Don't hold back, Ford man, tell us what do you really think...
12-25-2007, 08:00 AM
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Don't hold back, Ford man, tell us what do you really think...
An interesting post from 68fastback, from svtperformance.com...
I know the topic has been done to death and BMW are usually a good benchmark when it comes to DOHC engines, but not only is this guy waxing lyrical about Fords 2011 7.0L Hurricane/Boss but he's given GM the biggest back-handed compliment in regards to their LSX engines.
Don't get me wrong, I enjoyed reading his informative post (he sounds like an 'insider') but how can he be that critical of GM's approach to V8 development, particularly in light of how GM V8s still manage to outperform many more complex (and heavier) engines of similar horsepower (e.g. LS7 vs M5 V10).
If the Vette manages such good fuel economy simply because of its light weight, how is it that the GM trucks don't suffer in comparison to comparable trucks from the competition?
http://www.svtperformance.com/forums...&postcount=816
I know the topic has been done to death and BMW are usually a good benchmark when it comes to DOHC engines, but not only is this guy waxing lyrical about Fords 2011 7.0L Hurricane/Boss but he's given GM the biggest back-handed compliment in regards to their LSX engines.
Don't get me wrong, I enjoyed reading his informative post (he sounds like an 'insider') but how can he be that critical of GM's approach to V8 development, particularly in light of how GM V8s still manage to outperform many more complex (and heavier) engines of similar horsepower (e.g. LS7 vs M5 V10).
If the Vette manages such good fuel economy simply because of its light weight, how is it that the GM trucks don't suffer in comparison to comparable trucks from the competition?
I cringe at some of the misuderstandings I'm reading in this thread.
Like OHV being superior (or even comparable) to OHC.
Don't confuse a specific instance with an architecture. The mods have narrow bore spacing. The reason the revs are constrained is because of narrow bore spacing, not DOHC. How do those realate? To get to higher displacements, like 5.0 and 5.4, the modulars need long strokes relative to bore (undersquare). Even at 4.6L the modulars are at their 'square-point!' If you de-stroked a mod to about 3.0-3.5L it would want to scream happily to 8,000rpm -- really.
So, what to do? Make an OHC motor with considerably larger bore spacing. One that doesn't hit its 'square-point' until over 7.0L . At 5.0-5.8L such a motor will scream.
This is exactly what Ford is doing. That engine in the roush-Bowles mule is most certainly an SOHC and most likelt a 3V. 2V would serve no purpose. 4V does not leave enough CC real-estate for multi-plug and DI. 3V designs can accommodate DI, 2 plugs, low-cost VCT and variable lift, and a practical DoD design.
Look at that Roush-Bowles pic carefully. That's no typical "experimental" motor. Even the cam covers are highly refined production pieces, complete with stress-relief/strengthening at the bolt-holes just like on the 3.5L V6.
Look at that pic and you are looking at the future of Ford V8s, imho.
Btw, someone mentioned about wanting HP without adders (me too! ). That 7.0L mule is making more HP that the pulleyed and ported Whipple 5.4 Ford-GT motor with head work that was in the EXACT SAME mule just weks before. And the 7.0L E85 motor ran quicker and faster in the 1/4-mile than the well-tweaked Ford-GT well-prepped and mooded race motor.
Do you think it's coincidence that, destroked to 5.8L, that mule motor has the highly overquare ratios of a SB302 and at 5.0L the oversquare ratio is more than the vintage SB289s?
Anyone who thinks DOHCs don't rev is just not a true earthling <lol> DOHC Indy motors have been turning over 16,000 rpm for a decade now! How do OHV motors compare in that rarified air? They don't -- that's why there aren't any.
Look, this should not be an OHV vs OHC issue in anyone's mind -- OHC is superior...period. Sorry to burst anyone's bubble. While it's true that once you get to bores sizes of 4.0" and over, two-valve arrangements for the street don't suffer too much of a handicap, OHC and multi-valve are still superior and that advantage as revs climb becomes greater and greater because the volume of air they can move as revs increase flow demand is flatly superior.
So how do the LSx engines get good milage and make good power. The bore is big enough to to adequately-well with 2V and GM uses the 'vette to pay for the development of a lot of titanium pieces to offset the OHV liability. They've done an excellet job at that and the PR game too. But make no mistake, not only is OHC superior, GM will return to OHC in the not too distant future. Right now GM is milking the OHV engine for as long as they possibly can because, a number of years ago, they made to cost-saving decision not to not invest the R&D for a larger Northstar-like OHC motor for the 'vette.
If big V8s die off for political reasons in the next 5-10 years <yikes!> they will have serendipitously made the right business decision -- even though they have a revised DOHC design in R&D right now ...just in case the HP wars do continue (yeah!) and they are forced to step-up to a modern long term replacement that can accommodate all the new tech that will become necessary in the not to distant future.
Will the need for DI, VCT/VVT/Variable-lift/DoD force GM to go OHC? Well, there is plenty of room in a 2V pushrod CC for DI and a plug <lol>, variable timing is not a problem (tho sophisticated differential I/E timing management is a problem), and DoD exists. And the 'vette gets good milage tho that's mostly because of it's light-weight and also because GM plays the EPA testing suite with that silly forced 1->4 shift under 3,000 rpm. But, ultimately, OHC is superior here too and GM will likely move their R&D OHC motor into production by the time the ground-up all-new mustang (2012?) arrives.
As enthusiasts we all have another rason to be extatic that Ford is biting the OHC bullet right now on this new motor and that's because, in acommodating new-tech like VVT/VCT/DI/variable-lift/Variable-displacement (<-Ford's term), there is a much greater likelihood that truly hi-performance engines can co-exist in an ever tightening CAFE/CO2 and give us GOOD PRODUCTION VOLUMES!!!. Without such tecnologies Ford would be foreced to restrict volumes of hi-po engines to levels that would make them unavailable to the average mustang buyer and with huge ADMs. So, such technologies are actually key to the Mustang species as a VOLUME performance car - -and Ford is making that investment now, it would appear. I, for one, genuinely appreciate such forward thinking.
It's sort of ironic, imo, that Ford got into its tough financial position by Jacques Nasser milking existing technology and not reinvesting in the longer future just to make good financial numbers in the shorter term and be the stock-holder's hero on his 'watch' (can you say GM OHV engines?). That thoroughly deficient 'look-good' approach has now run its course at Ford in favor of doing what really needs to be done (else perish!) and they are actually s-l-o-w-l-y turning the corner ...and are fairly well on schedule financially, tho the fat lady ain't sung yet <lol>.
So it's ironic to me that Ford should garner any criticism at all for making the dificult decision and huge attendant investments to develop such a new motor when it would be far easier and cheaper (in the short term) to drop back to a less-capable design -- both from performance and CAFE viewpoint.
Like OHV being superior (or even comparable) to OHC.
Don't confuse a specific instance with an architecture. The mods have narrow bore spacing. The reason the revs are constrained is because of narrow bore spacing, not DOHC. How do those realate? To get to higher displacements, like 5.0 and 5.4, the modulars need long strokes relative to bore (undersquare). Even at 4.6L the modulars are at their 'square-point!' If you de-stroked a mod to about 3.0-3.5L it would want to scream happily to 8,000rpm -- really.
So, what to do? Make an OHC motor with considerably larger bore spacing. One that doesn't hit its 'square-point' until over 7.0L . At 5.0-5.8L such a motor will scream.
This is exactly what Ford is doing. That engine in the roush-Bowles mule is most certainly an SOHC and most likelt a 3V. 2V would serve no purpose. 4V does not leave enough CC real-estate for multi-plug and DI. 3V designs can accommodate DI, 2 plugs, low-cost VCT and variable lift, and a practical DoD design.
Look at that Roush-Bowles pic carefully. That's no typical "experimental" motor. Even the cam covers are highly refined production pieces, complete with stress-relief/strengthening at the bolt-holes just like on the 3.5L V6.
Look at that pic and you are looking at the future of Ford V8s, imho.
Btw, someone mentioned about wanting HP without adders (me too! ). That 7.0L mule is making more HP that the pulleyed and ported Whipple 5.4 Ford-GT motor with head work that was in the EXACT SAME mule just weks before. And the 7.0L E85 motor ran quicker and faster in the 1/4-mile than the well-tweaked Ford-GT well-prepped and mooded race motor.
Do you think it's coincidence that, destroked to 5.8L, that mule motor has the highly overquare ratios of a SB302 and at 5.0L the oversquare ratio is more than the vintage SB289s?
Anyone who thinks DOHCs don't rev is just not a true earthling <lol> DOHC Indy motors have been turning over 16,000 rpm for a decade now! How do OHV motors compare in that rarified air? They don't -- that's why there aren't any.
Look, this should not be an OHV vs OHC issue in anyone's mind -- OHC is superior...period. Sorry to burst anyone's bubble. While it's true that once you get to bores sizes of 4.0" and over, two-valve arrangements for the street don't suffer too much of a handicap, OHC and multi-valve are still superior and that advantage as revs climb becomes greater and greater because the volume of air they can move as revs increase flow demand is flatly superior.
So how do the LSx engines get good milage and make good power. The bore is big enough to to adequately-well with 2V and GM uses the 'vette to pay for the development of a lot of titanium pieces to offset the OHV liability. They've done an excellet job at that and the PR game too. But make no mistake, not only is OHC superior, GM will return to OHC in the not too distant future. Right now GM is milking the OHV engine for as long as they possibly can because, a number of years ago, they made to cost-saving decision not to not invest the R&D for a larger Northstar-like OHC motor for the 'vette.
If big V8s die off for political reasons in the next 5-10 years <yikes!> they will have serendipitously made the right business decision -- even though they have a revised DOHC design in R&D right now ...just in case the HP wars do continue (yeah!) and they are forced to step-up to a modern long term replacement that can accommodate all the new tech that will become necessary in the not to distant future.
Will the need for DI, VCT/VVT/Variable-lift/DoD force GM to go OHC? Well, there is plenty of room in a 2V pushrod CC for DI and a plug <lol>, variable timing is not a problem (tho sophisticated differential I/E timing management is a problem), and DoD exists. And the 'vette gets good milage tho that's mostly because of it's light-weight and also because GM plays the EPA testing suite with that silly forced 1->4 shift under 3,000 rpm. But, ultimately, OHC is superior here too and GM will likely move their R&D OHC motor into production by the time the ground-up all-new mustang (2012?) arrives.
As enthusiasts we all have another rason to be extatic that Ford is biting the OHC bullet right now on this new motor and that's because, in acommodating new-tech like VVT/VCT/DI/variable-lift/Variable-displacement (<-Ford's term), there is a much greater likelihood that truly hi-performance engines can co-exist in an ever tightening CAFE/CO2 and give us GOOD PRODUCTION VOLUMES!!!. Without such tecnologies Ford would be foreced to restrict volumes of hi-po engines to levels that would make them unavailable to the average mustang buyer and with huge ADMs. So, such technologies are actually key to the Mustang species as a VOLUME performance car - -and Ford is making that investment now, it would appear. I, for one, genuinely appreciate such forward thinking.
It's sort of ironic, imo, that Ford got into its tough financial position by Jacques Nasser milking existing technology and not reinvesting in the longer future just to make good financial numbers in the shorter term and be the stock-holder's hero on his 'watch' (can you say GM OHV engines?). That thoroughly deficient 'look-good' approach has now run its course at Ford in favor of doing what really needs to be done (else perish!) and they are actually s-l-o-w-l-y turning the corner ...and are fairly well on schedule financially, tho the fat lady ain't sung yet <lol>.
So it's ironic to me that Ford should garner any criticism at all for making the dificult decision and huge attendant investments to develop such a new motor when it would be far easier and cheaper (in the short term) to drop back to a less-capable design -- both from performance and CAFE viewpoint.
12-25-2007, 09:48 AM
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Well he's right about the valvetrain issue. OHC>OHV, before the faithful get thier panties in a twist, other than packaging, OHC is the least stressful of the two, which typically shows up as an engine (all things being equal) that can rev higher. Combine this with mutlivalve arrgements and cam timing as well as lift can be minimized. What screws the pooch in the case of Ford is the pathetic bore spacing and the resultant small bore, which nessecitated a multivalve cylinderhead to get the kind of airflow that doesn't require a camshaft that makes a cam out of a prostock or top fuel engine look like something from a briggs&straton lawnmower motor.
Dunno why people get hung up on the bore to stroke ratio and wether its square, under, or oversquare. Its a good indicator to be sure, but if the cylinderhead can flow enough air to feed the cylinder then its a moot point (the 4v heads on the 5.4 flow in the 280 cfm range on a 3.55 bore, more than enough for any 5.4 or 4.6 liter engine on the street). Displacement on the other hand is where the big difference is. Big engines make big torque, big torque is useful for making big horsepower (as an example the ft lbs./liter spread between the 4.6 3v, the LS7 and the V12 in the Fiorano(sp?) is only about 11 ft lbs. , but you have 300hp, 500hp, and 600hp engines).
As to why the mod motors cant rev higher, that has more to do with the long strokes employed and materials used on the recipocating assembly combined with high piston speeds rather than a limitation brought about by its OHC arragement.
Dunno why people get hung up on the bore to stroke ratio and wether its square, under, or oversquare. Its a good indicator to be sure, but if the cylinderhead can flow enough air to feed the cylinder then its a moot point (the 4v heads on the 5.4 flow in the 280 cfm range on a 3.55 bore, more than enough for any 5.4 or 4.6 liter engine on the street). Displacement on the other hand is where the big difference is. Big engines make big torque, big torque is useful for making big horsepower (as an example the ft lbs./liter spread between the 4.6 3v, the LS7 and the V12 in the Fiorano(sp?) is only about 11 ft lbs. , but you have 300hp, 500hp, and 600hp engines).
As to why the mod motors cant rev higher, that has more to do with the long strokes employed and materials used on the recipocating assembly combined with high piston speeds rather than a limitation brought about by its OHC arragement.
Last edited by bossco; 12-25-2007 at 09:51 AM.
12-25-2007, 10:21 AM
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I'm sure everything he says is true. I mean just look what happened when chevy made a DOHC engine. It made 400HP NA way back in the early 90's. A feat ford hasn't matched yet in over a decade.
You see the problem isn't ohc vs ohv. It's ford can't build and engine to save it's life.
So someday that ford guy is going to have an engine that's OHC, rev's to 8 grand and does all the great things he raves they can do.
He's just going to have a hard time explaining the chevy valve covers to his friends.
You see the problem isn't ohc vs ohv. It's ford can't build and engine to save it's life.
So someday that ford guy is going to have an engine that's OHC, rev's to 8 grand and does all the great things he raves they can do.
He's just going to have a hard time explaining the chevy valve covers to his friends.
Last edited by Aaron91RS; 12-25-2007 at 10:25 AM.
12-25-2007, 12:54 PM
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I'm sure everything he says is true. I mean just look what happened when chevy made a DOHC engine. It made 400HP NA way back in the early 90's. A feat ford hasn't matched yet in over a decade.
You see the problem isn't ohc vs ohv. It's ford can't build and engine to save it's life.
So someday that ford guy is going to have an engine that's OHC, rev's to 8 grand and does all the great things he raves they can do.
He's just going to have a hard time explaining the chevy valve covers to his friends.
You see the problem isn't ohc vs ohv. It's ford can't build and engine to save it's life.
So someday that ford guy is going to have an engine that's OHC, rev's to 8 grand and does all the great things he raves they can do.
He's just going to have a hard time explaining the chevy valve covers to his friends.
12-25-2007, 03:40 PM
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Well he's right about the valvetrain issue. OHC>OHV, before the faithful get thier panties in a twist, other than packaging, OHC is the least stressful of the two, which typically shows up as an engine (all things being equal) that can rev higher. Combine this with mutlivalve arrgements and cam timing as well as lift can be minimized. What screws the pooch in the case of Ford is the pathetic bore spacing and the resultant small bore, which nessecitated a multivalve cylinderhead to get the kind of airflow that doesn't require a camshaft that makes a cam out of a prostock or top fuel engine look like something from a briggs&straton lawnmower motor.
...
As to why the mod motors cant rev higher, that has more to do with the long strokes employed and materials used on the recipocating assembly combined with high piston speeds rather than a limitation brought about by its OHC arragement.
...
As to why the mod motors cant rev higher, that has more to do with the long strokes employed and materials used on the recipocating assembly combined with high piston speeds rather than a limitation brought about by its OHC arragement.
As noted above, if Ford can't design the engines to save themselves... is not GM's problem. GM build the right engines for their intended application and their target market. I don't know if the ever toughening emission laws are going to force GM to adopt OHC technology across the board, but I can't imagine wanting to rev my V8 to 8,000 just to reach it's 'sweet spot'. Not on the street anyhow. Yes BMW build such engines but their rich boys' toys... I can't help but think GM's DOHC is destined for Cadillac and not it's performance cars/trucks.
Having said that, I hope for Ford's sake the new donk is a ripper but it can't come soon enough especially for it's diehard fans. As alluded to, GM will (or should?) have their DOHC V8 out by that time so it will make for interesting comparisons.
I just don't believe that 68fastback is right on all counts, not unless Ford will deliver an engine that will outdo BMW. I can definitely sense his enthusiasm however...
12-25-2007, 08:31 PM
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Yes but we're talking street engines, here, not Indy. Revs don't mean diddly squat as the OHVs make enough revs for them to be well within their powerband for the street/strip. Not only that but they do better for fuel economy, despite their generally larger displacement.
As noted above, if Ford can't design the engines to save themselves... is not GM's problem. GM build the right engines for their intended application and their target market. I don't know if the ever toughening emission laws are going to force GM to adopt OHC technology across the board, but I can't imagine wanting to rev my V8 to 8,000 just to reach it's 'sweet spot'. Not on the street anyhow. Yes BMW build such engines but their rich boys' toys... I can't help but think GM's DOHC is destined for Cadillac and not it's performance cars/trucks.
Having said that, I hope for Ford's sake the new donk is a ripper but it can't come soon enough especially for it's diehard fans. As alluded to, GM will (or should?) have their DOHC V8 out by that time so it will make for interesting comparisons.
I just don't believe that 68fastback is right on all counts, not unless Ford will deliver an engine that will outdo BMW. I can definitely sense his enthusiasm however...
Ultimately OHC is the way to go if your squeezing the last little bit out of the engine, even in a street car, especially when your talking a multivalve layout.
12-25-2007, 08:37 PM
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He also does not have a Cobra R.
Bob
12-25-2007, 09:26 PM
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My intention on here is not to bag any of the guys on svtperformance as they're a pretty mature crowd and some interesting topics discussed (usually without bias) particularly the latest developments of the H/B engine. It's always interesting to get their collective perspective of all things GM related... probably the reason why I posted the topic in the first place. 
But do some there realize that development of the mundane GM 'smallblock' is about to move up a gear? DI will see a significant improvement, VVT a little again, AFM might see an economy gain... there's so much more technology that could be introduced. Surely there's a lot of life left in the GM smallblock. And we haven't yet discussed power adders like on the LS9.
But do some there realize that development of the mundane GM 'smallblock' is about to move up a gear? DI will see a significant improvement, VVT a little again, AFM might see an economy gain... there's so much more technology that could be introduced. Surely there's a lot of life left in the GM smallblock. And we haven't yet discussed power adders like on the LS9.
12-25-2007, 09:29 PM
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Let's see if I can summarize:
1. OHC, especially DOHC, breathes better at high RPM
2. DOHC makes variable valve timing easier (especially for varying intake and exhaust separately
3. OHV makes a smaller package
4. OHV makes DoD easier
It seems that the choice of valvetrain comes down to a bunch of tradeoffs that will vary over time. If super-sophisticated valve timing and lift becomes necessary, I'd expect GM to switch to DOHC out of necessity. If not, then why not stick with OHV, since the current engines breathe fine?
1. OHC, especially DOHC, breathes better at high RPM
2. DOHC makes variable valve timing easier (especially for varying intake and exhaust separately
3. OHV makes a smaller package
4. OHV makes DoD easier
It seems that the choice of valvetrain comes down to a bunch of tradeoffs that will vary over time. If super-sophisticated valve timing and lift becomes necessary, I'd expect GM to switch to DOHC out of necessity. If not, then why not stick with OHV, since the current engines breathe fine?
