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Machine Elf
01-31-2011, 08:05 AM
Back around 2000 I got a chance to drive my brother's Porsche Boxster. I had owned a manual-transmission Acura Legend for several years prior to that, and had developed some skill at smooth, low-RPM clutch engagements from a dead stop. However, I had extreme difficulty getting my brother's Boxster moving from a dead stop: I stalled the engine maybe half a dozen times before I found a combination of RPM, throttle and clutch engagement that got the car rolling.

Ever since then, my suspicion has been that Porsche made the engine with a very light flywheel, providing no extra inertia to aid in launches and requiring significantly greater skill on the part of the driver. Although more difficult to get the car moving from a dead stop, the minimization of driveline inertia would also make it easier to shift gears rapidly for two reasons:

-the engine RPM drops more rapidly when you lift off of the accelerator, allowing you to match RPM's (for clutch reengagement) more quickly, and

-the chassis doesn't lurch much (threatening stability) if there happens to be an RPM mismatch during clutch engagement.

Conversely, my suspicion is that non-sports cars with a manual gearbox like my old Acura (and now my '02 Maxima) are designed with a heavier flywheel to aid inept drivers in launching from a standing start. The revs don't drop as quickly when you get off the gas, and you need to be more careful about matching RPM's during a shift, but the average Maxima owner isn't going to take it out on the racetrack, and so it's not a huge problem.

So is my theory correct? Or did the Boxster just have a super-sticky clutch?

Throatwarbler Mangrove
01-31-2011, 08:21 AM
Very high end sports cars (Ferraris and the like) are exactly as you describe, to the point that most of them are not available with a manual transmission. The engine revs so quickly that only a computer controlled clutch can manage the shifting and still be somewhat useful as a street car. The Porsche Carrera GT (http://en.wikipedia.org/wiki/Carrera_GT) was the last car of this type to feature a manual transmission and it is widely known to be virtually un-drivable on the street by a non-race car driver.

I don't know about the Boxster specifically. It might indeed be faster revving with a lighter flywheel but your description seems a bit over the top.

Philster
01-31-2011, 09:23 AM
My Infiniti G35 coupe (300+ HP)is notorious for being hard to shift smoothly.

From a stop, it is almost impossible to pull away with any grace and the 1-2 shift is a total pain to execute.

There are 'fixes' all over the web that involve tinkering with how the clutch engages. I know that most of these are compensating for the overall effect of having a engine that makes power at higher RPM (lack of hard-pulling low-end torque) , the flywheel weight and the beefed up clutch for these high-shifting HP monsters.

It's common in various cars. If I went to the new G37, I'd opt for the 7-speed autostick. Manual trans cars had advantages over automatics that are long gone.

justrob
01-31-2011, 09:32 AM
I'm pretty sure the reason for a lighter flywheel isn't so it's easier to match RPMs for shifting (although that might be an added benefit) I think it's so you have quicker throttle response. An engine with a lighter flywheel will respond to more or less throttle quicker but one with a heavier flywheel will be smoother.

Machine Elf
01-31-2011, 10:00 AM
I'm pretty sure the reason for a lighter flywheel isn't so it's easier to match RPMs for shifting (although that might be an added benefit) I think it's so you have quicker throttle response.

Can you explain what you mean by "quicker throttle response?"

If you're talking about overall vehicle acceleration, then I'd assert that this is not strongly influenced by flywheel inertia, unless you've fitted the engine with a solid carbide flywheel five feet in diameter. My Maxima has a pretty hefty flywheel, and if I mash the accelerator in neutral, the engine goes from 600 RPM to 6000 RPM in well under a second, versus taking at least a couple of seconds to do so when accelerating the car in first gear.

Or did you mean something other than vehicle acceleration?

Machine Elf
01-31-2011, 10:02 AM
It's common in various cars. If I went to the new G37, I'd opt for the 7-speed autostick. Manual trans cars had advantages over automatics that are long gone.

Coincidence, I've been lusting after the G37 with a manual gearbox recently. You're right about the advantages of manual-trans having been largely negated by auto-trans technology - but they're still more interesting to drive. :D

steronz
01-31-2011, 10:29 AM
Can you explain what you mean by "quicker throttle response?"

Throttle response is generally defined as the amount of time it takes the engine to get to the RPM you want it to be, with the assumption being that there's no load on the engine (mid-shift, for example). A lot of things can affect the throttle response, from timing and shape of the throttle body to mass of the rotating assembly. It's most often used to describe the feel of the car -- a quick throttle response might not help performance much, but if the car is instantly responding to your inputs it feels pretty awesome. A lighter flywheel can certainly increase the throttle response.

Also, your logic is correct. A lighter flywheel can make a car harder to drive since the revs will drop faster when the clutch starts to grab. However, I don't think that's the case here. I can't find specific numbers, but the Boxster flywheel should weigh in the ballpark of 24 lbs, which is roughly the same as your Maxima. Flywheel weights are picked less for performance and more for refinement, so in my experience, sports cars will actually have heavier flyhweels than some small econoboxes. A heavy flywheel will decrease driveline chatter and smooth engine response. Most people don't have perfectly steady feet, especially most old geezers who buy sports cars, so having a heavy flywheel in there can make the car a bit more forgiving. Heavy flywheels also wear better and are probably less of a headache for automakers.

For the record, most aftermarket flywheels weigh in the 8.5 to 12 pound range, so we're talking a 50-75% weight reduction. And even then they're not always noticeable. A couple pounds wouldn't make a whole lot of difference.

As for why the Boxster was hard to drive, I think a large part of it would be the smaller engine. With less torque on tap than your Maxima or the V6 Legend, the Boxster would require higher revs to take off from a stop. It also probably has a grabbier clutch. Combine those two and you get a car that's tricky to drive.

A friend of mine switched cars with me once -- his was a 6 speed 5.7L Camaro, I had a 1.6L Honda. I revved his car up to 4000 rpms like I was used to doing and promptly lit up the rear tires. He revved mine up to 1000 rpms like he was used to doing and stalled it repeatedly. It was somewhat amusing. We had to recalibrate our brains.

Philster
01-31-2011, 10:35 AM
I beat my chest all the time about how real men drive manual trans cars, but by the time one smoothly engages the G35 clutch and gets around to making a 1-2 shift, it's a total mess of time and a completely annoying adventure.

The average 5-speed automatic in a family sedan just went from 0-30 in a few seconds, under normal throttle, and the 1-2 shift took place in what seems milliseconds from the first application of throttle.

I'm a gear head. I don't even need refinement. I loved numerous manual trans cars I've owned, but I can't take the sloppy engagement off the line and the 1-2 shift. It destroys any pleasure in driving the car.

The high-end automatics give up almost nothing to internal slip/lag now, and their clutches are so stunningly fast, it's truly mind boggling.

I'll take the IPL G Coupe with magnesium paddle shifters for the 7-speed trans. It has rev matching built in. The 6MT is dead to me.

http://www.infinitiusa.com/configurator_infiniti/app?service=external/Page&page=SelectTrim&mo=2011:iplgcp&bs=iplgcp&tool=Model.Build

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Dog80
01-31-2011, 11:26 AM
Sports cars have clutches made of higher friction material to avoid slipping. This makes harder to modulate the clutch grip on the flywheel and start the car smootly.

I've once driven a car with an aftermarket four puck disk. The clutch was like an on-off switch.

Alka Seltzer
01-31-2011, 11:36 AM
As for why the Boxster was hard to drive, I think a large part of it would be the smaller engine. With less torque on tap than your Maxima or the V6 Legend, the Boxster would require higher revs to take off from a stop. It also probably has a grabbier clutch. Combine those two and you get a car that's tricky to drive.

I don't think the smaller engine would make a lot of difference. It's not difficult to pull away in my 2.0 L Primera in 1st, 2nd or even 3rd gear. That's a heavier car than the Boxter with a less powerful and less torquey engine. Sounds like the problem was with the clutch to me.

steronz
01-31-2011, 11:51 AM
I don't think the smaller engine would make a lot of difference. It's not difficult to pull away in my 2.0 L Primera in 1st, 2nd or even 3rd gear. That's a heavier car than the Boxter with a less powerful and less torquey engine. Sounds like the problem was with the clutch to me.

It's not so much that it's more difficult, just that it's different. If you're used to driving gigantic US market V6s like the 3.5L in the Maxima, a short stroke 2.7L Boxster engine might be different enough that a driver would under-rev it on takeoff. I've been driving small cars my whole life and when I drive something like a Mustang GT I really have to concentrate to avoid revving it to 3000 rpms before dumping the clutch. 4.6L V8s can take off from an idle without skipping a beat.

Alka Seltzer
01-31-2011, 11:59 AM
Yes, but even a small engine can pull away easily at low revs if the clutch doesn't snatch. I've driven cars with 1.0L engines, and I didn't have to rev hard to pull away (probably little more than 2000 rpm). My current car will pull away on the flat without touching the throttle. The clutch makes the biggest difference. Remember, the OP reported that he stalled several times.

Machine Elf
01-31-2011, 01:04 PM
Sports cars have clutches made of higher friction material to avoid slipping. This makes harder to modulate the clutch grip on the flywheel and start the car smootly.

:confused:

I'm quite certain that my Maxima, with its 3.5-liter engine, makes a good bit more torque than the Boxster's 2.5-liter engine (the Boxster in question was a '98 (http://en.wikipedia.org/wiki/Porsche_Boxster#986)). But my Maxima is far easier to launch.

Philster
01-31-2011, 01:53 PM
::sigh::

We're talking in generalizations here. GENERALLY, premiums sports cars have parts in the transmission/drivetrain that, while beefier and more prone to putting the power down better, are less friendly, not as comfortable to launch, are more abrupt when shifting and don't offer the smoothest experience.

Beefier clutches....more durable material... aggressive clutches.... pedal progression and various other factors result in a less refined feeling.

As for the Maxima: Who knows really? I doubt that Nissan is going to make the driving experience harsh for that model, but it might be identical to a g35 (I doubt it) Now, for a Porsche or a G35 6MT (a car in which you have to delete the auto and which has a rep with the tuner crowd), one should not be shocked to fine a clutch that is operated via a very unforgiving pedal action, slams the power on AND is mated to a tranny with such a short first gear that the human hand/feet cannot even react fast enough for a seemless 1-2 shift.

So, it depends on just what went into your car and how it was set up. There are message boards full of posts by enthusiasts the despise a number of setups, from the G35 to the Porsche. BMW has an almost spotless rep for smooth shifting manuals. Some shifters are rubbery in feel, but the clutch is a dream.

It depends. Generally, the more aggressive setups, aimed at cars/buyers who expect the aggressiveness, deliver rougher launches and/or shifting. Some comes because the clutch is beefier, the flywheel lighter... etc.

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