David writes:
This is a quote from Nissan’s specs for the current Sentra SE-R Spec V: “6-speed close-ratio manual transmission with dual-mass flywheel.” Ok, so I am interested in buying one of these top dollar Sentras, but would like to know what a “dual mass” flywheel is. The Spec V is the only Sentra with it. Thanks!
Sajeev Replies:
One of the biggest advantages to a dual-mass flywheel is the ability to lower the engine’s NVH (noise, vibration, harshness) levels inside the cabin. You can read far more detailed information here, if so inclined. For applications that need it, the technology is sound and proven after decades of use.
Back to the Sentra: considering the Spec V revs like a mother (6600 revs to make peak power) with those 200 horses, having a dual-mass unit ain’t a bad idea for a chubby street car that’s a far cry from it’s sport compact origins dating back to the early 1990s. Then again, what modern car isn’t bigger than its britches?
Bonus! A Piston Slap Nugget of Wisdom:
Sticking with the SE-R Ain’t What It Used To Be theme: it’s ironic that the only manual cog swappers in the lineup are the super-strippo Sentra, or the top dollar SE-R Spec V. Everything in between has the fun-sucking CVT. Even the SE-R, albeit with paddle shifters that must help with…something!
Perhaps Nissan should take a page from their marketing tagline, do us all a favor and “Shift The Way They Move?”
(Send your queries to mehta@ttac.com)
Don’t you mean “Shift shifting” instead?
High-revving? Hondas certainly get up there, and thanks to the wonders of VTEC they get there loudly. I wonder if they’ve considered dual-mass to help with that.
Honda has considered dual-mass flywheels, and some models come equipped with them.
One major disadvantage of a DMF however is that if the flywheel needs to be replaced they are pricey, add to that the fact that they don’t cope very well with abuse it can be a potential problem. If you don’t plan on giving the clutch too much of a hiding you should be sweet.
As for CVT, I still think that they are under-appreciated by most people, you just need to learn how to drive them right to get the best performance. FWIW I find that manual shifting a CVT is more frustrating than just driving to suit the trans, the shifts are just so sloppy!
Really the only NVH they reduce is torsional vibration transmitted from the engine to the driveline. So technically, they only reduce vibration, and maybe a bit of harshness, but not really noise.
Engines with relatively large displacement per cylinder, especially those with few cylinders (i.e. 2.5L 4-cylinders like the Sentra SE-R) and engines with high compression (especially diesels) have larger torsional vibration or torque pulses.
This is secondhand info, but a late coworker of mine had previously worked as a design engineer at a couple Class 8 truck manufacturers and many (if not all) of these trucks use dual-mass flywheels to reduce the tremendous torsional vibrations of the large diesels. When debating how to improve transmission life in a far-different vehicle with a tiny 3-cyl diesel I brought up a dual-mass flywheel and he went ballistic, saying those were a huge POS that broke down on large trucks all the time. He even detailed one model/engine combo that had to retrofit a solid flywheel because they couldn’t get a dual-mass one to hold up to the engine.
edit: On the engine speed comment, I believe the damping characteristics of the dual-mass flywheel are more biased toward the low-end of the spectrum. Typically high frequency vibrations are much more easily damped by rigid structures. In a “screamer” engine the torque pulses should be of relatively minor amplitude at high frequencies near peak power, but at speeds below peak torque the amplitude of the torsional vibration would be larger and consequently very much larger as a percentage of total instantaneous torque throughput.
Correct, they work on the “NV” part, not the “H”. But it seems like most engineers group them all together, so I did too.
Your engine speed comments make sense, and that torsional vibration issue is probably a big problem on small, peaky motors like this Spec V. It’s probably less of an issue on a high revving 370Z, Gallardo, etc simply because of engine design.
Since when does a paltry 6600 rpm qualify for “rev like a mother” status?
That’s not the redline, that’s peak power. Which isn’t terribly useful on the street. Which is exactly where these sport compact cars live.
That’s where almost all cars live. I looked up a few dyno pulls and the original SE-R peaked out around the same rpm, and even the pushrod slowboat GM LS3 delivers the mustard at 5900 rpm.
8000 rpm would be matronly.
For what it’s worth, the SE-R lineup is the same as in the last generation: the Spec-V is manual, and the “base” SE-R isn’t (automatic last time, CVT this time). So that’s not a change or anything. Sentras have never had great manual transmissions, imo.
Go ask Porsche how their dual mass flywheel experience went.
Hint – google the 964 era of cars.
Perhaps DMF technology has advanced ever so slightly in the past 15-20 years. I’m guessing that’s why they’re still using them (996/997)
VW TDI diesels have dual-mass flywheels. Usually that (and the clutch that goes with it) is the first thing that needs to be chucked out and replaced with a conventional flywheel and clutch when you hot-rod them, and a few unfortunates have had the DMF mechanism let go on a stock vehicle. I haven’t had a hint of trouble with mine, though.
The first generation MINI Cooper S has a dual mass flywheel. Ours failed three times in less than 30,000 miles. It’s a very common, and expensive, failure in MINIs with the 6-speed transmission. If it’s a sound and proven technology, please head over to MINI and tell them where to source the sound and proven ones.
Been there done that. Ford used a dual mass flywheel on their diesel light trucks (F250 up). Replaced many because of vibrations. Upon taking them out you would find the springs inside were broken. They were similar to dual spring valve springs. Also, each time one of the manuals needed a clutch I would find the DM flywheel had broken springs and needed replacing as well. I haven’t worked in repair since the mid 90s (work for a manufacturer now) so there may be some improvement. But knowing how those old ones were built I don’t have confidence in them. the problem was the springs were not sealed and dust from the clutch got in them and with the vibration would wear the springs down till they broke. Just my 02.
Honest John, (the Sajeev Mehta of the Daily Telegraph's motoring section) is not a fan of DMFs by any stretch of the imagination.