(Nismo)Transmission the cement grinder effect
03-12-2007, 07:23 AM
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(Nismo)Transmission the cement grinder effect
Drivetrain Modification:
Putting the Power Down
Irrespective of whether you make modifications to the engine to increase its horsepower, consideration should be given to getting more out of what you already have through modifications to the drivetrain….that interface between the horsepower generated at the engine’s crankshaft, and the power that is truly what counts….that which is evident at the rear wheels.
Losses of power between the engine and the wheels can be anywhere from 17% to 20% for most cars, and the G is no exception. The manual transmission will be at the more efficient end of that estimation and the automatic at the less efficient end, the result of greater weight and the greater energy required to operate the torque converter in the automatic transmission.
What are the things that you can do that will cost effectively provide better efficiency in taking the power you already have in your engine and converting it to power on the road, while still keeping your driveability and civility demands fulfilled?
One of the first to consider with a manual transmission is the clutch and flywheel combination. The stock G has a dual mass flywheel that weighs 38 pounds. It is wonderfully smooth and quiet………..as you would expect from a luxury unit. But heavy mass flywheels take more energy to overcome the inertia of their mass, and that is more strain on the engine, and slower response to acceleration and deceleration demands. A lightweight flywheel allows the motor to jump its revolutions rapidly in response to throttle input, allowing for faster matched rpm shifts, as well as allowing more power to get to the wheels due to the lesser energy needed to turn the flywheel. Engine braking is more aggressive as well, as the inertial force of the flywheel is lower when you downshift due to that same lower weight. A rough rule of thumb often used is that for each pound of flywheel weight shed, you achieve an accelerative benefit roughly equivalent to 20 pounds of chassis weight shed. For a daily driver, this really does not matter much, but for a track car….weight is your enemy. It takes more power to get it moving, and more braking force to slow it down. A “heavy” lightweight Nismo flywheel only weighs 23 pounds, a “medium” lightweight JWT flywheel weighs about 14 pounds and a “racing” lightweight Tilton flywheel weighs a miniscule 8 pounds! Those translate to reductions of 300, 480, and 600 pounds respectively. Off a car that weighs about 3400 pounds, those are impacts that are not to be casually disregarded. How much horsepower does it take to match up with the reduction of weight? Lots. So more efficiency is a very important factor. Especially for a track and road car where deceleration and acceleration into and out of the corners is critical to achieving fast lap times.
NISMO clutch disk, clutch cover, flywheel JWT Clutch disk, clutch cover, flywheel Tilton Parts
So what is the catch? There are several. Cost is about the same for all units, roughly $400 for the parts, and labor is about the same amount on top of that, most of it for taking down the transmission. Thus it is often recommended that this mod be done when you are replacing the clutch anyway so that the labor associated with its installation is minimal and incidental to the clutch replacement.
Noise is a consideration. Much of the weight being shed is associated with sound damping material in the stock flywheel. The heavier Nismo has one layer of such material, and while some sound of the flywheel can be heard at idle (with the clutch out) on occasion, and perhaps some grind at rpms below 2500 under load, it is actually hard to notice unless you are aware of it and listening for it specifically. With the medium weight JWT, the noise is more apparent, a sort of classic “cement mixer” sound, again at idle and usually at a stop light with the clutch pedal out. It is not particularly objectionable sounding to me, but you will notice it. Once in awhile somebody might throw you a puzzled look at a stoplight and wonder what might be loose in there. But it is reasonably civil. Just audible. The ultra light Tilton is another matter…it sounds like a cement truck mixer. If you depress the clutch of course the unit engages and the rattle goes away, but this is a weight range that cannot escape the auditory consequence of that little lightweight wheel spinning.
Civility is the biggest issue to me on this choice. The performance gains are not disputable, but at what cost to the driveability? With lighter weight will come lower inertial force, and that means…..easier to stall. You have to match bringing on the rpm affirmatively or that little flywheel is going to mate up to the inertial resistance of the clutch clamping to the drive and ……kaplunk. The stock G 35 is very forgiving and hard to stall, although the frequent stock delivery alignment of the clutch engage point way off the floor probably promotes more frustration and jerkiness in shifting than any other single factor. The heavy flywheel keeps that motor turning when you are off the ideal transition in clutch shifting. A little late or a little soon on the pedals in the stock G35, does not matter so much because you get some feedback through the pedals, the ears and the butt that you need a little more gas or a little less, or a little more clutch or a little less, and you slip your way out of it. That is the way a mass produced daily driver should be, especially given the general level of coordination of most drivers. The lightweight Nismo unit is still pretty heavy, and with an adjustment to the clutch pedal engage point to closer to the floor, really is the way I think the car should come to begin with. The increase in responsiveness is immediately noticeable, and there is almost no perceptible negative trade off. The medium lightweight JWT is a bit more sensitive, and requires a willingness to pay close attention to the shifting and clutch pedal coordination. If you someone that enjoys that mechanical process, and is not frustrated in traffic, this is a good choice. You will from time to time stall this unit. (Hey, don’t we all stall the standard one from time to time when we are not paying attention?) I went with the Nismo out of a concern for civility, but if I had it to do over again, I think an offering in the 14 pound medium lightweight range would be the way I would go, now that I have experienced and lived with the Nismo for awhile. The Tilton type, however, is for the very few. Stalling is often, you practically need to “launch” your starts from a dead stop, taking your foot off the gas is almost like hitting the brakes! The mere prospect of stopping at an uphill street intersection in San Francisco with four people in front and six behind will bring beads of sweat to your temples as you launch the car and then brake to” frog hop”your way upwards without smacking the car in front of you, or stall out. You will be a very busy bee. On a race track most of the negative compromises associated with the Tilton are not evidenced, while the positives are all on display. Standing on the brake and then just blipping the throttle with the heel as you downshift to get an instant jump in revs to match up. On the street the negatives are constantly in evidence, and the conditions for enjoying its strengths are much more limited. Also, note that with those JWT and Tilton units, you really should change the clutch to properly match the flywheel. So again, since a clutch costs about $400, assuming you are replacing a clutch anyway at the time the change is done, that is not necessarily a negative (unless you are using an exotic cerametallic unit that is much more expensive, in some cases several thousand dollars).
Because the results are so appreciable, and can be had for relatively little incremental funds when timed properly, this is a modification that has to be seriously considered by every driver that considers him/herself an enthusiast. If you have an automatic transmission then there is no flywheel/clutch to play with. And it has been assumed that you are not really going to be going to the track occasionally if you have a auto tranny. But do not lose heart if you are looking for more spirited performance from your drivetrain, because it is available through a change of the torque converter in your transmission. This is not relevant to my car so I will not go into it in detail, but suffice to say that you can improve your drivetrain performance even on the auto transmission and if this intrigues you, do some research on the offerings available.
Putting the Power Down
Irrespective of whether you make modifications to the engine to increase its horsepower, consideration should be given to getting more out of what you already have through modifications to the drivetrain….that interface between the horsepower generated at the engine’s crankshaft, and the power that is truly what counts….that which is evident at the rear wheels.
Losses of power between the engine and the wheels can be anywhere from 17% to 20% for most cars, and the G is no exception. The manual transmission will be at the more efficient end of that estimation and the automatic at the less efficient end, the result of greater weight and the greater energy required to operate the torque converter in the automatic transmission.
What are the things that you can do that will cost effectively provide better efficiency in taking the power you already have in your engine and converting it to power on the road, while still keeping your driveability and civility demands fulfilled?
One of the first to consider with a manual transmission is the clutch and flywheel combination. The stock G has a dual mass flywheel that weighs 38 pounds. It is wonderfully smooth and quiet………..as you would expect from a luxury unit. But heavy mass flywheels take more energy to overcome the inertia of their mass, and that is more strain on the engine, and slower response to acceleration and deceleration demands. A lightweight flywheel allows the motor to jump its revolutions rapidly in response to throttle input, allowing for faster matched rpm shifts, as well as allowing more power to get to the wheels due to the lesser energy needed to turn the flywheel. Engine braking is more aggressive as well, as the inertial force of the flywheel is lower when you downshift due to that same lower weight. A rough rule of thumb often used is that for each pound of flywheel weight shed, you achieve an accelerative benefit roughly equivalent to 20 pounds of chassis weight shed. For a daily driver, this really does not matter much, but for a track car….weight is your enemy. It takes more power to get it moving, and more braking force to slow it down. A “heavy” lightweight Nismo flywheel only weighs 23 pounds, a “medium” lightweight JWT flywheel weighs about 14 pounds and a “racing” lightweight Tilton flywheel weighs a miniscule 8 pounds! Those translate to reductions of 300, 480, and 600 pounds respectively. Off a car that weighs about 3400 pounds, those are impacts that are not to be casually disregarded. How much horsepower does it take to match up with the reduction of weight? Lots. So more efficiency is a very important factor. Especially for a track and road car where deceleration and acceleration into and out of the corners is critical to achieving fast lap times.
NISMO clutch disk, clutch cover, flywheel JWT Clutch disk, clutch cover, flywheel Tilton Parts
So what is the catch? There are several. Cost is about the same for all units, roughly $400 for the parts, and labor is about the same amount on top of that, most of it for taking down the transmission. Thus it is often recommended that this mod be done when you are replacing the clutch anyway so that the labor associated with its installation is minimal and incidental to the clutch replacement.
Noise is a consideration. Much of the weight being shed is associated with sound damping material in the stock flywheel. The heavier Nismo has one layer of such material, and while some sound of the flywheel can be heard at idle (with the clutch out) on occasion, and perhaps some grind at rpms below 2500 under load, it is actually hard to notice unless you are aware of it and listening for it specifically. With the medium weight JWT, the noise is more apparent, a sort of classic “cement mixer” sound, again at idle and usually at a stop light with the clutch pedal out. It is not particularly objectionable sounding to me, but you will notice it. Once in awhile somebody might throw you a puzzled look at a stoplight and wonder what might be loose in there. But it is reasonably civil. Just audible. The ultra light Tilton is another matter…it sounds like a cement truck mixer. If you depress the clutch of course the unit engages and the rattle goes away, but this is a weight range that cannot escape the auditory consequence of that little lightweight wheel spinning.
Civility is the biggest issue to me on this choice. The performance gains are not disputable, but at what cost to the driveability? With lighter weight will come lower inertial force, and that means…..easier to stall. You have to match bringing on the rpm affirmatively or that little flywheel is going to mate up to the inertial resistance of the clutch clamping to the drive and ……kaplunk. The stock G 35 is very forgiving and hard to stall, although the frequent stock delivery alignment of the clutch engage point way off the floor probably promotes more frustration and jerkiness in shifting than any other single factor. The heavy flywheel keeps that motor turning when you are off the ideal transition in clutch shifting. A little late or a little soon on the pedals in the stock G35, does not matter so much because you get some feedback through the pedals, the ears and the butt that you need a little more gas or a little less, or a little more clutch or a little less, and you slip your way out of it. That is the way a mass produced daily driver should be, especially given the general level of coordination of most drivers. The lightweight Nismo unit is still pretty heavy, and with an adjustment to the clutch pedal engage point to closer to the floor, really is the way I think the car should come to begin with. The increase in responsiveness is immediately noticeable, and there is almost no perceptible negative trade off. The medium lightweight JWT is a bit more sensitive, and requires a willingness to pay close attention to the shifting and clutch pedal coordination. If you someone that enjoys that mechanical process, and is not frustrated in traffic, this is a good choice. You will from time to time stall this unit. (Hey, don’t we all stall the standard one from time to time when we are not paying attention?) I went with the Nismo out of a concern for civility, but if I had it to do over again, I think an offering in the 14 pound medium lightweight range would be the way I would go, now that I have experienced and lived with the Nismo for awhile. The Tilton type, however, is for the very few. Stalling is often, you practically need to “launch” your starts from a dead stop, taking your foot off the gas is almost like hitting the brakes! The mere prospect of stopping at an uphill street intersection in San Francisco with four people in front and six behind will bring beads of sweat to your temples as you launch the car and then brake to” frog hop”your way upwards without smacking the car in front of you, or stall out. You will be a very busy bee. On a race track most of the negative compromises associated with the Tilton are not evidenced, while the positives are all on display. Standing on the brake and then just blipping the throttle with the heel as you downshift to get an instant jump in revs to match up. On the street the negatives are constantly in evidence, and the conditions for enjoying its strengths are much more limited. Also, note that with those JWT and Tilton units, you really should change the clutch to properly match the flywheel. So again, since a clutch costs about $400, assuming you are replacing a clutch anyway at the time the change is done, that is not necessarily a negative (unless you are using an exotic cerametallic unit that is much more expensive, in some cases several thousand dollars).
Because the results are so appreciable, and can be had for relatively little incremental funds when timed properly, this is a modification that has to be seriously considered by every driver that considers him/herself an enthusiast. If you have an automatic transmission then there is no flywheel/clutch to play with. And it has been assumed that you are not really going to be going to the track occasionally if you have a auto tranny. But do not lose heart if you are looking for more spirited performance from your drivetrain, because it is available through a change of the torque converter in your transmission. This is not relevant to my car so I will not go into it in detail, but suffice to say that you can improve your drivetrain performance even on the auto transmission and if this intrigues you, do some research on the offerings available.
03-12-2007, 07:26 AM
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hopefully this will get u guys to sleep at night when u here a weird noise coming from your tranny. I'm sure we all know the difference between a grind and a clutch shatter as well.
03-12-2007, 09:30 AM
#4
Good writeup. I too have the Nismo flywheel but it is still sitting on the shelf waiting to be put in whenever my OE clutch needs to replaced. Glad to hear the Nismo is as civil as I've read about and yet comes with benefits of a lightened flywheel.
03-12-2007, 09:43 AM
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I am working on having a Billet Steel flywheel made for the Z to resolve some of the driving issues and yet still have a marginal benefit over the stock. The last I checked it was still "in production" with no ETA. After thinking about this same issue last week and I was curious if a dampened crank pulley would help with the noise like an ATI Street Damper.
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