake, which is no surprise.
For runner cross-sectional area, using traditional formulas, I calculate something in the area of 3.2 in^2. That's a diameter of 2". Other calculations say 2.5", which is quite a bit bigger.
Camshaft:
The camshaft is somewhat tricky and will look like no other existing camshaft. The following is somewhat qualitative and generic, but you'll get the idea.
Overlap: We know we have to keep the overlap at less than -12 deg @ .050" in order to keep the stock idle. This has been demonstrated with some aftermarket cams. We can put the overlap period a couple degrees late to help get the rpm range up.
IVC: In order to get the peak way up at 7900 rpm, the IVC will need to be in the neighborhood of 58 deg ABDC. For comparison, most aftermarket LS1 cams are in the 40 - 46 range.
EVO: I would normally choose an EVO around 70 deg BBDC to match the rpm range of the intake, but an EVO that early will kill the gas mileage. EVO doesn't generally have a dramatic effect on power, so we can put it at a more conventional 55 deg BBDC.
The final spec's come out at about 230/230-121, installed 2 deg retarded. That doesn't sound as ridiculous as I expected, consider the LS7 cam is 210/230-120, +4.
Anyone have any technical comments?
Mike
This is my analysis of whether or not 100 hp/liter (570 hp from 5.7 liters) is possible with the LS1 architechture with good driving characteristics. I define good driving characteristics as a glass smooth idle, low emissions, and decent fuel mileage.
Benchmarking:
I picked out three engines to benchmark. Two of them achieved 100 hp/liter, while the other has a very high piston speed.
1. 1992 Yamaha Seca II. This is a 600 cc streetbike engine that makes 100 hp/liter (61 hp) at 8500 rpm using 10/1 compression and 2 valves per cylinder. We can't rev a stock stroke LS1 to 8500 rpm (see "Bottom End" below) so we have to play with the numbers a bit.
2. Patrick G's LS1. Stock bottom end 346 LS1 with AFR 205's and a lumpy cam. It makes 500 rwhp (about 100 hp/liter) at 6500 rpm.
3. LS7. This is chosen simply because the accepted max piston speed for production engines stayed below 4000 ft/min for years, and GM demonstrated that you can get to ~4700 in a production engine.
Bottom End:
In order to make 100 hp/liter, you have to have a high bmep, or alot of rpm. 2 valve heads can achieve a very high bmep, but you have to use alot of overlap, which is out of the question for smooth idle and low emissions. See #2 above, which achieves a bmep of 200 psi at 6500 rpm. Not bad. #1 above only gets a bmep of 155 psi, but it's way up at 8500 rpm.
8500 rpm is alot for a 350, so we have to look at piston speed. #3 above reaches a piston speed at fuel-cut of over 4700 ft/min, which is astounding for a production engine. Assuming we can bump that up a tad to 4800 ft/min, then the rpm limit of the stock 3.62 stroke becomes 8000 rpm at fuel-cut. Take about 500 rpm off this and peak hp needs to be at 7500 rpm. We gotta' cut it close here.
We need to see if the Seca II engine could still achieve 100 hp/liter but at 1000 rpm lower. You could raise the compression from 10 up to 11.5/1, which has been demonstrated to work on the street. That would bump it up to about 66 hp at 8500. Play with the cam timing to lower peak hp back down to 61 hp (100 hp/liter) and the rpm at peak drops to about 7900. Any lower than this is getting into 4v bmep territory.
So now, we're basically screwed. The fuel-cut needs to be at 8000 rpm to limit piston speed and peak power is at 7900 based on demonstrated low-overlap 2v technology. Not good. Based on this, I doubt you could get 100 hp/liter (that's 570 hp out of 5.7 liters) and a smooth idle out of a 2v LS1 using the stock 3.62" stroke. The fuel cut needs to be at about 8500 rpm to take advantage of peak power at 7900. At 4800 ft/min piston speed, the stoke would have to be shrunk to 3.4". To stick with 350 cid, the bore would have to be enlarged to 4.050, which isn't unreasonable at all.
So now we've determined that the peak power will be at 7900 rpm, rev limiter at 8500 rpm, bore x stroke to be 4.050" x 3.400", and bmep at peak power to be 165 psi.
Cylinder Heads:
This is where things need to get exotic. You can't put a big cam in this thing to get 100 hp/liter, so the heads have to flow exceptionally well, especially at low and mid lift. Unfortunately, I couldn't find the intake valve size in the Seca II motor, but I do know that the ports are at a very high angle. The LS7 and L92 went that direction by raising the port off the deck surface considerably. Valve skirt area needs to be maximized, so very large valves are needed. I don't think you can fit the LS7 valves in a 4.050" bore, but correct me if I'm wrong. At minimum, this project would take a set of heavily worked L92 heads. Raising the roof's and epoxying the floors would help to prevent flow-separation along the floor at 8000 rpm.
Intake Manifold:
Of course, no existing production intake manifold would work at the required rpm. SP might do the trick.
The basic runner length equation says that you need an 11" runner to peak at 7600 rpm. This is from the valve, so it's significantly shorter than the stock intake, which is no surprise.
For runner cross-sectional area, using traditional formulas, I calculate something in the area of 3.2 in^2. That's a diameter of 2". Other calculations say 2.5", which is quite a bit bigger.
Camshaft:
The camshaft is somewhat tricky and will look like no other existing camshaft. The following is somewhat qualitative and generic, but you'll get the idea.
Overlap: We know we have to keep the overlap at less than -12 deg @ .050" in order to keep the stock idle. This has been demonstrated with some aftermarket cams. We can put the overlap period a couple degrees late to help get the rpm range up.
IVC: In order to get the peak way up at 7900 rpm, the IVC will need to be in the neighborhood of 58 deg ABDC. For comparison, most aftermarket LS1 cams are in the 40 - 46 range.
EVO: I would normally choose an EVO around 70 deg BBDC to match the rpm range of the intake, but an EVO that early will kill the gas mileage. EVO doesn't generally have a dramatic effect on power, so we can put it at a more conventional 55 deg BBDC.
The final spec's come out at about 230/230-121, installed 2 deg retarded. That doesn't sound as ridiculous as I expected, consider the LS7 cam is 210/230-120, +4.
Anyone have any technical comments?
Mike
No one can say that you didn't put any thought into the post.
07-10-2007, 12:25 AM
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Originally Posted by black_knight
for all you know, it would be easier to reach your goal with more cubes.
Engine weight and packaging - As the cubes get higher, eventually the engine will have to be larger and therefore heavier. This detriments other aspects of vehicle performance (aerodynamics, centre of gravity, ideal weight distribution, braking, cornering, etc...)
Fuel Economy - All else being equal, an engine with more swept cylinder area and larger bearing surfaces to support the larger cubes, will be using more power to overcome rotational friction even burning the same amount of air/fuel (at the same RPM). Also consider the pumping losses from the closed throttle at lower loads. Engine RPM could be lowered to compensate, and cam re-optimized for the lower RPMs, but we now have a larger engine doing the same job as the smaller (lighter) one in same vehicle, which just doesn't make sense.
Of course, if you're name's "Ford" and you build a higher output engine but do it by adding weight and size (weight up high, in the wrong place for a performance car to boot...) You'd better make damn sure the benefits of the higher output make up for the weight and packaging issues... Or prepare to lose races. Where the F-body truly dominate the Mustangs is in road-racing and auto-x, this is the superior packaging of the engine really come into play.
I do believe when it come to "Hot Rodding" a vehicle to acheive a certain performance level the best idea is maximize your cubic inches given economic and packaging restraints. Then, once displacement is maximized for the desired packaging, get at much specific output as possible from that engine. For most people working on these cars "economic restraints" is a huge factor, otherwise I think we can all agree we'd want at least a 427 (utilizing a LS-series block of some sort) under the hood (this being LS1tech).
As to the issue of responding to original question... Hindsight is 20/20 but maybe black_knight, you should have started your own thread, entitled "Why I think building an engine for a high specific output is a poor approach". The poster asked a question, and obviously had a thinly masked opinion, but I think we should debate facts and not opinions too much. I know I come to "Advanced Tech" for the type of post engineermike just came up with! Makes me feel better about the 226/226 cam I have sitting in closet... I'm not convinced going bigger on a 346 benefits power enough for the loss of driveability... And no, I'm not going for 100 hp/L!