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OMG!!!!!!!!!!! you guys can turn anything around to suit you cant you????
we all know the advantages of OHV engines!!! all im trying to point out is the advantages of multi (ie more than 2per cylinder) valve heads!
FORGET the Ford mod motor! its big and heavy and ford didn't do a great job on it, we all know that, even the ford guys!!!!
jeocar, who the F*CK told you a 2 valve setup can flow more than a 4 valver??? they need shotting. take a pair of compasses and a piece of paper. draw one BIG circle and then try and fit 3 smaller ones in the middle of that one. then mesure the circumfrence of the three and compare it to the one big one. i bet you you get a great number for the little ones than the one big one!!!! there you have it more "valve" flow potencial. now i know thats not taking into acount the port!!!!![Winky](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_wink.gif)
also why would you need to swap the heads on a well designed 4 valve setup??? you generally find that you can get a great flowing head just by doing some port work with a well deigned 4 valve per cyclinder set up (FORGET THE FORD MOTOR!!!!!!!). and the cams you use are much "softer" than with a 2 valver.
thanks Chris.
PS. lets not turn this into a slanging match. i hold my hands up now if i have offended anyone on this board, i am sorry that was not my intention. i really hope the mods dont close this thread down cos of what we are disscusing as its really what makes these boards soo great!
thanks again Chris.
we all know the advantages of OHV engines!!! all im trying to point out is the advantages of multi (ie more than 2per cylinder) valve heads!
FORGET the Ford mod motor! its big and heavy and ford didn't do a great job on it, we all know that, even the ford guys!!!!
jeocar, who the F*CK told you a 2 valve setup can flow more than a 4 valver??? they need shotting. take a pair of compasses and a piece of paper. draw one BIG circle and then try and fit 3 smaller ones in the middle of that one. then mesure the circumfrence of the three and compare it to the one big one. i bet you you get a great number for the little ones than the one big one!!!! there you have it more "valve" flow potencial. now i know thats not taking into acount the port!!!!
![Winky](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_wink.gif)
also why would you need to swap the heads on a well designed 4 valve setup??? you generally find that you can get a great flowing head just by doing some port work with a well deigned 4 valve per cyclinder set up (FORGET THE FORD MOTOR!!!!!!!). and the cams you use are much "softer" than with a 2 valver.
thanks Chris.
PS. lets not turn this into a slanging match. i hold my hands up now if i have offended anyone on this board, i am sorry that was not my intention. i really hope the mods dont close this thread down cos of what we are disscusing as its really what makes these boards soo great!
thanks again Chris.
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#42
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right so forget trying to fit this into anything, and forget the weight of it for a min.
can you imagine the power and torque that a 3 valve LS7 could make???? if you can get 500bhp out of a 7.0ltr with 2 valves and you get 10% more flow from the 3valver. plus you can take it to about 7500rpm.
im thinking a bomb proof 600bhp from the factory could be posiable (and not that exspencive) and very doable!!! agree or disagree?????
thanks again guys
Chris.
can you imagine the power and torque that a 3 valve LS7 could make???? if you can get 500bhp out of a 7.0ltr with 2 valves and you get 10% more flow from the 3valver. plus you can take it to about 7500rpm.
im thinking a bomb proof 600bhp from the factory could be posiable (and not that exspencive) and very doable!!! agree or disagree?????
thanks again guys
Chris.
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disagree. a hydrolic roller isn't gonig to be happy at 7500rpm.
also, you guys seem to forget the valvestem area and other factors of fluid flow when talking about this. its not as simple as biggest valve area.
also, you guys seem to forget the valvestem area and other factors of fluid flow when talking about this. its not as simple as biggest valve area.
#44
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This has been discussed ad nauseum
https://ls1tech.com/forums/advanced-engineering-tech/437433-benefits-32-valve-heads.html#post4147794
http://www.autoblog.com/2005/12/08/a...finitive-rant/
https://ls1tech.com/forums/advanced-engineering-tech/437433-benefits-32-valve-heads.html#post4147794
http://www.autoblog.com/2005/12/08/a...finitive-rant/
Autoblog Feature: OHC vs. OHV - the definitive rant
Posted Dec 8th 2005 7:00PM by Eric Bryant
OHC vs OHV
Spurred on by Joel's post on pushrod engines and some of the comments that it generated, I think it's time to take a closer look at the differences between OHC and OHV engines. We all "know" that OHC engines rev higher, produce less torque, increase specific output (power per unit displacement), operate more smoothly, and so on and so forth. Those are stereotypes, but ones that are indeed based on some honest real-world experiences. So were do these characteristics come from?
To figure this out, we need to first understand that engines are air pumps, and the volume of that air is what affects both power and torque characteristics. Peak power is basically determined by the limit of airflow per unit time. Peak torque is determined by airflow per combustion cycle; essentially, how much air is crammed into the cylinder on every intake stroke. This should hint towards the intertwined relationship between horsepower and torque, but we’ll cover that at some other time.
Peak power is relatively easy to achieve, airflow on a naturally-aspirated engine mostly being a function of the cross-section of the intake tract (the exhaust tract is important as well, but less so because there’s more pressure available to expel the exhaust gases). Specifically, the smallest cross-section of the intake port is going to present the largest restriction to flow if an even velocity is achieved throughout the port (and that’s a big “if”)*.
Valve curtain area
Usually, the area of the intake valve(s) is the ultimate determining factor, but this assumes that the intake valve is fully opened. By this, I mean that it’s lifted off the seat by at least 0.25 times the valve’s diameter, which is where the valve “curtain area” (the circumference of the valve times lift) equals the area of the valve itself. This should allow the valve to flow at its maximum - we’ll come back to this in a moment.
To achieve a large valve area, we need to maximize the diameter of the valves. In a two-valve head, this places each valve alongside the edge of the cylinder, a condition called “shrouding”. Due to the proximity of the cylinder wall along a part of LS6 chamber with cylinder outlinethe valve diameter (shown to the right as a red line superimposed on the combustion chamber), a significant portion of that curtain area becomes unusable. This is why it’s often necessary to lift the valve well beyond the 0.25 x diameter figure of merit in order to achieve peak flow. This is also why, all things being equal in terms of displacement, larger bores usually make more peak power - it frees up room for more valve area. Four-valve setups take advantage of more of the cylinder area, but almost as importantly, they suffer less from shrouding since the smaller diameter of the valves doesn’t as closely follow the cylinder wall (the valves can shroud each other, but that’s less of an issue).
All of the above points to an obvious airflow advantage for four-valve heads, given a fixed cylinder bore size. But there’s yet another advantage, this one related to the curtain area. Since multiple valves necessarily result in smaller valve diameters, this means that less valve lift is required to maximize flow. Less lift and smaller (read: lighter) valves makes the job of the valve springs much easier. Indeed the difficulty of closing the valves is often a limiting factor to how high an engine can safely rev, and it’s an extremely difficult problem to work around in a production engine where a valve spring life of a few thousand miles just isn’t acceptable.
This clearly points towards a multi-valve design - and almost by default, overhead cams** - as being superior for peak power. No big surprise, eh? But peak power is rarely what we’re after in a production engine.
More important is maintaining a healthy amount of torque over the usable rev range. No, this isn’t some sort of claim that Torque Is King, since proponents in that camp are usually interested only in peak numbers, and preferably at a low RPM. To obtain this, we need to fill the cylinder as much as possible across the rev range. Simply maximizing the valve area is not the way to accomplish this task, and choking down the intake tract to maintain velocity at low revs isn’t the way to go, either.
Assuming that sufficient bore diameter is available, and that there is enough displacement - such a nasty word! - to keep the maximum operating speed under, say, 6000 RPM (for those engines not employing exotic valvetrain components such as titanium or hollow-stem valves), it is quite possible to achieve great results with a 2V pushrod engine. Spend enough money on the valvetrain, and that arbitrary rev limit goes away, too. Additionally, the low-RPM airflow characteristics of a 2V wedge-type head are usually superior to those of a pent-roof narrow-angle 4V design, with more swirl (airflow rotation parallel to the cylinder axis) and tumble (perpendicular to the cylinder axis). Additionally, the area of the chamber that’s not occupied by valve allows the addition of addition quench area, which adds further turbulence to the mixture during the compression stroke. All of this can add up to excellent low-speed and part-throttle performance, which is why an engine like Chevrolet’s LS7 can offer nearly 75% of its peak torque anywhere between idle and redline, offer up 10% additional usable revs after hitting peak power, and manages to pull down some extremely respectable economy numbers. Hey, there’s a reason that Honda’s VTEC system on its V6 Accords barely cracks open one of the two intake valves below 3000 RPM.
For those that evaluate an engine based on mass, packaging volume, and fuel efficiency, OHV designs are very attractive, for stuffing a pair of cams into the cylinder heads adds volume and mass at just about the worst possible place on a V-configuration engine. Add in some roller followers and tall valve springs, and all of a sudden we’ve got V6s that are larger than V8s, and “small” V8s that are larger than the big-blocks of the 60s. During an SAE presentation that I attended, Chevy’s Dave Hill stated that the Nissan VQ35 DOHC V6 was benchmarked during the development of the C5 Corvette, and was clearly found to provide significantly less power per unit mass and unit volume than the GM’s GenIII V8. Peak-power-per-unit-displacement is strictly an amateurish way to compare two engines.
What about smoothness, NVH, power delivery, the touchy-feely stuff - do OHC engines really offer an advantage? To some extent, yes. The OHV valvetrain tends to create a rather long string of mechanical interfaces, each bringing with it the potential for noise and vibration. And rocker arms can make a heck of a racket as well (as anyone who as installed a set of aftermarket roller rockers knows). But OHC engines necessarily place the cams far away from the crankshaft, which means that the cam drive system often has an opportunity to emit noise. As well,
Posted Dec 8th 2005 7:00PM by Eric Bryant
OHC vs OHV
Spurred on by Joel's post on pushrod engines and some of the comments that it generated, I think it's time to take a closer look at the differences between OHC and OHV engines. We all "know" that OHC engines rev higher, produce less torque, increase specific output (power per unit displacement), operate more smoothly, and so on and so forth. Those are stereotypes, but ones that are indeed based on some honest real-world experiences. So were do these characteristics come from?
To figure this out, we need to first understand that engines are air pumps, and the volume of that air is what affects both power and torque characteristics. Peak power is basically determined by the limit of airflow per unit time. Peak torque is determined by airflow per combustion cycle; essentially, how much air is crammed into the cylinder on every intake stroke. This should hint towards the intertwined relationship between horsepower and torque, but we’ll cover that at some other time.
Peak power is relatively easy to achieve, airflow on a naturally-aspirated engine mostly being a function of the cross-section of the intake tract (the exhaust tract is important as well, but less so because there’s more pressure available to expel the exhaust gases). Specifically, the smallest cross-section of the intake port is going to present the largest restriction to flow if an even velocity is achieved throughout the port (and that’s a big “if”)*.
Valve curtain area
Usually, the area of the intake valve(s) is the ultimate determining factor, but this assumes that the intake valve is fully opened. By this, I mean that it’s lifted off the seat by at least 0.25 times the valve’s diameter, which is where the valve “curtain area” (the circumference of the valve times lift) equals the area of the valve itself. This should allow the valve to flow at its maximum - we’ll come back to this in a moment.
To achieve a large valve area, we need to maximize the diameter of the valves. In a two-valve head, this places each valve alongside the edge of the cylinder, a condition called “shrouding”. Due to the proximity of the cylinder wall along a part of LS6 chamber with cylinder outlinethe valve diameter (shown to the right as a red line superimposed on the combustion chamber), a significant portion of that curtain area becomes unusable. This is why it’s often necessary to lift the valve well beyond the 0.25 x diameter figure of merit in order to achieve peak flow. This is also why, all things being equal in terms of displacement, larger bores usually make more peak power - it frees up room for more valve area. Four-valve setups take advantage of more of the cylinder area, but almost as importantly, they suffer less from shrouding since the smaller diameter of the valves doesn’t as closely follow the cylinder wall (the valves can shroud each other, but that’s less of an issue).
All of the above points to an obvious airflow advantage for four-valve heads, given a fixed cylinder bore size. But there’s yet another advantage, this one related to the curtain area. Since multiple valves necessarily result in smaller valve diameters, this means that less valve lift is required to maximize flow. Less lift and smaller (read: lighter) valves makes the job of the valve springs much easier. Indeed the difficulty of closing the valves is often a limiting factor to how high an engine can safely rev, and it’s an extremely difficult problem to work around in a production engine where a valve spring life of a few thousand miles just isn’t acceptable.
This clearly points towards a multi-valve design - and almost by default, overhead cams** - as being superior for peak power. No big surprise, eh? But peak power is rarely what we’re after in a production engine.
More important is maintaining a healthy amount of torque over the usable rev range. No, this isn’t some sort of claim that Torque Is King, since proponents in that camp are usually interested only in peak numbers, and preferably at a low RPM. To obtain this, we need to fill the cylinder as much as possible across the rev range. Simply maximizing the valve area is not the way to accomplish this task, and choking down the intake tract to maintain velocity at low revs isn’t the way to go, either.
Assuming that sufficient bore diameter is available, and that there is enough displacement - such a nasty word! - to keep the maximum operating speed under, say, 6000 RPM (for those engines not employing exotic valvetrain components such as titanium or hollow-stem valves), it is quite possible to achieve great results with a 2V pushrod engine. Spend enough money on the valvetrain, and that arbitrary rev limit goes away, too. Additionally, the low-RPM airflow characteristics of a 2V wedge-type head are usually superior to those of a pent-roof narrow-angle 4V design, with more swirl (airflow rotation parallel to the cylinder axis) and tumble (perpendicular to the cylinder axis). Additionally, the area of the chamber that’s not occupied by valve allows the addition of addition quench area, which adds further turbulence to the mixture during the compression stroke. All of this can add up to excellent low-speed and part-throttle performance, which is why an engine like Chevrolet’s LS7 can offer nearly 75% of its peak torque anywhere between idle and redline, offer up 10% additional usable revs after hitting peak power, and manages to pull down some extremely respectable economy numbers. Hey, there’s a reason that Honda’s VTEC system on its V6 Accords barely cracks open one of the two intake valves below 3000 RPM.
For those that evaluate an engine based on mass, packaging volume, and fuel efficiency, OHV designs are very attractive, for stuffing a pair of cams into the cylinder heads adds volume and mass at just about the worst possible place on a V-configuration engine. Add in some roller followers and tall valve springs, and all of a sudden we’ve got V6s that are larger than V8s, and “small” V8s that are larger than the big-blocks of the 60s. During an SAE presentation that I attended, Chevy’s Dave Hill stated that the Nissan VQ35 DOHC V6 was benchmarked during the development of the C5 Corvette, and was clearly found to provide significantly less power per unit mass and unit volume than the GM’s GenIII V8. Peak-power-per-unit-displacement is strictly an amateurish way to compare two engines.
What about smoothness, NVH, power delivery, the touchy-feely stuff - do OHC engines really offer an advantage? To some extent, yes. The OHV valvetrain tends to create a rather long string of mechanical interfaces, each bringing with it the potential for noise and vibration. And rocker arms can make a heck of a racket as well (as anyone who as installed a set of aftermarket roller rockers knows). But OHC engines necessarily place the cams far away from the crankshaft, which means that the cam drive system often has an opportunity to emit noise. As well,
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Warning..long post.
I was thinking the exact same thing. Also, as stated there are size constraints due to the design of the chassis. Make a smaller more efficient DOHC head? How? For the same size head, there is no way possible that you can make 4 valves flow like 2 valves. If you have 2 intake valves, you are probably going to have 2 intake runners. They need a wall to divide the two of them. This wall eats possible runner cross-section and size, whereas having one single runner would be able to use that space.
If you are going to have one intake runner with two intake valves in it, then you have the same possible intake runner volume, but the air has to hit the area between the two valves and split. Not all of that air is going to route to each side right away. First it is going to have to hit that big obstruction in the middle (area in the runner between the two valveseats), and then go into the cylinders. This will hurt intake air pulses.
Same goes for the exhaust. We all like the idea of long tube headers because each individual exhaust runner has its own space for a while. Having two valves go into one single exhaust runner forces the exhaust waves to slam into each other. I understand that the pulses from these two valves will be at the same time, so its not like there will be problems with the exhaust pulese at different times (i.e. AFTER the head, it will act the same as regular heads and exhaust manifolds). However, you have two groups of air Y-ing into each other to exit the head into the manifold. Again, air is being re-directed into each other. So make two separate exhaust runners to avoid this problem. But then again you have a wall that's taking up runner space. Not to mention the more complicated intake/exhaust manifolds required by this.
Keep in mind the above situations are assuming you're trying to make a 4-valve head the same size as a 2-valve head (and of course I'm not taking into account the extra area required on the top of the head to accomadate the extra rockers/springs, etc.) To make a 4-valve head flow better than a 2-valve head, the head needs to be larger to be able to supply each individual valve with more air (so that two valves will actually flow better than the single valve) to be beneficial.
At this point the spark plug will also be put into the top of the head I imagine, which again requires a larger head (more top surface area). Spark plugs may be easier to change, but at the cost of a much larger/heavier engine.
Obviously this larger head size adds weight, and because of the required designs of the intake and exhaust manifolds to optimize the 4-valve setup, the intake and exhaust manifolds will both be larger and weigh more.
This isn't even talking about the length of the engine, which also needs to be longer on a DOHC motor to provide room for the large timing set on each head vs. the small timing set on a OHV motor. I'm also not a big fan of changing timing belts/cams on OHC motors.
With an OHC motor, you're also going to want to run timing belts instead of chains because of the extra length required of the timing belt/chain. A chain would be far heavier and louder at those sizes. Then you have two belts that need to be changed every 60k miles. Having cams in the heads also means more heat will be produced in the heads because all of the rolling surfaces of the cam are in the heads (i.e. bearing and lifter frictional heat, which is better to be absorbed in the bottom end). Hotter heads means more chances of detonation, and more heat to soak into the incoming air tract (via the intake and the actual intake runners themselves).
I'd rather not have to rev to the moon to make more power. DOD is a very cool technology that, as stated (and as the name implies), gives more displacement only when needed, giving you the gas mileage of a smaller engine, but the power of a larger engine, without adding extra stress on the internals by revving higher. I want to see a Mercedes/BMW motor make power to trap 118-120 and still get 32mpg on its way home from the track. My pushrod motor does, and that's with poor traction and smaller-than-optimal intake. I do realize that this isn't exactly a fair comparison though, given that the Mercedes/BMW will idle and drive FAR smoother than my car.
Originally Posted by treyZ28
also, you guys seem to forget the valvestem area and other factors of fluid flow when talking about this. its not as simple as biggest valve area.
If you are going to have one intake runner with two intake valves in it, then you have the same possible intake runner volume, but the air has to hit the area between the two valves and split. Not all of that air is going to route to each side right away. First it is going to have to hit that big obstruction in the middle (area in the runner between the two valveseats), and then go into the cylinders. This will hurt intake air pulses.
Same goes for the exhaust. We all like the idea of long tube headers because each individual exhaust runner has its own space for a while. Having two valves go into one single exhaust runner forces the exhaust waves to slam into each other. I understand that the pulses from these two valves will be at the same time, so its not like there will be problems with the exhaust pulese at different times (i.e. AFTER the head, it will act the same as regular heads and exhaust manifolds). However, you have two groups of air Y-ing into each other to exit the head into the manifold. Again, air is being re-directed into each other. So make two separate exhaust runners to avoid this problem. But then again you have a wall that's taking up runner space. Not to mention the more complicated intake/exhaust manifolds required by this.
Keep in mind the above situations are assuming you're trying to make a 4-valve head the same size as a 2-valve head (and of course I'm not taking into account the extra area required on the top of the head to accomadate the extra rockers/springs, etc.) To make a 4-valve head flow better than a 2-valve head, the head needs to be larger to be able to supply each individual valve with more air (so that two valves will actually flow better than the single valve) to be beneficial.
At this point the spark plug will also be put into the top of the head I imagine, which again requires a larger head (more top surface area). Spark plugs may be easier to change, but at the cost of a much larger/heavier engine.
Obviously this larger head size adds weight, and because of the required designs of the intake and exhaust manifolds to optimize the 4-valve setup, the intake and exhaust manifolds will both be larger and weigh more.
This isn't even talking about the length of the engine, which also needs to be longer on a DOHC motor to provide room for the large timing set on each head vs. the small timing set on a OHV motor. I'm also not a big fan of changing timing belts/cams on OHC motors.
With an OHC motor, you're also going to want to run timing belts instead of chains because of the extra length required of the timing belt/chain. A chain would be far heavier and louder at those sizes. Then you have two belts that need to be changed every 60k miles. Having cams in the heads also means more heat will be produced in the heads because all of the rolling surfaces of the cam are in the heads (i.e. bearing and lifter frictional heat, which is better to be absorbed in the bottom end). Hotter heads means more chances of detonation, and more heat to soak into the incoming air tract (via the intake and the actual intake runners themselves).
I'd rather not have to rev to the moon to make more power. DOD is a very cool technology that, as stated (and as the name implies), gives more displacement only when needed, giving you the gas mileage of a smaller engine, but the power of a larger engine, without adding extra stress on the internals by revving higher. I want to see a Mercedes/BMW motor make power to trap 118-120 and still get 32mpg on its way home from the track. My pushrod motor does, and that's with poor traction and smaller-than-optimal intake. I do realize that this isn't exactly a fair comparison though, given that the Mercedes/BMW will idle and drive FAR smoother than my car.
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Originally Posted by DuronClocker
I was thinking the exact same thing. Also, as stated there are size constraints due to the design of the chassis. Make a smaller more efficient DOHC head? How? For the same size head, there is no way possible that you can make 4 valves flow like 2 valves. If you have 2 intake valves, you are probably going to have 2 intake runners. They need a wall to divide the two of them. This wall eats possible runner cross-section and size, whereas having one single runner would be able to use that space.
For the record, most every GM DOHC that GM has ever built has had one intake runner per cylinder, despite having 2 valves. The 3.4l DOHC V6, the 3.6l DOHC V6, every 4 cylinder since the Quads (Including Saturns), the 4.4/4.6l DOHC V8s, and God knows what else. There are two valves, but they converge to a single runner even before the head surface. On the 3.4l DOHC, the split is about halfway down the intake port, and it's all but knife-edged from the factory (Port = head surface to valve, Runner = head surface to plenum). The LT5 is an exception obviously, but for good reason (Dual stage intake).
If you are going to have one intake runner with two intake valves in it, then you have the same possible intake runner volume, but the air has to hit the area between the two valves and split. Not all of that air is going to route to each side right away. First it is going to have to hit that big obstruction in the middle (area in the runner between the two valveseats), and then go into the cylinders. This will hurt intake air pulses.
Same goes for the exhaust. We all like the idea of long tube headers because each individual exhaust runner has its own space for a while. Having two valves go into one single exhaust runner forces the exhaust waves to slam into each other. I understand that the pulses from these two valves will be at the same time, so its not like there will be problems with the exhaust pulese at different times (i.e. AFTER the head, it will act the same as regular heads and exhaust manifolds). However, you have two groups of air Y-ing into each other to exit the head into the manifold. Again, air is being re-directed into each other. So make two separate exhaust runners to avoid this problem. But then again you have a wall that's taking up runner space. Not to mention the more complicated intake/exhaust manifolds required by this.
Keep in mind the above situations are assuming you're trying to make a 4-valve head the same size as a 2-valve head (and of course I'm not taking into account the extra area required on the top of the head to accomadate the extra rockers/springs, etc.) To make a 4-valve head flow better than a 2-valve head, the head needs to be larger to be able to supply each individual valve with more air (so that two valves will actually flow better than the single valve) to be beneficial.
At this point the spark plug will also be put into the top of the head I imagine, which again requires a larger head (more top surface area). Spark plugs may be easier to change, but at the cost of a much larger/heavier engine.
![Embarassed](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_emb.gif)
Obviously this larger head size adds weight, and because of the required designs of the intake and exhaust manifolds to optimize the 4-valve setup, the intake and exhaust manifolds will both be larger and weigh more.
This isn't even talking about the length of the engine, which also needs to be longer on a DOHC motor to provide room for the large timing set on each head vs. the small timing set on a OHV motor. I'm also not a big fan of changing timing belts/cams on OHC motors.
With an OHC motor, you're also going to want to run timing belts instead of chains because of the extra length required of the timing belt/chain. A chain would be far heavier and louder at those sizes. Then you have two belts that need to be changed every 60k miles. Having cams in the heads also means more heat will be produced in the heads because all of the rolling surfaces of the cam are in the heads (i.e. bearing and lifter frictional heat, which is better to be absorbed in the bottom end). Hotter heads means more chances of detonation, and more heat to soak into the incoming air tract (via the intake and the actual intake runners themselves).
I'd rather not have to rev to the moon to make more power. DOD is a very cool technology that, as stated (and as the name implies), gives more displacement only when needed, giving you the gas mileage of a smaller engine, but the power of a larger engine, without adding extra stress on the internals by revving higher. I want to see a Mercedes/BMW motor make power to trap 118-120 and still get 32mpg on its way home from the track. My pushrod motor does, and that's with poor traction and smaller-than-optimal intake. I do realize that this isn't exactly a fair comparison though, given that the Mercedes/BMW will idle and drive FAR smoother than my car.
This post was flawed from the minute you started typing. You have little knowledge on GM's DOHC motors, and this is brutally obvious. Don't preach ignorance. I am pro-DOHC, but can respect the advantages (TRUE advantages, not the bull$hit ones you dreamed up), of today's pushrod engines (Namely the LSX).
Last edited by FieroZ34; 10-25-2006 at 11:01 PM.
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Then why is it that hp/lbs. and hp/$, OHV wins. Most cars with all those variable intake designs and multiple throttle bodies are rediculously expensive. Don't get me wrong, the M3 and M5 are stunning cars, but I don't think GM is aiming to compete at that level. DOHC is definately better for max effort, but not in price. Doesn't anyone remember the LT5? What happened there? Why didn't GM keep the DOHC design when they released the C5? Maybe the price has something to do with it.
We definately need some controls for this debate. I feel like everyone is talking about different subjects. This 2V 4V thing is getting rediculous. They are both good. I guess in theory 4 Valve should FLOW better than 2. Then again, look at the F20C in the S2000, The LS7 heads outflow them. The LS7 uses cubes to reach it's flow instead of RPMs. Keep in mind the LS7 stock setup doesn't even allow it to reach the full potential of the heads. So the gatekeeper here are the heads. I'm sure people are making over 550whp, that's says alot for stock heads. It doesn't matter how many vavles an engine have, it's only going to flow so much, and GM did a great job on those heads at 360cfm. We can't even port LS6 heads to do that. How they chose to make power was up to them. I personally would use cubes to reach peak flow heads.
Another thing is I don't think people are thinking about engine geometry and variable vavle timing/lift. Let's just face it, pushrod engines are not going to have high overlap and sick idles from the factory, not unless they come up with some new radical valve timing technology. Remember the state of CALIFORNIA. So you can forget about scavenging. With a 4.00 stroke they probably don't want to take it any higher anyways. The piston speeds are crazy at the moment. It already has titanium con rods. You could reduce the stroke, but keeping it a 427 with a shorter stroke is going to make it a really wide engine, that you would need to design a totally different engine.
We definately need some controls for this debate. I feel like everyone is talking about different subjects. This 2V 4V thing is getting rediculous. They are both good. I guess in theory 4 Valve should FLOW better than 2. Then again, look at the F20C in the S2000, The LS7 heads outflow them. The LS7 uses cubes to reach it's flow instead of RPMs. Keep in mind the LS7 stock setup doesn't even allow it to reach the full potential of the heads. So the gatekeeper here are the heads. I'm sure people are making over 550whp, that's says alot for stock heads. It doesn't matter how many vavles an engine have, it's only going to flow so much, and GM did a great job on those heads at 360cfm. We can't even port LS6 heads to do that. How they chose to make power was up to them. I personally would use cubes to reach peak flow heads.
Another thing is I don't think people are thinking about engine geometry and variable vavle timing/lift. Let's just face it, pushrod engines are not going to have high overlap and sick idles from the factory, not unless they come up with some new radical valve timing technology. Remember the state of CALIFORNIA. So you can forget about scavenging. With a 4.00 stroke they probably don't want to take it any higher anyways. The piston speeds are crazy at the moment. It already has titanium con rods. You could reduce the stroke, but keeping it a 427 with a shorter stroke is going to make it a really wide engine, that you would need to design a totally different engine.
#53
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Originally Posted by redfulcrum
Then again, look at the F20C in the S2000, The LS7 heads outflow them
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really though the two hionda engines you have mentioned have some of the best head work form the fortory ever!!! they are outstanding. the only thing on this level (well 4 pot anyway) is the Ford Duratec.
i have to agree with Z34 on this. great post mate. no offence to Duron of course!
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HAHAHAAHAHAHAHAAHA great one joecar!
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thanks Chris
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#54
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Chevy’s Dave Hill stated that the Nissan VQ35 DOHC V6 was benchmarked during the development of the C5 Corvette, and was clearly found to provide significantly less power per unit mass and unit volume than the GM’s GenIII V8. Peak-power-per-unit-displacement is strictly an amateurish way to compare two engines.
I don't understand why one would argue in favor of a technological marvel, only lose 22% of the available power [(400-311)/400=0.2225] in the process. Yes, I'm comparing that engine to the LS2 instead of the LS1 like the author I quoted, but keep in mind that the LS7 also fits in, essentially, the same space. So how about a hot rodded 3.5L or 4.0L that reaches something like 350 - 375 HP instead of the LS7's 505 HP.
Bet they'll sell great!
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#55
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Originally Posted by chuntington101
so are you guys honnestly saying that you would favour a 2 vales per cyclinder LS7 to a 3 valve per cyclinder one, even if the packaging was only slightly bigger???
if so you seriously need your heads looking at (aprdon the pun! lol)!!!
more valves means more flow! you already have the cubes! now its time for some heads to let you use them all!!!
Chris.
if so you seriously need your heads looking at (aprdon the pun! lol)!!!
more valves means more flow! you already have the cubes! now its time for some heads to let you use them all!!!
Chris.
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Originally Posted by 11 Bravo
I need my head looked at because I think the LS7 flows enough air. Post up the 4V heads that flow as much bone stock. If GM needs to change anything, it's the intake.
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Originally Posted by FieroZ34
The pushrod folks were the ones who brought up cost, so it's fair that we use that as well. Those are factory CNC ported heads. My 4v heads, which flow nearly as much (How much do the LS7s flow?), were as-cast, with no 4 billion dollar multi-axis CNC machine needed.
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$4 billion dollars? damn, what are you machining?
anyway, you can get great cast heads that flow wonderfully for very cheap.
as far as GM is concerned, I wouldn't be surprised if the cost of 3 more camshafts, 15 more cam bearings, 16 more valves, 16 more valve springs, 16 locks, retainers etc, a timing chain 5-10x as long, extra aluminum in the heads, cost in CAFE for lost MPG etc all cost way more than a quick CNC on 16 ports.
They are already getting machined in many places to begin with. Its just a bit more machine time and a one time programing cost. They are porting an aluminum runner, not making parts for a jet engine (despite what saab comercials tell you!)
anyway, you can get great cast heads that flow wonderfully for very cheap.
as far as GM is concerned, I wouldn't be surprised if the cost of 3 more camshafts, 15 more cam bearings, 16 more valves, 16 more valve springs, 16 locks, retainers etc, a timing chain 5-10x as long, extra aluminum in the heads, cost in CAFE for lost MPG etc all cost way more than a quick CNC on 16 ports.
They are already getting machined in many places to begin with. Its just a bit more machine time and a one time programing cost. They are porting an aluminum runner, not making parts for a jet engine (despite what saab comercials tell you!)
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Originally Posted by redfulcrum
Then again, look at the F20C in the S2000, The LS7 heads outflow them.
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You guys are making this way too complicated. 4 valves flow more than two because they have significantly more valve circumference so they flow better, especially at low lifts. They are less susceptible to valve float because the typical OHC has significantly less reciprocating weight. Why do you think that virtually all recent race engine designs and every recent sportbike design has 4 (or more) valves per cylinder? The LSx motors were designed with being applicable to a wide range of vehicles being a priority. Sports cars to Trucks had to use the same basic engine to keep costs where GM wanted them. And they have produced an excellent engine working around that necessity. But don't kid yourselves, a 4 valve engine with the same displacement could be more powerful in every aspect without any insurmountable drawbacks. And the argument that they won't fit in an F body doesn't work either. I have pix of a Northstar in a 4th gen. It fits. And if the car was designed around it, it would fit even better.