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[quote=Ferrer;966801]So even the traditional plus point of the straight six is not true?[/quote]
His statement could have more application in a racing engine.
I PM'd some UCP dudes here and I think (but I don't want to misquote them) they seemed to indicate that the biggest drawback of an I6 design in a [I]road car[/I] (say, a BMW) was packaging in the engine bay - kinda like the design issues faced by using flat-X engine a la Porsche and Subaru.
When it comes to engines used in prototype race cars, I think the criteria all change quite drastically - and regulations are a large part of why certain engine configurations are favoured.
I ain't no engineer, but even for me, it seems exceptionally odd that AM went for an I6. AMR-One seems to be a mess right now, and even with more development time I would be surprised if it could compete with the diesels let alone the best gasoline cars.
Off topic, I have been reading a bit about the regs for LMPs on another forum and it really seems to me that the various subclasses has created quite a minefield for potential entrants. As Wouter's article indicated, that new HPD V6 is woefully uncompetitive, and I have heard Hindy complain that older engines have an advantage, and while Honda has adhered to the spirit of the regulations, others have not.
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I am of the firm opinion that the more power strokes per revolution the better. But this ends at a certain point as you've got more rotating mass and more friction to deal with, as well as size constraints. So I feel the v10 would be the best configuration. I will reference the LFA V10 for this. It is a remarkably light motor and revs incredibly fast, producing decent torque and great top end power. Plus it is relatively compact compared to a v12 and even a v8 (such as the Ford 5.0 or BMW 4.0), not to mention having a lower center of gravity (over a v8 that is). Then you have the potential of a stiffer block over an inline engine, and none of the balance issues of a flat engine.
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Mag, I think it hugely depends on application.
Here is my useless example: the F142 in the 458 has more hp and torque than the 1LR-GSE in the LFA, and it has about 300 ccs less.
Ultimately, I am just trying to show that this shit is variable, and there is not one "ideal" solution.
Also, as I understand it, the ideal V angle for a V10 is 72 degrees; and a V8, 90 degrees (amongst others potentially, maybe 180 as well?), so a V8 should have a lower centre of gravity all going well.
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True, their is not one ideal, but it all depends on who is building it. Everyone makes compromises and other take different alternatives so thus everything will be different.
But I would like to know, which is the lighter motor, the F142 or the 1LRGSE?
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[quote=Ferrer;966801]So even the traditional plus point of the straight six is not true?[/quote]
It's overly simplified, as many other things. There is a reason, hopefully, why I went through a second degree. :p
Not suggesting I remember all I've studied so far. :D
Anyway, it applies to all engines in different measures. At low speeds but high loads the forces applied by the combustion are more relevant, while at higher revs it's the inertial contribution that creates more vibrations.
So while the first situation is more frequent on an everyday car, the second definitely applies to any engine and even more to racing engines.
[quote=Kitdy;966812]Mag, I think it hugely depends on application.
Here is my useless example: the F142 in the 458 has more hp and torque than the 1LR-GSE in the LFA, and it has about 300 ccs less.
Ultimately, I am just trying to show that this shit is variable, and there is not one "ideal" solution.
Also, as I understand it, the ideal V angle for a V10 is 72 degrees; and a V8, 90 degrees (amongst others potentially, maybe 180 as well?), so a V8 should have a lower centre of gravity all going well.[/quote]
And then there is Ferrari, using 65 degrees as opposed to the 60 degrees otherwise considered standard for V12 engines.
I may suggest AM went for an I6 VS I4 hoping for more power and lower inertial loads. Then again the gain in friction should be relevant because of the higher speeds than in a road engine. Structural weakness is still the first thing that pops to mind.
It makes even less sense as it's not their "old" V12 cut in half, so even the internal fluid dynamics is new
As other mentioned, having more room for an interesting aero pack is maybe the reason, but then again it doesn't look like that's the case, unless they have yet to implement it.
That may explain it, developing the car one step at a time, and maybe they were hoping to get it ready for Le Mans, if it wasn't for their initial problems at the LM test day.
Given the car has enough room to add such aero pack, and I didn't check, I guess they wanted to just check the car in base-specs at the test day, and have it evolved for taking it at Spa, but eventually they faced problems they didn't expect.
My completely uneducated [I]guestimation [/I].
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A 6 has pistons at opposite ends of crank in same firing position thus avoids secondary harmonics.
The firing is NOT 90 degrees and so avoids primary harmonics.
Other "harmonics" in the casing are minor in comparison and sympathetic harmonics dont really turn up in large masses like car engines until you are looking at valve stems (thin/light) and high revs.
It's the torsional twist that is the issue.
Old Newton, for every force there is an equal and opposite.
So on combustion, the force pushing the piston down is the SAME as the force trygin to push the head up and the longer a block is the bigger the problem becomes and thus requires significatn engienering in the casting, webbing and internal struts. The same is true for each bank of a V12, jsut that there the bottom crankcase provides a wider/stronger base shared across both banks AND a car with a V12 can survive extra weight. A W makes it even MORE weight penalty -- thus the Veyron saga on weight problems :)
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That's not exactly what I meant.
This torsional stress would be equally there event with just two cylinders, and it's not given by the fact they are moving into opposite directions.
Given the crank is not really a rigid body, when masses connected to it are subject to an angular acceleration, or even just one of them, the angular position of these masses, or the only one who received the acceleration, changes. Thing is the angular position of each mass changes differently from the others, from a general point of view. Even more when the angular acceleration is provided by forced which are never the same, on the same mass let alone between all of them.
With a flat crank there is a good chance all the various forces create harmonics of the same phase, eventually leading to a torsion focused on a point of the crank between the flywheel and the rest of the crank itself. Add to that the fact that the flywheel has the bigger inertia of all the masses connected to the crank, and there is your weakness.
A flat crank is found in an inline engine. If it wasn't flat though you'd get also flexion.
Now purely guessing as the class on this specific argument has yet to progress, a V12 engine should have all the advantages of an I6 when it comes to flexion, but also reduce the disadvantages when it comes to torsion.
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I think you are missing that with a long block then control of the torsional stiffness is difficult.
A twin, has a square cross section adn that is inherently stronger than a long ladder.
It's not so much the crank, that is about the balance.
YES, crank has issues too especially with the length, but that is partly resovable with enough journals.
The crank and the block are two distinct issues.
The long block of an I6 as I've repeated is about making it strong enough to ahndle the forces OPPOSING the piston and crank :)
btw a straight 6 is not a flat crank. Each is at 120 degrees. This is what keeps a triple in balance and doubly so the 6.
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[quote=Kitdy;966808]His statement could have more application in a racing engine.
I PM'd some UCP dudes here and I think (but I don't want to misquote them) they seemed to indicate that the biggest drawback of an I6 design in a [I]road car[/I] (say, a BMW) was packaging in the engine bay - kinda like the design issues faced by using flat-X engine a la Porsche and Subaru.
When it comes to engines used in prototype race cars, I think the criteria all change quite drastically - and regulations are a large part of why certain engine configurations are favoured.
I ain't no engineer, but even for me, it seems exceptionally odd that AM went for an I6. AMR-One seems to be a mess right now, and even with more development time I would be surprised if it could compete with the diesels let alone the best gasoline cars.
Off topic, I have been reading a bit about the regs for LMPs on another forum and it really seems to me that the various subclasses has created quite a minefield for potential entrants. As Wouter's article indicated, that new HPD V6 is woefully uncompetitive, and I have heard Hindy complain that older engines have an advantage, and while Honda has adhered to the spirit of the regulations, others have not.[/quote]
HPD V6 is down on power according to my friend working at Wirth, but there are other reason why the Acura/HPD car is less competitive than before. Namely the car is actually not a budget capped car like most others in class, thus the car has more restriction than other P2 car.They are sorting it out though, as Spa result have shown with the Strakka car finishing 3rd in class, and apparently was only due to them being caught out by safety car and lost a lap. ILMC does not have ALMS' new complicated safety car procedure to prevent that from happening....
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[quote=Matra et Alpine;966827]I think you are missing that with a long block then control of the torsional stiffness is difficult.
A twin, has a square cross section adn that is inherently stronger than a long ladder.
It's not so much the crank, that is about the balance.
YES, crank has issues too especially with the length, but that is partly resovable with enough journals.
The crank and the block are two distinct issues.
The long block of an I6 as I've repeated is about making it strong enough to ahndle the forces OPPOSING the piston and crank :)
btw a straight 6 is not a flat crank. Each is at 120 degrees. This is what keeps a triple in balance and doubly so the 6.[/quote]
I wasn't talking about the block, just the crank, but I agree on your points about it.
You're also right on the I6's crank, proof I shouldn't post about tech stuff after a day at uni and that I need to ask a few more stuff to my teacher. :)
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[quote=Kitdy;966808]
Off topic, I have been reading a bit about the regs for LMPs on another forum and it really seems to me that the various subclasses has created quite a minefield for potential entrants. As Wouter's article indicated, that new HPD V6 is woefully uncompetitive, and I have heard Hindy complain that older engines have an advantage, and while Honda has adhered to the spirit of the regulations, others have not.[/quote]
All LMP2 engines for this year are new. The HPD was initially more restricted, (because as RM said, it was not a budget car) and now has been rectified. Danny Watts took pole at Spa with the Strakka car, so they are competitive.
Old engines are found in the P1 class, which basically has now the same engine rules as P2 last year. There are new engines (the factory diesels, the Rebellion Toyota) adn old ones, such as the old diesel and the JuddV10 in the Pescarolo, but these have been resticted to reduce performance. It IS a fact though that the grandfathered cars so far have dominated the non-factory cars.
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[quote=LeonOfTheDead;966831]I wasn't talking about the block, just the crank, but I agree on your points about it.[/quote]
No probs, why I clarified as it has been the block all along I have been talking of in the main. The crank is a "given" :)
[quote]You're also right on the I6's crank, proof I shouldn't post about tech stuff after a day at uni and that I need to ask a few more stuff to my teacher. :)[/quote]
I know the feeling. It gets worse the older you get :)
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[quote=Kitdy;966808]I PM'd some UCP dudes here and I think (but I don't want to misquote them) they seemed to indicate that the biggest drawback of an I6 design in a [I]road car[/I] (say, a BMW) was packaging in the engine bay - kinda like the design issues faced by using flat-X engine a la Porsche and Subaru.[/quote]
I wouldnt be surprised to see something as trivial as pedestrian crash regulations cause the extinction of I6 engines in road cars.
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[quote=Matra et Alpine;966611]hmmm, find it hard to believe the M3 torque relative to capacity is higher than other cars. Do you have source for the claims ?[/quote]
The M3 CSL,
at 262lb/ft or 81.8lb-ft per litre used to be listed in wiki here:-
[ame="http://en.wikipedia.org/wiki/List_of_automotive_superlatives"]List of automotive superlatives - Wikipedia, the free encyclopedia[/ame]
I see it's now changed.
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[quote=culver;966645]................. while the weakest of the LSx motors, the LS1 was 345hp (same as the stock Supra turbo) yet weighted in at under 500lb with flywheel. The LS1 can't handle as much power with out internal upgrades but it doesn't carry so many unneeded pounds either.[/quote]
Hello Culver,
not wishing to split hairs here; the "weakest" LS engine was the RPO LR4 4.8 V8.
There is also a 5.3 V8 (RPO LM7) followed by the now out of production LS1 and LS6
5.7 V8's.
The LS1 came in various stages of tune from 290 (Holden Caprice) to 382hp (HSV R8 & HSV GTO).
The LS6 used all the same internal parts as the LS1 but used "243" heads and a different cam; this was validated at 400hp (J1349 standard, not J607 like the majority of other manufacturers).
The LS1 is capable of making 550hp without up-grading the internals.(source:- Richard Holdener, GMPP Group Manager)
link: [url="http://www.cartechbooks.com/vstore/showdetl.cfm?DID=6&Product_ID=2277&CATID=3"]CarTech, Inc.: Browsing How to Build High-Performance Chevy LS1/LS6 V-8s[/url]
Someone asked if there was a racing M3 with a straight-six;
The American Le Mans series used M3 GTR's with the 3.2 six but found it lacking against the Porsche 996 GT3's. It was then fitted with a 4.0 V8 for the 2001 season.
