Right, got it. So it's all down to the NVH for street car use.
This explains why I've come across references to the Mirage endurance race cars having massive vibration problems when they were fitted with the Cosworth DFV used as a stressed member. I'd never thought about that engine being a flat plane unit.
In reply to Keith Tanner :
And that's a 3 liter engine! Imagine the ruckus a 5.5 would do.
Knurled. said:In reply to frenchyd :
It's not the rocker and pushrod weight so much as the valve weight and how single valves require a lot more lift, therefore more acceleration. A DOHC with .5" of lift would be considered a massive race setup...
You're at least partially right. One big valve is heavier than 2 little valves, then you add the longer length required to deal with stiffer springs at an affordable cost and the weight goes up more.
Then you need to deal with the drag of a rocker arm across the tip of a longer velve. Roller tipped rockers solve the issue but at higher cost and bulkier mass. Todays's pushrod engines deal with it by using longer guides. Which again adds to the length ( and weight) of the valve.
The lifter on DOHC deals with that issue, without the expense or weight of today's current roller lifters.
Take the weight of roller lifters, pushrods, rockers, and valve's that's a lot of mass to constantly move and then have the springs force closed in a big hurry.
In reply to frenchyd :
Rocker tips are mainly a friction benefit, has nothing really to do with RPM capability. But they are great for reducing fuel consumption at idle.
The modern thing with OHC is to use rockers/followers, sometimes with rollers and sometimes not (usually race efforts do NOT have rollers, they add unneccessary weight), because buckets have a lot more friction, a lot more weight, and severely limit what you can do lift-wise without going to ever larger diameter buckets, which add more weight. Plus, buckets are stuck at a fixed 1:1 lift ratio, you can do so much more with a follower. Plus plus, you can much more easily do valve deactivation or variable lift with rockers.
One of the ways the VW 07K (DOHC 5 cylinder) is so much better than the old 034 type DOHC fives (think iconic Audi rally cars) is you can get MUCH more valve lift per duration with their finger followers than you could ever get with the buckets in the old engine. Way more power capability. And then just to twist the knife,a stock 07K casting has more and better flow than even a max ported full race 034 head.
In reply to Knurled. :
I understand the advantage of rockers but see serious race motors not use them. Perhaps it's a RPM limited advantage? Close to stock and rockers offer benefits. Up in that 20,000 rpm range of F1 buckets?
Knurled. said:Y'know, if it was a hot vee, they could get the benefits of flat plane crank without the hassles...
Some of the benefits, anyway. You'd still have that heavy crossplane crankshaft. Getting equal-length 180° headers . . . probably not a trivial detail.
Norm
alfadriver said:RE- bore-stroke...
FWIW, as efficiency requirements get more and more demand- you will see longer strokes than bores- seems like the ideal B/S ratio is pushing .8-.88 or so.
Not for racing motors, but for real motors.
Racing motors will stay way over 1.
Fun fact- thanks to the difference in strokes, mean piston speed for an 18k rpm F1 motor is virtually the same as a 9k NASCAR motor.
Anyway, that was just about one of the thread tangents that has been brought up.
It's pretty interesting that GM has a 100% unique motor for their race car. Expensive as all heck, though. While the GT's motor has a crank made from unobtanium, the rest of the engine was mostly off the production line. So this new engine puts HUGE pressure on the car to win. Given the previous history of the Vette racing, my gut tells me they will win, a lot
Respectfully . . . why wouldn't a motorsports enthusiast want the characteristics of his motor to align more toward those of a racing engine than to an engine optimized for low rpm minivan or entry-level commuter-car use? Especially as far as his fun car is concerned? FWIW, the poster-boy for long-stroke engines was probably the Jaguar 4.2 inline six at about 0.91 bore to stroke.
I've been thinking in terms of mean piston speed as well, and just because 4500 fpm in a regular production (and warranted) engine is do-able now, where 50 years ago it wasn't doesn't mean that the downsides have gone away. Or the related matter of peak piston accelerations.
I wouldn't mind seeing a version of that 5.5L engine available as a crate motor. Not at all. Make mine normally aspirated, though.
Norm
Why wouldn’t a Motorsport enthusiast want a real racing suspension for the street? Because it would be terrible. Street cars are not race cars. The original Miata 1.6 was a revvy little thing optimized for top end, and customers keep asking the aftermarket for “more low end” and swapping in the lazier 1.8 because it’s a better street engine.
The Ford flat plane is not available as a crate because of vibration problems - they will take themselves apart. The whole drivetrain needs to be engineered to suit. That may be the same for this Chevy unit.
NormPeterson said:FWIW, the poster-boy for long-stroke engines was probably the Jaguar 4.2 inline six at about 0.91 bore to stroke.
K24A: 0.88 Bore/stroke
Keith Tanner said:customers keep asking the aftermarket for “more low end” and swapping in the lazier 1.8 because it’s a better street engine.
That and Americans seem to want their engines to only ever run at idle speed in any situation.
frenchyd said:In reply to Knurled. :
I understand the advantage of rockers but see serious race motors not use them. Perhaps it's a RPM limited advantage? Close to stock and rockers offer benefits. Up in that 20,000 rpm range of F1 buckets?
F1 was using rockers.
Honda has a neat paper about switching to rockers in 2006 for all the reasons I mentioned.
Knurled. said:frenchyd said:In reply to Knurled. :
I understand the advantage of rockers but see serious race motors not use them. Perhaps it's a RPM limited advantage? Close to stock and rockers offer benefits. Up in that 20,000 rpm range of F1 buckets?
F1 was using rockers.
Not to mention pneumatic valves, exotic materials, etc. I don't understand this constant, "Well a race engine can do it, why can't a street engine do it?"
bobzilla said:In reply to Harvey :
i think you're discounting that almost 200ftlbs of torque between those two. IT's like honda engines. They rev and make a ton of power up top. But you're not there every shift. You're usually half that where the torque makes a massive difference in driving feel.
HP is great, but its that torque you feel day to day and where I'll put my money.
As noted the S65 motor is a 4.0 liter and the LS7 is a 7.0 liter, that's a significant difference in displacement. If you look at a dyno plot of an E92 M3 the car makes 90% of its max torque very early, around 3000rpm hitting peak at 3800 and then it's a flat line all the way to redline. The LS7 peaks later at 4800 and then drops after that. The S65 has plenty of usable torque. I had a 1997 540i sport (6 speed) for a while and that V8 was amazingly smooth. I'm really looking forward to seeing what Chevy can do with a DOHC architecture in the Corvette. The Blackwing motor shows they can do cool stuff.
Keith Tanner said:Why wouldn’t a Motorsport enthusiast want a real racing suspension for the street? Because it would be terrible. Street cars are not race cars. The original Miata 1.6 was a revvy little thing optimized for top end, and customers keep asking the aftermarket for “more low end” and swapping in the lazier 1.8 because it’s a better street engine.
The Ford flat plane is not available as a crate because of vibration problems - they will take themselves apart. The whole drivetrain needs to be engineered to suit. That may be the same for this Chevy unit.
I didn't say all the way to full race spec. Just more toward that end of the spectrum than at what's preferred for mindless low-speed trundling about from here to there and back again. Same goes for suspensions; they aren't all-or-nothing, base or full race/nothing in between in nature either.
I dare suggest that those who complained about the character of the Miata's original engine weren't hardcore sports roadster fans where you adapt to the car and what it needs. No, they pressured the car into being adapted to their preferences. I realize that the argument could be made that Mazda started a little too small, that the Miata could have been closer to essentially being a detuned S2000.
FPC V8's of 5.0 L and up are probably all going to be 'shakers', particularly in 'square' or 'undersquare' engine configurations. Destroked to something like 4.4L, they ought to get a lot smoother (F430-ish keeps coming to mind). I'm personally a little surprised that V8 displacements haven't already started to shrink as mpg requirements increase.
Norm
NormPeterson said:Keith Tanner said:Why wouldn’t a Motorsport enthusiast want a real racing suspension for the street? Because it would be terrible. Street cars are not race cars. The original Miata 1.6 was a revvy little thing optimized for top end, and customers keep asking the aftermarket for “more low end” and swapping in the lazier 1.8 because it’s a better street engine.
The Ford flat plane is not available as a crate because of vibration problems - they will take themselves apart. The whole drivetrain needs to be engineered to suit. That may be the same for this Chevy unit.
I didn't say all the way to full race spec. Just more toward that end of the spectrum than at what's preferred for mindless low-speed trundling about from here to there and back again. Same goes for suspensions; they aren't all-or-nothing, base or full race/nothing in between in nature either.
I dare suggest that those who complained about the character of the Miata's original engine weren't hardcore sports roadster fans where you adapt to the car and what it needs. No, they pressured the car into being adapted to their preferences. I realize that the argument could be made that Mazda started a little too small, that the Miata could have been closer to essentially being a detuned S2000.
FPC V8's of 5.0 L and up are probably all going to be 'shakers', particularly in 'square' or 'undersquare' engine configurations. Destroked to something like 4.4L, they ought to get a lot smoother (F430-ish keeps coming to mind). I'm personally a little surprised that V8 displacements haven't already started to shrink as mpg requirements increase.
Norm
In case you're not aware, I work at Flyin' Miata. The people contacting FM for upgrades do tend to be some of the more hardcore sports roadster types. The 1990 Miata could pretty easily be characterized as a detuned, lighter, more affordable S2000 given available tech, it had a motor that was pretty similar in nature given the era. And the S2000 also moved to a lower redline, higher torque motor fairly quickly. Maybe there just aren't that many hardcore sports roadster fans buying cars and who are willing to make driveability sacrificies for purity.
Keith Tanner said:NormPeterson said:Keith Tanner said:Why wouldn’t a Motorsport enthusiast want a real racing suspension for the street? Because it would be terrible. Street cars are not race cars. The original Miata 1.6 was a revvy little thing optimized for top end, and customers keep asking the aftermarket for “more low end” and swapping in the lazier 1.8 because it’s a better street engine.
The Ford flat plane is not available as a crate because of vibration problems - they will take themselves apart. The whole drivetrain needs to be engineered to suit. That may be the same for this Chevy unit.
I didn't say all the way to full race spec. Just more toward that end of the spectrum than at what's preferred for mindless low-speed trundling about from here to there and back again. Same goes for suspensions; they aren't all-or-nothing, base or full race/nothing in between in nature either.
I dare suggest that those who complained about the character of the Miata's original engine weren't hardcore sports roadster fans where you adapt to the car and what it needs. No, they pressured the car into being adapted to their preferences. I realize that the argument could be made that Mazda started a little too small, that the Miata could have been closer to essentially being a detuned S2000.
FPC V8's of 5.0 L and up are probably all going to be 'shakers', particularly in 'square' or 'undersquare' engine configurations. Destroked to something like 4.4L, they ought to get a lot smoother (F430-ish keeps coming to mind). I'm personally a little surprised that V8 displacements haven't already started to shrink as mpg requirements increase.
Norm
In case you're not aware, I work at Flyin' Miata. The people contacting FM for upgrades do tend to be some of the more hardcore sports roadster types. The 1990 Miata could pretty easily be characterized as a detuned, lighter, more affordable S2000 given available tech, it had a motor that was pretty similar in nature given the era. And the S2000 also moved to a lower redline, higher torque motor fairly quickly. Maybe there just aren't that many hardcore sports roadster fans buying cars and who are willing to make driveability sacrificies for purity.
Classic. Keith, those people that modify the Miata instead of adapting to what the car needs, those people are not hardcore enough. You know, all your customers. ROFL!
Harvey said:As noted the S65 motor is a 4.0 liter and the LS7 is a 7.0 liter, that's a significant difference in displacement.
Outside displacement-limited racing classes and poorly crafted rules/regulations, displacement is completely and totally irrelevant in the real world...As are things like HP/L and TQ/L. Similarly, making a greater percentage of max hp/tq at a given rpm doesn't matter one iota if there is still less of it.
You have already admitted that the LS7 is physically smaller, makes significantly more power, significantly more torque, and gets significantly better fuel economy than the S65...Where the rubber meets the road, the LS7 is significantly better in every objectively measurable way. The only potential real world advantage I can see is for the S65 the emotional one that come from the particular sounds that all the added complexity (cost) makes, and that's purely subjective.
Driven5 said:Harvey said:As noted the S65 motor is a 4.0 liter and the LS7 is a 7.0 liter, that's a significant difference in displacement.
Outside displacement-limited racing classes and poorly crafted rules/regulations, displacement is completely and totally irrelevant in the real world...As are things like HP/L and TQ/L. Similarly, making a greater percentage of max hp/tq at a given rpm doesn't matter one iota if there is still less of it.
You have already admitted that the LS7 is physically smaller, makes significantly more power, significantly more torque, and gets significantly better fuel economy than the S65...Where the rubber meets the road, the LS7 is significantly better in every objectively measurable way. The only potential real world advantage I can see is for the S65 the emotional one that come from the particular sounds that all the added complexity (cost) makes, and that's purely subjective.
As far as the fuel economy, it would be interesting to see what the S65 would do in the dramatically lighter and more slippery Corvette body. An E90 M3 is like 3700 lbs without a driver.
z31maniac said:As far as the fuel economy, it would be interesting to see what the S65 would do in the dramatically lighter and more slippery Corvette body. An E90 M3 is like 3700 lbs without a driver.
They both apparently have the same .31 drag coefficient and are within 1sq-ft of each other (taller vs wider) in frontal area. So the Vette only has a very slight (4%) advantage in CdA, and thus total drag force. I can't speak to the weight, as I've found numbers all over the place for the E92 M3, from under 3500 to over 3900, but weight is not a major factor in highway fuel economy either way. So I'd be quite surprised if that could even come close to making up the difference.
Driven5 said:Harvey said:As noted the S65 motor is a 4.0 liter and the LS7 is a 7.0 liter, that's a significant difference in displacement.
Outside displacement-limited racing classes and poorly crafted rules/regulations, displacement is completely and totally irrelevant in the real world...As are things like HP/L and TQ/L. Similarly, making a greater percentage of max hp/tq at a given rpm doesn't matter one iota if there is still less of it.
You have already admitted that the LS7 is physically smaller, makes significantly more power, significantly more torque, and gets significantly better fuel economy than the S65...Where the rubber meets the road, the LS7 is significantly better in every objectively measurable way. The only potential real world advantage I can see is for the S65 the emotional one that come from the particular sounds that all the added complexity (cost) makes, and that's purely subjective.
Quoted for truth.
+1
Driven5 said:z31maniac said:As far as the fuel economy, it would be interesting to see what the S65 would do in the dramatically lighter and more slippery Corvette body. An E90 M3 is like 3700 lbs without a driver.
They both apparently have the same .31 drag coefficient and are within 1sq-ft of each other (taller vs wider) in frontal area. So the Vette only has a very slight (4%) advantage in CdA, and thus total drag force. I can't speak to the weight, as I've found numbers all over the place for the E92 M3, from under 3500 to over 3900, but weight is not a major factor in highway fuel economy either way. So I'd be quite surprised if that could even come close to making up the difference.
I'd rather see a BSFC curve for both motors. Still too many variables. And measuring highway fuel economy on a motor that powerful is effectively measuring it at what... 3% of peak output?
Driven5 said:Harvey said:As noted the S65 motor is a 4.0 liter and the LS7 is a 7.0 liter, that's a significant difference in displacement.
Outside displacement-limited racing classes and poorly crafted rules/regulations, displacement is completely and totally irrelevant in the real world...As are things like HP/L and TQ/L. Similarly, making a greater percentage of max hp/tq at a given rpm doesn't matter one iota if there is still less of it.
You have already admitted that the LS7 is physically smaller, makes significantly more power, significantly more torque, and gets significantly better fuel economy than the S65...Where the rubber meets the road, the LS7 is significantly better in every objectively measurable way. The only potential real world advantage I can see is for the S65 the emotional one that come from the particular sounds that all the added complexity (cost) makes, and that's purely subjective.
Doesn't matter overall how you spin it, I win either way, I have the LS7 in the garage. If you drive both you'll find out the differences are not subjective, there are objective reasons that I've already noted as to why you would prefer one over another.
That said its a pyrrhic victory at best since the LS7 seized due to oiling issues.
You'll need to log in to post.
