HP per Liter - Why not HP per weight of engine?
08-29-2004, 11:25 PM
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Well, Shinkaze you have an interesting argument. In addition it seems you are more knowlegdable about both engine's valvetrain etc as well, but I would like to rebuttle with the following. 
Well Apeal is more MARKETING than TECHNOLOGY. I have to admit the M5 apeals to more then the Z06, but that's not because of technology.
I'll give you that, the way it was marketed several months before it came out made it seem like the end all be all (similar to the ls1/ls6 IIRC). When in fact you right it weighs more, costs more to manufacture, costs more to maintain, and generally is harder to work on if you take it apart. Unlike the lsx variants, which I understand are very easy to work on, and because of the simplified valvetrain easy to upgrade etc. sounds like a better choice.
This is the two vs one intake valve issue. here is the thing you can tune a 2V motor to make the same flow as a 4V motor for a specific RPM. However, because the 4V motor pushes higher velocities it can create a wider range of power potential creating better combustion. So its not so much flow as it is velocites can be maintianed over a wider range. to combat this the 2V motor has to be designed to make power over a wide range and thus compromise it's ability to make power at a specific RPM.
You hit the nail on the head there...the ls6 is/was tuned to do exactly that. Make more power over a wider range. In fact the combinaton of the high end and that low end of the GM smallblock is very suprising considering the cost and size. The packaging of that was so tight that from those excellent pictures it's eas to see above the smaller V6 take up just about the same room. More factories need to do this.
Nevertheless, the M5's exotic valvetrain has something which is impossible for a pushrod if I'm not mistaken, and that's variable valve timing (BMW's VANOS). Unfortunately I am not familiar enough with it to comment in detail, but as I understand, it makes it seem like there are many different cams in the motor, when in fact there is only one. That way, it is focused on not only low-end hp but also addresses top-end power as well. I don't know if that is valid for lift or duration, or both, but it offsets the extra weight you may incur by a large margin IMO, because of the "best of both worlds" analogy. I think that's what you were talking about, please correct me if I'm wrong.
yes and no. The M5 Valvetrain is so complicated that truely high RPM potential isn't really there because there are so many more potential points of failure. Additionally high RPM potential is meaningless. The Engine's ability to hold Torque over time (RPM) is meaningful so if the Motor can hold Power (Torque) into higher RPMs that would be beneficial but only if the curve is still increasing. a 4v design does give you a wider torque curve for a given displacement, so a 4V motor can hold torque better into a higher RPM range without sacrificing low end RPM. a 2v motor cannot because of the port velocity compromise I mentioned above.
I would have to agree that the M5's valvetrain is more complicated, but I disagree that because it may contain more points of failure, it makes for an unwise choice. Now I'm looking at the original design by BMW, which yes it does have more moving parts. However, how they combine all the parts to fit together to combat stresses and failures is the key choice. Although there is nothing new, or ground breaking, about the valvetrain (execpt for the VANOS mentioned above), it does have one thing going for it: the R&D and durability of setups. BMW is one of the manufacturers that race what they sell. I mean, today lot of people do that, but they are able to create tight enough tolerances and parts that work together so well there is little risk of failure. More factories have started to pick up on this a few years ago, like when GM started racing the C5R and even early in the 90s when they were developing the C5 for this reason. But when's the last time you heard of a top-end failure or valvetrain failure in BMWs? It just doesn't happen that often (according to general comments by racing directors fwiw...) so maybe the extra weight is worth it for performance sake. They are easily able to overcome setbacks during R&D because of how familiar they are with their own stuff. If you believe that the Ford DOHC design is anything that resembles the BMW DOHC cam you have another thing coming lol.
As far as the RPM vs tq vs hp argument, you make a valid point. I mean, weight itself is meaningless if you can counter with the appropriate hp, right? So for example, lets take the most "prestigous" of racing again, Formula-1. They are running valvetrains that operate on compressed air, not springs, because springs are not able to keep up with the RPMs they are pushing (18k+ RPMs!!!). On the other hand, they have lots of time and engergy spent into making this happen, not for extra-ordinary tq values, but to extend the tq out as far as they need to, which it turn hits horsepower values they shoot for from the onset. You know, they are probably not going to go much past 18k RPMs at this point, because there is no need to. They have hit a sweet spot, so to speak, and have plenty of success with that compromise of hp and reliabilty. I don't know what an F1 engine weighs for sure, so maybe that is not the correct analogy or way to get the point accross.
Dinan's numbers are at the Crank not RWHP.
I know, that's why I posted that. It would be unfare to compare the numbers directly, sure. But 500 bhp is around what, 420 rwhp, which is pretty impressive for no headers, cam, or even head work, from a 5liter, don't you agree.
No, the Ls6 has less Valve train weight. However the M5 has low valve train inertia because it's a OHC design which does give it a high rev potential, but it has considerably more valve train parasitic loss as it's much more complicated. The reason DOHC motor apear to rev quicker is because they have higher port velocities becuse they use 2 intake valves instead of 1. This gives the motor a freeer reving feel.
I agree. In fact, because of just that fact, I would assume the ls6 has an advantage in pure revving top end. Of course if can't match the revving with the support parts, it would not be a complete package. I.e., the ls6 intake manifold is RPM limited, which is why hp reaches a plataue right after 6.5k all the time as per the original design. But back to the original argument though, it would be difficult to add more to say that the extra weight of the M5 would be worth it, because after all it would still weigh more and not develop an appropriate proportion of more power.
In summary, there are several differences betweeen the ls6 and current Gen M5 engine. No doubt there is no right or wrong, and both have their list of things I would die for. However if you were to say which one is more advanced technology wise, the nod goes to the M5 IMO.
Well Apeal is more MARKETING than TECHNOLOGY. I have to admit the M5 apeals to more then the Z06, but that's not because of technology.
I'll give you that, the way it was marketed several months before it came out made it seem like the end all be all (similar to the ls1/ls6 IIRC). When in fact you right it weighs more, costs more to manufacture, costs more to maintain, and generally is harder to work on if you take it apart. Unlike the lsx variants, which I understand are very easy to work on, and because of the simplified valvetrain easy to upgrade etc. sounds like a better choice.
This is the two vs one intake valve issue. here is the thing you can tune a 2V motor to make the same flow as a 4V motor for a specific RPM. However, because the 4V motor pushes higher velocities it can create a wider range of power potential creating better combustion. So its not so much flow as it is velocites can be maintianed over a wider range. to combat this the 2V motor has to be designed to make power over a wide range and thus compromise it's ability to make power at a specific RPM.
You hit the nail on the head there...the ls6 is/was tuned to do exactly that. Make more power over a wider range. In fact the combinaton of the high end and that low end of the GM smallblock is very suprising considering the cost and size. The packaging of that was so tight that from those excellent pictures it's eas to see above the smaller V6 take up just about the same room. More factories need to do this.
Nevertheless, the M5's exotic valvetrain has something which is impossible for a pushrod if I'm not mistaken, and that's variable valve timing (BMW's VANOS). Unfortunately I am not familiar enough with it to comment in detail, but as I understand, it makes it seem like there are many different cams in the motor, when in fact there is only one. That way, it is focused on not only low-end hp but also addresses top-end power as well. I don't know if that is valid for lift or duration, or both, but it offsets the extra weight you may incur by a large margin IMO, because of the "best of both worlds" analogy. I think that's what you were talking about, please correct me if I'm wrong.
yes and no. The M5 Valvetrain is so complicated that truely high RPM potential isn't really there because there are so many more potential points of failure. Additionally high RPM potential is meaningless. The Engine's ability to hold Torque over time (RPM) is meaningful so if the Motor can hold Power (Torque) into higher RPMs that would be beneficial but only if the curve is still increasing. a 4v design does give you a wider torque curve for a given displacement, so a 4V motor can hold torque better into a higher RPM range without sacrificing low end RPM. a 2v motor cannot because of the port velocity compromise I mentioned above.
I would have to agree that the M5's valvetrain is more complicated, but I disagree that because it may contain more points of failure, it makes for an unwise choice. Now I'm looking at the original design by BMW, which yes it does have more moving parts. However, how they combine all the parts to fit together to combat stresses and failures is the key choice. Although there is nothing new, or ground breaking, about the valvetrain (execpt for the VANOS mentioned above), it does have one thing going for it: the R&D and durability of setups. BMW is one of the manufacturers that race what they sell. I mean, today lot of people do that, but they are able to create tight enough tolerances and parts that work together so well there is little risk of failure. More factories have started to pick up on this a few years ago, like when GM started racing the C5R and even early in the 90s when they were developing the C5 for this reason. But when's the last time you heard of a top-end failure or valvetrain failure in BMWs? It just doesn't happen that often (according to general comments by racing directors fwiw...) so maybe the extra weight is worth it for performance sake. They are easily able to overcome setbacks during R&D because of how familiar they are with their own stuff. If you believe that the Ford DOHC design is anything that resembles the BMW DOHC cam you have another thing coming lol.
As far as the RPM vs tq vs hp argument, you make a valid point. I mean, weight itself is meaningless if you can counter with the appropriate hp, right? So for example, lets take the most "prestigous" of racing again, Formula-1. They are running valvetrains that operate on compressed air, not springs, because springs are not able to keep up with the RPMs they are pushing (18k+ RPMs!!!). On the other hand, they have lots of time and engergy spent into making this happen, not for extra-ordinary tq values, but to extend the tq out as far as they need to, which it turn hits horsepower values they shoot for from the onset. You know, they are probably not going to go much past 18k RPMs at this point, because there is no need to. They have hit a sweet spot, so to speak, and have plenty of success with that compromise of hp and reliabilty. I don't know what an F1 engine weighs for sure, so maybe that is not the correct analogy or way to get the point accross.
Dinan's numbers are at the Crank not RWHP.
I know, that's why I posted that. It would be unfare to compare the numbers directly, sure. But 500 bhp is around what, 420 rwhp, which is pretty impressive for no headers, cam, or even head work, from a 5liter, don't you agree.
No, the Ls6 has less Valve train weight. However the M5 has low valve train inertia because it's a OHC design which does give it a high rev potential, but it has considerably more valve train parasitic loss as it's much more complicated. The reason DOHC motor apear to rev quicker is because they have higher port velocities becuse they use 2 intake valves instead of 1. This gives the motor a freeer reving feel.
I agree. In fact, because of just that fact, I would assume the ls6 has an advantage in pure revving top end. Of course if can't match the revving with the support parts, it would not be a complete package. I.e., the ls6 intake manifold is RPM limited, which is why hp reaches a plataue right after 6.5k all the time as per the original design. But back to the original argument though, it would be difficult to add more to say that the extra weight of the M5 would be worth it, because after all it would still weigh more and not develop an appropriate proportion of more power.
In summary, there are several differences betweeen the ls6 and current Gen M5 engine. No doubt there is no right or wrong, and both have their list of things I would die for. However if you were to say which one is more advanced technology wise, the nod goes to the M5 IMO.
08-30-2004, 03:04 AM
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"I know, that's why I posted that. It would be unfare to compare the numbers directly, sure. But 500 bhp is around what, 420 rwhp, which is pretty impressive for no headers, cam, or even head work, from a 5liter, don't you agree. "
Thats because the motor isn't as detuned as your average LS6. The heads as well as cams in those engines are already performance oriented. Not only that, usually their headers resemble shorty headers already from the factory. IMO.. A good comparison would be how the LS6 is still rather mild, but makes 350-360rwhp, over an LS1. If you end up changing out the heads/cam/headers on each, obviously the LS1 would gain the most. Much like the LS6, BMW motors often have healthy sized camshafts in order to turn those rpms and make power, as well as very high flowing heads.. and something that resembles a shorty header. You would be hard pressed to make near the kind of gains an LS1 would make in its detuned state. Its not uncommon for a z06 to make 400rwhp with mild cams due to the increased headflow of the ls6 over the ls1. It would not be very difficult to slightly upgrade the heads/cam/headers/intake and squeeze 420rwhp out of a smooth idling package still shifting before 7k. I believe the only difference is the power downlow might decrease slightly more than your average variable valve timing engine would. More or less I'm saying.. Your not going to put different heads/cam/headers on the m5 motor and make an additional 150rwhp like you can on an ls1, for the same reason that your not going to be able to put heads/cam/headers on an ls6 and make an additional 150rwhp. There just isn't as much to gain when its already had some tuning done from the factory. In an essence just like the ls6 has heads/cam/manifolds over the ls1.. saying without cams/heads/headers on the m5, is not saying much.. as they don't stand to gain near as much.
Josh
Thats because the motor isn't as detuned as your average LS6. The heads as well as cams in those engines are already performance oriented. Not only that, usually their headers resemble shorty headers already from the factory. IMO.. A good comparison would be how the LS6 is still rather mild, but makes 350-360rwhp, over an LS1. If you end up changing out the heads/cam/headers on each, obviously the LS1 would gain the most. Much like the LS6, BMW motors often have healthy sized camshafts in order to turn those rpms and make power, as well as very high flowing heads.. and something that resembles a shorty header. You would be hard pressed to make near the kind of gains an LS1 would make in its detuned state. Its not uncommon for a z06 to make 400rwhp with mild cams due to the increased headflow of the ls6 over the ls1. It would not be very difficult to slightly upgrade the heads/cam/headers/intake and squeeze 420rwhp out of a smooth idling package still shifting before 7k. I believe the only difference is the power downlow might decrease slightly more than your average variable valve timing engine would. More or less I'm saying.. Your not going to put different heads/cam/headers on the m5 motor and make an additional 150rwhp like you can on an ls1, for the same reason that your not going to be able to put heads/cam/headers on an ls6 and make an additional 150rwhp. There just isn't as much to gain when its already had some tuning done from the factory. In an essence just like the ls6 has heads/cam/manifolds over the ls1.. saying without cams/heads/headers on the m5, is not saying much.. as they don't stand to gain near as much.
Josh
08-30-2004, 10:20 PM
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Excellent analogy. 
I stand corrected. From that point of view indeed the ls6 is underrated. The argument by Dinan fans is that their attitude is that of working with the car at various tuning modes. I.e., stage I, II, III, etc etc. By approaching the R&D like that, they are able to avoid common pitfalls along the way and have something they can print in the car mags. Dinan has more marketing parts than performance parts almost, so that makes a huge difference in the final product if you need to get coverage. However you are absolutely correct the M5 is based on a tighter hp level from the start so initial development goes to BMW for putting out a product that forces tuners to be more imaginative that usual. If you spend that kind of time to test and test and test parts for an engine that is already at 80% capacity you must be dilligent as BMW has done most of the work for you right?
I stand corrected. From that point of view indeed the ls6 is underrated. The argument by Dinan fans is that their attitude is that of working with the car at various tuning modes. I.e., stage I, II, III, etc etc. By approaching the R&D like that, they are able to avoid common pitfalls along the way and have something they can print in the car mags. Dinan has more marketing parts than performance parts almost, so that makes a huge difference in the final product if you need to get coverage. However you are absolutely correct the M5 is based on a tighter hp level from the start so initial development goes to BMW for putting out a product that forces tuners to be more imaginative that usual. If you spend that kind of time to test and test and test parts for an engine that is already at 80% capacity you must be dilligent as BMW has done most of the work for you right? 
