Close

Page 3 of 10 FirstFirst 12345 ... LastLast
Results 51 to 75 of 238
  1. #51
    Join Date
    Dec 2012
    Posts
    56
    Rep Points
    163.7
    Mentioned
    0 Post(s)
    Rep Power
    2


    Reputation: Yes | No
    An automatic without a torque converter could yes, i.e Mercedes MCT . But having driven both, the Dct responds faster every time and thus improves the experience of driving , instant flat out shifts aside. The problem is they left the torque converter in this one for cylinder deactivation 4 cylinder mode bull$#@!. It would have been ok with a wet clutch auto without a torque converter.

  2. #52
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    Every gear has an electrohydraulic clutch. With the proper design and calibration, I don't see why it wouldn't be able to match a DCT in shift speed.
    Because you can't have two clutches engaged at the same time.

  3. #53
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Because you can't have two clutches engaged at the same time.
    Right, but you dont have both clutches in a DCT engaged at the same time. The DCT is essentially two automated manual transmissions sharing the same housing. The shift rod for your current gear is engaged, as well as the shift rod for your next gear. All the DCT has to do to switch gears, is disengage one clutch and engage the other. Planetary automatic transmissions don't use shift rods. Thinking of it the same way as the DCT, an 8 speed auto is basically 8 separate transmissions sharing the same housing, more or less.

    Now, as I stated before, the automatic transmission (particularly the electronic controls) would have to be designed with quick shifting in mind, and when the torque converter isn't locked up, you'd still have that mushy automatic feel, but I believe it is possible for an auto to match a DCT in shift speed.

  4. #54
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    Right, but you dont have both clutches in a DCT engaged at the same time. The DCT is essentially two automated manual transmissions sharing the same housing. The shift rod for your current gear is engaged, as well as the shift rod for your next gear. All the DCT has to do to switch gears, is disengage one clutch and engage the other.
    You're correct that it is essentially two manual transmissions but you essentially have the next gear pre-selected with that clutch responsible for it. So you essentially have no interruption in the torque driving the wheels as there is no need to disengage and reengage the same clutch as one clutch is responsible for even and one for odd. So how do you not have both gears at the same time exactly when one clutch is only responsible for even and one for odd? I think maybe we're confusing both gears and clutches at the same time but regardless I don't see how you can exceed this:

    Double clutch transmissions can in fact have two gears engaged at the same time (with of course at least one of the clutches disconnected , or else there'd be double trouble). What's the point, you may ask? Let's say you have just set off, rolling in first gear. The DCT unit will engage second gear and when it's time to actually shift gears all it has to do is disengage the odd clutch and engage the even one. This can happen completely simultaneously, with both clutches slipping.


    So you can use both clutches at the same time which obviously requires a dual clutch trans.

  5. #55
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    1 out of 1 members liked this post. Reputation: Yes | No
    Double clutch transmissions can in fact have two gears engaged at the same time (with of course at least one of the clutches disconnected , or else there'd be double trouble)

    and when it's time to actually shift gears all it has to do is disengage the odd clutch and engage the even one


    These are the key points that you quoted (added bold for emphasis). In an automatic transmission, there is no mechanical gear engagement as in a conventional manual, SMG, or DCT. Each gear has its own clutch pack, and they are engaged purely by hydraulic pressure, basically how the two DCT clutches work. In fact, many modern automatic transmissions generally start building hydraulic pressure to the next gear (but not enough to lock up that clutch) in anticipation of the next shift. They generally are not as aggressive as a DCT. But they can be made that way.

    So let's say you're in 1st gear, accelerating hard. The 1st gear clutch is fully locked, max hydraulic pressure. As you approach redline, the TCM anticipates you will shift up to 2nd gear. It starts building hydraulic pressure to 2nd clutch. When you hit redline and pull the paddle (or run in auto mode and the TCM decides to shift), it opens the bleed solenoid to dump pressure from 1st, and at the same time opens the pressure solenoid to give 2nd max pressure. Basically the same as a DCT.

  6. #56
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge




    These are the key points that you quoted (added bold for emphasis). In an automatic transmission, there is no mechanical gear engagement as in a conventional manual, SMG, or DCT. Each gear has its own clutch pack, and they are engaged purely by hydraulic pressure, basically how the two DCT clutches work. In fact, many modern automatic transmissions generally start building hydraulic pressure to the next gear (but not enough to lock up that clutch) in anticipation of the next shift. They generally are not as aggressive as a DCT. But they can be made that way.

    So let's say you're in 1st gear, accelerating hard. The 1st gear clutch is fully locked, max hydraulic pressure. As you approach redline, the TCM anticipates you will shift up to 2nd gear. It starts building hydraulic pressure to 2nd clutch. When you hit redline and pull the paddle (or run in auto mode and the TCM decides to shift), it opens the bleed solenoid to dump pressure from 1st, and at the same time opens the pressure solenoid to give 2nd max pressure. Basically the same as a DCT.
    Good post and I understand what you're saying regarding building pressure but you still can't have both gears engaged at the same time. The main point of similarity seems to be how it anticipates the next gear but not in having the next gear pre-selected.

  7. #57
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    2 out of 2 members liked this post. Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Good post and I understand what you're saying regarding building pressure but you still can't have both gears engaged at the same time. The main point of similarity seems to be how it anticipates the next gear but not in having the next gear pre-selected.
    Right, but I think we may mean different things when we say a gear is engaged.

    In a manual, dual clutch, sequential, or independent shift rod (a la Aventador) transmission, there is a clutch (or two) between the engine and transmission that transfers driving force. Inside the transmission, there are shift rods and collars that select the individual gears. Most use one shift rod per two gears, though the ISR is an exception. In order for a gear to be engaged and driving the wheels, the gear must be engaged by a shift collar, and the clutch must be engaged.

    In an automatic, there are no shift rods and no shift collars. Typically they use planetary gear sets (as does this 8 speed in the Z06), though there are some oddballs like Honda that use conventional gearsets. In place of the shift rods and collars, automatic transmissions use clutch packs and hydraulic pressure to engage gears.

    So in a single clutch manual, automated or not, when you shift, the clutch is disengaged, interrupting power flow. Then, the shift rod moves to disengage the current gear and either the same rod or another engages the next gear. Finally, the clutch can be engaged again, and the shift is completed. The ISR transmission reduces this time a bit by having separate shift rods for each gear, so as one is being disengaged, the next can be engaged simultaneously. There is still the delay from having to disengage and reengage the single clutch.

    In a dual clutch, two gears are engaged simultaneously by the shift rods, with the clutch for the inactive gear disengaged. When a shift is performed, hydraulic pressure is bled from the currently engaged clutch, and applied to the next clutch. The shift is completed at this point.
    This obviously greatly reduces shift time. There is an almost unnoticeable interruption in power flow, though it is still there. Moving the shift rods is accomplished while the clutch for that gearset is disengaged, so that part is completely eliminated from the shifting time.

    In an automatic, there is no need to interrupt the power flow from the engine, because gear engagement is controlled with hydraulic clutches. When a shift is performed, hydraulic pressure is bled from the currently engaged clutch, and applied to the next clutch. The shift is completed at this point.

    Notice the similarity in what happens during a shift with a dual clutch and an automatic. Click here to enlarge

    Also, as I stated before, most automatics are not programmed to be this aggressive, because most buyers aren't interested in that.

  8. #58
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    Right, but I think we may mean different things when we say a gear is engaged.

    In a manual, dual clutch, sequential, or independent shift rod (a la Aventador) transmission, there is a clutch (or two) between the engine and transmission that transfers driving force. Inside the transmission, there are shift rods and collars that select the individual gears. Most use one shift rod per two gears, though the ISR is an exception. In order for a gear to be engaged and driving the wheels, the gear must be engaged by a shift collar, and the clutch must be engaged.

    In an automatic, there are no shift rods and no shift collars. Typically they use planetary gear sets (as does this 8 speed in the Z06), though there are some oddballs like Honda that use conventional gearsets. In place of the shift rods and collars, automatic transmissions use clutch packs and hydraulic pressure to engage gears.

    So in a single clutch manual, automated or not, when you shift, the clutch is disengaged, interrupting power flow. Then, the shift rod moves to disengage the current gear and either the same rod or another engages the next gear. Finally, the clutch can be engaged again, and the shift is completed. The ISR transmission reduces this time a bit by having separate shift rods for each gear, so as one is being disengaged, the next can be engaged simultaneously. There is still the delay from having to disengage and reengage the single clutch.

    In a dual clutch, two gears are engaged simultaneously by the shift rods, with the clutch for the inactive gear disengaged. When a shift is performed, hydraulic pressure is bled from the currently engaged clutch, and applied to the next clutch. The shift is completed at this point.
    This obviously greatly reduces shift time. There is an almost unnoticeable interruption in power flow, though it is still there. Moving the shift rods is accomplished while the clutch for that gearset is disengaged, so that part is completely eliminated from the shifting time.

    In an automatic, there is no need to interrupt the power flow from the engine, because gear engagement is controlled with hydraulic clutches. When a shift is performed, hydraulic pressure is bled from the currently engaged clutch, and applied to the next clutch. The shift is completed at this point.

    Notice the similarity in what happens during a shift with a dual clutch and an automatic. Click here to enlarge

    Also, as I stated before, most automatics are not programmed to be this aggressive, because most buyers aren't interested in that.
    Your post is very well done and honestly some of these posts are good enough for their own thread I think.

    I have no doubt automatics can be made much more aggressive but ultimately I see no way for it to physically match the DCT. The reason for this is because the clutches do not work independently as they do in a DCT unless I'm mistaken here. In the automatic it is for the shift to be performed one clutch is disengaged then pressure is applied to the next clutch. That next clutch can not work until the previous one disengages.

  9. #59
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    I think this explains what you are saying well:

    Like torque converters, wet multi-plate clutches use hydraulic pressure to drive the gears. The fluid does its work inside the clutch piston, seen in the diagram above. When the clutch is engaged, hydraulic pressure inside the piston forces a set of coil springs part, which pushes a series of stacked clutch plates and friction discs against a fixed pressure plate. The friction discs have internal teeth that are sized and shaped to mesh with splineson the clutch drum. In turn, the drum is connected to the gearset that will receive the transfer force. Audi's dual-clutch transmission has both a small coil spring and a large diaphragm spring in its wet multi-plate clutches.To disengage the clutch, fluid pressure inside the piston is reduced. This allows the piston springs to relax, which eases pressure on the clutch pack and pressure plate.

  10. #60
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Your post is very well done and honestly some of these posts are good enough for their own thread I think.
    Thanks, I appreciate it. Feel free to copy paste into a new thread. In this one I was trying to be fairly brief in describing transmission operation.

    I have no doubt automatics can be made much more aggressive but ultimately I see no way for it to physically match the DCT. In the automatic it is for the shift to be performed one clutch is disengaged then pressure is applied to the next clutch. That next clutch can not work until the previous one disengages.
    Auto transmission clutches, like most* dual clutch systems are wet multiplate units designed to have a certain amount of slippage at varying pressure levels. You are saying that during a DCT gearchange, the first clutch remains partially engaged until the second clutch is fully engaged and takes over? That makes sense, as it would greatly reduce shift-shock at the expense of extra heat from more clutch slippage. There is no reason an automatic transmission could not be engineered to do this. It would be more expensive, due to the requirement of beefier clutch packs to resist heat, and greater fluid volume and cooling systems to maintain proper fluid temperature. I suspect this is exactly what GM engineers did on this Z06 8-speed. It makes me really want to drive an auto Z06 to see what it's like.

    Obviously you could not have both DCT clutches fully engaged at the same time, that would just lock up the transmission. The same would be true of an automatic (in most situations. Most autos don't actually have a gear for 1:1 ratio, they just lock up one clutch at the front of the "barrel" and one at the rear so the whole thing spins).

    The reason for this is because the clutches do not work independently as they do in a DCT unless I'm mistaken here.
    On this, specifically. Mainstream autos, particularly older and/or cheaper units, tend to be more limited in their ability to operate clutches independently because to save money, they use a smaller number of solenoids. You don't need 8 or more solenoids to operate a 6 speed automatic if some gears share hydraulic circuits. I suspect this is not the case with this new Z06 automatic.

    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    I think this explains what you are saying well:
    Yes, that's exactly what I'm talking about. Auto transmission clutch packs usually have wave springs or small diaphragm springs to oppose lockup.

    *I seem to recall reading about some company's dual clutch unit that used dry clutches. Probably to save money. Seems like it would wear itself out fairly quick
    Last edited by andrew20195; 01-17-2014 at 09:02 PM.

  11. #61
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    Thanks, I appreciate it. Feel free to copy paste into a new thread. In this one I was trying to be fairly brief in describing transmission operation.



    Auto transmission clutches, like most* dual clutch systems are wet multiplate units designed to have a certain amount of slippage at varying pressure levels. You are saying that during a DCT gearchange, the first clutch remains partially engaged until the second clutch is fully engaged and takes over? That makes sense, as it would greatly reduce shift-shock at the expense of extra heat from more clutch slippage. There is no reason an automatic transmission could not be engineered to do this. It would be more expensive, due to the requirement of beefier clutch packs to resist heat, and greater fluid volume and cooling systems to maintain proper fluid temperature. I suspect this is exactly what GM engineers did on this Z06 8-speed. It makes me really want to drive an auto Z06 to see what it's like.

    Obviously you could not have both DCT clutches fully engaged at the same time, that would just lock up the transmission. The same would be true of an automatic (in most situations. Most autos don't actually have a gear for 1:1 ratio, they just lock up one clutch at the front of the "barrel" and one at the rear so the whole thing spins).



    On this, specifically. Mainstream autos, particularly older and/or cheaper units, tend to be more limited in their ability to operate clutches independently because to save money, they use a smaller number of solenoids. You don't need 8 or more solenoids to operate a 6 speed automatic if some gears share hydraulic circuits. I suspect this is not the case with this new Z06 automatic.



    Yes, that's exactly what I'm talking about. Auto transmission clutch packs usually have wave springs or small diaphragm springs to oppose lockup.

    *I seem to recall reading about some company's dual clutch unit that used dry clutches. Probably to save money. Seems like it would wear itself out fairly quick
    It seems the 8L90 is pretty advanced. It also seems it's doing a lot of what a DCT is just going about it with slightly different architecture although there also are similarities in the multi-plate clutch designs.

    I can see how it can shift damn fast. I still don't understand how it it can outshift the PDK but I'm going to read up more on the trans and namely the number of solenoids.

  12. #62
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    I still don't understand how it it can outshift the PDK but I'm going to read up more on the trans and namely the number of solenoids.
    This is what I'm learning. The PDK has two multi place wet clutches and the GM 8L90 has multiple multi-plate wet clutches. Very similar philosophy actually and it makes me feel like they should call it a multi-clutch transmission.

    Seems torque converter automatics still have quite a life ahead of them in performance applications.

  13. #63
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    This is what I'm learning. The PDK has two multi place wet clutches and the GM 8L90 has multiple multi-plate wet clutches. Very similar philosophy actually and it makes me feel like they should call it a multi-clutch transmission.

    Seems torque converter automatics still have quite a life ahead of them in performance applications.
    That's the thing! All automatic transmissions are multi-clutch units. It's just that, for the most part, they are designed to be slushboxes rather than high performance units. It's only recently that they're starting to develop direct controls for each clutch. I suspect it has more to do with fuel economy than anything else. In a situation like the 8L90, I think the engineers said, "Hey, since we're doing this with our mid-range transmissions already..."

    I'm still not a huge fan of torque converters. The size of the torque converter clutch is limited compared to, say, the AMG transmissions with the giant wet multiplate clutch in the bellhousing. Though with the 4 cylinder operation, it makes sense why they went with that. When you're just cruising you want smooth anyway.

  14. #64
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    That's the thing! All automatic transmissions are multi-clutch units. It's just that, for the most part, they are designed to be slushboxes rather than high performance units.
    Yes but this one functions similarly to a high performance DCT trans.

    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    I'm still not a huge fan of torque converters. The size of the torque converter clutch is limited compared to, say, the AMG transmissions with the giant wet multiplate clutch in the bellhousing. Though with the 4 cylinder operation, it makes sense why they went with that. When you're just cruising you want smooth anyway.
    It's going to be more smooth than anything else but I just wondering if it will feel 'sloppy' instead of direct and connected during paddle gearshifts.

  15. #65
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    2 out of 2 members liked this post. Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    It's going to be more smooth than anything else but I just wondering if it will feel 'sloppy' instead of direct and connected during paddle gearshifts.
    That's the question. It's all about feel. In many cases, a "hard" shifting auto transmission is actually causing less mechanical wear than a smooth shifting transmission, at the expense of occupant comfort, and if it's really hard, smooth transitions on a racetrack. I've always been a fan of manual transmissions, but I'm at the point in my life where I like a good manual, but I'd rather have a good auto than a bad manual. And there are plenty of bad manual transmissions out there.

    As a good example of a performance oriented torque converter automatic, I'd recommend driving a FR-S/BRZ with the 6 speed auto. The gear ratios are too long, and make an already slow car even slower, but in sport mode the shift feel and speed are actually pretty damn good.

  16. #66
    Join Date
    Sep 2012
    Posts
    1,116
    Rep Points
    962.7
    Mentioned
    14 Post(s)
    Rep Power
    10


    Reputation: Yes | No
    Click here to enlarge Originally Posted by andrew20195 Click here to enlarge
    That's the thing! All automatic transmissions are multi-clutch units. It's just that, for the most part, they are designed to be slushboxes rather than high performance units. It's only recently that they're starting to develop direct controls for each clutch. I suspect it has more to do with fuel economy than anything else. In a situation like the 8L90, I think the engineers said, "Hey, since we're doing this with our mid-range transmissions already..."

    I'm still not a huge fan of torque converters. The size of the torque converter clutch is limited compared to, say, the AMG transmissions with the giant wet multiplate clutch in the bellhousing. Though with the 4 cylinder operation, it makes sense why they went with that. When you're just cruising you want smooth anyway.
    Awesome post ! Learned alot from reading your post thats what im on forums for not n54=2jz lolz ...

    Since you brought up the AMG MCT id like to get your input. I have a c63 coupe equipped with the MCT and their is not much public knowledge available on it. The mbworld forums are full of dopes and 99% cosmetic and their isnt much AMG traffic here yet. I love the MCT in my car and actually prefer it to the only DCT ive had extensive seat time in(GTR)

    From what i understand it has one big wet clutch used as a "take off" clutch to give more direct response verses the slushiness of a torque converter and it def does its job the throttle is very direct. The pre facelift (08-11) C63 had the 7G trans which is supposedly the same as the MCT just with a torque converter instead of the Wet clutch of the MCT. The shifts are considerably faster in the MCT and the old 7G had a max power rating in the low 500 wheel while the MCT has been tested at 700-800 wheel and holding up.

    How is the MCT shifting faster and holding much more power if the individual gears are responsible for the shifts and the Wet "start up" clutch doesnt engage during shifts? I seem to remember people blowing torque converters on the older c63 so maybe the stronger clutch it just holding the power and the individual gears were always able to handle the power. Just not 100% sure on the operation of the trans and would love to hear your input. Appreciate your time.

  17. #67
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by ezec63 Click here to enlarge
    and their isnt much AMG traffic here yet
    Not as much AMG foot traffic but believe it or not the hardcore guys (and the knowledge) are all here.

  18. #68
    Join Date
    May 2011
    Posts
    168
    Rep Points
    219.9
    Mentioned
    3 Post(s)
    Rep Power
    3


    Reputation: Yes | No
    Click here to enlarge Originally Posted by ezec63 Click here to enlarge
    How is the MCT shifting faster and holding much more power if the individual gears are responsible for the shifts and the Wet "start up" clutch doesnt engage during shifts? I seem to remember people blowing torque converters on the older c63 so maybe the stronger clutch it just holding the power and the individual gears were always able to handle the power. Just not 100% sure on the operation of the trans and would love to hear your input. Appreciate your time.
    Right, so, keep in mind I'm not an engineer, just an engineering dropout who has been working on cars and trying to keep up with technical education for 12 years...

    That being said, with the older cars "blowing out" torque converters, that seems to indicate that is a weak spot for that transmission. If the torque converter clutch was strong enough to hold the torque being generated, you'd see more internal transmission failures. I'm not a Mercedes tech, so I'm not positive on this, but I assume that the TC clutch partially disengages during shifts to make them feel smoother, and that would generate quite a bit of heat. This may be what's causing those to fail. With the MCT, instead of a torque converter, you have a very large wet multiplate clutch. This should be much better at handling high temperature situations. It's quite possible that even with the MCT, the pressure is reduced during shifts allowing some slip for a smooth transition. Again, I have no specific training on this unit, my reply is based on what I know of other systems.

  19. #69
    Join Date
    Apr 2012
    Location
    9400' ASL, Colorado
    Posts
    886
    Rep Points
    1,301.6
    Mentioned
    7 Post(s)
    Rep Power
    14


    Reputation: Yes | No
    Let's see what they've actually been able to pull off with this new auto trans before writing it off. They are still offering a manual for those not interested in the auto, which is something even Porsche isn't doing on the GT3 and turbo models now.
    Current: '00 S2000
    Previous: '15 M235i xDrive | '15 Macan S | '15 WRX STi | '06 Cayman S | '12 E92 335is w/JB4 | '10 STi

  20. #70
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by ultimateendz Click here to enlarge
    LT4 Engine’s Chief Engineer Hints More Power Is Coming



    http://www.bimmerboost.com/images/im...2640x480-1.jpgThe 2015 Corvette Z06 features an all-new LT4 engine. The supercharged, 6.2L V-8 will deliver more than 625 horsepower, and 635 lb-ft of torque.

    The estimated 625-horsepower figure quoted for Chevy’s new 6.2-liter supercharged LT4 at the Detroit Auto Show unveiling of the upcoming 2015 Corvette Z06 is likely to spiral upwards when the final production model hits the dealerships early next year, according to the engine’s chief engineer.
    “We fully expect to beat that number, but we came up with a safe estimate for the show,” boasts Jordan Lee, program manager for GM’s small-block program, also noting that the estimated 634 lb-ft of peak torque should escalate, as well.
    The LT4 not only sports a new Eaton supercharger model, but nearly every standard Corvette LT1 engine component was modified, massaged or updated to support the power and packaging goals of the LT4 powertrain team.
    http://www.bimmerboost.com/images/im...1640x235-1.jpgThe new LT4 engine will power the 2015 Corvette Z06.

    “The challenge for us was to add 160-plus horsepower but not get any bigger [than the LT1],” Lee tellsEngineLabs. “As remarkable as the LT1 is in power density, the LT4 beats it in droves.”
    http://www.bimmerboost.com/images/im...3400x300-1.jpgHere’s how the LT4 looks in the Z06 engine bay, zans a few plumbing items.

    The LT1, of course, is first of the Gen V small-block engines to hit the market in the new C7 Corvette platform. As EngineLabs demonstrated in previous stories covering the engine’s introductionand an in-depth analysis of the combustion strategy, the LT1 is one of the smallest and most compact engines in the world that is capable of 460 horsepower naturally aspirated. GM wanted to ensure that the engine package didn’t inflate so the Corvette could be offered for sale in Europe.
    “We ended up about an inch taller only in the back where the supercharger has an airflow path into the intercooler,” says Lee.
    Key to the success of adding boost was working with airflow analysis and development engineers at Eaton to improve the supercharger’s efficiency, even though the blower is smaller than what GM utilized on the Gen IV LS9 engine found in the previous C6 Corvette ZR1. That 6.2-liter engine was rated at 638 horsepower at 6,500 rpm with 608 lb-ft peak torque at a stump-pulling 3,800 rpm.
    “The LT4 supercharger is 85mm shorter in height than the one on the LS9, and it weighs 20 pounds less,” says Lee.
    Eaton rates the new R1740 TVS supercharger at 1.7-liter, which means it moves that much air with each revolution of the rotors. The previous LS9 supercharger was rated at 2.3-liter.
    “We shrunk the capacity down to 1.74 liter,” says Lee, “but we wanted the same airflow characteristics. So we had to spin the supercharger faster.”
    The LT4 will weigh close to the LS9 engine, left photo, that powered the previous-generation Corvette ZR1. That engine used a larger 2.3-liter Eaton supercharger, shown on the right.

    The LT4 blower will spin up to 20,000 rpm, compared to the LS9 that maxed out at 15,000 rpm. The smaller rotors also help the supercharger get up to speed quicker, which should boost power earlier in the rpm band.“We worked a lot of the efficiencies through the supercharger to make sure the airflow was up to the quantity levels needed to make the power,” says Lee.
    As with the LS9, there is an air-to-water intercooler integrated into the cast-aluminum intake manifold. But unlike the LS9, the new setup features a clamshell core design with turbolator fins inside the water path compared to a traditional tube with aluminum vanes for the core.
    The Eaton twin-vortices TVS superchargers are designed with unique 4-lobe, Roots-style positive-displacement style rotors that feature a 160-degree helical twist for improved efficiency with less noise. They will be spinning up to 20,000 rpm on the 1.7-liter version found on the LT4 engine.

    “It’s a very efficient intercooler,” says Lee. “It’s about 23 percent less volume but has 10 percent improvement in heat-rejection efficiency. It’s probably not thee inches long in length but reduces the temperature of the inlet charge by 150 degrees.”
    Adding more air requires additional fuel. The Gen V engines feature direction injection with high-pressure feeds coming from a cam-driven fuel pump.
    http://www.bimmerboost.com/images/im...8400x299-1.jpg
    A cutaway of the new LT4 was on display at the Detroit Auto Show where the Z06 announcement was made. It’s shown next to a mockup of the 5.5-liter Gen V engine that powers the next C7.R race Corvette.
    “The biggest challenge was the fuel pump itself,” explains Lee, noting that other exotic DOHC powerplants have up to four pumps to serve the fuel system. “With only one pump we had to increase the size and displacement to handle 625-plus horsepower worth of fuel.”
    GM increased the piston size in the pump but didn’t have to change the tri-lobe cam design that drives the pump. Fuel pressure in the lines was increased — the LT1 fuel system operates at nearly 2,200 psi, but no figures were given for the LT4 — and the cylinder heads received larger injectors. The LT1 cylinder ports didn’t need any additional breathing room, but a lighter titanium intake valve was preferred, and the LT1 cast piston was swapped for a forged version that offers a lower 10:1 compression ratio (the LT1 was 11.5:1).
    “The 10:1 is till relatively high for a boosted engine,” says Lee, adding that max boost levels will be around 9.5 psi. “We also optimized the camshaft to get the torque and power curves we wanted. The lobe centerline spacing and lift profile are a little different from the LT1.”
    The LS9 was also equipped with titanium intake valves as well as titanium connecting rods.
    “We didn’t need titanium connecting rods to get the balance we required on the LT4,” counters Lee.
    http://www.bimmerboost.com/images/im...3300x450-1.jpgThe LT4 features dry-sump oiling, and the oil cooler has been enlarged over the standard Z51 option setup.

    In addition to the forged pistons, GM did beef up the entire rotating assembly. The crank is forged with a higher strength steel alloy than the LT1, and the connecting rods are fully machined.
    “We added a lot of extra machining on the flanks for light weight,” says Lee. “Also, we annodized the lands on the piston and went with a PVD-coated ring. Finally, the piston pin has DLC coating to handle the extra temperature and pressure.”
    Additional durability measures include constructing the cylinder heads with Rotocast A356T6 aluminum and casting the exhaust manifolds out of stainless steel.
    Overall, the engine weight will come close to the LS9.
    “The 20-pound decrease in the weight from the supercharger offsets the weight from the additional technologies like the DI pump, the cam phaser and AFM. We’ll end up with an estimate round 240 kilograms (529 pounds), which is where the LS9 came in.”
    Finally, GM officials refused to speculate on the future availability of an LT4 crate engine when reminded that the LS9 eventually became part of the Chevy Performance catalog. But Lee does offer a reassuring hint: “We pride ourselves on making the small-block available to the aftermarket.”
    Took the time to read thsi over.

    Ok, so basically we have lower compression pistons, an upgraded fuel pump, larger injectors, and a blower. Basically exactly what you would do to an LT1 when adding boost. Without the displacement increase basically anyone with an LT1 Stingray can turn their motor into the LT4 or better.

    It will be interesting to see if the fuel pump and injectors carry right over. I don't see why they wouldn't. So, the LT1 guys already have an upgraded fuel system available.

    It's interesting they only use one pump too.

    I don't like the smaller blower but I can see how it saves weight. They do have to spin it harder so they are generating more heat.

    Regardless, the LT4 is basically an LT1 just one with boost in mind.

  21. #71
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Sucks they don't have titanium connecting rods any longer either.

  22. #72
    Join Date
    Sep 2012
    Posts
    1,116
    Rep Points
    962.7
    Mentioned
    14 Post(s)
    Rep Power
    10


    Reputation: Yes | No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Took the time to read thsi over.

    Ok, so basically we have lower compression pistons, an upgraded fuel pump, larger injectors, and a blower. Basically exactly what you would do to an LT1 when adding boost. Without the displacement increase basically anyone with an LT1 Stingray can turn their motor into the LT4 or better.

    It will be interesting to see if the fuel pump and injectors carry right over. I don't see why they wouldn't. So, the LT1 guys already have an upgraded fuel system available.

    It's interesting they only use one pump too.

    I don't like the smaller blower but I can see how it saves weight. They do have to spin it harder so they are generating more heat.

    Regardless, the LT4 is basically an LT1 just one with boost in mind.
    basically if your buying the car for just straight line your money is better spent on a stingray with extra cash for mods and you'll have way more power. If you want a complete car that can also handle and be a canyon car as well as a straight line demon can't beat the z06 totally different much stiffer chassis and wider tracks front and rear with killer aerodynamics

  23. #73
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by ezec63 Click here to enlarge
    basically if your buying the car for just straight line your money is better spent on a stingray with extra cash for mods and you'll have way more power.
    If you are buying to mod, I think so. Even if you aren't buying to mod, it's just a way better value.

    Click here to enlarge Originally Posted by ezec63 Click here to enlarge
    If you want a complete car that can also handle and be a canyon car as well as a straight line demon can't beat the z06 totally different much stiffer chassis and wider tracks front and rear with killer aerodynamics
    Is the top on the Z06 removable? Obviously it will have better components but these should all be retrofittable.

    I'm not knocking the Z06 I just found the C6 Z06 more compelling versus the standard C6 than the C7 Z06 is over the standard C7 Stingray.

  24. #74
    Join Date
    Apr 2012
    Location
    9400' ASL, Colorado
    Posts
    886
    Rep Points
    1,301.6
    Mentioned
    7 Post(s)
    Rep Power
    14


    Reputation: Yes | No
    Hard to judge the car at all until we see the final specs and pricing. As ezec63 noted, the wider track and body on the Z06 will be one more thing to do to the standard Stingray to bring it up to spec. Also don't know off my head whether the Stingray has the forged/titanium components like the LT4. Then you get into the calibration of the driving modes, the magnetic ride control, etc, etc... It could be that by the time you finish tuning the Stingray to be truly equal to the Z06, you're not sitting too far behind the Z06 in terms of price. We have to wait for later this year know for sure.

    Let's not forget though that with the Z06 you're getting a ZR1 killer with a 5/100 warranty for 981 Cayman S money. Just based on the power/weight spec, out of the box you're running down 997 GT2 and LP-670 Lambos. If the downforce design works as well as they portray it to, it's going to also kill a lot of other cars out on track. A 7:0x at the ring perhaps?
    Current: '00 S2000
    Previous: '15 M235i xDrive | '15 Macan S | '15 WRX STi | '06 Cayman S | '12 E92 335is w/JB4 | '10 STi

  25. #75
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    117,835
    Rep Points
    31,573.1
    Mentioned
    2066 Post(s)
    Rep Power
    316


    Reputation: Yes | No
    Click here to enlarge Originally Posted by whoosh Click here to enlarge
    Also don't know off my head whether the Stingray has the forged/titanium components like the LT4
    It doesn't have the same pistons. They are cast. The LT4's are forged.

    I wonder if you can just order up the pistons from GM. I also wonder if the rods are shared.

    Click here to enlarge Originally Posted by whoosh Click here to enlarge
    It could be that by the time you finish tuning the Stingray to be truly equal to the Z06, you're not sitting too far behind the Z06 in terms of price. We have to wait for later this year know for sure.
    To know for sure, yes. But you can reach 550 whp with heads and a cam in the Stingray without boost. So, even once we get the pricing I doubt heads/cam plus Stingray will equal the Z06 in price.

    To me, the Z06 makes the Stingray look like an even better value. Of course the Z06 is the better buy if you want the warranty, don't want to tune or tweak, etc.

    It's an awesome car no doubt.

Page 3 of 10 FirstFirst 12345 ... LastLast

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •